Biomedical subjects

A C Simon

Publications and source records attributed to A C Simon.

At least 19 recordsLinked to original sources

PubMed1999

In vitro generation of endothelial microparticles and possible prothrombotic activity in patients with lupus anticoagulant.

Microparticles (MPs) resulting from vesiculation of platelets and other blood cells have been extensively documented in vitro and have been found in increased numbers in several vascular diseases, but little is known about MPs of endothelial origin. The aim of this study was to analyze morphological, immunological, and functional characteristics of MPs derived from human umbilical vein endothelial cells (HUVECs) stimulated by TNF, and to investigate whether these MPs are detectable in healthy individuals and in patients with a prothrombotic coagulation abnormality. Electron microscopy evidenced bleb formation on the membrane of TNF-stimulated HUVECs, leading to increased numbers of MPs released in the supernatant. These endothelial microparticles (EMPs) expressed the same antigenic determinants as the corresponding cell surface, both in resting and activated conditions. MPs derived from TNF-stimulated cells induced coagulation in vitro, via a tissue factor/factor VII-dependent pathway. The expression of E-selectin, ICAM-1, alphavbeta3, and PECAM-1 suggests that MPs have an adhesion potential in addition to their procoagulant activity. In patients, labeling with alphavbeta3 was selected to discriminate EMPs from those of other origins. We provide evidence that endothelial-derived MPs are detectable in normal human blood and are increased in patients with a coagulation abnormality characterized by the presence of lupus anticoagulant. Thus, MPs can be induced by TNF in vitro, and may participate in vivo in the dissemination of proadhesive and procoagulant activities in thrombotic disorders.

Antiphospholipid Syndrome↗

PubMed1994

Influence of HDL subfractions on erythrocyte aggregation in hypercholesterolemic men. PCVMETRA Group.

Recent studies have suggested that rheological mechanisms may be involved in the pathogenesis of ischemic syndromes in hyperlipidemias. We investigated the association between erythrocyte aggregation and components of lipoproteins in the blood of 60 normotensive, hypercholesterolemic men aged 45 +/- 8 years. The rheological parameters assessed were aggregation index (AI) and disaggregation shear rate threshold (gamma t) as determined by laser reflectometry, plasma fibrinogen, total serum protein, and hematocrit. The lipoprotein variables included total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol and its subfractions HDL2 cholesterol and HDL3 cholesterol, apolipoprotein (apo) B, apoA-I, HDL particles containing apoA-I without apoA-II (LpA-I), and HDL particles containing both apoA-I and apoA-II (LpA-I/A-II). Covariables considered for possible confounding effects were age, body mass index, and smoking behavior. Fibrinogen, total serum protein, and both aggregation parameters (AI and gamma t) were elevated in this hypercholesterolemic population. Univariate analysis showed that both AI and gamma t correlated positively with fibrinogen (P < .001) and total serum protein (P < .01) and negatively with HDL2 cholesterol (P < .01) and LpA-I (P < .01); gamma t also provided a positive correlation with LpA-I/A-II (P < .05). A multivariate model analysis demonstrated that HDL2 cholesterol, LpA-I, and LpA-I/A-II also emerged as significant factors influencing erythrocyte aggregation; 60% to 68% of the variance of AI and 47% to 64% of the variance of gamma t could be explained by these factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Single beat evaluation of circumferential aortic elastin elastic modulus in conscious dogs. Potential application in non-invasive measurements.

A description of the arterial wall elastic properties comprehends both collagen and elastin, clearly shown in a biphasic stress-strain relationship. From chronically instrumented conscious dogs, aortic pressure-diameter curves can be obtained in a single beat, which is impossible to perform in human beings. In control conditions, the collagen fibers are almost not distended and the resistance to stretch is mainly supported by the elastin fibers. Therefore, the mechanical properties of the aorta are almost purely elastic in the basal beat to beat conditions. In this study we propose and test five indexes, which include as variables: systolic, diastolic and mean arterial pressure and diameter; besides, arterial compliance and pressure-strain elastic modulus as suggested to evaluate the elastic behaviour of the elastic fibers. This data can be easily obtained by non-invasive methods, such as Doppler-ultrasound techniques and auscultative esphygmomanometrical measurements, while the indexes evaluated can be retrieved from a single beat evaluation. Of three measurements performed in chronically instrumented conscious dogs on different days, one of these indexes, the ME5 = [formula: see text] x Rdias proved to be an accurate and reliable parameter to evaluate the mechanical behaviour of arteries. This kind of parameter may be useful for research and evaluation of several diseases that markedly alter the arterial wall compliance.

