A closed lung system study of inert gas absorption

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Abstract
The demonstration that the rate of rise of the alveolar fraction of N2O is enhanced, when the inspired N2O concentration is high, is termed the concentration effect. A similar effect on a 2nd gas was termed the 2nd-gas effect. These effects were observed in open systems and attributed to differential changes between inspired and expired ventilation. These effects were studied in a closed system. In humans, a breath-holding maneuver was utilized with a high and low N2O concentration in Ar and O2. Breath holding with a high N2O concentration apparently concentrates both the alveolar fraction of N2O and Ar. These results are attributable to alveolar volume shrinkage as a consequence of the large absorption of N2O by the pulmonary blood. A mathematical model verified this interpretation and suggests that volume shrinkage can be important in breath-holding maneuvers designed for noninvasive measurement of cardiac output and lung tissue volume.