Influence of expiratory flow on closing capacity at low expiratory flow rates.
Single-breath oxygen (SBO2) tests at expiratory flow rates of 0.2, 0.5, and 1.01/s were performed by 10 normal subjects in a body plethysmograph. Closing capacity (CC)--the absolute lung volume at which phase IV began--increased significantly with increases in flow. Five subjects were restudied with a 200-ml bolus of 100% N2 inspired from residual volume after N2 washout by breathing 100% O2 and similar results were obtained. An additional five subjects performed SBO2 tests in the standing, supine, and prone positions; closing volume (CV)--the lung volume above residual volume at which phase IV began--also increased with increases of expiratory flow. The observed increase in CC with increasing flow did not appear to result from dependent lung regions reaching some critical "closing volume" at a higher overall lung volume. In normal subjects, the phase IV increase in NI concentration may be caused by the asynchronous onset of flow limitation occurring initially in dependent regions.
D000328:Adult; D006801:Humans; D008168:Lung / Q000502:physiology; D008176:Lung Volume Measurements; D008448:Maximal Expiratory Flow Rate; D008875:Middle Aged; D009584:Nitrogen; D010366:Peak Expiratory Flow Rate; D010993:Plethysmography, Whole Body; D011187:Posture; D012123:Pulmonary Ventilation; D012907:Smoking
D009584:Nitrogen