Brachial artery cross-sectional area and distensibility before and after arteriolar vasodilatation in men with sustained essential hypertension

Aortic stiffness is reduced beyond blood pressure lowering by short-term and long-term antihypertensive treatment: a meta-analysis of individual data in 294 patients

BACKGROUND

Arterial stiffness is an independent predictor of cardiovascular events and mortality in hypertensive patients. The influence of different antihypertensive drug classes on improving arterial stiffness beyond blood pressure reduction is not widely available. We aimed to determine whether the artery stiffness can be improved because of antihypertensive treatments independently of blood pressure lowering.

METHODS

We conducted a meta-analysis of individual data from 15 randomized, controlled, double-blind, parallel group trials performed in our laboratory between 1987 and 1994. The primary endpoint was the changes of carotid-femoral pulse wave velocity (PWV) after treatment in 294 patients with mild-to-moderate essential hypertension untreated. Treatments tested were placebo (n = 88), angiotensin-converting enzyme inhibitors (ACEIs) (n = 75), calcium antagonists (n = 75), beta-blocker (n = 30), and diuretic (n = 26).

RESULTS

In the short-term and long-term trials, PWV decreased significantly by -0.75 and -1.3 m/s in the active treatment group compared with by +0.17 and -0.44 m/s in the placebo group, respectively. Active treatment was independently related to the changes in PWV and explained 5 and 4% of the variance in the short-term and long-term trials, respectively. In the short-term trials, ACEIs were more effective than calcium antagonists and placebo on improving arterial stiffness. In the long-term trials, ACEI, calcium antagonists, beta-blocker, and diuretic reduced significantly PWV compared to placebo.

CONCLUSION

Our study shows that antihypertensive treatments improve the arterial stiffness beyond their effect on blood pressure.

Quantification of glyceryl trinitrate effect through analysis of the synthesised ascending aortic pressure waveform

OBJECTIVE

To establish through analysis of the radial pressure pulse waveform the dose dependent effects of glyceryl trinitrate (GTN) on properties of different blood vessels.

DESIGN

Radial pulse waveform was measured in randomised order before, during a five hour application of a GTN patch delivering 0.104-0.625 mg/h, and for two hours after patch removal. The radial pressure waveform (Millar applanation tonometer) was convolved into an ascending aortic wave using a generalised transfer function (SphygmoCor process) enabling measurement of aortic systolic, diastolic, pulse, mean, and augmented pressure and left ventricular ejection duration in addition to standard brachial cuff pressures.

SETTING

Fu Wai and Ren Ming hospitals in Beijing, China.

PATIENTS

46 recumbent hospitalised patients aged 56 (9) years, awaiting electrophysiological or other diagnostic studies, fasting, and with other treatments suspended.

MAJOR OUTCOME MEASURES

Conventional brachial pressure measures and data from the synthesised aortic pulse.

RESULTS

There was no consistent change in heart rate or brachial pressures except for a decrease in systolic and pulse pressures (p < 0.01) at dose > 0.416 mg/h. In contrast, there were substantial and significant (p < 0.0001) decreases in aortic systolic, pulse, and augmented pressures at all doses, mean pressure (p < 0.001) at doses > 0.416 mg/h, and ejection duration (p < 0.001) at doses > 0.208 mg/h.

CONCLUSIONS

Pulse waveform analysis exposes dose dependent effects of GTN on the aortic waveform, suggesting muscular conduit arterial dilatation with reduced wave reflection at the lowest dose, arteriolar dilatation and decreased peripheral resistance at the highest dose, and venous dilatation at the intermediate dose.