Algorithms↗

PubMed1992

Role of arterial compliance in the physiopharmacological approach to human hypertension.

Arterial compliance in humans is generally measured by modeling analysis of pulse tracing or of pulse wave propagation in the arterial tree. It is decreased in hypertension in part because elevation of blood pressure stiffens the arteries by stretching the rigid collagen fibres of their walls. Using a modeling evaluation of the compliance-pressure relationship in large arteries, it is possible to correct compliance from the mechanical effect (passive effect) due to pressure elevation. This makes it possible to show that, at the same pressure as in normal controls, hypertensive patients maintain decreased arterial compliance. This finding suggests that functional and/or structural changes other than pressure-mediated stretching of arteries (active effect) contribute toward reducing arterial compliance. Thus, the response of compliance to antihypertensive drugs must be studied by differentiating between passive and active effects. The diameter and compliance-pressure relationship in arteries allow differentiation of a passive arterial effect due to the pressure-lowering action of the drug, and an active pharmacological effect calculated at the same pressure before and after drug administration. Four drugs--ketanserin, urapidil, nitrendipine, and nicardipine (acute administration)--are given as examples. No active or passive compliance changes are observed with urapidil and ketanserin. In contrast, an active increase in compliance is observed in isobaric conditions with calcium antagonists, together with large-artery dilation due to a potent smooth muscle-relaxing effect. This active increase in compliance is potentiated by a passive increase due to the pressure-lowering effect that reduces the mechanical stretch exerted by blood pressure on arterial bioelastomers. Finally, an optimum increase in arterial compliance is achieved by drugs that vasodilate large arteries by smooth muscle relaxation and concomitantly decrease blood pressure. This may be of importance because low compliance has adverse effects on the cardiovascular system by contributing to the pathogenesis of systolic hypertension and left ventricular hypertrophy. Loss of arterial compliance may also be an early marker of atherosclerosis.

Antihypertensive Agents↗

PubMed1991

Development and implementation of a microcomputer-based multi-user MEDLINE system.

The Health Sciences Libraries Consortium, a group of health sciences libraries based in Philadelphia, PA, has implemented a MEDLINE database retrieval system based on the CD Plus PlusNet2 system. The system provides access to the entire MEDLINE database file through three centralized servers and four distributed servers, and is accessible over the HSLC wide-area network linking all of its members. This article describes the implementation process, from selection of the system to future development.

CD-ROM↗

PubMed1991

Physiopharmacological approach to mechanical factors of hypertension in the atherosclerotic process.

Hypertension may influence the atherosclerotic process of large arteries via pressure and shear forces. The pressure force dilates and stiffens arteries because of the non-linear elastic behaviour of arterial walls. This partly explains the increased diameter and decreased compliance of the brachial artery in hypertensive subjects compared with normotensive controls. However, pressure lowering by antihypertensive drugs does not always reverse large artery alterations indicating that other mechanisms are involved. Reversal of low compliance obtained with certain antihypertensive drugs is generally concomitant with large artery vasodilation, suggesting that smooth muscle relaxation plays a major role in the compliance response to drugs. Atherosclerosis associated with hypertension also causes additional loss of compliance and creates a vicious circle of sclerosis development by accelerating the biophysical fatigue of bioelastomers. Hypertension may contribute to atherogenesis by means of wall shear stress which is the frictional force exerted by the circulating blood column on the intima of arteries. Since it is likely that atherosis lesions may develop preferentially in low shear conditions, hypertension may promote the haemodynamic conditions of atherogenesis at the blood-wall interface. The response of wall shear to antihypertensive treatment is not unequivocal. For example, the beta-blocker, atenolol, does not change shear whereas carteolol increases shear rate and stress and these effects are closely related to change in platelet-free calcium concentration. This finding is consistent with the effect of shear forces on cell permeability to calcium demonstrated in vitro and points to the crucial role of wall shear as a biophysical signal capable of modifying the endothelial structure and function of arteries.

