Hypoxic Pulmonary Vasoconstriction

Overview

Hypoxic pulmonary vasoconstriction reduces perfusion in poorly ventilated regions of the lungs and redistributes perfusionto the well-ventilated areas. It therefore decreases venous admixture and optimizes the oxygenation of arterial blood. It isalready present in the foetal period when it contributes to the decrease of the overall pulmonary blood flow. It is acceptedtoday that all mechanism of hypoxic pulmonary vasoconstriction are localized in the pulmonary vascular smooth musclecells. The mechanisms of cellular oxygen sensing are still obscure. Hypoxia inhibits the potassium channels leading tomembrane depolarisation of smooth muscle cells and to the opening of voltage gated calcium channels. Then the influx ofcalcium ions into cytoplasm is increased. The release from the intracellular Ca2+stores participates also. The rise of freecytoplasmatic calcium induces vascular smooth muscle contraction.

Key words:
hypoxia – potassium channels – intracellular calcium – smooth muscle – membrane potential