Pulmonary Vasoconstriction

I AHPR = acute hypoxic pressor response T he pulmonary circulation responds to acute hypoxia with increases in pulmonary artery pressure and vascular resistance. This acute hypoxic pressor response (AHPR) is a unique physiologic feature distinguishing the pulmonary from the systemic circulation which dilates in response to hypoxia.’ Since Von Euler and Liljestrand described the phenomenon of acute hypoxic pulmonary vasoconstriction within the feline pulmonary circulation, it has fascinated vascular physiologists and stimulated a substantial number of studies aimed at defining the mechanism ofthis response. Airway hypoxia is a consequence of many lung diseases. In addition, abnormalities of the pulmonary vasculature are prominent features of the pathophysiOlO y of acute and chronic respiratory failure. In this context, the AHPR occupies a unique position at the interface between the normal and abnormal pulmonary circulation in transition from health to disease. We will review the major features ofthe AHPR, and summarize the important aspects of investigations aimed at defining the mechanism of this response. In addition, we will discuss the known factors which modify the response in the clinical setting. We will place special emphasis on information obtained within the last five years, especially recent findings concerning the vascular endothelium.