Distribution of blood flow and the pressure-flow relations of the whole lung

¹ Department of Medicine, Postgraduate Medical School, Hammersmith Hospital, London, England

Effects of changes in pulmonary arterial (Pa), venous (Pv), and alveolar (Pa) pressures on the over-all pressure-blood flow relations of an isolated dog lung have been re-examined. In the preparation used, the distribution of blood flow was predictable from previous measurements with radioactive gases. The results showed that the pressure-flow relations of the whole lung were greatly affected by the distribution of blood flow within it. For example, the pulmonary vascular resistance (PVR) of the lung depended on whether all the lung was perfused with blood or not, and thus whether there was an unperfused zone at the top of the lung where Pa was less than Pa (zone 1). Again the pressure-flow relations of the lung were shown to depend on how much of the lung had a Pv less than Pa (zone 2), and how much had a Pv which exceeded Pa (zone 3). The effects on PVR of changing Pv or Pa could be explained on this basis. No evidence of a critical closing pressure in the vessels of the expanded lung was found. It was concluded that although the over-all pressure-flow relations of the whole lung were complicated, the flow through individual vessels could be accounted for by the simple mechanical effects of pressures inside and outside the vessels.

Submitted on May 4, 1964

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