High-frequency oscillatory ventilation of a canine bronchopleural fistula

We hypothesized that during high-frequency oscillatory ventilation (HFOV) of a central bronchopleural fistula (BPF), gas flow through the fistula (Vleak) should vary with ventilatory frequency. In six pentobarbital-anesthetized, open-chested dogs, we inserted a cannula into the left lower lobe bronchus. After 30 min of HFOV at 5 Hz (fistula closed), they received four periods of HFOV (fistula open) at frequencies of 5, 10, 15, and 20 Hz. With the fistula open, we could adequately ventilate at all four frequencies. Vleak ranged between 5.1 +/- 0.7 and 4.1 +/- 0.7 L/min and it was not significantly different at any frequency by analysis of variance. Airway opening pressure (Pao) was 3.9 +/- 0.6 cm H2O with the fistula closed. Pao decreased significantly to 1.9 +/- 0.2 cm H2O during 5 Hz ventilation (fistula open). Pao at the other frequencies was similar to fistula-closed ventilation. We believe that expiratory flow limitation at frequencies greater than 5 Hz may explain our findings.