Antihypertensive Agents↗

PubMed1991

Risk factors and early extracoronary atherosclerotic plaques detected by three-site ultrasound imaging in hypercholesterolemic men. Prévention Cardio-vasculaire en Médecine du Travail METRA Group.

Ultrasonic detection of atherosclerotic plaque of carotid abdominal aortic and femoral arteries and evaluation of risk factors were performed in 208 hypercholesterolemic men without cardiovascular disease. Twenty-six percent of them had no plaque. Plaque at the carotid, aortic, and femoral sites was found in 37%, 48%, and 53% of subjects, respectively. Plaque was associated (1) in carotid arteries with increased total and low-density lipoprotein cholesterol; (2) in the aorta with increased age, pressure, glycemia, and smoking; and (3) in femoral arteries with increased age, systolic pressure, low-density lipoprotein cholesterol, and smoking. Multiple regression analysis showed correlations between carotid plaque and low-density lipoprotein cholesterol; aortic plaque and age, smoking, glycemia, and pressure; femoral plaque and age, smoking, and pressure. This suggests that multiple risk factors influence lesions, and risk profile differs according to atherosis site.

Adult↗

PubMed1990

Pulsatile flow and oscillating wall shear stress in the brachial artery of normotensive and hypertensive subjects.

STUDY OBJECTIVE - The aim of the study was to examine oscillating arterial wall shear stress in hypertension. DESIGN - Pulsatile flow and oscillating wall shear stress were measured in brachial artery in hypertensive v normotensive subjects using pulsed Doppler apparatus. Methods were tested in four subjects using a micrometric procedure of Doppler probe displacement providing instantaneous real time velocity profiles. SUBJECTS - 19 ambulatory male patients with mild to moderate hypertension (diastolic blood pressure 95-114 mm Hg) and 11 normotensive male controls of similar age were studied. All were non-smokers. MEASUREMENTS and RESULTS - Arterial diameter and pulsatile centreline blood velocity were determined with pulsed Doppler, and blood viscosity was measured with a coaxial cylinder viscometer. Shear rates corresponding to maximum (gamma Vmax), minimum (gamma Vmin), and pulse (gamma Vpulse) velocities were evaluated with a simplified method of computation of Womersley equations. Corresponding shear stresses (tau Vmax, tau Vmin, tau Vpulse) were calculated as the product between shear rate and viscosity. The differences in wall shear rates obtained with the Womersley method and with the micrometric procedure were less than 10%. Compared to normotensives, hypertensives had greater arterial diameter [0.508(SEM0.006) v 0.446(0.014), p less than 0.001], lower maximum velocity [36.2(1.5) v 46.3(2.4) cm.s-1, p less than 0.001], lower absolute value of minimum velocity [-8.3(1.2) v -14.3(2.3) cm.s-1, p less than 0.01], lower pulse velocity [44.5(2.2) v 61.2(3.9) cm.s-1, p less than 0.001], and higher blood viscosity [4.77(0.08) v 4.28(0.09) mPa.s, p less than 0.001]. gamma and tau Vmax, Vmin and Vpulse were all lower in absolute value in hypertensives. Overall mean blood pressure in all subjects was negatively correlated to gamma Vmax (r = -0.65), tau Vmax (r = -0.46), gamma Vmin (r = -0.45), tau Vmin (r = -0.37), gamma Vpulse (r = -0.63), and tau Vpulse (r = -0.48). In hypertensives, age was correlated negatively to gamma Vmax (r = -0.44), tau Vmax (r = -0.46), gamma Vmin (r = -0.57), tau Vmin (r = -0.57), gamma Vpulse (r = -0.58), and tau Vpulse (r = -0.58). In normotensives, age was not correlated with shear parameters, except for tau Vmax (r = -0.60) and tau Vpulse (r = -0.66). CONCLUSIONS - The hypertensive state is associated with a reduction in oscillating wall shear in large arteries despite an increase in blood viscosity. Age in combination with hypertension also decreases wall shear conditions.

Adult↗

PubMed1990

Non-invasive evaluation of segmental pressure drop and resistance in large arteries in humans based on a Poiseuille model of intra-arterial velocity distribution.

