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Effects of calcium entry blockers on distribution of blood volume
S Oren1, E Gossman, E D Frohlich
1Department of Internal Medicine, Ochsner Clinic, New Orleans, Louisiana, USA.
Insights
Calcium entry blockers (CEBs) like verapamil and isradipine reduce blood pressure by lowering peripheral resistance. Verapamil and isradipine also affect blood volume distribution, unlike diltiazem.
Area of Science:
- Cardiovascular Pharmacology
- Clinical Hypertension Research
Background:
- Calcium entry blockers (CEBs) are widely used antihypertensive agents.
- Understanding their effects on hemodynamics and blood volume distribution is crucial for optimizing treatment.
Purpose of the Study:
- To invasively evaluate the hemodynamic and blood volume distribution effects of isradipine, diltiazem, and verapamil in hypertensive patients.
- To compare the venodilatory and orthostatic responses to different CEBs.
Main Methods:
- Invasive hemodynamic monitoring in 24 hypertensive patients.
- Assessment before and after treatment with isradipine, diltiazem, and verapamil.
- Evaluation of supine and head-up tilt positions to assess volume shifts.
Main Results:
- All three CEBs reduced arterial pressure and total peripheral resistance without reflex tachycardia, preserving cardiac output.
- Verapamil and isradipine, but not diltiazem, altered central blood volume (CBV) and CBV/total blood volume (TBV) ratios.
- Verapamil and isradipine attenuated orthostatic reflex venoconstriction, indicated by accentuated decreases in stroke volume and CBV/TBV ratio during head-up tilt.
Conclusions:
- CEB-induced venodilatory effects vary, with verapamil > isradipine > diltiazem.
- Verapamil and isradipine impact peripheral and central blood volume distribution, affecting orthostatic responses.
- Diltiazem demonstrates minimal effects on volume distribution compared to verapamil and isradipine.
Abstract:
To evaluate the effects on hemodynamics and the distribution of blood volume of various calcium entry blocker (CEB) agents, we invasively studied 24 hypertensive patients before and after treatment with isradipine, diltiazem, and verapamil. All three agents reduced arterial pressure through a significant fall in total peripheral resistance without causing reflex tachycardia, while preserving stroke volume and cardiac output. Verapamil reduced the central blood volume (CBV) and the ratio of CBV to total blood volume (TBV) in the supine position (P < .05), suggesting peripheral venodilatation. Isradipine and verapamil modified the responses to head-up tilt. The orthostatic decrease in stroke volume was accentuated following treatment, and it was associated with a greater fall in the ratio of CBV to TBV, suggesting that these two agents attenuate the reflex venoconstriction induced by postural change. In contrast to verapamil and isradipine, diltiazem did not affect volume distribution in the supine or head-up positions. These results suggest that the effect of CEBs varies in order of venodilatory effect from verapamil to isradipine to diltiazem, with verapamil having the greatest effect.