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Biomedical subjects

A C Simon

Publications and source records attributed to A C Simon.

At least 73 records · Page 4Linked to original sources
PubMed1982

Effect of nitroglycerin on peripheral large arteries in hypertension.

1 Blood pressure, systemic arterial compliance, and diameter, blood flow velocity, volumic flow and impedance of the brachial artery were measured before and after intravenous administration of nitroglycerin (15 micrograms/min during 15 min) in 11 patients with sustained essential hypertension. 2 For the evaluation of the diameter of the brachial artery, a bidimensional pulsed Doppler was used, enabling the angle of the ultrasound beam relative to the flowing stream of blood to be measured with an error of less than 2%. 3 After nitroglycerin, systolic pressure significantly decreased (P less than 0.01) without significant change in diastolic and mean arterial pressures, cardiac index, stroke index and total peripheral resistance. 4 Systemic arterial compliance and brachial artery diameter significantly increased (P less than 0.001; P less than 0.01) while velocity and blood flow of the brachial artery were unchanged. 5 The pattern of the input impedance of the brachial artery was consistent with a predominant effect of nitroglycerin on the viscoelastic properties of peripheral large arteries. 6 The study provided evidence that, in hypertensive patients, nitroglycerin has a direct effect on peripheral large arteries, causing an increase in arterial diameter and compliance, thus leading to a predominant decrease in systolic pressure.

Adult↗
PubMed1982

Aldosterone in sustained essential hypertension.

Plasma aldosterone (PA), plasma renin activity (PRA), extracellular fluid volume (EFV) and hepatic blood flow were measured in forty-four patients with sustained essential hypertension and compared with forty-two normotensive controls of same age and sex. All patient had inulin clearances within the normal range and balanced sodium intake and urinary output. In hypertensives, PA, PRA, EFV and hepatic blood flow were within normal ranges; the log-ratio PA:PRA was significantly elevated (P less than 0.001). In normotensives, a negative relationship was observed between PA and EFV (r=-0.55; P less than 0.001) while a positive relationship was observed between PA and PRA (=+0.70; P less than 0.001). In hypertensives, the two relationships were disrupted or less significant: for a given value of EFV, PA was more elevated in hypertensives than in normotensives; for a given value of PRA, PA was more evaluated in hypertensives than in normotensives. The results could not be explained on the basis of a disturbance in hepatic blood flow and/or in the metabolic clearance rate of aldosterone. The study provided evidence that, in patients with sustained essential hypertension and equilibrated sodium balance, there is an excess of plasma aldosterone relative to the levels of extracellular fluid volume and plasma renin activity. The excess of probably related to an abnormality in the adrenal secretion.

Adult↗
PubMed1982

Plasma prostaglandins PGE2 and PGF2 alpha, total effective vascular compliance and renal plasma flow in essential hypertension.

Plasma prostaglandins PGE2 and PGF2 alpha, cardiac hemodynamics, total effective vascular compliance, plasma (PV), interstitial (IFV) and extracellular fluid volumes, and renal indices were determined in 13 men with either borderline or sustained essential hypertension. PGE2 measured in the central venous blood was increased in borderline and in sustained hypertensives (p less than 0.01), while PGF2 alpha remained within normal ranges. Pulmonary degradation of both prostaglandins was decreased. In the overall population, the PGE2/PGF2 alpha ratio was: (i) negatively correlated with central venous pressure (r = -0.68; p less than 0.01), and (ii) positively correlated with total effective vascular compliance (r = 0.76; p less than 0.001), the PV/IFV ratio (r = 0.63; p less than 0.02) and the renal plasma flow (r = 0.79; p less than 0.001). The study suggests that, in hypertensive patients, prostaglandins PGE2 and PGF2 alpha play an important role on the compliance of the venous system and on the control of renal blood flow, contributing to the autoregulatory mechanisms of the hypertensive vascular disease.

Adolescent↗
PubMed1982

Systolic hypertension in arteriosclerosis obliterans of the lower limbs.

Hemodynamic parameters were measured in 24 patients with arteriosclerosis obliterans of the lower limbs (AOLL) in comparison with 16 normal subjects of same age. Systemic artérial compliance was estimated from a simple visco-elastic model. In patients with (AOLL), systolic pressure was significantly increased (P less than 0.001) while diastolic pressure remained within normal ranges. Arterial compliance was reduced (P less than 0.01) and was negatively correlated with systolic pressure (r = - 0.72). Intravenous administration of nitroglycerin significantly decreased systolic pressure (P less than 0.05) and increased arterial compliance (P less than 0.01) without any change in mean arterial pressure. The study provided evidence that, in patients with AOLL the reduced systemic arterial compliance contributes in the increase in systolic pressure largely.

Arteries↗
PubMed1981

Renal filtration fraction, effective vascular compliance, and partition of fluid volumes in sustained essential hypertension.

