Abstract
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.
Keywords
gravity - Zone model - fractal - hypoxic pulmonary vasoconstriction - pulmonary vascular
resistance
