Compliance means the ability of the vessel to get stretch (dilate). If the vessel is easily stretched, it is considered to be highly compliant. Compliance is inversely related to elasticity.
Elasticity is the tendency to rebound back to original size from a stretch. A vessel with high elasticity will have low compliance.
Factors affecting compliance:
Endothelial dysfunction reduces compliance due to increase in arterial stiffness. This phenomenon is seen in hypertensive, diabetes, and smokers. Atherosclerosis will further aggravate this stiffness. Pulse contour analysis is a non-invasive method that allows easy measurement of arterial elasticity to identify patients at risk for cardiovascular events.
Age: Newborn will have higher compliant vessels compared to 50-year-old man. With the increase in age, compliance will decrease, and elasticity will increase. The less compliant artery will increase the total peripheral resistance that sometimes causes a pseudo-increase in blood pressure during blood pressure measurement in an elderly patient.
Fish oil alters vascular reactivity and favorably influences arterial wall characteristics in patients with non-insulin dependent diabetes mellitus.
Venous compliance is approximately 25 times larger than arterial compliance and contains nearly 70% of systemic blood volume. Arteries are high-pressure vessels and are very stiff because of the high muscular layer and therefore, arteries do not represent a significant blood reservoir. The aorta is most compliant in the arterial system.
Compliance is calculated using the following equation, where ΔV is the change in volume, and ΔP is the change in pressure; C = ΔV/ ΔP.
Pulse pressure will increase while going distally from the aorta (because compliance decreases). The pedal artery will have higher pulse pressure than femoral artery and femoral artery will have higher pulse pressure than the aorta.
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