To evaluate the relationship between the mechanical properties of the carotid artery wall and baroreflex function after acute reduction of blood pressure with lacidipine in essential hypertension.
After 15 days of placebo washout, the hypertensive patients underwent a single-blind haemodynamic study before and 90 min after administration of 4 mg lacidipine (a dihydropyridine calcium antagonist).
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 simultaneously by an echo-tracking technique. The mechanical properties of the carotid artery wall were evaluated by calculating Peterson's incremental elastic modulus (Ep) both as an averaged value of 10 heart cycles with stable blood pressure and as the dynamic correlation, on a beat-to-beat basis, of Ep and the systolic blood pressure during a 20mmHg increase in blood pressure following a bolus injection of phenylephrine. 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 correlating Ep and the electrocardiographic R-R' interval on a beat-to-beat basis during phenylephrine injections.
After lacidipine administration Peterson's elastic modulus, measured under resting steady-state conditions, was reduced (18.7 ± 7.4 versus 16.4 ± 6 x 105dyne/cm2), 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 blood pressure and Ep and between the systolic blood pressure and carotid systolic diameter over a 20mmHg increase in blood pressure were unchanged. Moreover, the correlations between the systolic blood pressure and the R-R' interval and between Ep and R-R' interval during the phenylephrine-induced blood pressure increase did not differ statistically.
The results suggest that the resetting of the baroreflex after an acute reduction in blood pressure caused by lacidipine is dissociated from mechanical changes in the carotid artery wall.