Hypoxic Pulmonary Vasoconstriction and Chronic Lung Disease

Erik R. Swenson, MD Departments of Medicine and Physiology and Biophysics University of Washington VA Puget Sound Health Care System Seattle, WA Hypoxic vasoconstriction in the lung is a unique and fundamental characteristic of the pulmonary circulation. It functions in health and disease states to better preserve ventilation-perfusion matching by diverting blood flow to better ventilated regions when local ventilation is compromised. As more areas of lung become hypoxic either with high altitude or global lung disease, then hypoxic pulmonary vasoconstriction (HPV) becomes less effective in ventilation-perfusion matching and can lead to pulmonary hypertension. HPV is intrinsic to the vascular smooth muscle and its mechanisms remain poorly understood. In addition, the pulmonary vascular endothelium, red cells, lung innervation, and numerous circulating vasoactive agents also affect the strength of HPV. This review will discuss the pathophysiology of HPV and address its role in pulmonary hypertension associated with World Health Organization Group 3 diseases. When sustained beyond many hours, HPV may initiate pulmonary vascular remodeling and lead to more fixed and less oxygen-responsive pulmonary hypertension if the hypoxic stimulus is maintained.