One aspect of earthquake physics not adequately addressed is why some earthquakes generate thousands of aftershocks while other earthquakes generate few, if any, aftershocks. It also remains unknown why aftershock rates decay as ~1/time. Here, I show that these two are linked, with a dearth of aftershocks reflecting the absence of high-pressure fluid sources at depth, while rich and long-lasting aftershock sequences reflect tapping high-pressure fluid reservoirs that drive aftershock sequences. Using a physical model that captures the dominant aspects of permeability dynamics in the crust, I show that the model generates superior fits to observations than widely used empirical fits such as the Omori-Utsu Law, and find a functional relationship between aftershock decay rates and the tectonic ability to heal the co- and post-seismically generated fracture networks. These results have far-reaching implications, and can help interpret other observations such as seismic velocity recovery, attenuation, and migration. In this study, the authors propose that a fluid rich environment is necessary to generate long-lasting aftershock sequences. Based on this premise, the study presents a theory for modeling fluid-driven earthquake sequences Eight foreshocks (M ≥ 4.5 and M ≤ 6.5) preceded the M6.4 Puerto Rico earthquake (2020), spawning 85 aftershocks (M ≥ 4) in the subsequent three weeks. One can argue that the intermediate depths of the Peru (78 km) and Mexico (48 km) earthquakes, or the oceanic crust of Jamaica, are mixing apples with oranges when comparing to the shallow crustal Ridgecrest and Puerto Rico earthquakes, but even directly comparing apples raises questions. For example, the 2001 Kunlun (M7.8) earthquake was a surface-rupturing crustal strike-slip earthquake with a lateral extent of about 400 km. The 2002 Denali (M7.9) earthquake was also surface-rupturing crustal strike-slip earthquake with a lateral extent of about 400 km. The Kunlun earthquake generated a total of 12 aftershocks (M ≥ 4) in the first three weeks, with eight of those occurring in the first 24 h. This differs (by more than an order of magnitude) with the Denali earthquake, which was preceded by a M6.1 foreshock, and generated 157 aftershocks (M ≥ 4) in the subsequent three weeks, 90 of which occurred in the first 24 h.Aftershock sequences display a wide spectrum of behavior . In contrast, Puerto Rico is integrated into the Caribbean subduction system, with potentially abundant deep fluid sources available, while Ridgecrest is underway in and near the Coso hydrothermal region with significant deep CO2 and H2O sources capable of driving this sequence. Finally, an obvious candidate for the order-of-magnitude discrepancy observed for the Kunlun and Denali earthquakes is that Tibet rests upon 65–80 km of crust3 thickened by the Himalayan orogeny, with no obvious mechanism for generating deeply derived fluids, while an active subduction zone (with the concomitant abundance of volatiles) lies 60 km beneath Denali4. These observations suggest that, in the absence of trapped and high-pressure fluid reservoirs at depth, aftershocks are suppressed, while access to deep fluid sources produce robust and long-lived aftershock sequences.One plausible explanation for these large differences in aftershock behavior is the availability of deeply trapped high-pressure fluids to drive the aftershock sequence. In the cases of Peru and Mexico  event, are likely triggered by dynamic or Coulomb stress changes. Statistical models such as ETAS9 nicely fit aftershock data because each aftershock is allowed to produce its own sequence, but currently lacks any physical basis. An alternative view is that aftershocks are fluid-driven from pore pressure diffusion12, or at least that high fluid pressures are involved19. Since rocks fail by some combination of increasing Coulomb failure stress or increasing pore fluid pressure, the dominant mechanism is likely the one with the widest range of amplitudes. ΔCFS models that seem to correlate, if they correlate5, are on the order of fractions of MPa, while expected changes in fluid over-pressure can range from zero to the minimum principal stress .The prevailing view of aftershocks is that they result from a combination of stress-triggering by changes in Coulomb Failure Stress (ΔCFS)20 first empirically observed in 1894 that aftershocks decay as approximately 1/t. The modified Omori-Utsu Law21 (among many of its variations22) is an empirical fit to the number of aftershocks with time n(t) following an earthquake:t is time and A, c, and p are constants used to fit the data. In this work, I normalize by the maximum number of aftershocks, so the productivity parameter A is 1. To date, the only physical models that predict Omori-type behavior are the rate-state formulation of friction23 and damage models24.The underlying physical mechanism driving aftershocks of large earthquakes has remained elusive since OmoriHere I propose a hypothesis that long-duration aftershock sequences are predominantly fluid-driven, and test the hypothesis by comparing results of a physically-based non-linear diffusion numerical model against observations of tens of thousands of aftershocks following three large earthquakes in California. I show that this  model produces superior fits to aftershock rates than widely used empirical laws, and find strong spatial correlations with measured hypocenters and the calculated elevated fluid pressure for all sequences investigated. I also show that aftershock rates are controlled by the orientation of the cluster with respect to the direction of the maximum horizonal stress (SHmax) because SHmax represents the dominant mechanism for permeability recovery.25 (M ≥ 1.5) generated for the 1992 (M7.3) Landers, the 1999 (M7.1) Hector Mine, and Fig. Figure 26. These data are relevant because the azimuth of SHmax, relative to the orientation of the aftershock cluster, is shown below to contribute to controlling the aftershock decay rate. Each of the curves  an exponential dependence of permeability on the effective normal stress28, (2) a step-wise increase in permeability at the onset of slip29, followed by; (3) an exponential decrease in permeability with time mimicking post-seismic healing/sealing of the permeability network. Therefore, permeability prior to failure is expressed as28:2], σe is the effective normal stress [Pa] , τ is the shear stress [Pa], μ is the friction coefficient, P is pore pressure [Pa], and σ* [Pa] constrains the permeability response to σe.A conceptual model of permeability dynamics constrains a formulation for permeability that mimics the essence of permeability dynamics through the earthquake cycle29, while permeability recovery via tectonic stresses and/or crack healing and sealing is assumed to decrease exponentially in time. This results in the following formulation for permeability after failure:d is a co-seismic step-increase in permeability at slip [m2] to mimic the increase in permeability associated with a fresh fracture or slip on a pre-existing frictional interface. Permeability then exponentially decreases over a timescale defined by α [s−1], returning to its effective-stress-dependence at long times.Permeability increases co-seismically because the creation of a fracture or slip on a frictional surface may increase permeability by orders of magnitudeSubstituting Eq.  into the31, or via direct generation of high-pressure fluid sources through temperature-induced dehydration and de-carbonatization. Theoretical studies of thermal pressurization focus on the expansion of entrained pore fluids in thin fault zones, and show that fluid pressures quickly diffuse because of the very limited fluid volume involved. However, dehydration and decarbonation reactions32 may also provide direct  high-pressure fluid sources within the fault zone that then diffuse into co-seismically generated damage zones33 at timescales that depend on the permeability structure. Recent numerical studies34 demonstrated a new and additional mechanism for generating high fluid pressures co-seismically by self-pressurization of fluid-bearing fault zones through elasto-plastic collapse of rapidly deforming fluid-filled pores. The co-seismically generated fault zone also provides a highly permeable conduit that can link to deeply trapped, supra-hydrostatic fluid reservoirs35. Since the geometry and location of trapped high-pressure fluid reservoirs are not known, I do not include them in this modeling study. Conceptually, an over-pressured fault zone would only enhance fluid flow because it would be highly permeable (Eq. t = 0), and thus an open channel for draining the hypothesized reservoirs at depth.Figure k0, d, σ*, and α. The values for k0 and σ* were chosen to result in an initial permeability field . The Landers Stepover is a right-lateral step in a right-lateral fault system (kinematic pull-apart) with no obvious mechanism for tectonically healing the co- and post-seismically generated fracture networks, thus implying sluggish permeability recovery . Model results  for Northridge and α = 4 × 10−4 days−1  for the Landers Stepover. Importantly, this is reflected in the p-value of Eq.  are reasonable for the strike-slip cases, and were therefore used for all subsequent simulations. This should be emphasized; all simulations presented below were identical to the Stepover case, with the exception of the value for α.It is important to note that a good match to the data was achieved for the Landers Stepover even though nd α Eq.  contribuHector North Wing and Hector Left Wing: The observations and modeling results for Northridge and the Stepover provides a working hypothesis. Namely, higher p-values indicate faster permeability recovery than relatively lower p-values. A good test of this hypothesis is to investigate two separate aftershock clusters spawned by the 1999 Hector Mine (M7.1) earthquake, one cluster trending North-South  for the North Wing and α = 6 × 10−3 days−1  for the Left Wing. Figure p-value of the empirical Omori-Utsu Law  indicates that this sequence occurred along a fault system optimally-oriented for slip and thus low normal stress , and consequently an expected behavior similar Hector’s North Wing Fig. . The ZMAcks Fig.  shows excks Fig.  encases αRightWing<αHypo<αLeftWing). With this in mind, I changed α to 5 × 10−3 days−1, resulting in similarly good fits with the data  implies that this sequence healed relatively quickly because the orientation of the cluster is almost normal to the azimuth of the maximum stress direction. Indeed, modeling using ons Fig.  comparedons Fig.  that shoα.Modeling other aftershock sequences from the three earthquakes studied here becomes redundant because the spatial distribution of hypocenters in the x-z plane always looks roughly the same, the model results always look the same, and the only difference between each sequence is the temporal decay of aftershocks, which in the model is controlled by A compendium of calculated pressure and permeability histories , β is the lumped compressibility (taken as 1e-8 Pa−1) of the pore space and fluid47, k is the permeability, and η is the dynamic viscosity of the fluid (taken as 10−3 at the surface and decreases with depth). Permeability k prior to failure takes the form28:ko is taken as 1e-15 m2 when a grid point is below the failure condition, σe is the effective normal stress , and σ* (taken as 35 MPa) defines how permeability changes in response to σe. When a numerical grid point reaches the Mohr-Coulomb failure condition permeability changes in time via:d  to mimic the increase in permeability associated with slip or fracture29. Such high values of permeability have been inferred for some aftershock sequences48. Permeability then exponentially decreases  over a timescale defined by α [plotted for convenience in days−1], returning to its effective-stress-dependence at long times.The finite difference numerical model solves the diffusion equation;The model calculates pore pressure diffusion through an evolving permeability field  angle θ to each numerical grid point, where θ is the angle measured from the normal to σ49. Since θ affects the effective normal stress (and thus permeability), the initial stress and permeability states are heterogeneous. As high fluid pressure diffuses into the hydrostatically-pressured surroundings, the stress state of a numerical grid point reaches the failure condition and a numerical aftershock is counted and located at that time. Further details of this model can be found elsewhere because it is the same model49 calibrated against the meso-scale fluid-injection experiment in Basel (Switzerland).In the strike-slip case, the virtual slip planes are out of the page, explained in detail elsewhere1 was assumed as twice σ3, which was taken as the weight of the overburden, and the fluid pressure P (above hydrostatic) was calculated. The initial overpressure was assumed as 70 MPa above hydrostatic to along a 450 m wide fault zone. Such a wide fault zone is likely overestimated, but does not have any significant influence on the results. The model domain was 300 × 300 finite-difference nodes, and no flow boundary conditions were imposed on the bottom and sides of the model, and a zero-pressure boundary at the top surface.For the thrust fault cases, σSupplmentary InformationPeer Review File


