Attenuation of hypoxic pulmonary vasoconstriction by pulsatile flow in dog lungs

We measured pulmonary arterial pressure in isolated lower lobes of dog lungs perfused in situ at several flows during ventilation with 95% O2-5% CO2 and with 3% O2-5% CO2. Pulsatile perfusion was provided by a piston pump, and steady perfusion was provided by a roller pump. The slope of the pressure-flow curve was 16.1 +/- 1.6 Torr X 1(-1) X min at all flows between 200 and 800 ml/min during 95-5 ventilation and increased to 19.4 +/- 3.7 in hypoxia. When flow was 600 ml/min, with 95-5 ventilation, mean arterial pressure was 16.2 +/- 1.2 Torr in steady flow and was unchanged at 15.0 +/- 1.0 Torr in pulsatile flow. At the same flow during hypoxic ventilation, mean arterial pressure increased to 27.9 +/- 2.4 Torr (P less than 0.01) when flow was steady but only to 19.3 +/- 1.6 Torr (P less than 0.01) when flow was made pulsatile. Thus hypoxia increased perfusion pressure by a nearly parallel shift of the pressure-flow curve to higher pressures, and this change was smaller in pulsatile than in steady flow.