AIRWAY-CLOSURE AND REOPENING ASSESSED BY THE ALVEOLAR CAPSULE OSCILLATION TECHNIQUE

An alveolar capsule oscillation technique was used to determine 1) the lobe pressure and volume at which airways close and reopen, 2) the ef fect of expiration rate on closing volume and pressure, 3) the phase i n the breathing cycle at which airway closure occurs, and 4) the site of airway closure. Experiments were conducted in excised dog lobes; cl osure was detected by an abrupt increase in the input impedance of sur face-mounted alveolar capsules. Mean transpulmonary pressure (Ptp) at closure was slightly less than zero (Ptp = -2.3 cmH(2)O); the correspo nding mean reopening pressure was Ptp = 14 cmH(2)O. The expiration rat e varied between 1 and 20% of total lobe capacity per second and had n o consistent effect on the closing volume and pressure. When lung volu me was cycled up to frequencies of 0.2 Hz, closure generally occurred on expiration rather than inspiration. These observations support the conclusion that mechanical collapse, rather than meniscus formation, i s the most likely mechanism producing airway closure in normal excised dog lungs. Analysis of measured acoustic impedances and reopening pre ssures suggests that closure occurs in the most peripheral airways. Re opening during inspiration was often observed to consist of a series o f stepwise decreases in capsule impedance, indicating a sequence of op ening events.