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Biomedical subjects

A C Simon

Publications and source records attributed to A C Simon.

At least 55 records · Page 3Linked to original sources
PubMed1985

The effect of acute and chronic nicardipine therapy on forearm arterial haemodynamics in essential hypertension.

By using simultaneous recording curves obtained with pulsed Doppler velocimetry and strain gauge mechanography, forearm arterial haemodynamics were studied in 26 patients with mild to moderate essential hypertension. Fifteen patients received a single oral dose of nicardipine 40 mg, and 11 patients were treated with nicardipine 30 mg three times daily for 3 months. In both groups of patients there was a similar and significant (P less than 0.001) reduction in mean, systolic, and diastolic pressures. There was a slight increase in heart rate (P less than 0.05) after the single dose, but no change after 3 months of treatment. The diameter, blood velocity, and blood flow of the brachial artery increased significantly in both treatment groups. The decrease in forearm vascular resistance was significant for both treatment groups. Brachial artery compliance increased (P less than 0.01) and characteristic impedance decreased (P less than 0.01) after both single-dose and long-term therapy with nicardipine. In patients who received nicardipine for 3 months, there were close correlations between the baseline serum calcium level and the percent change in vascular resistance (r = -0.73, P less than 0.01), blood flow (r = 0.89, P less than 0.001), and blood velocity (r = 0.91. P less than 0.001) of the forearm. No correlation was found between the baseline serum calcium and the change in arterial pressure. This study provided evidence that the blood-pressure-lowering effect of nicardipine was accompanied by a direct vasodilatory action in the small and large arteries of the forearm. An increase in peripheral blood flow with concomitant improvement of arterial compliance are the consequences of these arterial actions.

Blood Pressure↗
PubMed1985

Elevation of brachial arterial blood velocity and volumic flow mediated by peripheral beta-adrenoreceptors in patients with borderline hypertension.

Simultaneous determinations of cardiac output and brachial arterial blood flow were performed in patients with hypertension and high cardiac output in comparison with normal subjects of the same age. Brachial arterial blood flow was measured with a previously described pulsed Doppler apparatus that permitted the noninvasive determination of arterial diameter and blood flow velocity. In patients with borderline hypertension, brachial blood flow was significantly increased (136 +/- 11 vs 72 +/- 8 ml/min; p less than .001). After short-term administration of indomethacin, cardiac output decreased while brachial blood flow remained constant. After short-term administration of a selective beta 1-receptor antagonist (primidolol) and nonselective blocker (propranolol), cardiac output decreased significantly in both cases but the decrease in brachial blood flow was significant only after the administration of the nonselective beta-blocking agent. The study strongly suggested that in patients with borderline hypertension, the increased cardiac output is related to a prostaglandin and beta 1-adrenergic mechanisms whereas the increased brachial blood flow depends mainly on beta 2-adrenergic mechanisms.

Adult↗
PubMed1985

[Central and peripheral hemodynamic effects of nifedipine administered orally and sublingually in essential arterial hypertension].

The central and peripheral haemodynamic effects of the administration of 10 mg nifedipine sublingually in 6 patients with essential hypertension were compared with those observed after the administration of one 20 mg slow release tablet of nifedipine in 7 other hypertensive patients of the same age. The circulatory effects in the forearm were studied by pulsed Doppler velocimetry which allowed simultaneous measurement of the diameter of the brachial artery and of the velocity of blood flow. Both forms of administration significantly reduced the blood pressure by a significant reduction in total peripheral resistance. This reduction in total peripheral resistance was more significant (p less than 0.001 vs p less than 0.01) and more rapid with sublingual administration and was associated with a greater increase in heart rate and cardiac output. Both forms of administration induced an increase in brachial arterial blood flow due to a simultaneous increase in vessel calibre and velocity of blood flow. The results of this study show that both forms of administration act directly on the vessel wall of the arterioles and great arteries leading to a fall in blood pressure associated with an increase in peripheral blood flow. Sublingual nifedipine would seem to be the drug of choice for the treatment of hypertensive crises, whilst the slow release preparation with its lesser baroreflex stimulation would appear better suited for the long-germ treatment of essential hypertension.

Administration, Oral↗
PubMed1984

Captopril-induced changes in large arteries in essential hypertension.

