A closed lung system study of inert gas absorption

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.