Physiology of Hypoxic Pulmonary

Hypoxic pulmonary vasoconstriction is the unique re-sponse of the lung circulation to ventilation with hy-poxic gas, resulting in an increase in pulmonary arterial pressure and vascular resistance. The site of hypoxic vasoconstriction is the small pulmonary arteries. The hypoxic pressor response optimizes ventilation and per-fusion matching and thus preserves arterial oxygen ten-sion. The mechanism of this response is not clear, al-though considerable knowledge has been gained about its modulation. We review the current state of under-standing of the physiology and pathophysiology of hy-poxic pulmonary vasoconstriction. When lungs are ventilated with hypoxic gas, pulmo-nary arterial pressure and vascular resistance in-crease. This phenomenon, which is unique to the pulmonary circulation, was first described in 1946 [1]. In contrast, the systemic vasculature dilates in response to hypoxemia [2]. The hypoxic pressor response is part of the pathophysiology of lung dis-eases that result in alveolar hypoxia; many of these lung diseases may necessitate admission to an in-tensive care unit. We review the physiology and pathophysiology of hypoxic pulmonary vasocon-striction and the clinical significance of this re-sponse in the care of acutely ill patients