Induction of general anesthesia increases the hemodilution resulting from infusion of crystalloid fluid, which is believed to be due to slower distribution caused by arterial hypotension. When normal distribution returns is not known.− 1 of Ringer’s lactate was infused over 30 min to 25 volunteers just after induction of general anesthesia for open abdominal hysterectomy. A two-volume model was fitted to the repeated measurements of the blood hemoglobin concentration and the urinary excretion using mixed-effects modelling software. Individual-specific covariates were added in sequence.An intravenous infusion of 25 mL kg− 1 of lactated Ringer’s had been infused, of which virtually all remained in the circulating blood. Thereafter, the fluid kinetics was similar to that previously been found in awake volunteers except for the elimination rate constant (k10), which remained to be very low (0.86 × 10− 3 min− 1). Redistribution of infused fluid from the interstitium to the plasma occurred faster (higher k21) when the arterial pressure was low. No covariance was found between the fixed parameters and preoperatively concentrated urine, the use of sevoflurane or propofol to maintain the anesthesia, or the plasma concentrations of two degradation products of the endothelial glycocalyx, syndecan-1 and heparan sulfate.Distribution of infused fluid was interrupted during the first 20 min of the infusions. During this time 16.6 mL kg− 1 of crystalloid fluid had been infused. Plasma volume expansion during this period of time was pronounced.Induction of general anesthesia interrupted the distribution of lactated Ringer’s solution up to when 16.6 mL kgISRCTN81005631) on May 17, 2016 (retrospectively registered).Controlled-trials.com ( Pharmacokinetic methods can be applied to fluid volumes, which is of interest in anesthesia and surgery where large amounts are given by intravenous infusion. The most commonly used approach is volume kinetics, which uses the hemodilution and the urinary excretion as input in the calculations , 2. The One such issue is why excessive hemodilution from infused fluid develops when induction of general epidural, spinal or anesthesia is associated with hypotension –10 but n− 1 given before open hysterectomy.Another issue was to examine whether the urinary concentration of metabolic waste products before the operation reduces rate of subsequent elimination of infused fluid, which has been shown in conscious patients , 17. ForThe primary hypothesis was that the excessive intravascular fluid retention after induction of general anesthesia is caused by a reduction of the capillary leakage, as given by the kinetic model. The secondary hypothesis was that a mathematical link exists between volume kinetic parameters and the plasma concentrations of BNP, glycocalyx degradation products and the urinary concentration of metabolic waste products. The kinetic analysis served as primary outcome measure and the measurements of metabolic waste products and their associations with the kinetics as secondary outcome measures.controlled-trials.com as ISRCTN81005631 on May 17, 2016 . All patients gave us their written informed consent to participate. Patients were included if being aged 25–55 years, free from cardiopulmonary or renal disease, and complicated surgery was not expected. The study adheres to the CONSORT Guidelines. After fasting overnight, patients were given general anesthesia induced with propofol but maintained with either sevoflurane as inhaled anesthetic (N = 13) or an intravenous propofol infusion (N = 12). The result of that comparison is described elsewhere [A total of 25 clinical patients scheduled for elective abdominal hysterectomy were recruited to an open label randomized parallel clinical trial with the primary aim to compare two anesthesia methods, sevoflurane and intravenous propofol, with regard to their influence the degradation of the endothelial glycocalyx layer . Ethicallsewhere .− 1) was administered over 30 min. No more fluids were given except for the anesthesia drugs. No vasopressor or inotrophic agent was used. Blood (3 mL) was taken from a cubital vein for measurement of the blood hemoglobin (Hb) concentration on a Coulter HMx 5-diff  with a coefficient of variation (CV) of 0.7% was taken every 10 min during the 30-min infusions and then every 15 min up to the end of surgery.At the start of surgery, an intravenous infusion of Ringer’s lactate (25 mL kg− 1. Results below the limit of detection (10 ng L− 1) were set to that value. Moreover, the plasma concentrations of two endothelial shedding products, syndecan-1 and heparan sulfate, were analyzed using enzyme-linked immunosorbent assay (ELISA) kits from Diaclone, France, and Amsbio, Abingdon, UK, with CV% values of 6.2, and < 10%, respectively. The normal value of syndecan-1 for humans is 32 ng/mL (manufacturer data) and for heparan sulfate it is 5.9 μg mL− 1 [Blood (3 mL) and urine were also sampled at baseline, after anesthesia induction, and then at 30, 60, and 90 min later after the fluid infusion had been initiated, and 2 h after the anesthesia had been terminated. These samples were used to measure the plasma concentration of brain natriuretic peptide (BNP) on an Architect i2000, Abbott Park, Illinois, USA with a CV of 5.6%. The normal range is < 100 ng Lμg mL− 1 .Urinary creatinine concentration was measured within 36 h on a Cobas Integra 400 Plus instrument  with a CV of 2%. The urine osmolality was measured with an Osmomat 3000  and the urine-specific weight on a Urisys 2400  with CVs being 3 and 0.1%, respectively.Volume kinetics is a method for analyzing the distribution and elimination of infusion fluids , 2. The Vc) space and becomes distributed to the peripheral (Vt) fluid space. Fluid is translocated from Vc to Vt in proportion by a rate constant k12 to the central volume expansion, which is written as (vc – Vc). Fluid is returned from Vt to Vc via another rate constant, k21. Elimination occurs from Vc by one or two routes (k10 and kb) in proportion to (vc – Vc). The rate constant k10 represents fluid that is collected as urine while kb governs fluid filtered from Vc that does not equilibrate with Vc or Vt during the period of the study [All included patients are analyzed in a single run, and then the influence of various covariates on the model parameters is tested sequentially. The model is built to agree with physiological data where isotonic infusion fluids distribute between two compartments: the plasma and the interstitial fluid space. Several models have been attempted to characterize fluid kinetics during surgery, but the one shown in Fig. he study , 19, 20.The differential equations for the single-elimination route model are:Ro is the rate of infusion, vc and vt are the constantly changing volumes of distribution for newly infused fluid, and Vc and Vt are the baseline volumes.where Vc resulting from the infusion. Hence:The Hb-derived fractional plasma dilution was used to indicate the volume expansion of k10 as follows (AUC = area under the curve):Symbols in capital letters denote baseline values. A minor correction was made for the effects of surgical hemorrhage and blood sampling on the plasma dilution , 12. TheP < 0.05), the 95% confidence interval of the parameter estimate did not include zero, and the CV% for the inter-individual variability was < 50%.Twenty individual-specific covariates were evaluated in a forward stepwise fashion, as guided by plots of random effects (“eta” plots). The routine for identifying statistically justified covariates is described in detail elsewhere . In shor− 1 min− 1 and our belief was that the fluid kinetics would change depending on the infused volume. In the last situation, all time points up to 30 min were set to 1 and all time points after 30 min were given the value 0.Continuous covariates assessed only once were age, body weight, surgical blood loss, C-reactive protein, the use of sevoflurane or propofol for maintaining the anesthesia, the syndecan-1 and heparan sulfate concentrations before and 2 h after the surgery, and the preoperative urinary specific gravity, osmolality, and the urinary creatinine concentration. The plasma concentrations of syndecan-1 and heparan sulfate served as time-varying covariates and were included four times per operation, while heart rate and the systolic, diastolic, and mean arterial pressure (MAP) were assessed at every blood sampling time point. The time period before and after 10, 20, and 30 min were evaluated as categorical covariates in an exponential covariate model, as fluid was infused at a rate of 0.833 mL kgThe kinetic program used was Phoenix software for nonlinear mixed effects (NLME), version 1.3 . The goodness-of-fit of the model was illustrated by residual plots and the performance of the model by predictive checks.P < 0.01 level yielded N = 20. Data with a normal distribution are presented as the mean (SD), data with a skewed distribution as the median (25th–75th percentiles) and kinetic output as the mean (CI). P < 0.05 was statistically significant.The study was powered to detect a doubling of the plasma BNP concentration as a result of the volume loading, as described previously . An effeThe kinetic analysis was based on 298 time points during the 25 operations. All data are given in the Additonal file k10) corresponded to the measured urinary excretion.The search strategy used to find the optimal parameter estimates is shown in Table Comparisons between the measured and predicted urinary excretion and the plasma dilution based on the fixed parameters alone are shown in Fig. A predictive check the kinetic model, based on 1000 simulations, is given in Fig. k12, kb, and Vc showed lower values during the first 20 min of the infusion, when 2/3 of 25 mL kg− 1 = 16.6 mL kg− 1 (mean 1245 mL) of lactated Ringer’s was infused. An exponential covariate model was used to examine if a more precise prediction could be obtained by placing the cut-off at other points in time, but the fluid volume given up to 20 min was found to be the optimal. The strong inhibition of leakage of fluid from the plasma allowed the infusion to raise the plasma volume more rapidly. Consequently, the plasma volume reached a maximum by 20 min (instead of 30 min)  correlated closely Fig. a and b. P < 0.001 repeated-measures ANOVA) and remained most concentrated in the propofol group at 2 h  and an extravascular compartment (Vt), which probably represents the difficulty for fluid to expand the interstitial fluid space. The hemodilution pattern, and not the magnitude of the hemodilution, determines how much fluid is allocated to each one of the two spaces. In the present study, the Vc volume was 3.2 L, which is the volume with which the infused fluid quickly equilibrates. It also corresponds closely to the expected plasma volume.The pharmacokinetic approach used here, volume kinetics, uses the inverse of the hemodilution and the urinary excretion as input in pharmacokinetic calculations , 2. The − 1 body weight had been infused. The rate constant k12 was then reduced to a small fraction of the normal value found during the remainder of the experiment. Figure Vc at 20 min closely agrees with the total amount of fluid that had been infused at that time. The anesthesia-induced vasodilatation and the resulting drop in the MAP by 20 mmHg are sufficient to explain the almost complete “shut-off” of the distribution [The present study shows that induction of general anesthesia transiently changes the kinetics of infused crystalloid fluid. The most striking finding was a strong inhibition of the distribution of fluid during the first 20 min of the infusion, up to when 16.6 mL kgribution . However− 1 of crystalloid fluid from the expected 20% [The results would be quite different if anesthesia had not been induced. The hypotension-associated interruption of capillary filtration doubled the maximum plasma dilution in response to 25 mL kgcted 20% , 22 to 4k12 that prevailed until 16.6 mL kg− 1 of lactated Ringer’s had been infused  while the corresponding value in cohorts of conscious volunteers has varied between 0.015 and 0.028  [kb to the expansion of Vc at any given time. The fluid that was eliminated from the kinetic system by this mechanism remained in the body but did not equilibrate with the plasma during the period of the study. A higher kb than k10 has previously been reported only during general anesthesia [The diuretic response to infused fluid is reduced by approximately 90% during general anesthesia, which is strongly associated with the reduction of MAP –7. In th–50 min) , 20. Intesthesia , 24.