Alveolar pressure swings during high frequency ventilation in rabbits

In order to understand the pressures and volumes delivered during ventilation with the Emerson flow-interrupting high frequency ventilator, we have measured dynamic and mean pressures at the airway opening, trachea, and alveoli as well as delivered volumes in vivo in closed-chest adult rabbits ventilated at rates of 2-37.5 Hz. To measure alveolar pressure we opened the chest, glued an alveolar capsule to the visceral pleural surface, punctured the pleura and lung surface through the capsule, inserted a pressure transducer into the capsule and closed the chest. We measured delivered volume with a pressure plethysmograph. Alveolar pressure swings fell with increasing frequency, as did delivered volume. Alveolar pressure swings were always lower than those at the airway opening or in the trachea. Removal of the rib cage resulted in a decrease in alveolar pressure swings although muscle paralysis had little effect. Mean pressures were equal at the airway opening, trachea, and alveoli at all frequencies. These results suggest that using the high frequency ventilator tested, to minimize alveolar barotrauma one should choose the highest frequency where gas exchange is adequate.