ALVEOLAR GAS-COMPRESSION IN SMOKERS AND ASTHMATICS

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Abstract
To correlate the degree of alveolar gas compression with the severity of airway obstruction, exhaled and plethysmographic maximal expiratory flow volume (MEFV) curves were plotted separately in each of 4 healthy human nonsmokers, 4 asymptomatic smokers and 4 asymptomatic asthmatics. Spirometry, lung volumes, single breath N2 plateau (Phase III) and closing volumes (Phase IV) were normal in the smokers and nonsmokers, and they were either normal or showed evidence of mild airway obstruction in the asthmatics. MEFV curves were plotted by using exhaled flow (.ovrhdot.VE) vs. exhaled volume (VE), and by using plethysmographic flow (.ovrhdot.VL) vs. plethysmographic volume (VL). These curves were utilized to construct isovolume pressure-flow (IVPF) curves of esophageal pressure (Pes) vs. .ovrhdot.VE and vs. .ovrhdot.VL for each subject. Differences in the flow (.ovrhdot.VL minus .ovrhdot.VE) were calculated from these curves at 75% vital capacity (VC), 50% VC and 25% VC at the same Pes in all 3 groups. At 75% VC the mean flow difference in the asthmatic group was significant higher than in normals (P < 0.05); at 50% VC it was significantly higher in the asthmatics and the smokers (P < 0.05); at 25% VC there was no significant difference among the 3 groups. The mean plethysmographic forced vital capacity (FVC) exceeded exhaled FVC in all 3 groups, but the difference was significantly higher in smokers and asthmatics than in nonsmokers (P < 0.05). Significant alveolar gas compression may occur at 75% VC in mild asthmatics; in smokers it occurs at the middle portion of the VC.