Effects of hypoxic pulmonary vasoconstriction on pulmonary gas exchange

Abstract

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, and R. Lejeune, J.L. Vachièry, 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.

Hypoxic Pulmonary Arterial Hypertension in the Chicken Model

“…They concluded that HPV might "increase the blood flow to better aerated lung areas, which leads to improved conditions for the utilization of alveolar air". HPV shunts blood from poorly oxygenated areas to better ventilated lung segments, thereby optimizing ventilation-perfusion matching, reducing shunt fraction and optimizing systemic O 2 delivery in conditions such as atelectasis and pneumonia (Brimioulle et al, 1996). HPV onsets within seconds of moderate hypoxia and reverses quickly on restoration of normoxic ventilation.…”

Hypoxia-induced vasoconstriction in alligator (Alligator mississippiensis) intrapulmonary arteries: a role for endothelin-1?

“…HPV is considered important for local matching of blood perfusion to ventilation and improves pulmonary gas exchange efficiency (Von Euler and Liljestrand, 1946;Dawson, 1984;Brimioulle et al, 1996). The primary site of constriction is the small muscular resistance arteries (Weir and Archer, 1995).…”

Mechanisms underlying gas exchange alterations in an experimental model of pulmonary embolism

“…The complex abnormalities in gas exchange that occur are multiple, but the literature remains unassertive to elucidate the underlying mechanisms (1)(2)(3)(4)(5)(6)(7)(8)(9)(10).…”

“…The transfer of O 2 is jeopardized when this equilibrium is altered and this proportion is reduced (2,4).…”

“…Correction of mismatching alveolar ventilation to cardiac output (CO) ratio (V A /Q) may occur from the redistribution of the perfusion towards ventilated areas or from a fall in ventilation of areas with limited or absent perfusion (3)(4)(5)(6)8,10,13,14). Indeed, Levy and Simmons (15) observed that in PE there is a partial auto-regulation of the alveolar ventilation and perfusion at the lobar and segmental levels in order to maintain the equilibrium of the V A /Q (4,16). This phenomenon has only recently been confirmed with technology based on positron emission tomography scan that quantifies the redirection of the ventilation to alveoli with maintained perfusion, called effective or regional alveolar ventilation (V A eff) (14,17,18).…”