response (including vascular compliance and vascular resistance) a matter of medical and pharmacologic complexity beyond mere hydraulic considerations (which are complex enough by themselves). The relationship between vascular compliance, pressure, and flow rate is Q=C(dP/dt) Q=flow rate (cm3/sec) Arterial compliance The classic definition by MP Spencer and AB Denison of compliance (C) is the change in arterial blood volume (ΔV) due to a given change in arterial blood pressure (ΔP). They wrote this in the "Handbook of Physiology" in 1963 in work entitled "Pulsatile Flow in the Vascular System". So, C = ΔV/ΔP. Arterial compliance is an index of the elasticity of large arteries such as the thoracic aorta. Arterial compliance is an important cardiovascular risk factor. Compliance diminishes with age and menopause. Arterial compliance is measured by ultrasound as a pressure (carotid artery) and volume (outflow into aorta) relationship. Compliance, in simple terms, is the degree to which a container experiences pressure or force without disruption. It is used as an indication of arterial stiffness. An increase in the age and also in the systolic blood pressure (SBP) is accompanied with decrease on arterial compliance. Endothelial dysfunction results in reduced compliance (increased arterial stiffness), especially in the smaller arteries. This is characteristic of patients with hypertension. However, it may be seen in normotensive patients (with normal blood pressure) before the appearance of clinical hypertension. Reduced arterial compliance is also seen in patients with diabetes and also in smokers. It is actually a part of a vicious cycle that further elevates blood pressure, aggravates atherosclerosis (hardening of the arteries), and leads to increased cardiovascular risk. Arterial compliance can be measured by several techniques. Most of them are invasive and are not clinically appropriate. Pulse contour analysis is a non-invasive method that allows easy measurement of arterial elasticity to identify patients at risk for cardiovascular events. See also Cardiovascular System Dynamics Society Windkessel effect References External links Respiratory physiology Cardiovascular physiology