Regional pulse wave velocities in hypertensive and normotensive humans

Abstract

Study objective: The aim was to compare regional wave transmission and reflection properties along the aorta in age matched normotensive and hypertensive subjects.

Design: Simultaneous upstream and downstream micromanometer pressures were recorded at five regions from the ascending aorta to the iliac artery. Recordings were made in the baseline condition in both groups and during sustained isometric handgrip exercise in the normotensives to see if increasing the blood pressure to hypertensive levels would eliminate baseline differences between the two groups.

Subjects: Only subjects who had no coronary or valvular heart disease were studied. Normotensive subjects (n = 8) were selected from those undergoing electrophysiological testing whose blood pressures were consistently in the normal range (systolic less than 140, diastolic less than 90 mm Hg). Age matched hypertensive subjects (n = 17) were those in whom secondary causes of hypertension were excluded and who had repeated measurements of raised blood pressure.

Measurements and results: In each region pulse wave velocity was estimated from the simultaneous upstream and downstream pressure records using the foot to foot method, and apparent phase velocity was obtained from Fourier analysis of the two pressures. The intensity of wave reflections was judged by the magnitude of fluctuations of the harmonics of apparent phase velocity about the mean of the higher frequency harmonics. In both groups in the baseline state there were regional variations in the pulse wave velocity with the lowest values occurring just proximal to the renal arteries and highest values occurring in the iliac artery. Likewise, in both groups the extent of wave reflections varied regionally--pronounced reflections were seen in the ascending aorta and from just proximal to the renal arteries to the aortic bifurcation but not in the mid-thoracic or iliac regions. The hypertensives had higher pulse wave velocity than normotensives only in the iliac artery (780 v 567 cm.s-1) and had more reflections in the three regions in which reflections were evident. Although handgrip in the normotensive group eliminated regional differences in pulse wave velocity between the groups, reflections were still greater in the hypertensives.

Conclusions: Essential hypertension affects the regional properties of the aortic wall. These alterations are manifested by increased peripheral wave-speed and increased wave reflections along the aorta. The differences in wavespeed but not reflection properties are eliminated when the pressures are matched by handgrip, suggesting that factors other than the level of blood pressure per se are responsible for the alterations in reflection properties.