The effect on large arteries of the converting enzyme inhibitor captopril was studied in men with sustained essential hypertension with two different hemodynamic parameters: (1) systemic arterial compliance and (2) brachial artery diameter. After captopril administration, a 20 percent increase in arterial compliance was observed. The same increase was obtained with a 5 percent (acute experiment) and a 15 percent (short-term experiment) decrease in blood pressure, indicating that the decrease in pressure could not explain exclusively the increase in compliance. This assumption was studied with determinations of brachial artery diameter using original pulsed Doppler systems. After captopril administration, brachial artery diameter increased markedly despite the decrease in blood pressure. In addition to its effect on small arteries, the converting enzyme inhibitor captopril also has a special effect on the large arteries of patients with essential hypertension.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1984

Comparison of oral MK 421 and propranolol in mild to moderate essential hypertension and their effects on arterial and venous vessels of the forearm.

The efficacy of MK 421 and propranolol was compared in 48 patients with mild to moderate hypertension. Each patient was randomly assigned to receive 1 of the drugs for 12 weeks. Additionally, a subgroup of 28 patients underwent studies of forearm arterial and venous circulation by means of pulsed Doppler and mercury-in-silastic plethysmography. Both drugs reduced supine and standing blood pressure (BP) (p less than 0.001). Propranolol reduced heart rate (p less than 0.001), while MK 421 did not change it. Brachial artery diameter, blood velocity and flow increased after MK 421 (p less than 0.001), but were not changed after propranolol therapy. Forearm vascular resistance decreased after MK 421 (p less than 0.001) and after propranolol (p less than 0.05). Forearm venous tone was unaffected on MK 421, but increased after propranolol (p less than 0.01). Thus, in moderate hypertension, 3 months of treatment with MK 421 or propranolol similarly decrease BP, but affect the forearm circulation differently: MK 421 dilates both the brachial artery and the arterioles of the forearm, but does not affect the venous vessels, and propranolol causes little arterial change but increases the forearm venous tone.

Adult↗
PubMed1984

Peripheral hemodynamic effects of short-term nadolol administration in essential hypertension.

A study of forearm arterial and venous hemodynamics by pulsed Doppler velocimetry and plethysmography was performed in 21 patients with essential hypertension, aged 16 to 54 years, before and after short-term nadolol administration at a dose of 0.05 mg/kg. Because of a large intersubject variability in the responses of the hemodynamic parameters to nadolol, an unconventional statistic approach was used to divide the overall population of patients into two homogeneous groups. The first included nine patients (group 1) and the second 12 patients (group 2). In patients of group 1, nadolol significantly decreased the systolic blood pressure (p less than 0.001), venous tone (p less than 0.01), and brachial artery flow (p less than 0.05). In patients of group 2, nadolol did not affect any forearm parameters. Each group of patients was compared to an age- and pressure-matched group of patients receiving propranolol at equiblocking doses. Contrary to nadolol, propranolol was found to increase significantly the forearm vascular resistance in patients of groups 1 and 2 (90 +/- 19%, p less than 0.001; 63 +/- 10%, p less than 0.001, respectively). Thus the hemodynamic beta-blocking effects of nadolol in the forearm were less marked than those of propranolol, suggesting that the effects of acute beta blockade by nadolol could be offset by other effects, such as a peripheral partial-agonist effect.

Adolescent↗
PubMed1984

Systemic compliance, renal hemodynamics, and sodium excretion in hypertension.

Extracellular fluid volume (ECF), plasma volume (PV), glomerular filtration rate (GFR), renal plasma flow (RPF), efferent arteriolar oncotic pressure (pi E), sodium output (UNaV), and sodium clearance (CNa) were determined in 150 men including 50 normal controls (NC) and 100 sustained essential hypertensive patients (EH). Total effective vascular compliance (TEVC) and central venous pressure (CVP) were measured in 17 normotensives and 24 EH. EH had a decreased RPF and TEVC (P less than 0.001), while CVP and pi E were higher than in NC (P less than 0.001). ECF, GFR, UNaV, and CNa were identical in EH and NC. A positive correlation between RPF and CNa (P less than 0.01) and a negative correlation between pi E and CNa existed in both groups with a significant reset of the curve in EH: For any given RPF or pi E the CNa was higher in EH. In the overall population TEVC was negatively correlated with CVP (P less than 0.01) and pi E (P less than 0.01); CVP was positively correlated with pi E (P less than 0.01). The results suggest that physical properties of the low pressure system could participate in the natriuretic adaptation of the kidney in EH man.

Adult↗
PubMed1984

Forearm arterial compliance: the validation of a plethysmographic technique for the measurement of arterial compliance.