STUDY OBJECTIVE: The aim of the study was to evaluate in hypertensive subjects the longitudinal pressure drop and segmental resistance in a large artery in relation to shearing forces of the circulating blood column at the arterial wall. DESIGN: Arterial diameter, blood velocity, and flow were measured in the brachial artery using pulsed Doppler apparatus. Blood viscosity was measured at 96 s-1 with a low shear viscometer. Segmental resistance per unit arterial length was calculated using the basic Poiseuille resistance expression from the ratio between blood viscosity and the fourth power of arterial diameter. Longitudinal pressure drop was deduced as the product between segmental resistance and blood flow. The Poiseuille model of velocity distribution also enabled wall shear rate and stress to be calculated from the ratio between blood velocity and arterial diameter and from the product between shear rate and blood viscosity respectively. PATIENTS: 19 ambulatory male patients with mild to moderate hypertension and 11 normotensive male controls of similar age were studied. RESULTS: Compared to controls, hypertensive patients had higher arterial diameter (p less than 0.001) lower blood velocity (p less than 0.05), higher blood viscosity (p less than 0.01), lower segmental resistance and pressure drop (p less than 0.001, p less than 0.01) and lower shear rate and stress (p less than 0.01, p less than 0.05). A negative correlation existed in the overall normotensive and hypertensive population between pressure drop and mean blood pressure (r = -0.55, p less than 0.01). CONCLUSION: The hypertensive state is associated with a clear reduction in large artery segmental resistance and longitudinal pressure drop concomitantly with a decrease in shear conditions at the arterial wall. The mechanisms of reduced resistance and pressure drop are related to decreased wall shear and increased diameter of the artery, both of which reduce the frictional forces at the blood-arterial wall interface.

Adult↗

PubMed1990

Abnormal wall shear conditions in the brachial artery of hypertensive patients.

Brachial artery wall shear phenomena were studied in 20 untreated essential hypertensive patients and in 11 normotensive controls of similar age. A pulsed-Doppler velocimeter was used to measure brachial artery internal diameter and mean cross-sectional and systolic centreline blood velocities. A coaxial-cylinder viscometer was used to measure blood viscosity at a shear rate of 96 s-1. A Poiseuille model of velocity distribution across the arterial lumen was used to determine wall shear rate and stress from, respectively, the ratio of blood velocity to arterial diameter and the product of shear rate and blood viscosity. Mean and systolic shear rates and stresses were calculated using, respectively, mean cross-sectional and systolic centreline blood velocities. Hypertensive patients had larger brachial artery diameters (P less than 0.001), lower systolic centreline and mean cross-sectional blood velocities (P less than 0.001, P less than 0.05), higher blood viscosity (P less than 0.001), lower mean and systolic wall shear rates (P less than 0.01, P less than 0.001) and lower systolic wall shear stress (P less than 0.05) than normotensive controls. In all subjects, mean blood pressure was negatively correlated both with mean and systolic shear rates (r = -0.38, P less than 0.05;r = -0.45, P less than 0.01). Thus the hypertensive state was associated with decreases in both mean and systolic wall shear rates, and in systolic wall shear stress. These shear abnormalities merit attention because of the atherogenic effect of low-shear conditions.

Adult↗

PubMed1989

Effects of nicorandil on arterial and venous vessels of the forearm in systemic hypertension.

The effects of a single oral dose of 20 mg of nicorandil were evaluated in 12 untreated patients with mild to moderate essential hypertension. Serial measurements of arterial pressures were obtained by means of an automatic device (Dynamap) up to 120 minutes after drug administration. Forearm hemodynamics were determined with a pulsed Doppler velocimeter, or strain gauge mecanography and plethysmography enabling measurement of the diameter, velocity and flow of the brachial artery as well as the arterial pulse wave velocity and forearm venous tone. In addition, local vascular resistance, compliance and impedance were deduced. Nicorandil administration produced a significant decrease in systolic and diastolic blood pressure, from 18 minutes after dosing which lasted up to the end of the study (i.e., 120 minutes after drug administration) (p less than 0.01). This decrease in blood pressure was not associated with reflex tachycardia. The brachial artery diameter increased significantly (p less than 0.01) with no change in brachial artery blood flow. A decrease in brachial-radial pulse wave velocity and arterial impedance (p less than 0.01) and an increase in arterial compliance were observed. Thus, this study demonstrated an antihypertensive activity of a single oral administration of nicorandil without baroreflex activation. This decrease in blood pressure was associated with a dilation of peripheral large arteries leading to an increase in arterial compliance. Thus, clinical testing to evaluate the antianginal activity of nicorandil, especially in hypertensive patients with coronary heart disease, should be encouraged.

