Modeling the alveolar Ar after been squeezed by inspiring room air

Abstract

The experiment of inhaling 1.9L of 79% argon in O2 was modeled previously (Cruz. Respir. Physiol. 86:1, 1991). To account for the argon inhaled, 1.501L, a large dead space, 0.425L, was necessary. Moreover, 1.9L of air was inhaled to reach TLC. Thus, the alveolar Ar that was inhaled previously was squeezed and pushed in to the end of Weibel's generations. We recently showed that the expired CO2, previously diluted in the alveoli, became more evident with the forced expiration and revealed the effect of alveolar CO2 diffusion from RV to ERV (Caucha's et al. FASEB J. 24:1063.5, 2012). Now, we modified Caucha's model to simulate the Ar expirogram, changing the number of generations assigned for convection, convection‐diffusion and diffusion in the seven parallel regions from apex to base of the lung. The Figure shows two kinds of experiments, the first one simulates the experiment of Cruz in 1991. This is depicted on the left scale (dashed curve) with a volume expired of 4.5L. The “sandwich” experiment is shown on the right scale (for clarity) with a volume expired of 6.4L. The total argon inhaled is now in the alveoli and 1.24L of Ar was exhaled. Thus, more Ar was diffused to RV to reach 0.234L in the model presented (error of 1.7%). Note that the curve shown is the one that would be obtained during expiration after the alveolar argon was diluted and squeezed by inhaling air. The alveolar plateau reached the ideal alveolar gas mixing, 0.20 [Amount of Ar/(Total Lung Capacity‐Dead space)] at 3.8L‐4.23L (horizontal dotted line). However, the slope of phase IV is negative.Supported in part by CEIS (Centro de Enseñanza, Investigación y Servicios).