Smooth muscle relaxation: effects on arterial compliance, distensibility, elastic modulus, and pulse wave velocity

Compliance, distensibility, incremental elastic modulus (E(inc)), and pulse wave velocity are all terms used to describe the mechanical properties of arteries. Previous studies assessing the effects of smooth muscle relaxation on each of these parameters have produced conflicting results. Our laboratory has previously demonstrated that intrabrachial infusion of nitroglycerin in normal human subjects results in a large increase in brachial artery compliance without changing arterial wall stiffness as measured by E(inc). In the present study, the relationships among compliance, distensibility, E(inc), and pulse wave velocity under different levels of vascular tone are shown using data acquired by intravascular ultrasound as well as theoretical curves. We demonstrate that the effects of smooth muscle relaxation can be depicted as 2 separate steps: (1) a rightward shift to a new theoretical curve describing the relationship between 2 of the above elastic parameters that is solely due to changes in vessel geometry and (2) a shift along the new curve that is dependent on changes in wall stiffness.

Physiologic aspects of drug therapy and large artery elastic properties

Vasoactive drugs alter smooth muscle tone not only in arterial resistance vessels, but also in large conduit arteries. The resultant changes in smooth muscle tone alter both conduit vessel size and stiffness and hence influence pulsatile components of left ventricular afterload. The effects of smooth muscle relaxation and contraction on arterial elastic properties are complex and have not been fully characterized. Several recent studies have utilized a new intravascular ultrasound technique to study the effects of changes in smooth muscle tone on brachial artery elastic mechanics in normal human subjects in vivo. Smooth muscle relaxation with nitroglycerin improves isobaric brachial artery compliance without significantly altering arterial wall stiffness as measured by incremental elastic modulus (Einc). The improvement in compliance with smooth muscle relaxation is the net result of factors that: (1) increase wall stiffness (increased tension in parallel elastin and collagen fibers); (2) decrease wall stiffness (decreased tension in the smooth muscle and its associated series elastic component); and (3) increase vessel lumen size. Using a modified Maxwell model for the arterial wall, smooth muscle relaxation is also shown to shift the predominant elements contributing to wall stress and Einc from smooth muscle and the collagen fibers in series with the smooth muscle to collagen fibers in parallel with the smooth muscle. A better understanding of the mechanisms contributing to changes in arterial elastic mechanics following alterations in smooth muscle tone will help in developing pharmacologic therapies aimed at reducing pulsatile components of left ventricular afterload.

Carotid artery stiffness with applications to cardiovascular pharmacology

1. Increased carotid stiffness is a characteristic feature of cardiovascular aging, hypertension and, to a lesser extent, atherosclerosis. 2. The pharmacological approach, using nitrates, converting enzyme inhibitors, calcium entry blockers and blockers of the autonomic nervous system, may decrease carotid stiffness through 3 different mechanism: passive decrease in blood pressure, active change in smooth muscle tone, and structural modifications of the carotid arterial wall. 3. In recent years, such changes have been studied in vivo, in both humans and rats, using original in situ carotid preparations and echotracking ultrasound techniques of high resolution, allowing to evaluate both static and dynamic stiffness. 4. This new approach for investigating arterial vessel through changes in both stiffness and thickness should provide a better evaluation of drug effects in cardiovascular pharmacology and new interpretations for cardiovascular events related to morbidity and mortality.

Direct effects of smooth muscle relaxation and contraction on in vivo human brachial artery elastic properties

The direct effect of smooth muscle relaxation on arterial elastic properties is controversial. Studies in animals show both a decrease and an increase in elastic modulus. In human subjects, the contribution of smooth muscle to arterial elastic mechanics has been limited by difficulty in separating the direct effects of a vasodilator drug on the arterial wall from the indirect effects due to reduced blood pressure. The purpose of the present study was to assess the direct contribution of vascular smooth muscle to brachial artery elastic mechanics in normal human subjects in vivo. We measured brachial artery compliance and incremental elastic modulus (Einc) in eight normal subjects (age, 22 to 51 years) by using intravascular ultrasound. A 3.5F 30-MHz intravascular ultrasound catheter was placed through a sheath into the brachial artery, and intraarterial pressure, cross-sectional area, and wall thickness were measured simultaneously under baseline conditions and after the administration of intra-arterial nitroglycerin (100 micrograms) and norepinephrine (1.2 micrograms). A pressurized cuff surrounding the brachial artery was inflated to reduce transmural brachial artery pressure. Using this technique, we were able to measure the following arterial characteristics for the first time in human subjects in vivo: (1) the effective unstressed arterial radius and (2) the pressure-area, stress-strain, and pressure-Einc relations over a wide pressure range (0 to 100 mm Hg). Intra-arterial nitroglycerin increased brachial artery area by 22% and intraarterial norepinephrine decreased brachial artery area by 17% at 100 mm Hg transmural pressure (P < .001 versus baseline).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute and subacute effects of nicorandil and isosorbide dinitrate on vessel wall properties of large arteries and hemodynamics in healthy volunteers