Adult↗

PubMed1989

Comparative haemodynamic effects of ketanserin and ritanserin in the proximal and distal upper limb circulations of hypertensive patients.

The effects of ketanserin (40 mg p.o.) on blood pressure and brachial haemodynamics (brachial artery diameter, brachial blood velocity and blood flow) have been compared in a double-blind study with those of ritanserin (10 mg p.o.) and placebo. Haemodynamic parameters were measured before and 1 h after treatment. Patients with mild to moderate essential hypertension participated in this study, 6 each on ketanserin, ritanserin and placebo. Placebo significantly reduced heart rate and did not modify the other parameters. Compared to placebo, ketanserin significantly reduced systolic and diastolic blood pressure, increased brachial blood velocity and flow, and decreased forearm vascular resistance. Compared to placebo, ritanserin slightly decreased blood pressure and slightly increased blood flow, but neither effect was significant. When blood circulation to the hand was excluded, neither ketanserin nor ritanserin modified the proximal arterial resistance or blood flow. It is concluded that the actions of ketanserin and ritanserin essentially occurred in the distal part of the upper limb, and alpha 1-receptor blockade is probably involved.

Arm↗

PubMed1988

Brachial artery hemodynamic response to acute converting enzyme inhibition by enalaprilat in essential hypertension.

To assess the vascular involvement of renin-angiotensin system inhibition in human hypertension, acute effects of intravenous enalaprilat on brachial artery diameter, blood flow, and blood velocity were investigated in hypertensive patients by pulsed Doppler technique and compared with effects of saline vehicle. Compared with saline vehicle, enalaprilat reduced blood pressure (P less than 0.001) and increased brachial arterial diameter (P less than 0.01) and brachial blood flow (P less than 0.01). Enalaprilat effect on arterial pulse pressure was dependent on preinjection pulse pressure (r = -0.76; P less than 0.001), but its effect on mean blood pressure was not dependent on preinjection mean blood pressure. On the other hand, enalaprilat effect on arterial blood flow was negatively correlated with preinjection blood pressure (r = -0.64; P less than 0.02). The findings point to different responses of large and small arteries to intravenous enalaprilat.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1988

Combined effects of gender and hypertension on the geometric design of large arteries. Sexual differences in normal and hypertensive forearm arteries.

The effects of sex, hypertension, morphologic status, and heart rate were assessed on the large arteries of 46 normotensive subjects (23 men and 23 women) and 50 hypertensive patients (25 men and 25 women) by means of pulsed Doppler determination of diameter and blood velocity of the brachial artery. Compared to men, women had lower height, weight, and forearm volume (P less than 0.001), higher heart rate (P less than 0.001), and lower brachial artery diameter (P less than 0.001) both in the normotensive and hypertensive groups. Compared to normotensives, hypertensives of the same sex showed an increase in brachial artery diameter, only significant in men (P less than 0.001), and an increase in heart rate, only significant in women (P less than 0.001). The multiple regression analysis of brachial artery diameter showed significant coefficients for sex and hypertension (P less than 0.001), and for age and heart rate (P less than 0.05); the multiple regression analysis of blood velocity showed that only the coefficient of hypertension was significant (P less than 0.05). The study of first-order interactions between the independent variables revealed that effect of sex on arterial diameter did not depend on the other variables. In contrast the effects of age and heart rate were influenced by the presence or the absence of hypertension, and arterial caliber was positively related to age in normotensive subjects (P less than 0.05) but not in hypertensive patients, and negatively related to heart rate in hypertensive patients (P less than 0.001) but not in normotensive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Aortic pulsatile pressure and diameter response to intravenous perfusions of angiotensin, norepinephrine, and epinephrine in conscious dogs.

