Technical pitfalls in middle ear gas studies: Errors introduced by the gas permeability of tubing and additional dead space
Conclusions We demonstrated errors introduced by the gas permeability of the tubing and additional dead space. Materials with practically no permeability, such as glass, must be used to overcome the loss or gain of gas through the walls of tubes used for studying ME gas variations. Experiments conducted at a constant volume (variable pressure) require the smallest possible tubing volume in order to obtain good sensitivity and improve the accuracy of the results. Objectives Experimental studies that investigate middle ear (ME) gas exchanges, using either pressure measurements or volume changes, are conducted using various tubing connections between the ME and a measuring device. The aims of this study were to highlight experimental problems due to the errors introduced by (i) the gas permeability of the tubing used and (ii) additional dead space in experiments conducted at constant volume. Material and methods The problem of the gas permeability of the tubing was addressed by comparing three types of tube (silicone, polyethylene, PVC) with a glass tube. Horizontally placed tubes were connected to a syringe filled with pure CO2 via a gas-tight valve. The end of each tube tested was plunged into colored water (5% Coomassie Brilliant Blue R-250). The tube was washed out with CO2 until gas bubbles were seen leaving it. The valve was then closed and the movement of water in the tube was observed. The same experiments were repeated for pure O2. The problem of the error introduced by the additional dead space volume was addressed at a theoretical level using the well-known gas laws. Two conditions were studied: condition A, in which the experiment was conducted at constant pressure and the volume was measured; and condition B, in which the experiment was conducted at constant volume and the pressure was measured. The main outcome measure of each condition was the calculated variation in the final number of moles of gas involved. Results No water movement was observed in glass tubes. In contrast, plastic tubes exhibited significant gas permeability effects for both CO2 and O2. The colored solution advanced at a faster rate with CO2 than O2 but differently for each type of tubing. For condition A, gas transfer was independent of the volume of the external tubing and was accurately measured by the displacement of the droplet in the lumen. In contrast, for condition B, the pressure variations were influenced by the volume of the tubing.
Middle ear gas loss in inflammatory conditions: The role of mucosa thickness and blood flow
Several middle ear (ME) pathologies are associated with ME gas deficit. These include in particular the chronic otitis media diseases that are associated with inflammation (hence, increased ME mucosal blood flow) and/or reduced Eustachian tube (ET) function. The present study models the trans-mucosal gas exchange in normal and inflamed middle ears of rats. The model evaluates the role of the gas diffusion path in the ME mucosa using mucosa thickness as its index and the role of the mucosal blood flow rate on ME gas economy in order to compare between normal and inflamed MEs. An experimental method employing ME gas volume changes at constant pressure due to trans-mucosal gas exchange, and blood gas values from the literature, was used in anaesthetized rats to corroborate the model. Mucosa thickness was measured as an index of the gas diffusion path between the ME space and the ME circulation. ME inner surface area was estimated from its measured gas volume. Inflammation was inflicted by applying lipopolysaccharide (LPS) into one ear. The contralateral ear served as control. ME gas volume decreased significantly faster with time (p=0.02) in inflamed ears (-0.107 microL min(-1) +/- 0.034 S.D., n=10) versus control ears (-0.067 microL min(-1) +/- 0.036 S.D., n=10). Mucosa thickness was significantly thicker in inflamed ears (48.4 microm +/- 11.0 S.D.) versus controls (20.5 microm +/- 10.1 S.D.). The mathematical model, the experimental results, and the blood gas values were used to estimate the relative effective mucosal blood flow rate. The model predicts that in spite of almost doubling mucosa thickness in LPS treated ears, the increased gas loss in inflamed ears may be explained by increased mucosal blood flow rate. We suggest that the ability to estimate ME blood flow as obtained by applying the model to the measurements, is relevant to medical management of inflamed ME.
Numerical tools applied to power reactor noise analysis
In order to be able to calculate the space- and frequency-dependent neutron noise in real inhomogeneous systems in two-group theory, a code was developed for the calculation of the Green's function (dynamic transfer function) of such systems. This paper reports on the development as well as the test and application of the numerical tools employed. The code that was developed yields the space-dependence of the fluctuations of the neutron flux induced by fluctuating properties of the medium in the two-group diffusion approximation and in a two-dimensional representation of heterogeneous systems, for both critical systems and non-critical systems with an external source. Some applications of these tools to power reactor noise analysis are then described, including the unfolding of the parameters of the noise source from the induced neutron noise, measured at a few discrete locations throughout the core. Other concrete applications concern the study of the space-dependence of the Decay Ratio in Boiling Water Reactors, the noise-based estimation of the Moderator Temperature Coefficient of reactivity in Pressurized Water Reactors, the modeling of the beam- and shell-mode core-barrel vibrations in Pressurized Water Reactors, and the investigation of the validity of the point-kinetic approximation in subcritical systems driven by an external source. In most of these applications, calculations performed using the code are compared with at-power plant measurements. Power reactor noise analysis applications of the above type, i.e. core monitoring without disturbing plant operation, is of particular interest in the framework of the extensive program of power uprates worldwide.