[Measurements of blood flow velocity in pulmonary microvessels with laser-Doppler microscope and investigation of several factors affecting the blood flow velocity (author's transl)].
To examine the blood flow in pulmonary microvessels and its change during positive lung inflation and deflation as well as during regional lung hypoxia or hypercapnia, the blood flow velocity in the microvessels which were observed on the exposed lung surface of anesthetized bullfrogs was measured. This was performed by means of a laser-Doppler microscope and both mean flow velocity (MV) and pulsatile amplitude (PA) were calculated from the obtained flow velocity contour. Hypoxia (pure N2) or hypercapnia (10% CO2) was applied on the regional lung surface of 6 mm in diameter. The blood flow in the pulmonary microvessels was pulsatile and its pulsatility was greatest in arterioles and smallest in capillaries. MV and the ratio of PA to MV in capillaries were 1.46 mm/sec and 0.20, respectively. This ratio was considerably smaller than that in human pulmonary capillaries, which was previously measured by using body plethysmography. The reason for this discrepancy was discussed. During lung inflation and subsequent deflation, the alterations in MV and PA against transpulmonary pressure (TPP) revealed an optimum TPP and an apparent hysteresis. During lung inflation MV was slightly increased until TPP reached about 2.8 cmH2O but was markedly decreased at the larger TPP than the value. During subsequent deflation, MV was slightly lower at any given TPP than during inflation but its change was almost parallel to that in inflation. The change in PA was similar to that in MV. The observed alteration in flow velocity in pulmonary microvessels seemed related to the geometric change in pulmonary vessels. Both lung regional hypoxia and hypercapnia induced the decrements in MV and PA in pulmonary microvessels, which were caused by the vasoconstriction in arterioles and venules. The maximal percentage change in MV and PA in capillaries were -11% and -35% during hypoxia, and -13% and -44% during hypercapnia.
D000818:Animals; D001783:Blood Flow Velocity; D008168:Lung / Q000098:blood supply*; D008176:Lung Volume Measurements; D008833:Microcirculation; D008853:Microscopy; D010100:Oxygen / Q000097:blood; D011892:Rana catesbeiana
D010100:Oxygen