The aortic elastic behavior has been studied in conscious dogs chronically instrumented with a pressure microtransducer and two ultrasonic crystals. Pressure and diameter measurements were analyzed in terms of their mean values and systolic-diastolic variations, enabling calculation of Peterson elastic modulus, and were displayed in the x-y form to obtain pressure diameter hysteresis loops. After recovery from surgery and under autonomic blockade, intravenous perfusions of angiotensin, norepinephrine, and epinephrine were made at incremental steps of doses until steady-state pressure-diameter changes were achieved. The slopes of the positive pressure-diameter correlations obtained at each dose of the same vasoactive substance were higher for angiotensin than norepinephrine (p less than 0.01) and epinephrine (p less than 0.001) and were higher for norepinephrine than epinephrine (p less than 0.05). Similarly, the slopes of the elastic modulus to mean pressure relation were significantly lower for angiotensin than for norepinephrine (p less than 0.05) and epinephrine (p less than 0.001) and were significantly lower for norepinephrine than epinephrine (p less than 0.001). Thus, at the same transmural pressure, the distension and stiffness of the aorta were lower and higher with epinephrine than with norepinephrine, respectively, and with norepinephrine than with angiotensin suggesting different potencies of these drugs in terms of smooth muscle activation in the aorta.

Angiotensin II↗

PubMed1988

[Effect of age on brachial and carotid circulation in human arterial hypertension].

Right brachial artery and common carotid artery haemodynamic parameters were studied using pulsed Doppler velocimetry enabling non invasive measurements of their internal diameters and blood velocities in 74 untreated essential hypertensive patients subdivided in two groups of younger than (33 patients) and older than 45 years (41 patients). There were no significant differences in the haemodynamic parameters of brachial artery (i.e. diameter and blood velocity) between the two groups of patients. In the patients older than 45, there were no changes in the diameter of common carotid artery, but there was a decrease in carotid artery blood velocity as compared with patients younger than 45 (p less than 0.001). In the patients younger than 45, there were no correlations between the haemodynamic parameters of both circulations; in contrast, in patient older than 45 significant relationship were found between the common carotid artery diameter and the brachial artery diameter (r = 0.45, p less than 0.01) and between the blood velocity in the common carotid artery and in the brachial artery (r = 0.55, p less than 0.001). Thus, in these hypertensive patients, brachial artery circulation was not affected by age; but age older than 45 was associated with a decrease in common carotid blood flow, with no change in common carotid artery diameter. However, the existence of strong correlations between brachial and carotid artery diameters and blood velocities in patients older than 45, suggests that age might interfere, in hypertensive patients, with the specific regulatory adjustments of the brachial and carotid circulations.

Adult↗

PubMed1987

Heterogeneity of the atherosclerotic process in systemic hypertension poorly controlled by drug treatment.

A cross-sectional study of 85 patients with poorly controlled treated hypertension was performed to detect, by means of aortic pulse wave velocity measurement and ultrasonic examinations, subclinical alterations of arteries. Pulse wave velocity was related to the product of age and diastolic blood pressure (BP) according to a nomogram obtained from normotensive subjects, and was found inside the nomogram in 37 patients (group I) and outside in 48 (group II). Group II had higher systolic and pulse BP (p less than 0.01), lower diastolic BP (p less than 0.01), higher proportion of cigarette smokers (p less than 0.05) and higher blood glucose levels (p less than 0.02) than group I. In group II a positive correlation existed between blood glucose and pulse wave velocity (p less than 0.01). Group II had a higher frequency of carotid artery stenosis (p less than 0.05) and a trend toward increased frequency of aortic and lower limb atherosclerotic lesions. The results indicate a heterogeneous pattern of arterial alterations in which systolic BP, cigarette smoking and blood glucose level are implicated.

Age Factors↗

PubMed1987

The efficacy of a transdermal formulation of clonidine in mild to moderate hypertension and its effects on the arterial and venous vasculature of the forearm.

We have studied the efficacy of clonidine hydrochloride administered transdermally once a week for 9 to 15 weeks in 12 patients with mild to moderate hypertension. Clonidine reduced both supine and standing blood pressures on average, but only 8 subjects were responders, i.e. had a decrease in supine diastolic blood pressure to below 90 mm Hg or more than 10% from baseline. Supine heart rate was unchanged, but in the responders the orthostatic increase in heart rate was reduced by clonidine from baseline (p less than 0.05). Moreover, in all the patients the change in the orthostatic increase in heart rate was correlated with the change in supine diastolic pressure (p less than 0.05). Brachial artery blood flow, forearm arterial compliance, vascular resistance, and venous tone were not affected by clonidine. Thus, transdermal clonidine reduced blood pressure, probably by a baroreflex-mediated effect, but did not affect the vasculature of the forearm.

Administration, Cutaneous↗