Abstract
The isolated left middle lobes of canine lungs were perfused in situ, by stepwise elevation of the blood flow. The weight gain of the lung lobe per initial bloodless dry lung weight (delta w g/min.IdQ1) showed a significant (p less than 0.001) correlation with the blood flow per body weight (F, ml/min.kg) with a regression line of delta w = 8.3 X 10-4F2.3. The pulmonary venous pressure (Pv) correlated significantly (p less than 0.001) with the pulmonary artery pressure (Pa), i.e. Pa = 11.2 + 1.3 Pv, with a constant left atrial pressure (Pla). The total pulmonary vascular resistance [TPVR = (Pa - Pla)/F] and the small pulmonary artery resistance [SR = (Pa-Pv)/F] decreased by steps with a constant pulmonary venous resistance (VR = TPVR-SR), and VR/TPVR increased by steps as the flow was increased. By incremental blood flow through the restricted lung tissue, we conclude that fluid filtration into the interstitium was flow-dependent, the pulmonary capillaries and precapillaries provided a large capacity for blood flow and the resistance to the flow was directed to the postcapillary site.
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