Nicorandil (N) and isosorbide dinitrate (ISDN) are vasodilator drugs used in patients with angina. In 24 healthy male volunteers (18-32 years), the acute effect of a single oral dose (20 mg) of N and ISDN on arterial diameter (D), distensibility, and compliance of the elastic common carotid artery (CCA) and the muscular femoral (FA) and brachial (BA) arteries were investigated. The effects on systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), cardiac index (CI), systemic vascular resistance index (SVRI), and venous hemodynamics were also assessed. In addition, the subacute effects after 8 days of treatment with N (2 x 20 mg/day) and ISDN (3 x 20 mg/day) on these parameters were evaluated. After a 20 mg single oral dose, blood pressure decreased significantly more with ISDN (SBP: 6%; DBP: 14%) than with N (SBP: 2%; DBP: 6%), but after 8 days this decrease in blood pressure was not statistically different between ISDN and N. The diameter of CCA increased more with ISDN (11%) than N (5%) acutely as well as subacutely (ISDN: 12%; N: 9%). Heart rate increased only with ISDN (7% acutely, 3% subacutely). No differences between ISDN and nicorandil were found for acute and subacute effects on SVRI, venous hemodynamics, diameter of muscular arteries (FA, BA), and the distensibility and compliance of elastic (CCA) and muscular (FA, BA) arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered hemodynamic response to isosorbide dinitrate in essential hypertension

Relaxation produced by nitrates on venous, arteriolar, and large arterial vessels is well known but has never been studied in human hypertensive aortas studied in vivo. In this investigation, the effects of acute oral administration of 20 mg of isosorbide dinitrate were evaluated in 12 patients with sustained essential hypertension and nine normotensives of the same age. Noninvasive measurements of systolic, diastolic, and mean arterial pressure, carotid-femoral pulse wave velocity and aortic-arch diastolic diameter using suprasternal echocardiography were determined before and 3 hours after drug administration. In normal subjects, isosorbid dinitrate significantly decreased systolic blood pressure and pulse pressure but did not affect diastolic and mean arterial pressure. In contrast, in hypertensives, the same dosage of isosorbid dinitrate decreased together systolic, diastolic mean, and pulse pressure. In both populations, pulse wave velocity decreased significantly whereas aortic arch diastolic diameter increased markedly. The increase was observed mainly in normal subjects. The study provided evidence that (1) both in normal subjects and hypertensives, isosorbide dinitrate caused an increase in aortic diameter together with an increase in arterial distensibility; and (2) the changes in mean arterial pressure were significant only in hypertensives, indicating that the altered vasodilator response in essential hypertension is not endothelium-mediated.

Arterial distensibility and ambulatory blood pressure monitoring in essential hypertension

Arterial distensibility estimated by carotid femoral pulse wave velocity was evaluated in 22 patients with sustained essential hypertension, together with 3 different methods of blood pressure (BP) measurement: mercury sphygmomanometer, semiautomatic BP recording using the Dinamap apparatus and 24-hour ambulatory BP monitoring using a Spacelabs monitor. Although pulse wave velocity did not correlate with BP measured by mercury sphygmomanometer, it strongly and positively correlated with BP measurements using the other 2 procedures. The best correlation was observed with ambulatory BP with respect to systolic BP only (r = 0.685, p less than 0.001). Since cardiovascular morbidity and mortality in hypertensive patients is mainly related to lesions of the large arteries, the determination of pulse wave velocity together with ambulatory BP measurements is proposed for the evaluation of cardiovascular risk.