383 Carotid arterial flow control in hypertensive patients- analysis by wave intensity

Abstract

Background: Wave reflection from the head and neck augments pressure and decelerates flow in the carotid artery. Wave intensity (WI) has the potential to separate peripheral (head and neck) effects from ventricular effects on pressure and flow waves. WI is defined as the product of the time derivatives of blood pressure (P) and velocity (U): WI=(dP/dt)(dU/dt). The negative value of WI indicates that the effects of reflected waves are predominant. Therefore, the integral of negative values (NA) of common carotid arterial WI in a cardiac cycle is attributed to reflection from the head and neck. To elucidate the characteristics of carotid arterial flow control in hypertensive subjects, we applied WI analysis. Methods: We measured WI in 64 hypertensive patients (HT) (mean age 63±4 years, mean systolic/diastolic pressure 149±11/82±10 mm Hg) and 63 agematched normal subjects (N) (mean age 63±7 years, mean systolic/diastolic pressure 121±17/70±10 mm Hg) with a noninvasive WI measuring system (SSD 6500, Aloka Co), which simultaneously measured common carotid arterial blood flow velocity and diameter change. The diameter change waveform calibrated by blood pressure by upper arm automated sphygmomanometry was used as the pressure waveform. The volume flow rate (Q) was calculated as the integral of the product of cross-sectional mean velocity and cross-sectional area of the artery over a cardiac cycle, multiplied by heart rate. Results: The maximum diameter was larger (8.30±0.7 vs 7.8±0.7 mm, p<0.0001) and the maximum blood flow velocity was lower (50±14 vs 55± ± 11 cm/s, p<0.05) in HT than N. NA was greater (38±19 vs 26±15 mm Hg m/s2, p<0.0001) in HT, which suggests higher reflection from the head and neck. There was no difference in the highest values of WI and Q between HT and N (WI: 10.6±6.4 vs 8.6±3.6 mm Hg m/s3, Q: 658±158 vs 680±178 ml/min). Conclusions: The common carotid artery in HT had larger diameter and lower blood velocity, i.e. reduced shear stress. Q was maintained at the same values as N with enhanced reflection from the cerebral circulation.