Extracellular fluid volume, hemodynamic parameters, total effective compliance, and renal indices were measured in 58 patients with sustained essential hypertensive in comparison with 56 normotensive subjects of the same age and sex. All subjects had a balanced sodium intake and urinary output with inulin clearance and extracellular fluid volume within normal ranges. In patients with hypertension, the ratio between plasma volume (PV) and interstitial fluid volume (IFV) was decreased (P less than 0.01) and was negatively correlated with the filtration fraction (FF) (r = -0.43; P less than 0.001). Total effective compliance was significantly reduced (P less than 0.001) and was positively correlated with the PV/IFV ratio (r = 0.73; P less than 0.001) and negatively correlated with FF (r = -0.56; P less than 0.001. The study provides evidence that the relationships between PV/IFV, FF, and vascular compliance reflect an alteration of the postcapillary segment of the circulation in hypertension.

Adult↗
PubMed1981

Regional blood flow in borderline and sustained essential hypertension.

1. Cardiac output, lower-limb blood flow, hepatic and renal blood flows were studied in 16 patients with borderline and 16 patients with sustained essential hypertension and compared with 16 age-matched control subjects. 2. In borderline hypertension cardiac output and lower-limb blood flow were significantly elevated, while hepatic and renal blood flows were within the normal range. Cardiac output and lower-limb blood flow were positively correlated. 3. In sustained hypertension cardiac output, lower-limb blood flow and hepatic blood flow were within the normal range. Renal blood flow was significantly reduced. Lower-limb blood flow was negatively correlated with mean arterial pressure. 4. If borderline hypertension is an early stage of fixed hypertension, the present study suggests that the changes in cardiac output observed in hypertension are mainly related to lower-limb (and muscle) blood flow.

Adult↗
PubMed1981

Central haemodynamics and plasma prostaglandin E2 in borderline and sustained essential hypertensive patients before and after indomethacin.

1. In basal conditions, plasma arterial prostaglandin (PG) E2 was significantly increased in borderline hypertensive patients (BH) (28.5 +/- 6.7 pg/ml) in comparison with sustained essential hypertensive patients (EH) (11.6 +/- 3.2 pg/ml) and in comparison with control normotensive subjects (NTS) (5.8 +/- 1.4 pg/ml). 2. Plasma arterial PGE2 was positively significantly correlated with cardiac index and negatively significantly correlated with total peripheral resistance in basal conditions. 3. Indomethacin induced more pronounced haemodynamic changes in borderline than in sustained hypertensive patients, with a significant increase in arterial blood pressure and total peripheral resistance and a significant decrease in stroke volume and cardiac index. 4. Indomethacin significantly decreased arterial PGE2 in borderline hypertensive patients. The decrease was less important in sustained hypertensive patients. 5. In the overall population, a significant positive correlation between arterial PGE2 concentration and cardiac index was observed before and after indomethacin treatment. 6. The study suggests an important role of PGE2 in the regulation of cardiac output (positive inotropic effect) and blood pressure of essential hypertensive patients.

Adult↗
PubMed1981

Systemic arterial compliance and diastolic runoff in essential hypertension.

Systemic arterial compliance was estimated in 31 men, including 15 patients with sustained essential hypertension and 16 normal subjects of the same age. Values were derived from analysis of the monoexponential blood pressure-time curve during diastole, according to a simple viscoelastic model. In normal subjects, baseline arterial compliance was 2.56 +/- 0.18 ml/mm Hg. A significant decrease (1.88 +/- 0.13 ml/mm Hg; P less than 0.001) was observed in hypertensives. Administration of vasoactive substances (angiotensin and sodium nitroprusside) showed that, for the same blood pressure levels, normal subjects and hypertensives had similar values for compliance. However, the correlation between the basal values of diastolic pressure and compliance was significant in normal subjects (r = --0.76) but not in hypertensives (r = --0.33); these results suggested differences between acute and long-term conditions in patients and controls. Calculated diastolic runoff was similar in both groups, approximating 58 and 55% of the stroke volume respectively. This study provides evidence that, in sustained essential hypertension, (1) the reduced arterial compliance cannot be related exclusively to the level of blood pressure, but also requires some abnormality of the volume of large arteries, and (2) the reservoir role of the large arteries is maintained.

Adult↗
PubMed1980

Haemodynamics in patients with phaeochromocytoma.

1. Cardiac haemodynamics were studied in 14 male patients with phaeochromocytoma, in comparison with 33 normal male subjects and 65 males with essential hypertension. 2. At the time of investigation, seven patients with phaeochromocytoma were hypertensive and seven were normotensive. Cardiac output was within normal limits. Total peripheral resistance was elevated in the hypertensive patients. Heart rate was elevated both in the normotensive and in the hypertensive patients, but decreased after surgical treatment. 3. The relationships between blood volume and blood pressure and between blood volume and cardiac output were the same as those observed in the control groups. 4. During tilt, a predominant systolic orthostatic hypotension was observed and was associated with decreased stroke volume and impaired adaptation of total peripheral resistance during tilt, indicating inadequate arteriolar and venous reflexes. 5. The study suggested that, except for tachycardia, the haemodynamic pattern of patients with phaeochromocytoma and with essential hypertension was nearly the same.

Adrenal Gland Neoplasms↗
PubMed1980

Relationship between renin and extracellular fluid volume in normotensive and hypertensive subjects.

