Hypoxic pulmonary vasoconstriction
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Hypoxic pulmonary vasoconstriction is the phenomenon when pulmonary arterioles vasoconstrict in the presence of hypoxia (low oxygen levels) without hypercapnia (high carbon dioxide levels).
The process is at first illogical, as low oxygen levels should theoretically lead to increased blood flow to the lungs to receive increased gaseous exchange.
It is explained, however, by the fact that constriction leads to more bloodflow to unused parts of the lungs, which increases the total area of lungs that are involved in gaseous exchange.
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Several factors inhibit this process including increased cardiac output, hypocarbia, hypothermia, acidosis/alkalosis, increased pulmonary vascular resistance, inhaled anesthetics, calcium channel blockers, PEEP, HFV, isoproterenol, nitrous oxide, vasodilators.