− 1 (Fig. The poor diuretic response to infused fluid might also explain the lack of covariance between fluid kinetics and concentrated urine, which is index of low habitual intake of water and/or overt dehydration , 26. An − 1 Fig. c. The th− 1 of crystalloid fluid in awake volunteers [Although the diuresis was very small, an elevated BNP was associated with slightly increased urine volumes Fig. c, f. Thilunteers  but appak12 or kb, which are else the relevant parameters to indicate increased capillary leakage.A currently popular view is that surgical trauma and hypervolemia cause degradation of the endothelial glycocalyx layer whereby the capillary leakage of macromolecules and fluid would increase –15. The Limitations include that capillary filtration was regained only after having administrated a fairly large bolus volume of Ringer’s. When a Starling equilibrium adequate for general anesthesia has developed after infusion of smaller amounts of fluid, such as 500 mL, is unknown. Slow capillary refill of the same kind as during induction of anesthesia would probably continue but, in any event, equilibrium would certainly occur later than the 20 min found here.The cut-off points for changed fluid kinetics were evaluated only at 10-min intervals. A higher resolution could have been obtained by sampling blood at shorter intervals. Not only the infused fluid volume, but also the time from the anesthesia induction, might contribute to restoration of the distribution function. No massive elevations of the biomarkers for cardiac strain and glycocalyx degradation were found, which limits the possibilities to identify them as covariates. Finally, the kinetic model is constructed to reasonably well agree with known body physiology, but what the fixed kinetic parameters represent is still not finally proven.− 1 of lactated Ringer’s has been infused. The small urinary excretion did not cause intravascular overload as fluid could be filtered to extravascular tissues both with and without being in equilibrium with the plasma.A fluid volume kinetic method shows the excessive hemodilution occurring when crystalloid fluid is infused after induction of general anesthesia corresponds to a nearly complete interruption of the capillary filtration up to the point in time when 16.6 mL kgAdditional file 1.Additional file 2.


The cochlea is filled with two lymphatic fluids. Homeostasis of the cochlear fluids is essential for healthy hearing. The sensory epithelium called the organ of Corti separates the two fluids. Corti fluid space, extracellular fluid space within the organ of Corti, looks like a slender micro-tube. Substantial potassium ions are constantly released into the Corti fluid by sensory receptor cells. Excess potassium ions in the Corti fluid are resorbed by supporting cells to maintain fluid homeostasis. Through computational simulations, we investigated fluid mixing within the Corti fluid space. Two assumptions were made: first, there exists a longitudinal gradient of potassium ion concentration; second, outer hair cell motility causes organ of Corti deformations that alter the cross-sectional area of the Corti fluid space. We hypothesized that mechanical agitations can accelerate longitudinal mixing of Corti fluid. Corti fluid motion was determined by solving the Navier–Stokes equations incorporating nonlinear advection term. Advection–diffusion equation determined the mixing dynamics. Simulating traveling boundary waves, we found that advection and diffusion caused comparable mixing when the wave amplitude and speed were 25 nm and 7 m/s, respectively. Higher-amplitude and faster waves caused stronger advection. When physiological traveling waves corresponding to 70 dB sound pressure level at 9 kHz were simulated, advection speed was as large as 1 mm/s in the region basal to the peak responding location. Such physiological agitation accelerated longitudinal mixing by more than an order of magnitude, compared to pure diffusion. Our results suggest that fluid motion due to outer hair cell motility can help maintain longitudinal homeostasis of the Corti fluid. The top surface of the OoC separates two lymphatic fluids—K+-rich endolymph and Na+-rich perilymph , about half of transduction channels in the outer hair cells are open, causing the so-called silent current3. The silent current of outer hair cell is large for a cellular current—on the order of 1 nA. Acoustic pressure waves enter the cochlea at its base and propagate toward the apex, thereby causing the organ of Corti (OoC) to vibrate. The OoC, the auditory epithelium consisting of sensory receptor cells and their supporting cells, is sandwiched between acellular matrices called the tectorial and the basilar membranes Fig. . The OoC4. For individual hair cells, an influx of K+ through mechanotransduction channels is balanced with efflux through basolateral K+ channels3. K+ extruded out of the outer hair cells is constantly resorbed by the spiral ligament fibrocytes and relayed to stria vascularis where K+ is secreted back to the endolymph space. How K+ is transported from outer hair cells to ligament fibrocytes remains unclear. There is evidence that K+ is diffused through the Corti fluid before being absorbed by the supporting cells6. The supporting cells in the OoC are connected by the gap junctions through which K+ can be transported7. Meanwhile, no gap junctions have been detected between hair cells and supporting cells. Due to the proximity to K+ source (hair cells), Corti fluid has higher K+ level than the perilymph in the scalar tympani (the cavity below the OoC)6.The OoC has substantial extracellular fluid (Corti fluid), such as the fluid in the tunnel of Corti, Nuel’s space, and the outer tunnel Fig. B. These 8), while the transduction conductance becomes greater toward the base (> a factor of 5 in the gerbil cochlea9). This implies that there is more than ten times of burden to clear K+ in the Corti fluid toward the base of the cochlea. We explored if mechanical advection can alleviate the burden of cochlear fluid homeostasis in the basal cochlea by longitudinal fluid mixing. This hypothesis was motivated by two previous observations. A study reported longitudinal fluid motion along the tunnel of Corti, correlated with the outer hair cell motility10. Another study showed that the top and bottom surfaces of the OoC vibrate out-of-phase at stimulations below the best-frequency11, implying the cross-sectional area change of the OoC. The cross-sectional area change along the cochlear traveling waves is reminiscent of peristalsis. In this study, we use computational simulations to test the hypothesis.Longitudinal inhomogeneity of the Corti fluid is the subject of this study. The OoC cross-sectional area becomes larger toward the apex of cochlea  and velocity (u) of an incompressible fluid is described by the Navier–Stokes equations and continuity equation14.ν is the kinematic viscosity, ρ is the fluid density, and t is time. Fluid viscosity has been considered19 or neglected23 per the purpose of studies. To our knowledge, no previous study regarding cochlear fluids analyzed the effect of advection  was to reduce boundary effects by decreasing wave amplitude towards the boundary (x = 0 or L). While the values of f, λ, and a were chosen within the physiologically reasonable range, the traveling wave created by Eq. After approximating the Corti fluid space to a circular tube and assuming an axial symmetry, the geometry was reduced to a 2-D rectangle . There were approximately 90,000 triangular elements as well as 8,000 quadrilateral elements in the boundary layer regions along the bottom and the left boundaries. Both of the element types used the third-order shape functions. Mesh size was 1–2 μm for the triangular elements, and it was reduced by a factor of four toward the boundaries, considering the boundary layer thicknesses estimated from the diffusive distance of an oscillating plate .Considering expected time scale for mixing (hours) and the time step size (µs), computing time was a practical challenge. We took advantage of the simulating condition—oscillatory vibrations. As the fluid flow under our considered condition is laminar, the flow pattern became cyclic after a brief transient period (< 1 ms). The convergence to a steady flow pattern was confirmed by comparing velocity fields after consecutive cycles. It took about 4 h to simulate 10 cycles, after which the cyclic solution reached a steady state  can be better represented by removing the oscillatory component of fluid particle motion. The trajectory T (= 1/f) as long as sufficiently many particles have been tracked. The trajectory of each particle can be extended by appending the one-period path that begins where the prior one ends. Repeating the procedure allows determining particle drifts over long times and significantly reduces computation expense. The Stokes drift velocity uD is defined for the particle passing through location Here C of interested ions evolves over time because of diffusion and advection. For the time scale of Corti fluid diffusion, the effective advection can be represented by the Stokes drift velocity, so that the dynamics is described by14D is the diffusion coefficient of potassium ions in the Corti fluid. Since this is nonconservative form of advection–diffusion equation, this advection diffusion equation is independent of the Navier–Stokes equations. Thus the time and spatial grid sizes of the two governing equations are not the same. The time step size for Eq. –9 per a stimulation cycle for Eqs. –4 over a second for Eq. The concentration entclass1pt{minimaIt should be noted that this study cannot discuss ion homeostasis because the source and the sink of ions are not incorporated. The mixing (homogenization) of fluid in micro-tube is the topic of this study. Given an assumed initial inhomogeneity, the time course of homogenization is simulated. To evaluate the mixing performance, in the following section, a mixing parameter is introduced. The parameter depends on the spatial distribution of ions, but not the absolute ion concentration.A 6 mm-long and 25 µm-thick fluid domain was subjected to traveling waves along one longitudinal boundary  cause large longitudinal motion, as shown in Fig. λ/r0 < 1), longitudinal and transverse velocities become comparable. For a long wave, there was minimal pressure gradient in the transverse direction, thus the fluid was forced to move longitudinally. On the contrary, for a short wave (λ/r0 < 1), the pressure varied appreciably in both transverse and longitudinal directions (results not shown). Mammalian cochleae have r0 < 50 µm and experience wavelengths ranging from 100 µm to a few millimeters, so the long-wave case shown in panels A–C represents the natural conditions better than the short-wave cases.Long waves (a and the wave speed c (= fλ). As shown in panel E, as long as the wave velocity is the same, combinations of different frequencies and wavelengths resulted in comparable fluid velocity. In the plot, fluid velocity was represented by the root-mean-square velocity over the entire fluid domain.Overall fluid velocity was proportional to the vibration amplitude The result in Fig. uD results in the trajectories in Fig. Figure uD) in solving Eq. The Stokes drift velocity field that represents these vortex patterns is a way to better visualize these traveling paths for greater time scale than the period of vibration. The vortex patterns were affected by wavelength and boundary conditions. For example, the right-most vortex was generated due to the rigid boundary along the right edge. The other vortices have sizes roughly comparable to the wavelength . The direction of advective flow was counterclockwise—along the wave propagation direction near the boundary and against the wave propagation direction in the middle. As fluid particles tend to circulate within vortices, long vortices are expected to enhance longitudinal mixing more than short ones. These velocity fields shown in Fig. To evaluate fluid mixing in terms of ion concentration, advection–diffusion equation Eq.  was solvχ was defined using the standard deviation of ion concentration across the fluid space:Over time, the fluid was mixed and homogenized due to diffusion and advection. To quantify the level of homogeneity, the mixing parameter χ(t) and the line of χ = 1 , defined as D is the diffusion coefficient. The Péclet number represents the contribution in mass transport due to advection relative to diffusion. Consistent with