The pulmonary circulation is a low-pressure, low-resistance circuit whose primary function is to deliver deoxygenated blood to, and oxygenated blood from, the pulmonary capillary bed enabling gas exchange. The distribution of pulmonary blood flow is regulated by several factors including effects of vascular branching structure, large-scale forces related to gravity, and finer scale factors related to local control. Hypoxic pulmonary vasoconstriction is one such important regulatory mechanism. In the face of local hypoxia, vascular smooth muscle constriction of precapillary arterioles increases local resistance by up to 250%. This has the effect of diverting blood toward better oxygenated regions of the lung and optimizing ventilation–perfusion matching. However, in the face of global hypoxia, the net effect is an increase in pulmonary arterial pressure and vascular resistance. Pulmonary vascular resistance describes the flow-resistive properties of the pulmonary circulation and arises from both precapillary and postcapillary resistances. The pulmonary circulation is also distensible in response to an increase in transmural pressure and this distention, in addition to recruitment, moderates pulmonary arterial pressure and vascular resistance. This article reviews the physiology of the pulmonary vasculature and briefly discusses how this physiology is altered by common circumstances.

肺循环是低压、低阻力回路，其主要功能是将脱氧血液输送至肺毛细血管床，并从肺毛细血管床输送含氧血液，以实现气体交换。肺血流的分布受到多种因素的调节，包括血管分支结构的影响、与重力相关的大尺度力以及与局部控制相关的更精细尺度因素。缺氧肺血管收缩就是这样重要的调节机制之一。面对局部缺氧，毛细血管前小动脉的血管平滑肌收缩使局部阻力增加高达250%。这具有将血液转移到肺部含氧更好的区域并优化通气-灌注匹配的效果。然而，面对全身缺氧，净效应是肺动脉压和血管阻力增加。肺血管阻力描述了肺循环的血流阻力特性，由毛细血管前阻力和毛细血管后阻力产生。肺循环也会因跨壁压的增加而扩张，并且这种扩张除了肺复张之外，还可以调节肺动脉压和血管阻力。本文回顾了肺血管系统的生理学，并简要讨论了常见情况如何改变这种生理学。