Dissociation of mean airway pressure and lung volume during high-frequency oscillatory ventilation

Eight kittens were studied during high-frequency oscillatory ventilation (HFOV) using an airway vibrator. HFOV was performed at 1000 and 1800 cycle/min at three present oscillatory amplitude settings and with lungs normal and injured by saline lavage. Change in lung volume (LV) during HFOV was compared to change in LV obtained during static inflation at matched mean airway pressure (Paw) of 5, 10, 15 and 20 cm H2O. LV during HFOV was significantly higher than during static inflation, and increased as oscillatory amplitude increased. LV was significantly lower after lung injury for matched HFOV settings, and was not affected by rate. Dissociation of Paw and LV during HFOV is observed implying that mean alveolar pressure (Palv) exceeds Paw during HFOV in this experimental model. The safe clinical application of HFOV may involve measurement of Palv or LV.