DYNAMICS OF SOLUBLE GAS-EXCHANGE IN THE AIRWAYS .3. SINGLE-EXHALATIONBREATHING MANEUVER

The exchange characteristics of a highly soluble gas with the pulmonar y airways during a single-exhalation maneuver were analyzed using a ma thematical model previously described by our group (M. E. Tsu et al. A nn. Biomed. Eng. 16: 547-571, 1988). The model integrates the simultan eous exchange of water, heat, and a soluble gas with the pulmonary air ways. The purpose of this paper is to provide experi mental data for m odel validation. Exhaled ethyl alcohol concentration profiles of human subjects were measured with an Intoxilyzer 5000 and were plotted agai nst exhaled volume measured with a wedge spirometer. Each subject perf ormed a series of breathing maneuvers in which exhalation flow rate wa s the only variable. Phase III has a positive slope (0.047 +/- 0.0089 mol alcohol in air.mol alcohol in alveolus(-1).1(-1)) that is statisti cally independent (P > 0.05) of flow rate. Reducing the molecular diff usion coefficient of alcohol in the nonperfused tissue layer improves the fit of the model to the experimental data. The optimal diffusion c oefficient of alcohol for all subjects was 12 +/- 5.3 (SD) X 10(-7) cm (2)/s, which is 8% of the diffusion coefficient of alcohol in water (1 .6 X 10(-5) cm(2)/s). We concluded that the experimental data showing a positive slope of the exhaled alcohol profile are consistent with a reduced diffusivity of alcohol in the respiratory mucosa. The reduced diffusion coefficient enhances reabsorption of alcohol by the airways on exhalation and creates a positive phase III slope.