the physical implication of Pe, the mixing time for advection–diffusion became inversely proportional to the wave speed when Pe >  > 1. When Pe <  < 1, the mixing time approached to the value of pure diffusion (filled square). Note that the physiological speed range (> a few m/s) corresponds to the domain of advective mixing.The mixing parameter is zero initially and it approaches one as the fluid space becomes homogeneous. The absolute value of concentration does not affect the mixing parameter. Figure = 1 Fig. B. Initia= 1 Fig. B. There = 1 Fig. C. For th25. The original measurement was made at a location where the best responding frequency was 9 kHz. Sound tones at different frequencies were delivered at 70 dB sound pressure level (SPL) and vibrations were measured at the basilar membrane  which results in cross-sectional area change. Second, the top of the OoC vibrates more than the bottom (basilar membrane)28.Physiological traveling waves differ from the simple traveling wave of Eq. 29. The envelope length depends not only on frequency but also on sound pressure—louder sounds result in wider wave envelope. Waves with longer envelopes have higher mixing parameters if the entire domain is considered. Local mixing matters because, in reality, Corti fluid mixing is an ensemble of many waves. At a specific location, the most efficient wave component will dominate the mixing. Therefore, mixing of the entire cochlear length by a single wave does not represent Corti fluid mixing well.Using the same Corti fluid model as the one in Figs. x = 0) of the traveling wave. This location-dependence of mixing is reasonable considering that the wave speed decays  decreases as the waves propagate, dropping from over 100 m/s at the onset to a few m/s at the peak , but the fluid was subjected to the velocity field in Fig. The phenomenon we observe is consistent with the theory of Taylor dispersionime Fig. . Initialime Fig. A, there ime Fig. B, there 6 observed an increase of K+ concentration as the probing electrode penetrated the basilar membrane toward the Corti fluid. This implies that the basilar membrane has a finite permeability for potassium ions. While the findings of our study hold regardless of basilar membrane permeability, if one wants to predict a specific potassium level, finite permeability of the basilar membrane will need to be considered.Several simplifications were made for simulation that could affect mixing performance. First, the Corti tube was reduced to a circular tube and then to a two-dimensional rectangle after assuming axisymmetry for simplicity. As the fluid motion relevant to our conclusion is along the length, the assumption of axisymmetry may make minimal difference. Second, the Corti tube is not a uniform fluid space. It is penetrated by columnar microstructures such as the pillar cells and outer hair cells. They are likely to reduce mixing by slowing the flow but also enhance mixing by perturbing the flow pattern, like stirrers. Third, due to computational expense, we simulated pure tones. In natural hearing environments, the cochlea is subjected to numerous waves in which tail regions, where mixing is strongest, are spread all over the cochlear length. For this reason, our simulated condition might be conservative rather than exaggerated, and that mixing may occur more effectively under physiological conditions. Finally, the Corti fluid space was considered as if an isolated fluid domain. Unlike the top boundary of the organ of Corti tightly sealed with gap junctions, ions must diffuse across the basilar membrane. In a previous study, Johnston et al.32 which is considered to saturate around 60 dB SPL. At a higher level, while mixing is not much better than 60 dB SPL case, potential damage due to excessive sounds may overwhelm the advantage of mixing. Our findings suggest that normal hearing environments with modest sounds are beneficial for hearing health. On the other hand, loss of outer hair cells or their motility will reduce the longitudinal fluid motion in the Corti tube and cause problems in fluid homeostasis in the organ of Corti. Although we focused on the specific example of potassium, our findings apply to any longitudinal chemical inhomogeneity. For instance, longitudinal advection could help clear away accumulations of metabolic waste.It should be noted that, despite our result, higher sound intensity does not necessarily mean faster mixing. Our study suggests that the vibrations resulting in organ of Corti cross-sectional area change is the driving force for mixing. The cross-sectional area change might be caused by outer hair cell motility33. Typically, a solution with 100 times higher concentration than the half-maximal effective concentration (indicated with either EC50 or IC50) is applied at the round window so that the drug can diffuse across the window membrane and move along the scala tympani. There were experiments that measured the time of drug delivery along the cochlear length. In some studies, drugs affecting outer hair cell motility such as salicylic acid and gentamicin were used . We predict that, when a drug not affecting outer hair cells is applied at the round window, the presence of sounds will facilitate drug delivery along the cochlear length.Another example of longitudinal inhomogeneity in the cochlear fluid is found in cochlear drug delivery. The predictions of this study will be testable with cochlear drug delivery experiments. For instance, in clinical trials, drugs such as steroids and antibiotics are delivered locally though the round window because systemic delivery is considered inefficient due to blood-labyrinth barrierSupplementary Information.


Adenocarcinoma in situ, minimally invasive adenocarcinoma, lepidic predominant adenocarcinoma and invasive mucinous adenocarcinoma are relatively new classification entities which replace the now retired term, bronchoalveolar carcinoma (BAC). The radiographic appearance of these lesions ranges from pure, ground glass nodules to large, solid masses. A thorough understanding of the new classification is essential to radiologists who work with MDT colleagues to provide accurate staging and treatment. A 2-year review was performed of all surgically resected cases of adenocarcinoma in situ, minimally invasive adenocarcinoma and lepidic predominant adenocarcinoma in our institution. Cases are broken down by age, gender, tumour type and tumour location. A pictorial review is presented to illustrate the radiologic and pathologic features of each entity. To familiarise radiologists with the new pathological classification of adenocarcinoma of the lung.To illustrate the varying CT appearances of adenocarcinomas and describe the CT features which correlate with histologic features of invasive growth.To highlight how the new classification more accurately reflects the correlation between radiology, pathology and prognosis.A new, international, histopathologic classification of adenocarcinoma of the lung was introduced in 2011 by the International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS) and European Respiratory Society (ERS) [Adenocarcinoma is the most common histologic type of lung cancer and accounts for over 40% of non-small cell lung cancers .However, the terminology used to describe it has been inconsistent and non-uniform. For the radiologist, the new classification required some adjustment. The most striking change was the discontinuation of the term bronchoalveolar carcinoma (BAC).The first descriptions of this entity date back to the late 19th and early 20th centuries when Malassez  and MussSubsequent publications described tumours with similar features under a variety of names including ‘alveolar cell tumour of lung’, ‘pulmonary adenomatosis’ and ‘mucocellular papillary adenocarcinoma of the lung’ –8.Single noduleDisseminated nodulesDiffuseIn 1960, Liebow [In contrast to some of his predecessors, Liebow described a potential for pleural invasion, nodal metastases and distant metastases. However, the tumours were considered characteristically slow-growing, particularly the single nodule subtype.Localised. A well circumscribed tumour, usually peripherally located, without necrosis or haemorrhageMultinodular. Miliary nodules involving one or more lobesDiffuse. An appearance that mimics a pneumonic process, often multilobarFrom a pathological standpoint, 3 macroscopic subtypes of BAC were identified :LocalisA new classification system was introduced to provide more uniform terminology and diagnostic criteria. Four new entities were proposed: adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA), lepidic predominant adenocarcinoma and invasive mucinous adenocarcinoma.The aim was to separate tumours with a 100% (AIS)  and nearAdenocarcinoma in situ is defined as a tumour of ≤ 3 cm with pure lepidic growth but no lymphatic, vascular or pleural invasion and no tumour necrosis. The word lepidic means ‘scaly’ and is used to describe the growth of bland, pneumocytic-type tumour cells along alveoli without lymphovascular invasion.The typical CT appearance is a ground glass nodule, although part-solid lesions are common as well as lesions with bubble-like internal lucencies.Minimally invasive adenocarcinoma is defined as a tumour of ≤ 3 cm with either pure lepidic growth or predominant lepidic growth and ≤ 5 mm of stromal invasion. There is no lymphatic, vascular or pleural invasion and no tumour necrosis. There is 98% overall survival after surgical resection .The typical CT appearance is a ground glass nodule with a small, central solid component (≤5 mm). When adenocarcinoma of the lung includes invasive and non-invasive components, the invasive component is characteristically solid on CT and the non-invasive component is characteristically hazy and ground glass , 14. TheLepidic predominant adenocarcinoma is defined as a tumour of > 3 cm in total size and/or has > 5 mm lymphatic, vascular or pleural invasion with a non-mucinous lepidic predominant growth pattern.The CT appearance is variable but the most typical appearance is a part-solid nodule or mass.It is recommended that all invasive tumours which were previously known as non-mucinous adenocarcinomas are now described histopathologically according to the predominant subtype :Lepidic: As discussed aboveAcinar: Invasive tumour composed of acini and tubules with columnar or cuboidal cells that resemble bronchial-lining epithelial cellsPapillary: Invasive tumour arranged as papillae structures with a fibrovascular core and complicated secondary and tertiary branchesMicropapillary: Small papillary tufts containing tumour cells with peripheral nuclei but without a fibrovascular coreLepidic predominant adenocarcinoma has an excellent 5-year survival of 90% after surgical resection . On the Invasive mucinous adenocarcinoma refers to a subtype of invasive adenocarcinomas with apical mucin and small, basally oriented nuclei . These tThe CT appearance of these lesions varies wildly from consolidation and air bronchograms to solid and subsolid nodules and masses with a bronchogenic distribution . Both unA retrospective 2-year review was performed through our institution’s laboratory information system to identify all surgical lung resection specimens for which the final histopathological diagnosis was adenocarcinoma in situ, minimally invasive adenocarcinoma or lepidic predominant adenocarcinoma. The review covered the period January 1, 2017 to December 31, 2018.There were 35 cases in total which included 24 females and 11 males. The age range was 44 to 86 and the mean age at pathological diagnosis was 69. The cases were divided by histologic subtype into adenocarcinoma in situ (16), minimally invasive adenocarcinoma (13) and lepidic predominant adenocarcinoma  for morphological analysis but some studies have found FNA to be superior. Rekhtman et al. for example, found FNA cell blocks to be adequate for molecular analysis in 98% of samples . They suThere is a new classification system for adenocarcinoma of the lung which has been designed to more accurately reflect the correlation between radiology, pathology and prognosis. The classification describes a spectrum which includes pre-invasive, minimally invasive and invasive lesions. The pre-invasive and minimally invasive lesions have almost 100% survival after surgical resection.Diagnosis of these lesions is multidisciplinary, but primarily histopathological. The imaging features of lesions on this spectrum vary wildly with a significant amount of overlap. However, the take home message for the radiologist is that certain imaging features, including the size, shape and attenuation of the lesion, will help to determine on which side of the spectrum the lesion is likely to fall. Correct interpretation of the imaging features will help in accurate diagnosis and prognostication.


