Blood flow reduction in local pulmonary microvessels during acute hypoxia imposed on a small fraction of the lung

Abstract

Hypoxia was induced in a small fraction (<0.2%) of the whole lung by introducting pure nitrogen into a small gas chamber placed on the expose lug surface of bullfrogs. This method of gas application exposed only the several alveoli encircled by the chamber to hypoxia. Thus it produced changes in the microcirculation within a small localized test area. Blood flow velocity and vessel diameter were measured by means of a laser Doppler microscope with a scaled ocular lens on a lateral viewer. Mean blood flow velocity in arterioles and capillaries within the test area decreased by 21.7 ± 8.0% and 12.1 ± 4.5%, respectively, during hypoxia. Arteriolar vessel diameters decreased by 15.3 ± 7.0%. Therefore, the computed blood flow through the observed arterioles leading into the capillary bed within the test are decreased to 59% of tis control value. This large decrement in arteriolar flow rate should result in large reduction of the flow velocity in the capillaries, in contrast to the actually observed small reduction in capillary flow velocity. The efficiency of the hypoxic regulation of blood flow distribution in pulmonary capillary bet is probably reduced when hypoxia is imposed on a very small fraction of the frog lung.