Is arterial stiffness better than blood pressure in predicting cardiovascular risk?
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Corresponding author Michael F. O’Rourke, MD, DSc Suit 810, St. Vincent’s Clinic, 438 Victoria Street, Darlinghurst, NSW 2010, Australia. E-mail: [email protected] Current Cardiovascular Risk Reports 2008, 2:133–140 Current Medicine Group LLC ISSN 1932-9520 Copyright © 2008 by Current Medicine Group LLC
Measurement of systolic and diastolic pressure by cuff sphygmomanometer originally restricted our view of the underlying mechanisms of blood pressure to cardiac strength and peripheral resistance. As effects of arterial stiffening on the heart and vasculature became apparent over the past two decades, the focus changed from diastolic to systolic pressure and then to pulse pressure. Brachial pulse pressure was recognized as a measure of stiffness and predictor of cardiovascular risk, and then central aortic systolic and pulse pressure came into favor. Now the relationship of systolic to diastolic pressure in ambulatory recordings is seen as another, perhaps better, predictor. New measures have emerged from the analysis of arterial pulse wave forms. These measures, pulse wave velocity and augmentation index, can be obtained relatively easily and reproducibly in the clinic. Many studies suggest that these are the best predictors of risk—even targets for therapy—and give incremental information over conventional values of arterial pressure.
Introduction As a major factor determining the amplitude of systolic and pulse pressure, arterial stiffness causes progressive increases in these pressures with age and the development of isolated systolic hypertension. Brachial pulse pressure is a rough index of arterial stiffness but is influenced by other factors, notably stroke volume and variable amplification of the pulse in the upper limbs. Increases in pulse pressure with age are actually greater in central than in peripheral arteries because of progressively decreasing age-related amplification.
Indices of arterial stiffness independent of stroke volume and amplification of the pressure wave have been sought [1••]. This paper discusses the three that have become popular for clinical research and clinical trials. Two (pulse wave velocity [PWV] and augmentation index [AIx]) are based on features of the pulse wave, and one (ambulatory arterial stiffness index [AASI]) is based on the relationship between systolic and diastolic pressure over 24 hours. Perhaps the most obvious—direct measurement of arterial pressure/diameter change—is used only rarely because the small changes in diameter are hard to measure accurately and because measures of pressure in central arteries are difficult to calibrate reliably from the brachial cuff [1••].
Pulse Wave Velocity A long-accepted index of arterial stiffness, PWV is generally accepted as the gold standard in clinical studies. It is measured as %x/%t, the time delay (%t) between the foot of the pressure waveform at two sites %x centimeters apart in the line of travel of the pulse. “Aortic” PWV (usually measured between carotid artery and femoral artery) in childhood is usually about 5
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