Alveolar pressure, airflow rate, and lung inflation in man

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Abstract
Transairway pressure (Paw = Palv - Pao), flow rate (V), and thoracic gas volume (TGVPalv) were measured simultaneously in 5 healthy subjects, at up to maximal flows and over nearly the full vital capacity [VC]. during rebreathing at BTPS [body temperature and pressure saturated with water vapor] conditions. Isovolume pressure-flow (IVPF) curves and volumeflow (VV) diagrams were obtained. The constants in equations describing Paw-V relations were obtained at different lung inflations. IVPF points are not unique under some conditions: during inspiration Raw depends on preinspiratory volume (Raw higher during inspirations from near residual volume); during expiration considerable IVPF variability occurs at near-maximum flows. The latter phenomenon is discussed in terms of optimal and suboptimal Paw-V relations, depending on volume and flow history as well as on sudden pressure transients in the dynamically compressed airway segment. Hlstamine inhalation caused marked, dose-related, changes of expiratory IVPF points at small TGV, in the absence of dyspnea. Variations in Pst(l) largely account for between-subject variation of"relative conductance"(standardized for lung size), and for Gaw changes with lung inflation within subjects. Instantaneous expiratory power may exceed 50 w during forced expirations.

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