title: Effect of transpulmonary pressure on blood-flow velocity in pulmonary microvessels.
abstract: Flow velocity in the microvessels (30 to 90 micron in diameter) on the exposed lung surface of anesthetized bullfrogs was measured during positive lung inflation by means of a laser Doppler microscope. From the pulsatile flow-velocity contour generated by cardiac cycles, mean flow velocity (MV) and pulsatile amplitude (PA) were calculated and their alterations were studied as a function of transpulmonary pressure (TPP). At the lowest TPP of 1.3 +/- 0.8 cm H2O (mean +/- SD), MV and PA were 1.72 +/- 0.33 and 0.45 +/- 0.27 mm/sec, respectively. With moderate increments in TPP up to 2.8 +/- 1.3 cm H2O, both MV and PA increased, attaining maximum values of 2.11 +/- 0.42 and 0.69 +/- 0.28 mm/sec, respectively. But with further inflation they began to decrease, and there was a marked reduction or a complete arrest of blood flow at excessively high TPPs (6 to 9 cm H2O). With reduction of previously increased TPP, the alterations in MV and PA followed a pattern similar to that noted during elevation of TPP. There was an apparent hysteresis in both the MV-TPP and PA-TPP curves, most marked when excessively high TPP was applied.
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D008168:Lung / Q000502:physiology*; D008833:Microcirculation; D011652:Pulmonary Circulation