Arterial compliance and wave reflection.
Left ventricular "afterload" is the wall stress developed during systole by the ejecting ventricle. For any given ventricular conformation, this is given by the time course of pressure change in the left ventricle during ejection, and is approximated by the pressure measured in the ascending aorta. For a given flow ejection from the left ventricle, pressure generated in the ascending aorta is determined by the ascending aortic impedance. Impedance in turn is dependent on three properties of the systemic circulation--resistance, compliance and wave reflection. In conventional studies of left ventricular load and hypertension, attention is usually focussed entirely on peripheral resistance. Recent studies have shown a poor relationship between left ventricular mass and peripheral resistance, but a better relationship with compliance and indices of wave reflection. Hence compliance (or its inverse, aortic stiffness) and wave reflection must be considered in evaluating hypertension (especially "systolic hypertension") and the effects of drugs on ventricular load. Under ideal circumstances, as seen in youth, aortic compliance is high and wave reflection late, with the consequence that aortic systolic pressure is low and pressure is boosted throughout early diastole. With progressive aortic degeneration as seen with aging and in hypertension, systolic pressure in increased both directly by decreased compliance, and indirectly by early return of wave reflection. The effect of early wave reflection is not apparent from recordings of brachial systolic or diastolic pressure, but can be inferred from indirectly recorded carotid pressure, or from contour of the peripheral pressure wave.(ABSTRACT TRUNCATED AT 250 WORDS)
O'Rourke
M
M
Medical Professorial Unit, University of New South Wales, Saint-Vincent's Hospital, Sydney, Australia.
D001158:Arteries / Q000502:physiology*; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology*; D003187:Compliance; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D013318:Stroke Volume; D014655:Vascular Resistance / Q000502:physiology; D016277:Ventricular Function, Left / Q000502:physiology