Influence of bronchial arterial PO, on pulmonary vascular resistance

chid arterial PO, on pulmonary vascular resistance. J. Appl. Physiol. 70(l): 405-415, 1991.~In six anesthetized and me-chanically ventilated adult sheep, the bronchial artery was perfused with blood from an oxygenator-pump circuit. When the lungs were ventilated with 100 % 0, and the bronchial 0, tension (Pbr,,) was a600 Torr, the mean of the pulmonary vascular resistances (PVR) measured at the beginning (3.32 t 0.29 units) and end (3.17 t 0.13 units) of the experiment was 3.24,t 0.20 units. When the Pbro, was changed to 58-t 1 Torr, the PVR (2.99 t 0.14 units) did not change significantly. How-ever, when the lungs were ventilated with air as Pbr,, was decreased to 91 t 4,77,t 3, 56 t 2, and 42 ~fr 1 Torr, the PVR increased to 3.67,t 0.18,4.03 _t 0.16,4.79 t- 0.19, and 4.71 t 0.35 units, respectively. However, when the Pbr,, was decreased further to 26,t 1 and 13 t 1 Torr, the PVR decreased to 3.77 t 0.28 and 3.91 _t 0.30 units, respectively. In contrast, the bron-chial vascular resistance decreased monotonically as Pbroz de-creased. The bronchial circulation supplies vasa vasorum to the walls of all but the smallest pulmonary arteries, and it is therefore suggested that the PO, of the bronchial circulation is responsible for the bimodal response of the pulmonary vascu-lature, with stimulation of hypoxic pulmonary vasoconstric-tion at moderate hypoxemia and of hypoxic pulmonary vasodi-lation at profound hypoxemia. The physiological and patho-physiological significance of the influence of systemic PO, on pulmonary vascular tone is discussed. vasa vasorum; hypoxic pulmonary vasoconstriction HYPOXICPULMONARYVASOCONSTRICTION (HPV)is an important determinant of pulmonary vascular tone and the distribution of ventilation-to-perfusion ratios, par-ticularly in abnormal conditions (12). It is generally agreed that the hypoxic stimulus is a function of both alveolar and mixed venous PO, and that the site of con-striction is primarily located in the small precapillar