Effect of gas compression on pulmonary pressure, flow, and volume relationship

Abstract

The time course of lung volume change ([DELTA]VL) due to compression and displacement of gas as measured plethysmographically was simultaneously related to the time courses of expired volume ([DELTA] V), transpulmonary pressure (P) and flow (F) during vital capacities (VC) of varying effort in 5 normal subjects and 10 patients with obstructuve airway disease. Isovolume PF relationships based on [DELTA]V and [DELTA] VL were compared, as were F versus [DELTA]V and F versus [DELTA] VL curves. Over the lower 75% of the expiratory VC at higher pressures, flow was greater for a given [DELTA] VL than [DELTA] V. High pressure by compressing gas decreases lung volume more than [DELTA] W indicates. On isovolume [DELTA] VL PF curves maximal were poorly defined, as contrasted with isovolume [DELTA] V PF curves. These differences were reflected in F versus [DELTA] VL and F versus [DELTA] v curves. Large lung volumes and high airway resistance in patients with obstructive airway disease magnified these differences. PF relationships at a constant lung volume can only be obtained plethysmographically.