Direct in vivo Visualization of the Mechanical Interaction between Perialveolar Microcirculation and Individual Alveolar Respirations in Rats

Abstract

OBJECTIVE:To analyze in vivo mechanical interaction between perialveolar microcirculation and individual alveolar respirations in rats with our pencil-lens probe CCD videomicroscope.METHOD:Perialveolar microcirculation and alveolar respiration were observed via pleural visceralis. We compared the behavior of the microvessels and individual alveoli during mechanical ventilation with different tidal volumes, PEEP of 20 cmH2O, and exposure to hypoxia (10% O2). RESULTS:We observed the semi-collapsed sheet-like perialveolar capillaries at end-inspiration without cessation of flow, indicating existence of"waterfall phenomenon". When tidal volume was increased from 2 to 5 ml, the alveolar diameter was increased, and the velocity of perialveolar capillary erythrocytes was significantly decreased by about 90%, but the flow still continued through semi-collapsed capillaries during a respiratory cycle. When tidal volume was 5 ml with PEEP, the flows of arterioles and venules stopped at end-inspiration in various parts, indicating discontinuance of waterfall. We also demonstrated that precapillary arterioles clearly constricted by 18% in response to hypoxia (n=9, p<0.01).CONCLUSION:We succeeded in the visualization of in vivo perialveolar microcirculation and individual alveolar respirations. The mechanical interaction is crucial for understanding pathophysiology of pulmonary microcirculation. [Jpn J Physiol 54 Suppl:S112 (2004)]