We aimed at quantifying the load of water, sodium and chloride due to different fluid indications in our pediatric intensive care unit (PICU). We were particularly interested in the role of fluid Critically ill children aged ≤3 years and invasively ventilated for ≥48 h between 2016 and 2019 in a single tertiary center PICU were retrospectively enrolled. Need for renal replacement therapy, plasmapheresis or parenteral nutrition constituted exclusion criteria. Quantity, quality and indication of fluids administered intravenously or enterally, urinary output and fluid balance were recorded for the first 48 h following intubation. Concentrations of sodium and chloride provided by the manufacturers were used to compute the electrolyte load.creep (34%) and maintenance (24%) fluids. Patients received 14.4 ± 4.8 mEq/kg/day of sodium and 13.6 ± 4.7 mEq/kg/day of chloride, respectively. The majority of sodium and chloride derived from fluid creep (56 and 58%). Daily fluid balance was 417 ± 221 ml (64 ± 30 ml/kg/day) and was associated with total sodium intake .Forty-three patients (median 7 months (IQR 3–15)) were enrolled. Patients received 1004 ± 284 ml of water daily (153 ± 36 ml/kg/day), mainly due to enteral (39%), creep is quantitatively the most relevant fluid in the PICU and future research efforts should address this topic in order to reduce the inadvertent water and electrolyte burden and improve the quality of care of critically ill children.Critically ill children are exposed, especially in the acute phase, to extremely high loads of water, sodium and chloride, possibly contributing to edema development. Fluid  Water is the main constituent of the human body. Indeed, 60–70% of the body weight of an adult is made of water and the percentage rises up to 75–80% when dealing with infants and young children –3. Due tIntravenous fluid therapy is therefore a cornerstone of pediatric critical care medicine and the prescription of intravenous fluids needs to be approached as any other pharmacological treatment, i.e., intravenous fluids have clear indications, contraindications and possible side effects . Classic1) Fluid resuscitation, i.e. rapid infusion of parenteral fluids in order to correct an acute intravascular fluid deficit ; 2) fluicreep [In addition, a substantial and frequently neglected water and electrolyte amount is administered to patients as a vehicle for intravenous drugs , to provide patency of indwelling vascular catheters and to flush venous lines after blood withdrawal or drug administration –13. Thiscreep , in analcreep .creep [Isotonic saline, i.e. NaCl 0.9%, which is constituted of 154 mEq of sodium and 154 mEq of chloride per Liter, is the classical fluid creep . Besidescreep –20, NaClcreep . Furthercreep . It is cThe aim of the present retrospective study is to describe the current clinical practice regarding fluid therapy in the pediatric intensive care unit (PICU) of a tertiary Italian referral hospital, quantify the load of water, sodium and chloride due to different fluid indications and assess the association between sodium intake and water balance.This retrospective, single center study was approved by the institutional review board of our hospital (decision number 502/2019). The need for informed consent was waived owing to the retrospective nature of the study.All patients admitted to the 5-bed tertiary PICU of the Fondazione IRCCS Ca′ Granda – Ospedale Maggiore Policlinico, Milan between January 2016 and the end of May 2019 were screened for eligibility. The inclusion criteria were age ≤ 3 years and ≥ 48 h of continuative invasive mechanical ventilation. Exclusion criteria included patients < 28 days, patients who received renal replacement therapy, plasmapheresis and parental nutrition. Patients were studied for 48 h starting from the time of intubation or PICU admission if the endotracheal tube was already in place.2), and ratio of arterial partial pressure of oxygen to FiO2 (P/F ratio).Clinical data were extracted from the patient data management system of our PICU . Demographic data included age, gender, body weight, height, presence and type of comorbidities. The cause of PICU admission was categorized in 4 classes: respiratory failure, sepsis/septic shock, neurological disease and post-operative. Several variables were extracted from the digital records in order to describe the severity of patients’ clinical condition. These included the use of vasopressors and/or inotropes , rescue respiratory strategies (high frequency oscillatory ventilation (HFOV), prone position) and worst values of the 48-h study period for positive end-expiratory pressure (or mean airway pressure in case of HFOV), fraction of inspired oxygen , to provide patency of indwelling vascular catheters and to flush venous lines after blood withdrawal or drug administration.According to the medical records, each fluid administered was assigned to a fluid indication : fluid rDaily forms included also urinary output and a simplified daily fluid balance, calculated by subtracting total urinary output from the total input of parenteral and enteral water. Finally, the percentage of water, sodium and chloride administered with each indication were computed.P-value lower than 0.05 was considered as statistically significant.All data were tested for homogeneity of variance and normality of distribution using the Shapiro-Wilk test. Normally distributed data were expressed as mean ± standard deviation, while non-normally distributed data were reported as median and interquartile range. Pearson’s correlation was used to assess the association between sodium intake and cumulative water balance. Analysis was performed with SAS 9.4  and Sigma Plot 12.0 . A Fifty-four patients fulfilled the inclusion criteria, 11 presented exclusion criteria, leaving 43 patients for the analysis  and fluid maintenance . The quantitative role of fluid boluses/fluid resuscitation was minor (1.7%) and quantitatively similar to blood components (1.5%).Acetated Ringer’s was the preferred choice for both fluid resuscitation 88 ± 33%) and fluid maintenance (88 ± 26%). The other employed intravenous fluid for these purposes was NaCl 0.9%, which was also the only type of fluid used for fluid 3% and flFluids administered as a vehicle for intravenous drugs constituted 76 ± 12% of fluid creep, while fluids administered to provide patency of catheters and for flushes constituted the remaining 24 ± 12% of fluid creep. Among intravenously administered drugs, sedatives and antibiotics where the two major sources of fluid creep .The daily dose of sodium was 97 ± 42 mEq (14.4 ± 4.8 mEq/kg/day). Fluid creep represented the major source of sodium , followed by maintenance fluids (32.8%), enteral feed (6.9%), fluid resuscitation (2.3%) and blood components (2.2%) (Table The daily dose of chloride was 92 ± 40 mEq (13.6 ± 4.7 mEq/kg/day), slightly lower than sodium. Fluid creep represented the major source of chloride , followed by maintenance fluids (29.9%), enteral feed (8%), fluid resuscitation (2.1%) and blood components (1.7%). Figure 2 = 0.49, p < 0.0001) with cumulative fluid balance.Patients had an average daily urinary output of 602 ± 242 ml, i.e. 92 ± 32 ml/kg per day. Given the total fluid input  the strong association between total sodium input and positive fluid balance.We studied a population of young (≤3 years), severely ill, mechanically ventilated children during the first 48 h of the acute phase. The main findings of our study are (i) the overall extremely high water, sodium and chloride load, (ii) the predominant role of fluid creep, accounting for 34% of water input, followed by fluid maintenance. As already pointed out by other authors [creep, it is not surprising that this category of fluids represented the major source of sodium  as NaCl 0.9% was used for this purpose.The total chloride load was slightly lower than sodium (13.6 ± 4.7 mEq/kg/day). The prevalent use of acetated Ringer’s as maintenance fluid explains this finding. Indeed, acetated Ringer’s has a sodium and chloride concentration of 132 and 110 mEq/L, respectively. Consequently, the chloride load deriving from this source is slightly lower than the corresponding sodium load. On the contrary, sodium and chloride load deriving from fluid creep in particular, might contribute to the development of hyperchloremia, with the related side effects [creep. When analyzing the two major components of fluid creep, we found that the majority (76%) was due to the dilution of intravenous drugs, while the remaining part (24%) was due to the use of fluids to guarantee catheters’ patency.The high chloride burden due to fluid therapy in general, and fluid  effects . Hyperch effects , 20, alt effects , 27, pot effects . Further effects , 30. Ind effects . This is effects . InteresThe cultural awareness regarding intravenous fluids is certainly increasing –35 and cIndeed, there is strong consensus regarding the tonicity of fluids for resuscitation and replacement, i.e., in this context isotonic, possibly balanced fluids should be preferred. On the contrary, there is a great debate regarding the appropriate tonicity of maintenance fluids –39. Manycreep. Indeed, these fluids have been neglected for a very long time and only recently, the research interest in the topic is increasing [creep can account up to 50% of daily parenteral fluid administration and a similar percentage of total daily sodium load in critically ill children admitted to the PICU, we can firmly state that they are conceptually as important as, and quantitatively even more important than resuscitation, replacement and maintenance fluids. Indeed, in a recent before-and-after study performed in a single center adult ICU, Bihari and colleagues demonstrated that the sodium burden and positive fluid balance deriving from fluid creep can be safely reduced by switching from an isotonic solution, such as NaCl 0.9%, to a hypotonic solution, such as 5% glucose [Finally, it is not surprising that, at the time of writing, no indication exists regarding fluid creasing , 43, 44. glucose . This imOther possible strategies to reduce the water, sodium and chloride burden of intravenous fluids would be to favor, whenever possible, the enteral route for drug administration; to concentrate as much as possible parenteral drugs; to review, on a daily basis, the indications of intravenous fluids, i.e. to adopt strategies of fluid stewardship  and to aThere were several limitations to our study. First, the study was retrospective in nature and data derived from only 43 patients of the same PICU. Consequently, the small number of patients hampers the generalizability of our findings. The extensive use of non-invasive ventilation in our PICU and the established tendency to intubate and ventilate invasively patients only as last resort, might in part explain the limited number of included patients. Second, we had no data on urinary sodium and chloride excretion. It was thus impossible to assess sodium and chloride balance. Third, we did not consider the sodium content of antibiotics, which can be significant . Finallycreep is quantitatively the most relevant fluid in the PICU and future research and clinical efforts should address this topic in order to improve the quality of care of critically ill children.In conclusion, our study described the clinical practice regarding fluid administration in critically ill, mechanically ventilated patients under 3 years of age, treated at our PICU. We had established protocols in our unit for drug dilution, not necessarily employing the maximal possible concentration. Furthermore, we did not have local protocols to reduce the inadvertent amount of fluids deriving from crystalloids used to guarantee the patency of catheters. As a result, our current clinical approaches and habits unequivocally lead to an inadvertent and excessive water, sodium and chloride load, which might contribute to the development of edema and significantly impact on patients’ outcomes. Fluid