Arterial compliance was determined in eight normal subjects and 23 patients with hypertension and vascular disease by two independent techniques: (a) with a plethysmographic strain gauge (to measure pulsatile forearm volume changes as representing intra-arterial volume changes) and an automated sphygmomanometric system (to measure pulse pressure) and (b) calculation from the local pulse wave velocity and dimension of the brachial artery measured by pulsed wave Doppler ultrasound. Arterial compliance measured both by the plethysmographic technique and calculated from the pulse wave velocity was reduced in subjects with hypertension and vascular disease as compared with normal subjects. The regression equation between the compliance determined by the plethysmographic technique (x) and that calculated (y) from the pulse wave velocity and brachial arterial diameter was y = 3. 35x + 1.53, r = 0.77, P less than 0.001. The good correlation appears to validate the plethysmographic technique as a method of determining arterial compliance.

Adult↗
PubMed1984

Post-synaptic alpha-blockade and brachial artery compliance in essential hypertension.

Central (six patients) and brachial (12 patients) haemodynamics were studied in men with sustained essential hypertension before and after intravenous administration of an alpha post-synaptic adrenergic blocking drug, urapidil. Brachial arterial compliance was evaluated non-invasively from the simultaneous measurement of pulse wave velocity and arterial diameter. In basal conditions, arterial compliance was reduced in hypertensives. Urapidil caused a significant drop in blood pressure, due to a significant decrease in total peripheral resistance with no change in cardiac output and heart rate. Brachial arterial diameter and compliance did not change significantly. The results show that the decreased arterial compliance in hypertensive patients was not due exclusively to the elevation of blood pressure or to a predominant activation of the autonomic nervous system, or both. Such observations suggest that, in men with sustained essential hypertension, the decreased compliance was probably related to structural alterations of large arteries.

Blood Flow Velocity↗
PubMed1984

ACE inhibition and brachial artery haemodynamics in hypertension.

Brachial artery haemodynamics, including arterial diameter, blood flow velocity, blood flow and compliance of the brachial artery may be evaluated non-invasively in man, using pulsed Doppler methods. In patients with sustained untreated essential hypertension, brachial artery diameter is increased, blood flow is normal and arterial compliance is reduced independently of the level of blood pressure. Converting enzyme inhibition may reverse the large artery abnormalities, causing an increase in arterial diameter, blood flow and arterial compliance both in acute and long-term investigations. These changes in large arteries may contribute towards improved cardiovascular morbidity and less mortality in treated hypertensive patients.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1984

Large arteries in hypertension: acute effects of a new calcium entry blocker, nitrendipine.

Acute effects of a new calcium entry blocker, nitrendipine, on large arteries of the forearm were studied by using arterial pulse strain gauge mecanography and pulsed Doppler velocimetry of the brachial artery in 13 mild to moderate essential hypertensive patients. Ninety minutes after nitrendipine ingestion, patients exhibited significant decreases in blood pressure without changes in heart rate; increases in brachial artery diameter and decreases in brachial to radial pulse wave velocity; increases in arterial compliance and decreases in characteristic impedance; and increases in brachial artery blood velocity and flow and decreases in forearm vascular resistance. Lastly, amplitude of pulse pressure was decreased by nitrendipine and negatively correlated to the level of arterial compliance. These results suggest that nitrendipine exerts a direct benefit effect on the hypertensive large arteries whose two main consequences are a decrease in pulsatility of arterial pressure and an increase in arterial flow.

Adult↗
PubMed1983

Estimation of forearm arterial compliance in normal and hypertensive men from simultaneous pressure and flow measurements in the brachial artery, using a pulsed Doppler device and a first-order arterial model during diastole.

Simultaneous brachial artery pressure and blood flow measurements were made in 45 men. Blood flow was evaluated by means of a pulsed Doppler device with a double transducer probe. From analysis of the pressure-flow curves during diastole, forearm arterial compliance (FAC) was determined by using the model of the forearm arterial tree as a system of tubes, each with a storage capacitance, in series with the arteriolar resistances vessels. The value of FAC for seven normal subjects, aged 44 +/- 3 (mean +/- SEM) years, was between 0.78 and 1.73 X 10(-10) m5 . N-1. By comparison, a 30% reduction in FAC was observed in 38 men of the same age with essential hypertension, which was similar whether the intra-arterial diastolic pressure was above or below 90 mmHg. In the more severe group (Intra arterial diastolic pressure greater than 90 mmHg), the reduced FAC was associated with a significant increase in brachial artery diameter; after administration of dihydralazine, blood pressure and arterial diameter returned to normal but FAC remained diminished. The study is the first to evaluate FAC in intact men. The reduced FAC in hypertension is independent of blood pressure "per se" but may reflect adaptive change in the walls of the large arteries. In the more severe hypertension, arterial calibre was increased; this could be a mechanism which could prevent FAC from decreasing further with chronic elevation of blood pressure.

