Pulmonary blood flow regulation: Influence of positive pressure ventilation

Abstract

Positive pressure ventilation with PEEP has been reported to reduce hypoxic pulmonary vasoconstriction (HPV) and thus increase venous admixture. This effect was investigated in six chronically instrumented unanesthetized healthy sheep. The change in left pulmonary arterial blood flow (Q̇lpa, ultrasonic transit time) in response to unilateral lung hypoxia (10 min of N 2 alternately to the left (LLH) and right lung (RLH)) was evaluated during mechanical ventilation with and without PEEP of 10 cm H 2O in comparison to spontaneous breathing. In the spontaneously breathing animal and during mechanical ventilation without PEEP, Q̇lpa decreased during LLH from 30% to 16% of cardiac index, during RLH it increased to 51%. With 10 cm H 2O of PEEP, Q̇lpa showed an identical reaction to hypoxia both in the left and right lung. It is concluded that mechanical ventilation and PEEP up to 10 cm H 2O does not interfere with pulmonary blood flow regulation to hypoxia.