Are voters as polarized as political leaders when it comes to their preferences about how to cast their ballots in November 2020 and their policy positions on how elections should be run in light of the COVID-19 outbreak? Prior research has shown little party divide on voting by mail, with nearly equal percentages of voters in both parties choosing to vote this way where it is an option. Has a divide opened up this year in how voters aligned with the Democratic and Republican parties prefer to cast a ballot? We address these questions with two nationally diverse, online surveys fielded from April 8 to 10 and June 11 to 13, of 5,612 and 5,818 eligible voters, respectively, with an embedded experiment providing treated respondents with scientific projections about the COVID-19 outbreak. We find a nearly 10 percentage point difference between Democrats and Republicans in their preference for voting by mail in April, which had doubled in size to nearly 20 percentage points in June. This partisan gap is wider still for those exposed to scientific projections about the pandemic. We also find that support for national legislation requiring states to offer no-excuse absentee ballots has emerged as an increasingly polarized issue. Facing the threat of the COVID-19 crisis, elected officials have offered divergent prescriptions about how to run November’s election. Democratic Senators Klobuchar and Wyden have introduced legislation to expand access to voting through the mail and some states have proposed to run their primaries entirely through the mail ; PresideAmong voters, prior research has shown little party divide on voting by mail, with nearly equal percentages of voters in both parties choosing to vote this way in past studies , 5. Has To provide data that inform these conversations, we report how two samples of eligible voters want to see November’s election run. We present the results of two online surveys fielded on April 8 to 10 and then June 11 to 13 asking a nationally diverse sample of 5,612 and 5,818 eligible American voters for their views on how they would like to vote in November and their preferences about proposed changes in election policies. We embed a randomized experiment in these surveys presenting respondents with truthful summaries of the projections of two teams of scientists about the COVID-19 outbreak : one preWe preregistered three hypotheses. First, in line with previous research, we expected to observe no partisan gap in personal preference over how to cast a ballot for respondents in the control condition (H1). By contrast, we predicted that there would be partisan divides on support for national legislation expanding no-excuse absentee ballot availability (H2). Third, because recent work has shown that Republicans are less concerned with COVID-19 and less trusting of scientific efforts, the impact of expert COVID-19 projections in the treatment conditions should be attenuated for Republicans (H3). We find evidence against H1: A significant partisan divide has emerged in 2020 over how respondents prefer to cast their ballots. As expected, we also observe partisan polarization over vote-by-mail policies and differential treatment effects for respondents in different parties. We also show that the gaps in personal voting preferences and in views on election policy have grown significantly during the COVID-19 pandemic.P values are from one-tailed hypothesis tests based on the preregistered hypotheses. We pool treatment conditions because the effects of the treatments were not substantively different; all treated respondents read one of two scientific projections about COVID-19.Column (1) reports results from a model predicting a personal preference for voting by mail, rather than in person. In the control condition, Democrats were significantly more likely than Republicans to want to cast their own ballot by mail and this gap has grown since April. In April, 40.1% of Democrats indicated that they would like to vote by mail in November while 30.5% of Republicans wanted to vote by mail. In June, this gap doubled as 44.8% of Democrats and only 25.5% of Republicans indicated they would like to vote by mail at this point.Column (2) shows support for national legislation requiring states to implement no-excuse absentee ballots for all voters who request them, among those offering an opinion. Support is relatively high; in April, 87.3% of Democrats supported the policy and 64.1% of Republicans supported it. The coefficient representing the change between surveys shows a small drop in support for no-excuse absentee ballots for Democrats (2.3%) but a much larger decline for Republicans (12.6%), suggesting an increasing partisan divide on the issue.Turning to the experiment, the treatment moved Democratic respondents toward preferring to vote by mail in November. Reading scientific projections of when COVID-19 cases are likely to peak increased Democrats’ preference to vote by mail by 7.5 percentage points. Republicans showed a different pattern, as the treatment effect on the respondent’s preferred method to cast a ballot was significantly lower (and indistinguishable from 0). For policy preferences, Democrats were largely unmoved by the treatment, possibly due to very high levels of baseline support, while Republicans were moved slightly, shrinking the gap between partisans.These results shed light on how COVID-19 and the current national political climate might alter previous findings on voting by mail. While previous work showed no partisan gap related to voting by mail in American elections , our resConfirming our hypothesis, we found significant partisan differences in support for no-excuse absentee ballot legislation; a strong majority of Democrats support such a proposal while Republicans are more evenly split, although a majority also support it. Because this policy is but one of many possible approaches—9 states will automatically mail ballots for the 2020 Election and 10 will send out vote-by-mail applications, while 8 states require an excuse beyond COVID-19 fear to vote absentee  are significantly more likely to want to cast their ballot without visiting a polling place.We also found that personal preferences to vote by mail and support for national legislation expanding voting by mail have become increasingly polarized since April, with the gap in preferences over how to vote almost doubling. One potential explanation for this is increasing media coverage that frames voting by mail as a partisan issue.The experimental results show that exposure to information about the peak of the COVID-19 outbreak exacerbates the partisan gap, with Democrats becoming significantly more likely to want to cast their ballot by mail while the same information did not move Republican preferences. This finding matches existing research on the partisan divide in trust in experts (How will this affect the November election? This may depend upon local health conditions and a state’s election laws. If all voters have access to their preferred method of voting and feel safe casting a ballot through that method, Republicans could vote in person at high rates while many Democrats shift toward voting by mail, with no net impact. However, for Republicans in areas with high infection rates, concerns about COVID-19 exposure combined with reluctance to cast a mail ballot may lead to lower participation. A recent report shows that in Wisconsin’s 2020 presidential primary, in which 59% of votes were cast by mail, “Republican turnout declined near uniformly across the state relative to 2016” . For Dem•While no one can be certain how the COVID-19 outbreak will progress in the United States, one well-respected team of scientists at a leading university has projected that if social distancing measures are widely adopted  their peak in April, then gradually decline throughout the spring and into the summer./now but are lifted during the early fall, a new surge in cases will come and the effects of the virus will reach their peak in November or December.]The surveys were fielded from April 8 to 10 and June 11 to 13, 2020 using Luc.Id’s Fulcrum platform. This platform has been demonstrated to provide nationally diverse samples that exhibit treatment effects similar to samples from other sources . The samhttps://osf.io/ke8w2. Data and associated protocol will be available on Dataverse at https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/GF0XJA (https://escholarship.org/uc/item/6mb7764n.This study was reviewed by the institutional review board at the University of California San Diego and deemed exempt as it met the criteria for minimal risk and participants were debriefed at the end. Informed consent was collected before respondents answered any questions. The method and hypotheses were preregistered at N/GF0XJA  and are


Personalised treatment in oncology has seen great developments over the last decade, due to both technological advances and more in-depth knowledge of radiobiological processes occurring in tumours. Lung cancer therapy is no exception, as new molecular targets have been identified to further increase treatment specificity and sensitivity. Yet, tumour resistance to treatment is still one of the main reasons for treatment failure. This is due to a number of factors, among which tumour proliferation, the presence of cancer stem cells and the metastatic potential of the primary tumour are key features that require better controlling to further improve cancer management in general, and lung cancer treatment in particular. Imaging biomarkers play a key role in the identification of biological particularities within tumours and therefore are an important component of treatment personalisation in radiotherapy. Imaging techniques such as PET, SPECT, MRI that employ tumour-specific biomarkers already play a critical role in patient stratification towards individualized treatment. The aim of the current paper is to describe the radiobiological challenges of lung cancer treatment in relation to the latest imaging biomarkers that can aid in the identification of hostile cellular features for further treatment adaptation and tailoring to the individual patient’s needs. According to the latest Global Cancer Statistics, lung cancer is the most commonly diagnosed cancer worldwide, in both males and females  and the leading cause of cancer death (18.4%) [While the latest technological and pharmaceutical developments have increased the therapeutic index in lung cancer, research over the last decade reveals an imperative need to include radiobiological characteristics of cellular and subcellular structures as well as the tumour microenvironment into the big picture of personalised medicine . HypoxiaAlthough most of aforementioned tumour characteristics and their impact on tumour control are well