Plasma renin activity and extracellular fluid volume were determined in 34 normotensive and in 35 sustained essential hypertensive patients with normal renal function, balanced sodium intake and urinary output. In normotensives, plasma renin activity was negatively correlated to extracellular fluid volume (r = 0.54; p = 0.001). The 95% confidence limits of the normotensive curve was used as nomogram to classify the hypertensive patients into two groups: those (23 cases) that fell within the limits of the normal curve (group I) and those (12 cases) that were below these limits (group II). In comparison with group I, group II was characterized by: (i) similar values for age, blood pressure, inulin clearance and extracellular fluid volume and (ii) significantly but lower values (p less than 0.001) for plasma renin activity with maintenance of the relationship between extracellular fluid volume and renin. The study strongly suggests that (i) the hypertensives of group I had no abnormal regulation of the renin-angiotensin system in comparison with the control subjects and (ii) the hypertensives of group II had an extracellular fluid volume-renin relationship set for lower values of renin.

Adult↗
PubMed1980

Arterial compliance and systolic hypertension in men.

A methodology for the determination of arterial compliance in men was developped. Arterial compliance was estimated from analysis of the monoexponential blood pressure-time curve during diastole, according to a simple visco-elastic model. Arterial compliance and indices of ventricular ejection were measured in patients with systolic hypertension. In the younger patients, arterial compliance and stroke volume were within normal ranges. Rapid ejection time was significantly reduced, indicating an increased velocity in the first part of ventricular ejection. Systolic pressure decreased significantly after administration of propranolol, which also caused prolongation of rapid ejection time. In the older patients, indices of ventricular ejection were within normal values. Arterial compliance significantly reduced. Systolic pressure decreased significantly after administration of sodium nitroprusside, which caused an increase in arterial compliance. These findings provide evidence that the hemodynamic mechanisms of systolic hypertension differ in younger and older patients, and could influence the choice of drugs to decrease systolic pressure.

Adult↗
PubMed1979

Echocardiographic dimensions in borderline and sustained hypertension.

Echocardiographic dimensions and hemodynamic indexes were determined in 42 patients with borderline hypertension and in 22 with sustained hypertension and the results were compared with findings in 33 normal subjects. In patients with borderline hypertension the thickness of the interventricular septum (IVS) was significantly increased (P less than 0.001), whereas the posterior wall PW) thickness remained within normal range. The IVS/PW ratio was significantly elevated (P less than 0.001) and was correlated negatively with the cardiac index (P less than 0.01) and positively with the preejection period (P less than 0.01). In patients with sustained hypertension a symmetric cardiac hypertrophy was observed, and there was a significant positive correlation between the IVS/PW ratio and diastolic pressure (P less than 0.05). The study suggested that (1) in sustained hypertension the symmetric cardiac hypertrophy was secondary to a progressive increase in pressure load, whereas (2) in borderline hypertension the asymmetric cardiac hypertrophy could not be directly related to the level of blood pressure and was probably associated with abnormalities of the sympathetic nervous system.

Blood Pressure↗
PubMed1979

Effect of alpha-methyldopa on cardiac output in hypertension.

Hemodynamic and blood volume changes, systolic time intervals, and baroreflex mechanisms were studied in 20 patients with hypertension after methyldopa (12 +/- 0.9 mg/kg/day). The drug was administered orally during 7 days' hospitalization on a normal sodium diet (110 mEq/day). There was a fall in blood pressure and in total peripheral resistance, without significant change in cardiac index, heart rate, and stroke index. There were increases in plasma and blood volume (p less than 0.05) but no change in cardiopulmonary blood volume or systolic time intervals. The unchanged heart rate was associated with an increased sensitivity ( less than 0.05) of the baroreflex mechanisms. The study supports the view that the unchanged cardiac output after methyldopa is related to important changes in control of cardiac output, including redistribution of blood volume and modifications in baroreflex mechanisms.

Adult↗
PubMed1979

Guanfacine kinetics in patients with hypertension.

Guanfacine kinetics were studied in 19 patients with hypertension after single and repeated oral doses. The single-dose study was performed in two homogeneous groups who received 2 mg (n = 9) and 4 mg (n = 10). The plasma concentrations were fitted in a two-compartment open model with first-order absorption. After a lag time of 0.8 hr, the absorption occurred rapidly (t 1/2 congruent to 0.53 hr). The fast and slow elimination phases occurred with t 1/2s of 2 and 19 hr. At therapeutic levels the percent of drug in red blood cells (55%) was independent of total drug concentration. Peak plasma levels had small interindividual variations. Comparison of kinetic parameters and AUC at the two doses studied demonstrated that their bioavailability was equal and the kinetics were linear. In a multiple-dosing study, performed in the same subjects, the plasma levels at steady state were in good agreement with the predicted values (p less than 0.001) and proportional to daily dosage. A single method based on four blood samples collected after 24, 28, 32, and 36 hr allows a reasonable prediction of the effective steady-state plasma levels during chronic dosing with guanfacine.

Adult↗