Long volume during high frequency oscillation.

Previous investigators have reported alarming gas trapping during high frequency oscillation. We have assessed trapping by measuring the difference between occlusion pressure (alveolar pressure) and measured maximal mean airway circuit pressure. Under normal operating conditions, we were unable to demonstrate trapping in normal or lung-lavaged rabbits at 15 or at 25 Hz, or in infants with infant respiratory distress syndrome, but we could produce trapping by operating at unusually low mean airway pressure. At these low pressures, lung volume is low, and we believe that choke points develop that limit maximal expiratory flow.