RELATIONSHIP BETWEEN MECHANICAL-PROPERTIES OF THE CAROTID-ARTERY WALLAND BAROREFLEX FUNCTION IN ACUTELY TREATED HYPERTENSIVE PATIENTS

Objective To evaluate the relationship between the mechanical properti es of the carotid artery wall and baroreflex function after acute redu ction of blood pressure with lacidipine in essential hypertension. Des ign After 15 days of placebo washout, the hypertensive patients underw ent a single-blind haemodynamic study before and 90 min after administ ration of 4 mg lacidipine (a dihydropyridine calcium antagonist). Meth ods Brachial intra-arterial blood pressure was recorded in eight mild- to-moderate essential hypertensive patients aged 40-53 years (mean +/- SEM 46.8 +/- 4.7 years), The carotid pulse diameter was recorded simu ltaneously by an echo-tracking technique. The mechanical properties of the carotid artery wall were evaluated by calculating Peterson's incr emental elastic modulus (E(p)) both as an averaged value of 10 heart c ycles with stable blood pressure and as the dynamic correlation, on a beat-to-beat basis, of E, and the systolic blood pressure during a 20 mmHg increase in blood pressure following a bolus injection of phenyle phrine. The elastic properties of the carotid artery were investigated further by determining the correlation between the systolic pressure and systolic diameter, beat by beat, during a ramped increase of blood pressure after phenylephrine administration. The baroreceptor reflex sensitivity was measured simultaneously by the Oxford method and by co rrelating E(p) and the electrocardiographic R-R' interval on a beat-to -beat basis during phenylephrine injections. Results After lacidipine administration Peterson's elastic modulus, measured under resting stea dy-state conditions, was reduced (18.7 +/- 7.4 versus 16.4 +/- 6 x 10( 5)dyne/cm(2)), whereas the baroreflex sensitivity was unchanged (6.6 /- 3.3 versus 6.3 +/- 0.2 ms/mmHg) and resetting of the baroreflex had occurred, At the same time, the correlations between the systolic blo od pressure and E(p) and between the systolic blood pressure and carot id systolic diameter over a 20 mmHg increase in blood pressure were un changed, Moreover, the correlations between the systolic blood pressur e and the R-R' interval and between E(p) and R-R' interval during the phenylephrine-induced blood pressure increase did not differ statistic ally. Conclusions The results suggest that the resetting of the barore flex after an acute reduction in blood pressure caused by lacidipine i s dissociated from mechanical changes in the carotid artery wall.