Effects of hypoxic pulmonary vasoconstriction on pulmonary gas exchange

Several reports have suggested that hypoxic pulmonary vasoconstriction (HPV) might result in deterioration of pulmonary gas exchange in severe hypoxia. We therefore investigated the effects of HPV on gas exchange in normal and diseased lungs. We incorporated a:biphasic HPV stimulus-response curve observed in intact dogs (S. Brimioulle, P. Lejeune, J. L. Vachiery, M. Delcroix, R. Hallemans, and R. Naeije, J. Appl. Physiol. 77: 476-480, 1994) into a 50-compartment lung model (J. B. West, Respir. Physiol. 7: 88-110, 1969) to control the amount of blood flow directed to each lung compartment according to the local hypoxic stimulus. The resulting model accurately reproduced the blood gas modifications caused by HPV changes in dogs with acute lung injury. In single lung units, HPV had a moderate protective effect on alveolar oxygenation, which was maximal at near-normal alveolar PO2 (75-80 Torr), mixed venous PO2 (35 Torr), and PO2 at which hemoglobin is 50% saturated (24 Torr). In simulated diseased lungs associated with 40-60 Torr arterial PO2, however, HPV increased arterial PO2 by 15-20 Torr. We conclude that HPV can improve arterial oxygenation substantially in respiratory failure.