Inert Gas Measurements Research Articles

Conditions for equivalence of gas exchange in series and parallel models of the lung

The Fick principle was applied to series and parallel compartmental lung models to determine whether conditions existed under which their differentiation was theoretically possible. Respiratory and inert gases were examined under assumptions of steady-state gas exchange, continuous ventilation and bloodflow, perfect mixing within each compartment and alveolar-endcapillary diffusion equilibration. Algebraic analyses allowing broad generalizations were possible for inert gases but not for O 2 and CO 2 for which numerical methods were required. For trace amounts of inert gases present in venous blood but absent from inspired air, a given series model always had an exact parallel equivalent. When inert gases were then inspired, equivalence was lost if more than one ‘resident’ gas (inert or respiratory) was soluble, but the discrepancies were two orders of magnitude smaller than current experimental errors in inert gas measurements. Consequently, steady-state trace inert gas exchange cannot in practice be used to differentiate series from parallel models, but by the same token, if series gas exchange occurs, equivalent parallel analysis is possible.

An efficient optimization technique for recovering ventilation-perfusion distributions from inert gas data. Effects of random experimental error.

A variable metric optimization method of numerical analysis has been used to recover known distributions of intrapulmonary ventilation-perfusion ratios from inert gas data. Hypothetical lungs were simulated and corresponding inert gas retentions calculated. By using error-free retentions for seven gases and a 50-compartment model, it was possible to recover distributions containing up to three modes accurately and with greater efficiency than with other numerical methods. When random error of a magnitude consistent with present analytical techniques was introduced into retention data, the recovered distributions differed qualitatively from the original ones. This resulted from the ill-conditioned nature of the mathematical problem, which makes a recovered distribution extremely sensitive to small errors in retention. Thus, present levels of measurement error represent an important limitation in current techniques for deriving distributions from inert gas measurements.

Green spherules from Apollo 15: Inferences about their origin from inert gas measurements

Green spherules from the ‘clod’ 15426 and from fines 15421 contain about 100 times less trapped inert gases than normal bulk fines from Apollo 15. These spherules have apparently never been directly exposed to the solar wind. Spherules from other fines contain about 10 times more trapped gas than those from the ‘clod’. The gas in the former is surface correlated. However, spherules from fines 15401 are exceptionally gas-poor. (He4/Ne20) T in all spherules is commonly less than 10, which implies severe He4 losses. (Ne20/Ar36) T on the other hand is nearly always greater than 10; and ranges up to 20.3.

Inert gas measurements of coronary blood flow

Several factors which are of interest when measuring coronary blood flow by inert gas technics are reviewed. The major problems in these measurements arise when flow is not uniform throughout the heart. Methods of delivery and analysis of gas must be adequate to quantitate persistent venous-arterial (or tissue-arterial) differences produced by areas of low flow. The effects of these areas on measured gas exchange can vary with different experimental approaches. Methods of calculating flow from desaturation curves also vary and sometimes involve assumptions concerning the distribution of flow within the heart. Potential problems are also presented by right atrial “contamination” of sampled coronary venous blood, by extracardiac “contamination” of precordially monitored myocardial gas content, and by the contribution to measured gas exchange of cardiac adipose tissue. All these considerations are particularly important in measurements in disease states.