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Hemodynamic effects of diltiazem in hypertension
Insights
Diltiazem lowers blood pressure by reducing peripheral resistance, causing a temporary heart rate increase and brachial artery dilation. This contrasts with dihydralazine, which constricts arteries.
Area of Science:
- Cardiovascular Pharmacology
- Clinical Hypertension Research
Background:
- Essential hypertension management requires understanding drug-induced hemodynamic changes.
- Diltiazem and dihydralazine are vasodilating antihypertensives with distinct mechanisms.
- Peripheral large artery caliber changes are not fully characterized for these drugs.
Purpose of the Study:
- To investigate the hemodynamic effects of diltiazem in patients with essential hypertension.
- To compare the brachial artery caliber changes induced by diltiazem versus dihydralazine.
- To elucidate the role of peripheral resistance and baroreflex in diltiazem's antihypertensive action.
Main Methods:
- Evaluated cardiac hemodynamics, brachial artery diameter, and blood flow velocity using pulsed Doppler velocimetry in 11 hypertensive patients.
- Measured parameters before and after diltiazem administration (bolus and perfusion).
- Compared findings with hemodynamic data from dihydralazine administration.
Main Results:
- Diltiazem significantly decreased blood pressure and total peripheral resistance, with a transient increase in heart rate and cardiac index.
- Brachial artery caliber significantly increased after diltiazem administration.
- Dihydralazine administration resulted in sustained increased cardiac index and heart rate, and significantly decreased brachial artery caliber.
Conclusions:
- Diltiazem's antihypertensive effect is primarily due to reduced total peripheral resistance, accompanied by transient baroreflex-mediated tachycardia.
- Vasodilating drugs can differentially affect peripheral large artery caliber; diltiazem increases it, while dihydralazine decreases it.
- Understanding these distinct vascular responses is crucial for optimizing antihypertensive therapy.
Abstract:
Cardiac hemodynamics, diameter, blood flow velocity, and volumic flow of the brachial artery were studied before and after diltiazem administration in 11 patients with sustained essential hypertension. The study was compared with the hemodynamic effects of dihydralazine. The caliber of the brachial artery was evaluated with a pulsed Doppler velocimeter enabling the determination of the angle between the ultrasound beam and the vessel axis with a precision of 2%. After bolus administration of diltiazem, blood pressure and total peripheral resistance significantly decreased (P less than 0.001) while cardiac index and heart rate significantly increased (P less than 0.01). After 25 minutes of perfusion, cardiac output and heart rate returned toward control values, while blood pressure and total peripheral resistance remained decreased. The results contrasted with those observed after dihydralazine, which induced a sustained increase in cardiac index and heart rate. The caliber of the brachial artery decreased significantly (P less than 0.001) after dihydralazine and increased significantly after diltiazem (P less than 0.01). The study provided evidence that the antihypertensive effect of diltiazem was due to a fall in total peripheral resistance, associated with a transient baroreflex mediated tachycardia, and that--in addition to their effects on small arteries--vasodilating drugs may either increase (diltiazem) or decrease (dihydralazine) the caliber of peripheral large arteries.