known, there is still no clear-cut solution to manage treatment resistance due to high proliferative potential, the presence of cancer stem cells or circulating tumour cells that are indicative of tumour aggressiveness.In order to tackle the above challenges, one should first identify the hostile features and then target them with the best currently available techniques. In this respect, biomarkers play a key role, as their specific design allows the identification of tumour areas that are prone to treatment resistance, thus leading the way towards personalised, targeted therapies.The current paper focuses on the (radio) biological challenges described above applied to non-small cell lung cancer (NSCLC) and the latest imaging biomarkers that can aid in their identification, targeting and treatment outcome prediction. The main features discussed in the paper are related to tumour kinetics, via tumour proliferation and the presence of cancer stem cells, and tumour dynamics, via progression, invasion and distant metastasis through circulating tumour cells.Cellular proliferation is a prerequisite for tissue growth and development. Uncontrolled proliferation is characteristic of cancer cells and represents one of the hallmarks of neoplastic growth. The rate of tumour proliferation differentiates slowly proliferating from rapidly proliferating tumours, a feature that dictates the type of treatment required for tumour control. The evaluation of a tumour’s proliferative ability and of its growth kinetics are therefore critical aspects of cancer management.Cell proliferation rate is commonly assessed through the presence in the cell nucleus of the Ki-67 monoclonal antibody, during the active phases of the cell cycle. The Ki-67 antibody labels nuclei of proliferating cells, enabling the quantification of the proliferating cell fraction within a tumour . ClinicaThis study showed the importance of data analysis based on histological characteristics (rather than NSCLC as a group) and the definition/validation of a Ki-67 cut-off value for each histological type of NSCLC. Furthermore, it was suggested that the predictive power of Ki-67 labeling could be enhanced by the concurrent employment of other clinical/pathological parameters as well as imaging biomarkers, which would eventually lead to better patient stratification and treatment optimisation.Another important factor that controls cellular proliferation in lung cancers (and not only) is the epidermal growth factor receptor (EGFR). The EGFR is a transmembrane glycoprotein receptor of the ErbB family of cell surface tyrosine kinases with a role in regulating cell proliferation and apoptosis through signal transduction pathways . MutatioMore recently, research into tumour proliferation has been linked to microRNAs, owing to their role in multiple biological processes, including gene regulation . MicroRNCellular kinetic parameters are important indicators of tumour proliferation before, during and after therapy, thus their quantification warrants special consideration. As shown above, the most studied proliferation markers and, consequently, the most targeted molecules related to cellular proliferation in lung cancer imaging are EGFR and Ki-67. In this regard, numerous tracers have been developed and trialed with various results .p < 0.001). Similarly, in a study of 102 NSCLC patients with EGFR mutation (22%), KRAS mutation (27%) and wild-type profiles (51%), it was observed that 18F-FDG uptake was significantly higher in those harbouring KRAS mutations as compared to EGFR+ or wild-type  [Fluorodeoxyglucose-F18 (18F-FDG) is the most commonly used PET imaging radiotracer, being an indicator of tumour activity via glucose metabolism, and has an established role in tumour staging and treatment response monitoring. Its role in the assessment of tumour proliferation was also researched, with a considerable number of studies examining the potential of 18F-FDG in predicting EGFR mutation status in NSCLC patients. In a retrospective clinical study involving 109 NSCLC patients, Chen et al. showed that EGFR mutation decreases cellular accumulation of FDG via the NOX4/ROS/GLUT1 axis . The SUV< 0.001) . These f< 0.001) .N-(3-chloro-4-fluorophenyl)-7-(2-(2-(2-(2-18F-fluoroethoxy) ethoxy) ethoxy) ethoxy)-6-methoxyquinazolin-4-amine)—, those patients that are sensitive to EGFR-TKIs and to monitor the efficiency of EGFR-TKI therapy. The cut-off value for SUVmax was set at 2.23, showing a greater response to EGFR-TKI in those presenting with SUVmax ≥2.23 as compared to patients with values <2.23 (81.58% vs. 6.06%). Furthermore, 18F-MPG uptake positively correlated with median progression-free survival [A recent study reported on the development of a new PET tracer with high specificity to activating EGFR mutant kinase showing significant correlation between tracer uptake and the EGFR mutation status in both preclinical animal models and in patients with NSCLC . The stusurvival .p < 0.0001; r = 0.92), and concluded that 18F-FLT may be a better imaging marker than FDG for response assessment and outcome prediction [While 18F-FDG has its own merits in the functional imaging of lung cancer, it is not the optimal indicator of proliferation, showing poorer correlation with cellular proliferation markers than other PET tracers. Fluoro-3′-deoxythymidine-F18 (18F-FLT), a successfully used imaging marker of cellular proliferation, is a radiolabeled structural analog of a DNA nucleoside—thymidine—and its uptake relates to the activity of thymidine kinase 1 (TK1) that is expressed during DNA synthesis in the S-phase of the cell cycle . The uptediction . These oediction . In a recent pilot study, Kairemo et al. demonstrated the feasibility of 18F-FLT PET in monitoring treatment response by early signal activity in NSCLC patients receiving targeted therapies (c-MET inhibitors) . SeveralNext to the most common Fluor-based radiotracers employed in PET for tumour proliferation imaging, copper is another successful candidate. Functional imaging with PET employing 64Cu-ATSM (Cu-labeled diacetyl-bis(N(4)-methylthiosemicarbazone) and 18F-FDG was undertaken for the intratumoral distribution assessment of the two radionuclides in Lewis lung carcinoma tumour cells implanted in mice . Both prThis study is a clear illustration of the complexity of the tumour microenvironment and of the many factors that influence tumour development and response to therapy . Based on the above results, 64Cu-ATSM could potentially serve as a complex imaging biomarker to supply prognostic information for treatment adaptation and optimisation.Beside PET tracers, a number of researchers attempted to develop SPECT radioisotopes for novel insights into EGFR targeting. The capacity of 99mTc-HYNIC-MPG ((2-(2-(2-(2-(4-(3-chloro-4- fluorophenylamino)-6-methoxyquinazolin-7-yloxy)ethoxy)ethoxy)ethoxy)ethyl-6-hydrazinylnicotinate hydrochloride) was evaluated in detecting EGFR-activating mutations both in vitro and in vivo, using human NSCLC cell lines . The stuThe latest advances in biomaterials, specifically in nanomedicine, have greatly increased the sensitivity of imaging techniques using magnetic resonance to perform accurate and non-invasive functional imaging. In this regard, one of the recent developments is in the field of superparamagnetic iron oxide (SPIO) nanoparticles (40–50 nm), whereby polyethylene glycol-coated SPIO nanoparticles (PEG-SPIO) were synthesized and further labeled with high affinity anti-EGFR monoclonal antibody (cetuximab) for targeted delivery to lung cancer that overexpresses EGFR . The tarWhile Ki-67 is a marker of proliferation that is well studied in lung cancer, EGFR has a less clear impact and its prognostic role is obscured by new therapies currently employed in clinical practice (such as EGFR-TKIs). To justify further developments in the field of new tracers for EGFR positive NSCLC, also considering the rapid pace of treatment evolution in this subset of patients, a cost–benefit analysis would help clinicians in their decision making. While there are some promising reports, neither the treatment response prediction nor the prognosis of EGFR tumours offered by these biomarkers are convincing enough to support wide clinical implementation.Statistics show that recurrence rates among NSCLC remain as high as 30–50%, with low overall 5-year survival rates . One reaCancer stem cells (CSCs) are a subpopulation of cancer cells that coexist within a tumour with other, non-stem like cells. CSCs have several well-established properties that confer upon them immortality and resistance to both chemo and radiotherapy. Resistance to treatment is multifactorial and is due to the ability of CSCs to efficiently repair DNA damage, to recreate themselves via symmetrical division thus contributing to tumour repopulation, to preferentially reside in specific microenvironmental niches in order to conserve their status, to be recruited into the cell cycle from the quiescent phase, and to exhibit cellular plasticity that enables transformation from CSC to non-CSC state and vice versa ,34,35.While the first indicators about the presence of CSCs in lung cancer originate from the early 80s , today tOther putative lung CSCs markers that present multipotent characteristics of stem cells are CD166+/CD44+ and CD166+/EpCAM+ . Using the above markers, Zakaria et al. showed that isolated lung CSCs exhibit molecular signatures of both normal and cancer stem cells, with biological functions related to angiogenesis, mesenchymal cell differentiation, and cell migration .Another trialed CSC marker in solid tumours is CD133, with several studies demonstrating a link between CD133 expression and stem cell characteristics, including tumour aggressiveness ,41. A meOwing to their unique tumour-promoting properties, cancer stem cells must be identified in order to be targeted and eradicated. The identification and targeting of CSCs are greatly dependent on specific markers and/or a combination of markers that are expressed on the surface of cancer stem cells. As CSCs are relatively newly studied descriptors of tumour development and response to therapy, in vivo imaging of CSCs is still in its infancy. Functional imaging studies using CSC-specific radiolabeled markers have been reported for a number of solid cancers, although the majority are reported in tumour-bearing mice ,43,44,45Lewis lung carcinoma tumour cells implanted in mice were evaluated via PET imaging using 64Cu-ATSM and 18F-FDG for the assessment of intratumoral distributions of the radionuclides . Radionu3O4) nanoparticles (NPs) are widely studied and used from MRI to cancer therapy. One of the greatest advantages of these magnetic NPs is their flexibility to be designed and synthesized as multifunctional NPs, by adapting the surface ligands according to the intended application [Another imaging approach tested for CSC identification in NSCLC is MRI, via magnetic nanoparticles. Zhou et al. synthesized a multifunctional peptide–fluorescent–magnetic nanocomposite to be used for in vivo live fluorescence imaging and magnetic resonance imaging in lung tumour xenografts . Owing tlication . Specifilication , being nlication .While the number of imaging studies undertaken in lung tumours using biomarkers for CSCs is limited, they open new avenues towards personalised treatment and identify gaps that could promote further research in this field. Among imaging