RELATIONSHIP OF ARTERIAL COMPLIANCE TO BAROREFLEX FUNCTION IN HYPERTENSIVE PATIENTS

The objectives of this study were to determine whether carotid arterial compliance is reduced in patients with hypertension and to assess whether reduced arterial compliance is related to abnormal arterial baroreflex function. Accordingly, concurrent measurements of carotid arterial diameter (via computerized high resolution B-mode ultrasonography) and blood pressure were made to determine carotid arterial compliance in 23 normotensive and 16 age-matched hypertensive patients. In addition, arterial baroreflex function was assessed in 12 of the normal subjects and nine of the hypertensive patients by measuring the heart rate response to changes in blood pressure induced by infusions of nitroprusside and phenylephrine. Compared with the normotensive subjects, the patients with hypertension had reduced compliance (5.9 +/- 0.7 vs. 16.6 +/- 1.8 10(-7) m2/kPa, mean +/- SE, P < 0.001). The baroreflex slope relating the change in R-R interval to the change in systolic blood pressure during the drug infusions was less in the hypertensive than normotensive subjects (12.3 +/- 2 vs. 18.9 +/- 2 ms/mmHg, P < 0.05). Consequently, when both normotensive and hypertensive subjects were considered, there was a significant correlation between the baroreflex slope and compliance (r = 0.53, P < 0.05). However, there was no correlation between the baroreflex slope and compliance within either the normotensive group (r = 0.04, P = NS) or the hypertensive group (r = 0.43, P = NS) when analyzed separately. There was a significant correlation between age and compliance (r = -0.48, P < 0.01) but not between age and baroreflex function. It is concluded that in patients with hypertension, carotid arterial compliance is abnormal and arterial baroreflex regulation of heart rate is attenuated. Although these abnormalities both occur in patients with hypertension, the poor correlation suggests that reduced arterial compliance is not solely responsible for baroreflex dysfunction in these individuals.