Capillary pressure and distribution of vascular resistance in isolated lung

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Abstract
Isolated lobes of dogs' lungs were perfused with constant nonpulsatile blood flow and expanded by negative external pressure. The pressure under which Ringer solution was absorbed through the visceral pleura was measured by an osmometric method. From this pressure and the plasma colloid osmotic pressure, the pressure in the subpleural capillaries was calculated. The average value of the latter was 8.8 mm Hg when the pulmonary artery and vein pressures were 13.4 and 1.8 mm Hg, respectively. Assuming that the pressure in the intrapulmonary capillaries is similar to that in the subpleural capillaries, the vascular resistance on the arterial and venous side of the effective midpoint of pulmonary capillaries could be calculated. The average vascular resistance on the venous side was found to be 60% of the total intrapulmonary vascular resistance. Notwithstanding the limitations of the method this result suggests that in the pulmonary vascular bed the resistance on the arterial side and that on the venous side of the effective midpoint of capillaries are similar.

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