The HPV response is different with constant pressure vs constant flow perfusion

Hypoxic pulmonary vasoconstriction (HPV) may be manifest in one of two ways: either an increase in the pulmonary artery pressure, or flow diversion away from the portion of the pulmonary bed with reduced conductance. We tested the hypothesis that the magnitude of the HPV response differs under conditions of constant flow perfusion, where pulmonary artery pressure (Ppa) rises during hypoxia, vs conditions of constant pressure perfusion, where Ppa remains constant and flow (Q) is diverted away from the lungs during hypoxia. In isolated, perfused rabbit lungs, the HPV response to four levels of hypoxia (12, 6, 3 and 0% oxygen) was of greater magnitude and more sustained under conditions of constant pressure perfusion as compared to constant flow perfusion. The possible significance of these findings as they relate to interpretation of studies in both the perinatal and mature pulmonary circulation is discussed.