hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction occurs when alveolar PO2 decreases (e.g., due to airway obstruction, atelectasis, or high altitude), triggering constriction of pulmonary arterioles supplying that hypoxic alveolar unit. The mechanism involves inhibition of oxygen-sensitive potassium channels in pulmonary vascular smooth muscle cells, leading to membrane depolarization, calcium influx through voltage-gated calcium channels, and smooth muscle contraction. This is mediated in part by mitochondrial reactive oxygen species signaling changes under hypoxic conditions.

Physiologically, this response is adaptive at the local level—by shunting blood away from poorly ventilated alveoli, it minimizes wasted perfusion and improves overall gas exchange efficiency, maintaining V/Q matching. This is the opposite of systemic vessels, which vasodilate in response to hypoxia to increase oxygen delivery to tissues.

However, when hypoxia is global rather than regional (e.g., high altitude, COPD, obstructive sleep apnea, interstitial lung disease), HPV occurs diffusely throughout the lung, causing widespread pulmonary vasoconstriction. This increases pulmonary vascular resistance and pulmonary artery pressure, potentially leading to pulmonary hypertension and, if chronic, right ventricular hypertrophy and cor pulmonale.

Clinical relevance includes: (1) understanding why patients with chronic lung disease develop pulmonary hypertension and right heart strain; (2) anesthesia considerations during one-lung ventilation, where HPV helps redirect blood flow away from the collapsed lung, but volatile anesthetics can blunt this response; (3) altitude physiology and high-altitude pulmonary edema (HAPE) pathogenesis, thought to involve uneven HPV causing localized overperfusion and capillary stress failure.