Measuring oxygen consumption with an all-electronic multi-range digital respirometer
Oxygen consumption of animals is often measured for studies in physiological ecology. Usually a closed respiration chamber containing a carbon-dioxide-absorbing substance is used. Oxygen consumed by the animal is either compensated by reduction of the vessel volume (Kratochvil 1976) or replaced by electrolysis (Heusner etal. 1965; Rufeger 1968, 1980). Manometers of various kinds are always employed for pressure transmission. All chambers are kept at constant temperature by a thermostatically controlled water bath. The advantage of an electrolytic respirometer is that the quantity of oxygen generated is linearly dependent only on current and independent of air pressure and temperature. The breathing air composition before, during, and after measurement is constant. After equilibration such a system allows direct oxygen consumption measurements at various environmental temperatures without making corrections. In the apparatus described here power supply, time pulse generator, constant current generator, and the processor which controls the operation and calculates the results are joined in a common box. In front of it the counter displays and the switch board with optical and acoustic signals are arranged. A newly designed manometer with adjustable sensitivity and an infra-red sensor drives a digital position discriminator. This amplification of the manometer reading permits a very simple zero adjustment. All the usual types of gas chamber may be used, for instance equipment consisting only of an electrolytic cell, respiration chamber, and compensating chamber (Heusner et al. 1965), as well as extensive additional fittings, with pump-driven air circulation and separate carbon dioxide and humidity absorption vessels (Moyat 1957; Rufeger 1968, 1980). Contact manometers constructed earlier may be connected on a separate input.
(APPLICATION OF COULOMETRY TO THE MEASUREMENT OF OXYGEN CONSUMPTION)(FR).
L’appareil decrit permet d’enregistrer pendant de longues durees (jusqu’a deux semaines) de tres faibles consommations d’oxygene (50 μl h−1 a 10.000 μl h−1). On remplace quantitativement le volume d’oxygene consomme par de l’oxygene produit par electrolyse.
Optimized Delivery System Achieves Enhanced Endomyocardial Stem Cell Retention
Background—Regenerative cell-based therapies are associated with limited myocardial retention of delivered stem cells. The objective of this study is to develop an endocardial delivery system for enhanced cell retention. Methods and Results—Stem cell retention was simulated in silico using 1- and 3-dimensional models of tissue distortion and compliance associated with delivery. Needle designs, predicted to be optimal, were accordingly engineered using nitinol, a nickel and titanium alloy displaying shape memory and superelasticity. Biocompatibility was tested with human mesenchymal stem cells. Experimental validation was performed with species-matched cells directly delivered into Langendorff-perfused porcine hearts or administered percutaneously into the endocardium of infarcted pigs. Cell retention was quantified by flow cytometry and real-time quantitative polymerase chain reaction methodology. Models, computing optimal distribution of distortion calibrated to favor tissue compliance, predicted that a 75°-curved needle featuring small-to-large graded side holes would ensure the highest cell retention profile. In isolated hearts, the nitinol curved needle catheter (C-Cath) design ensured 3-fold superior stem cell retention compared with a standard needle. In the setting of chronic infarction, percutaneous delivery of stem cells with C-Cath yielded a 37.7±7.1% versus 10.0±2.8% retention achieved with a traditional needle without effect on biocompatibility or safety. Conclusions—Modeling-guided development of a nitinol-based curved needle delivery system with incremental side holes achieved enhanced myocardial stem cell retention.