Vascular Compliance
| Overview |
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- Vascular compliance is simply the basic concept of compliance applied to a vascular segment. In its application to blood vessels, the vascular compliance is the relationship between the volume of blood within a vascular segment and the blood pressure which is generated by the presence of that volume. For a given quantity of blood pressure, vessels with a high compliance can be filled with large volumes whereas vessels with low compliance can only be filled with small volumes.
| Compliance of Functional Vascular Segments |
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- Because of their thick, elastic or muscular vascular wall, arteries tend to have very low compliances. In contrast, because of their thin, floppy vascular walls, veins tend to have very high compliances. The compliance relationship can be visually appreciated using the Pressure-Volume graph displayed above. Note that for low compliance arteries small increases in blood volume result in large increases in their internal pressure whereas for high compliance veins, large increases in blood volume are required to even slightly enhance the internal blood pressure.
| Regulation of Compliance |
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- A major aspect of vascular physiology is the capacity to modulate the compliance of functional vascular segments. Modulation of vascular compliance is largely achieved via autonomic nervous innervation of the vasculature which is mediated by SNS fibers that synapse onto vascular smooth muscle cells. Release of norepinephrine on smooth muscle alpha1 receptors results in their contraction which in turn reduces the compliance of the innervated vascular segment. The levels of vascular compliance in a resting individual are in part due to baseline SNS stimulation. Consequently, the baseline vascular compliance of both arteries and veins can be increased by inhibiting SNS fibers or can be reduced by activating SNS fibers. The consequences of such compliance changes is discussed more fully in arterial physiology and venous physiology.