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Effects of nifedipine on systemic hydraulic vascular load in patients with hypertension
K C Chang1, K S Hsieh, T S Kuo
1Department and Institute of Electrical Engineering, National Taiwan University, Taipei, Republic of China.
Insights
Hypertensive individuals exhibit increased aortic stiffness and vascular tone compared to normotensives. Nifedipine effectively lowers blood pressure and vascular tone in hypertensives, but does not impact aortic stiffness.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Pharmacology
Background:
- Hypertension is associated with altered arterial hemodynamics.
- Aortic input impedance (AII) and its components reflect arterial stiffness and vascular tone.
- Understanding these parameters is crucial for managing hypertension.
Purpose of the Study:
- To compare aortic input impedance and derived parameters between hypertensive and normotensive individuals.
- To evaluate the acute effects of nifedipine on aortic impedance, compliance, and resistance in hypertensive patients.
Main Methods:
- High-fidelity multisensor catheter (Millar) used for aortic pressure and flow measurements.
- Fourier analysis applied to impedance spectra.
- Nifedipine (10 mg sublingual) administered to assess acute hemodynamic effects.
Main Results:
- Hypertensives showed increased peripheral vascular resistance (R), characteristic impedance (Zc), and first zero crossing frequency (fo) compared to normotensives.
- Arterial compliances (Cs, Cm, Cd) were significantly lower in hypertensives.
- Nifedipine reduced R, mean aortic pressure (Pm), and total external ventricular power (Wt) in hypertensives, but did not alter Zc, fo, or arterial compliances.
Conclusions:
- Hypertensives have increased proximal aortic stiffness and peripheral arteriolar tone.
- Nifedipine effectively reduces arterial pressure and peripheral arteriolar tone in hypertensives, without affecting aortic stiffness.
- The reduction in ventricular power after nifedipine is primarily due to decreased steady-state hydraulic power.
Study Objective:
The aim of the study was (1) to determine the difference in aortic input impedance and derived parameters between hypertensives and normotensives; and (2) to assess the acute effects of nifedipine on the aortic impedance, compliance, and resistance in patients with hypertension.
Design:
A high fidelity multisensor catheter (Millar) was used to obtain the aortic pressure and flow signals for impedance analysis. The acute effects of nifedipine on the impedance parameters were evaluated at steady state before and after (10-30 min) a sublingual dose of 10 mg.
Patients:
The patients included seven normotensive (mean blood pressure, 97 mm Hg) and nine hypertensive (mean blood pressure, 135 mm Hg), age matched, ethnic Chinese. Patients with clinical evidence of heart failure and valvular or congenital heart diseases were excluded.
Measurements And Main Results:
Pulsatile aortic flow and pressure were measured by Millar catheter inserted into the ascending aorta. Cross sectional area of aorta was estimated by echocardiograms. Cardiac output was determined by Fick principle with an oximeter. These data were subjected to Fourier analysis for impedance spectra. In comparison with normotensives, hypertensives had increased peripheral vascular resistance R, at 2751(705) v 1651(363) dyne.s.cm-5; increased characteristic impedance Zc, at 193(64) v 122(27) dyne.s.cm-5; and increased first zero crossing frequency of impedance phase angle fo, at 4.8(0.9) v 3.4(0.7) Hz. Arterial compliances corresponding to peak systolic pressure Cs were lower, at 0.32(0.19) v 0.90(0.32) ml.mm Hg-1, as was mean pressure Cm, at 0.55(0.25) v 1.24(0.38) ml.mm Hg-1, and end diastolic pressure Cd, at 0.83(0.29) v 1.65(0.44) ml.mm Hg-1. Although the values of external ventricular hydraulic power were higher in hypertensive subjects, the difference was not statistically significant. Nifedipine administration in 7/9 hypertensives significantly reduced R, from 2806(721) to 2433(664) dyne.s.cm-5; mean aortic pressure Pm, from 138(22) to 112(12) mm Hg; total external ventricular power Wt, from 1452(306) to 1121(135) mW; and steady external power Ws, from 1251(310) to 939(119) mW; but did not reduce Zc, fo, Cs, Cm, Cd, and oscillatory external power Wo.
Conclusions:
The results indicate that (1) the stiffness of proximal aorta and vascular tone of peripheral arterioles are higher in hypertensives than in normotensives; (2) in hypertensive subjects, sublingual administration of nifedipine reduces the arterial pressure and peripheral arteriolar tone, but not the stiffness of proximal aorta; (3) the decrease in total external ventricular power in hypertensives treated with nifedipine results from a reduction in the steady, but not the oscillatory, component of hydraulic external ventricular power.