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Hypoxic pulmonary vasoconstriction is a physiological phenomenon in which pulmonary arteries constrict in the presence of hypoxia (low oxygen levels) without hypercapnia (high carbon dioxide levels), redirecting blood flow to alveoli with a higher oxygen content. The process might at first seem illogical, as ''low'' oxygen levels should theoretically lead to ''increased'' blood flow to the lungs to receive increased gaseous exchange. However, it is explained by the fact that constriction leads to redistribution of bloodflow to better-ventilated areas of the lung, which increases the total area involved in gaseous exchange. This improves ventilation/perfusion ratio and arterial oxygenation, but is less helpful in the case of long-term whole-body hypoxia. This is seen in COPD, at altitude, and in heart failure. Several factors inhibit this process including increased cardiac output, hypocapnia, hypothermia, acidosis/alkalosis, increased pulmonary vascular resistance, inhaled anesthetics, calcium channel blockers, positive end-expiratory pressure (PEEP), high-frequency ventilation (HFV), isoproterenol, nitrous oxide, and vasodilators. ==High altitude pulmonary edema== (詳細はhigh altitude pulmonary edema (HAPE). For this reason, most climbers carry supplemental oxygen to prevent hypoxia, edema, and HAPE. The standard drug treatment of dexamethasone does not alter the hypoxia or the consequent vasoconstriction, but stimulates fluid reabsorption in the lungs to reverse the edema. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hypoxic pulmonary vasoconstriction is a physiological phenomenon in which pulmonary arteries constrict in the presence of hypoxia (low oxygen levels) without hypercapnia (high carbon dioxide levels), redirecting blood flow to alveoli with a higher oxygen content. The process might at first seem illogical, as ''low'' oxygen levels should theoretically lead to ''increased'' blood flow to the lungs to receive increased gaseous exchange. However, it is explained by the fact that constriction leads to redistribution of bloodflow to better-ventilated areas of the lung, which increases the total area involved in gaseous exchange. This improves ventilation/perfusion ratio and arterial oxygenation, but is less helpful in the case of long-term whole-body hypoxia. This is seen in COPD, at altitude, and in heart failure.Several factors inhibit this process including increased cardiac output, hypocapnia, hypothermia, acidosis/alkalosis, increased pulmonary vascular resistance, inhaled anesthetics, calcium channel blockers, positive end-expiratory pressure (PEEP), high-frequency ventilation (HFV), isoproterenol, nitrous oxide, and vasodilators.==High altitude pulmonary edema==(詳細はHigh altitude pulmonary edemaを参照)Climbing tall mountains can induce full lung hypoxia due to decreased atmospheric pressure. This hypoxia causes hypoxic vasoconstriction that ultimately leads to high altitude pulmonary edema (HAPE). For this reason, most climbers carry supplemental oxygen to prevent hypoxia, edema, and HAPE. The standard drug treatment of dexamethasone does not alter the hypoxia or the consequent vasoconstriction, but stimulates fluid reabsorption in the lungs to reverse the edema. 」の詳細全文を読む スポンサード リンク
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