Most importantly is the conversion of Angiotensin I to Angiotensin II by ACE located in the pulmonary vascular endothelium. The pulmonary circulation is a high flow, low pressure, low resistance system. Increases in flow passively decrease pulmonary vascular resistance because of vascular distension and recruitment. Increases or decreases in lung volume from FRC passively increase resistance via effects on alveolar and extra-alveolar vessels. Blood flow in the upright lung varies as a function of P a , P A , and P v .
Alveolar hypoxia causes pulmonary arterial vasoconstriction.
At a local level this will act to promote matching of ventilation and perfusion, but at a global level could be deleterious. Numerous vasoactive mediators modulate pulmonary vascular tone. All rights reserved. This information is presented for general educational purposes only and cannot be adapted for the diagnosis or treatment of a particular individual. Physicians and health care professionals are encouraged to consult other sources as no single reference can substitute for medical training, education, and experience.