Characteristics of Pulse Wave Reflection from the Cerebral Circulation in Hypertension - Analysis Using Wave Intensity

Background and purpose: Cerebral circulation is robustly controlled. There may be differences in autoregulation between hypertensive and normotensive subjects. However, auto-regulation in cerebral circulation is poorly reported because of difficulty in assessment. The purpose of this study was to characterize pulse wave reflection from the head in hypertensive and normotensive subjects by using wave intensity. Methods: Using an ultrasonic system, we measured common carotid arterial wave intensity (WI), stiffness parameter (beta), and volume flow rate (Q) at rest in 91 hypertensive patients (HT) and age matched normal subjects (Norm). Results: Both in Norm and HT, magnitude of reflection (NA) did not depend on age. NA was considerably greater in HT than in Norm (P < 0.0001). NA was correlated with the maximum pressure in Norm (r = 0.36, p = 0.0009), but not in HT. NA increased with the maximum velocity (max U) considerably in HT (r = 0.51, p < 0.0001), but slightly in Norm (r = 0.32, p = 0.004). Both in Norm and HT, max U has a tendency to decrease with an increase in beta, but not significantly. In Norm, NA did not depend on beta. In HT, however, NA unexpectedly decreased with an increase in beta (r = 0.21, p < 0.05). Conclusions: Increased reflection from the head indicates enhanced auto-regulation of blood flow in HT. The magnitude of reflection depended on the maximum velocity rather than the maximum pressure in HT, which suggests the regulation of blood flow dominates that of blood pressure in HT. Common carotid arterial WI has the potential for analyzing the mechanism of regulation of cerebral circulation.