P5.20 RELATIVE CONTRIBUTIONS OF FORWARD AND BACKWARD COMPRESSION WAVES TO PULSATILE COMPONENTS OF BLOOD PRESSURE IN HYPERTENSION

Abstract

To what degree elevated pulsatile components of blood pressure arise from a primary interaction of ventricular contraction with the impedance of the arterial tree or from more complex phenomena involving backward wave travel in the arterial tree is unknown. We used wave intensity analysis to explore the haemodynamic basis for elevated pulsatile components of blood pressure in 20 hypertensive subjects (47.4± 13.4 years, 158.5±27.7/98.7±14.2 mmHg, means ± SD) compared to 20 normotensive controls (52.2±12.3 years, 108.7±12.2/71.8±7.7 mmHg, means ± SD). Secondly we used dobutamine and norepinephrine as inodilators and vasoconstrictors in normotensive subjects to examine the contributions of ventricular contractility and peripheral vasoconstriction to waves disproportionately elevated in hypertensive compared to normotensive subjects. An elevated central pulse pressure in hypertensive subjects was accounted primarily by the forward wave component (50.4±3.4 vs 35.2±1.8 mmHg, P < 0.001) but the backward wave also contributed significantly (8.9±1.7 vs 1.6±0.4 mmHg, P < 0.002) and was a particularly important component of augmentation pressure (13.5±3.6 vs 0.3±0.6 mmHg, P < 0.01). The forward component arose from the primary forward compression wave (FCW) and the backward component from a backward compression wave (BCW). The BCW/FCW intensity was greater in hypertensive compared to normotensive subjects and in normotensive subjects could be increased by norepinephrine but not by dobutamine. Increased pulse pressure in hypertension results primarily from the FCW but the BCW provides a significant contribution to pulse pressure components particularly augmentation pressure.