Hypoxic Reduction in Blood Flow Velocity in Pulmonary Arterioles and Capillaries

Abstract

The vasoconstrictory effects of hypoxia on pulmonary circulation are well established. The ventilation of a single lung lobe with nitrogen causes a reduction in the blood flow in the hypoxic lung lobe. However, the question that remains unsolved is whether a regional hypoxia to which several alveoli and only small blood vessels are exposed could reduce the blood flow and affect the flow velocity contour in the microvessels of that region. We have now completed a study of the effects of local hypoxia on terminal segments of pulmonary microvessels observable on the lung surface. The hypoxia to which a small area of the lung surface was exposed reduced the oxygen tension only in the thin layer just beneath the lung surface in that region. Therefore, the larger vessels running in the deeper areas were not influenced by the local hypoxia. In turn, our technique allowed observations of microcirculatory responses to hypoxia in the absence of general systemic hemodynamic responses.