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Where Breath Meets Blood—Lung Perfusion 

Where Breath Meets Blood—Lung Perfusion
Chapter:
Where Breath Meets Blood—Lung Perfusion
Author(s):

James R. Munis

DOI:
10.1093/med/9780199797790.003.0015
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date: 05 May 2021

The pulmonary circulation is a low-resistance, low-pressure, high-flow system because its primary function is to oxygenate blood. For that reason, pulmonary circulation is different from systemic circulation. Because resistance is lower in pulmonary circulation, pressures across the pulmonary vascular bed also are substantially lower. An efficient system includes inherently low resistance. This allows the entire cardiac output to flow through without high-pressure areas, thereby diminishing the danger of rupturing thin gas-exchange surfaces. One other consequence of low resistance is that the pulmonary circulation is unusually susceptible to the effects of gravity. No substantial part of the cerebral circulation collapses in the head-up position because it is held open by the rigid cranium and the architecture of the venous sinuses. Pulmonary circulation is different. There is less ‘stenting open’ of pulmonary capillaries, and they are therefore more likely to partially or fully collapse when transmural pressure becomes negative.

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