Simulation of expired nitrogen (N2) after inhaling and exhaling fast a non‐N2 gas

Abstract

We don't know how much N2 is in the alveoli at the end of any expiration. The past April, expired N2 was presented after inhaling fast 1.9L of 79% Ar in O2 and exhaled fast (Cruz. FASEB J. 26:1082.3, 2012). Now, an attempt is made in simulating expired N2 after O2 inhalation from RV (1.4L) or FRC (4.L). The subject has a TLC=7.8L and a VC=6.4L. The model uses a VD=0.35L that is distributed from 0.018L at the apex, to 0.082L at the base of the lung. A N2=0.8 was assumed at RV or FRC. The model published (Cruz, Respir. Physiol. 86:1, 1991) has been improved by introducing the time variable to the exponential equation. Thus, the alveolar N2 fractions are now functions of lung volume and time. After exhaling to FRC or RV, 3.8L or 6.4L of O2 were inhaled in 2s and exhaled in 3s. The total expired N2 at FRC was 2.501L and at RV was 0.854L. The difference, 1.647, is exactly what would be exhaled if the total 2.08L of N2, present in the ERV, was diluted by O2. For clarity, only the classic maneuver is presented, which was executed fast to decrease the effect of alveolar gas diffusion and to avoid the cardiogenic oscillations during expiration (see Figure). The area under the expired curve was 0.854L and what remained at RV was 0.266, the balance of total N2 present at RV, prior to O2 inhalation. Remember that the curve is produced by the weighted average of uneven flows coming out from apex to base of the lung. Also, note the presence of Phase IV.Supported in part by Center of Teaching, Research and Services (CEIS).