Lung inflation and longitudinal distribution of pulmonary vascular resistance during hypoxia.

Using the low-viscosity bolus method, we examined the influence of lung inflation on the longitudinal distribution of vascular resistance during hypoxia in isolated cat lungs. During hypoxia, increasing transpulmonary pressure decreased vascular resistance but did not change the volume into the lung at which the maximum local resistance was located. This was in contrast to the normoxic situation in which inflation caused an increase in resistance over much of the transpulmonary pressure range studied and moved the maximum local resistance downstream. These results indicate that during hypoxia the major increase in resistance was in extra-alveolar vessels and that distension of these vessels by lung inflation decreased the magnitude of the pressor response. The increase in resistance in alveolar vessels, which occurred on inflation, was similar during control and hypoxic conditions but was a smaller part of the total resistance during hypoxia because of the much larger extra-alveolar vessel resistance.