Adult↗
PubMed1983

A noninvasive determination of fistula blood flow in dialysis patients.

Arteriovenous fistula (AVF) blood flow was evaluated in 32 dialysis patients using a pulsed Doppler velocimeter with two dominant features: a range-gated time system and a double transducer probe. With the proposed apparatus, the observation angle between the ultrasound beam and the vessel axis was known. In radial AVF, blood flow was 728 +/- 53 ml/min and was negatively correlated with the age of the AVF (r = -0.62; p less than 0.01). In brachial AVF, blood flow was 778 +/- 152 ml/min. In bovine heterograft AVF, blood flow was 1,225 +/- 125 ml/min. In the overall population, a negative relationship was observed between the diameter of the fistula and the blood flow velocity (r = -0.57; p less than 0.01). The study describes an accurate noninvasive method for the determination of fistula blood flow in dialysis patients, which may be helpful in the follow-up of the regional hemodynamics of this vascular access.

Adult↗
PubMed1983

Hemodynamic effects of head-down tilt in normal subjects and sustained hypertensive patients.

Central and forearm arterial and venous hemodynamics, arterial baroreflex sensitivity, plasma renin activity, and catecholamines were studied in supine position and after -10 degrees head-down tilt in 29 patients with sustained essential hypertension and in 29 normotensive controls of the same age and sex. In both populations, blood pressure, heart rate, and arterial baroreflex sensitivity did not change during the maneuver. Head-down tilt induced a similar increase in cardiopulmonary blood volume in controls and hypertensives, whereas the increase in central venous pressure, cardiac output, and forearm blood flow was higher in hypertensives. Forearm venous tone decreased in controls (from 16.6 +/- 0.8 to 13.8 +/- 0.9 mmHg X ml-1 X 100 g-1; P less than 0.01) but did not change in hypertensive patients (24.9 +/- 1.6 vs. 25.1 +/- 1.9. The magnitude of forearm vascular resistance changes induced by head-down tilt were significantly related to the basal venous tone in the overall population (P less than 0.01). The decrease in plasma renin activity and plasma catecholamines was similar in the two groups. The study provides the evidence that the higher increase in cardiac output and local flow observed in head-down tilt in hypertensive patients is probably due to a higher change in central venous pressure related to a decrease in venous distensibility.

Adult↗
PubMed1983

Baroreflex response and vasodilating drugs in essential hypertension.

Blood pressure, heart rate, and arterial diameter of the brachial artery were studied in patients with sustained essential hypertension before and after administration of three vasodilating drugs: dihydralazine, diltiazem, and dinitrate isosorbide (ISDN). The diameter of the brachial artery was measured using a pulsed Doppler device, enabling the angle between the ultrasound beam and the vessel axis to be evaluated with a precision inferior to 2 percent. The three drugs had similar effects in decreasing the blood pressure and the forearm vascular resistance. Dihydralazine reduced the arterial diameter (p less than 0.001) and increased heart rate. Diltiazem and ISDN increased markedly the arterial diameter (p less than 0.001) but did not change heart rate. Dihydralazine decreased the tangential tension of the arterial wall, while diltiazem and ISDN did not. The study provided evidence that, with vasodilating drugs, the changes in the caliber of peripheral large arteries, which are a determinant of wall arterial tension, can influence the baroreflex-mediated tachycardia caused by use of the drugs.

Adult↗
PubMed1983

Effect of oral MK-421 and propranolol on the forearm arterial circulation in essential hypertension: a preliminary report.

The efficacy of MK-421 was compared with that of propranolol in patients with mild to moderate essential hypertension, using a placebo-controlled double-blind randomized protocol. The two drugs reduced supine and standing blood pressures, but propranolol, unlike MK-421, reduced heart rate. Using a pulsed Doppler method, brachial artery diameter, blood velocity and blood flow were measured during the study. These indices increased after MK-421 but were not modified after propranolol. Forearm vascular resistance decreased both after MK-421 and propranolol. Thus, chronic treatment with MK-421 or propranolol in hypertension lowers blood pressure but acts differently on forearm circulation. MK-421 dilates both the brachial artery and the arterioles of the forearm while propranolol has no effect on these arterial indices.

Administration, Oral↗
PubMed1983

Hemodynamic effects of diltiazem in hypertension.

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.

Adult↗