techniques, perhaps the most relevant for further human trials are functional imaging methods employing PET/CT, SPECT and MRI.The field of functional imaging is continuously growing with new radionuclides (PET) and magnetic nanoparticles (MRI) that have affinity towards CSCs, which could assist in the quantitative assessment of these cancer stem cells within a tumour.Most of the current evidence on the value of CSC biomarkers is based on proof-of-concept studies. Since clinically applicable techniques for noninvasive CSC imaging in NSCLC are lacking, taking the existing pre-clinical research of CSC biomarkers to the next level is greatly desirable. To be clinically implementable, there is need for CSC markers with high sensitivity and specificity, which also allow for high-resolution monitoring. With well-designed biocompatible markers, identification and targeting of cancer stem cells using functional imaging techniques could be the next step towards personalised therapy in oncology.Circulating tumour cells (CTC) are epithelial malignant cells detached from the primary tumour that underwent the epithelial–mesenchymal transition (EMT) and gained the ability to intravasate into the blood stream, migrate to distant anatomic regions and extravasate to favourable metastatic sites. The CTC population is heterogenous and consists of various cellular sub-populations with different phenotypes and functional features, including the capacity of clustering with other blood cells such as leukocytes and platelets. Owing to their ability to convert from one state to the other via EMT, the CTC population includes a subset of multipotent cells with stem-like properties, that were described above as cancer stem cells, and in this context of circulating tumour cells they are the ones responsible for cancer dissemination and formation of micrometastases . FurtherWhile distant metastasis is known as a final-stage event during cancer progression, experimental studies have shown that cancer cells can actually spread to distant anatomic sites even at early stages of cancer development . FurtherMore research into the role of CTCs reveals important insights into various correlations between factors influencing tumour development and treatment outcome prediction in NSCLC. As discussed above, the identification of EGFR mutations in advanced NSCLC patients is a critical aspect of patient stratification for optimal targeted therapies. While tumour tissue is the commonly preferred standard sample for the evaluation of EGFR mutations, for many patients such samples are not available, which is the reason why a study has been undertaken to search for a surrogate marker for EGFR status through a more accessible way . CirculaIsolation and detection of CTCs is not without challenges as the capturing technique of these cells from blood must be highly sensitive and specific, which is the reason why different methods of CTC isolation often provided conflicting results. Traditionally, the definition of circulating tumour cells encompasses three components; accordingly, a CTC is a cell that is (1) negative for the hematopoietic cell marker CD45; (2) positive for cytokeratin, a structural protein expressed by epithelial cells; and (3) positive for the epithelial cell adhesion molecule EpCAM, an epithelial cell surface marker . Having ® system, the CTC chips or the Isolation by Size of Epithelial Tumour Cells (ISET) filter device. Both the CellSearch® system and the CTC chips employ the EpCAM  to capture CTCs. The detection rate varies as a function of lung cancer type (NSCLC or SCLC) and stage, with NSCLC patients presenting with lower counts of CTCs than those diagnosed with SCLC, even in late stages of the disease [®, which exploits size-based differences between CTCs and hematopoietic cells—could offer more reliable results [CTCs are currently detected in the peripheral blood at a single cell level, with the most commonly employed techniques in lung cancer being the CellSearch disease . This ob results ,56.Studies to date show the potential of circulating tumour markers (such as CTCs and circulating tumour DNA) to serve as surrogates or markers on their own to provide treatment response monitoring, prognosis prediction, detection of early recurrence, etc., which warrants further research in evaluating their role in NSCLC.Due to their highly heterogeneous nature, imaging of circulating tumour cells at a single time point might not be relevant for outcome prediction or treatment monitoring, which is the reason why established functional imaging techniques are not adequate for this task. Instead, to evaluate all steps involved in tumour metastasis, continuous monitoring of the primary tumour and of CTCs is recommended . In suppOne of the latest technologies for real-time in vivo imaging of CTCs and CSCs employs multiphoton microscopy and antibody conjugated quantum dots . The stup = 0.0084) [High definition imaging of CTCs in NSCLC was undertaken by means of automated digital microscopy using fluorescent labeling, with the aim of quantifying the CTCs and evaluating their prognostic value in lung cancer patients . For CTC 0.0084) . CTCs coBased on the premise that both CTC counts and metabolic parameters defined by 18F-FDG can be correlated with patient prognosis, a number of studies combined the two techniques (PET imaging and CTCs quantification) to find possible relationships between them. A multi-center study that included 71 NSCLC patients  who underwent 18F-FDG PET imaging was designed to evaluate CTCs from samples within 90 days and prior to surgery or radio-chemotherapy . CTCs weA prospective biomarker trial that enrolled 53 patients with advanced NSCLC found no correlation between circulating tumour DNA (cell-free DNA) and metabolic tumour volume or total lesion glycolysis based on FDG PET imaging, hypothesizing that cell-free DNA may be representative of more complex biological mechanisms . In a siThe association of CTCs with early relapse in resected NSCLC was analysed using PET images from 102 patients both before and 1 month after radical resection . CTCs weA recent study reported preliminary data on a cohort of 17 metastatic NSCLC patients that underwent 18F-FDG PET imaging with the aim of finding a correlation between CTC numbers (determined with the ISET method) and clinical/metabolic parameters. The results indicated a strong association of CTCs present in blood with tumour uptake characterized by SUVmean . CTCs weBased on the study findings, which are corroborated by data from previous reports, it was suggested that the combination between CTC quantification and FDG PET parameters could offer an improved prognostic stratification of NSCLC patients .While to date the number of studies is limited, identification and quantification of CTCs in NSCLC could have an important impact on the evaluation of treatment response and overall prognosis. Studies have indicated that treatment of NSCLC can influence the CTC population both negatively and positively . MobilizThe role of CTCs as prognostic biomarkers is already well understood. Future developments in CTC detection in clinical practice will occur together with liquid biopsy studies of circulating tumour DNA (ctDNA). While CTCs correlation with PET parameters often show conflicting results (or weak correlations) among existing studies, further investigations are required in order to understand patient heterogeneity among NSCLC sufferers. Moreover, identification and biological characterization of CTCs could offer real-time monitoring of personalised targeted therapies in combination with functional imaging modalities.p = 0.02), while the expression of p53 and Bcl-2 was significantly associated with metastasis-free survival (p < 0.01) [Apoptosis, or programmed cell death, is a key physiological feature that ensures tissue homeostasis in normal conditions. Evasion of apoptosis is one of the hallmarks of cancer. It is acknowledged that numerous effects of radio- and chemotherapy are mediated by apoptosis, including resistance to treatment through altered apoptosis, upregulation of anti-apoptotic signals and downregulation of pro-apoptotic ones . For ins < 0.01) . The autThe insulin-like growth factor 1 receptor (IGF-1R) is a transmembrane receptor tyrosine kinase overexpressed in neoplasms, having an anti-apoptotic effect through enhancement of survival and proliferation . FurtherImaging of apoptotic pathway can serve for treatment response monitoring after radio/chemotherapy through the evaluation of apoptotic death rate. Imaging biomarkers developed for programmed cell death include annexin V labelled with common PET radionuclides such as 11C, 18F, 64Cu and 68Ga ,75. MostThe role of apoptosis in cancer development and response to therapy is well established. Although apoptosis is acknowledged as a promising target for anticancer therapy, imaging biomarkers of apoptosis are still in their early days of development, as most radiolabelled markers have not seen clinical applications. As far as lung cancer is concerned, even pre-clinical studies on apoptotic cell death imaging are scarce, requiring translation from other anatomical sites that showed promising results. There is no doubt that, nowadays, the field of oncology is strongly oriented towards personalised treatment, irrespective of the type of cancer. The latest insights into the biological and radiobiological properties of tumours and their cellular sub-populations have offered the possibility to develop and clinically implement specific tracers and markers, allowing for more accurate diagnosis, treatment planning and delivery . NSCLC pThe world of new radiobiological tracers is greatly stimulating, owing to the possibility of studying the heterogeneity of lung cancers, of stratifying tumours by their prognostic characteristics and of overcoming the limit of biopsy that often does not allow a complete and exhaustive description of the biology of such tumours. The clinical management of tumour heterogeneity is a significant challenge as tumour response is dictated by the particular behaviour of each sub-group of cancer cells. Cellular heterogeneity given by proliferation kinetics, stemness, hypoxia or other factors calls for specific markers and targeting; therefore, the near future of biomarkers will rely on complementarity rather than a common solution valid for all (radio)biological particularities of a tumour .This paper focused on three main factors influencing tumour kinetics (development and proliferation of primary tumour) and tumour dynamics (infiltration and distant metastases) in the context of NSCLC: tumour proliferation, cancer stem cells and circulating tumour cells. While advances in knowledge cover all these aspects, there is potential for improvement on the clinical side to better understand tumour resistance to chemotherapy, to augment the efficiency of immunotherapy for primary as well as metastatic cancers, and to design clinical trials that employ specific biomarkers to identify and tackle resistant tumour sub-populations. The near future will likely bring further developments in the emerging areas, such as cancer stem cell biomarkers, where research is still in pre-clinical stages, whereas in the more established fields—of proliferation and tumour progression—research has advanced into clinical phases, with the expectation of more refined utilization and wider implementation.