High-Frequency Ventilation Attenuation of Hypoxic Pulmonary Vasoconstriction

In order to determine the effects of high-frequency ventilation on the pulmonary vascular response to hypoxia, we assessed pulmonary vascular resistance at 2 levels of inspired oxygen tension (PiO2), 200 and 30 mmHg, during conventional and high-frequency ventilation in the isolated, blood-perfused lungs of 10 sheep, 5 treated with indomethacin (40 µg/ml of perfusate) and 5 untreated. Resistance was assessed by measuring pulmonary artery pressure-flow curves generated over a wide range of flows (20 to 140 ml·min−1·kg body wt−1). Conventional ventilation was provided by an animal ventilator at a rate of 10 min−1 and a tidal volume of 10 ml·kg body wt−1. High-frequency ventilation was provided by a flow interrupter at a rate of 1,200 min−1 and a tidal volume less than 1.5 ml·kg body wt−1. In the 5 untreated lungs, the normoxic pressure-flow curve was unaltered by high-frequency ventilation, but the hypoxic pulmonary vasoconstrictor response was significantly attenuated. Furthermore, the net rate of change o...