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Biomedical subjects

A Amery

Publications and source records attributed to A Amery.

At least 55 records · Page 3Linked to original sources
PubMed1994

Relationship between erythrocyte cation transport systems and membrane and plasma lipids in healthy men.

The relationship between various transmembrane erythrocyte cationic fluxes and erythrocyte membrane and plasma lipids was examined in 53 healthy men. In single regression analysis, the erythrocyte Na+,Li(+)-countertransport and Na+,K(+)-cotransport activity was negatively related to the erythrocyte membrane cholesterol, phospholipids, and free fatty acids content. The Na+,K(+)-ATPase pump activity as assessed by the ouabain-sensitive Na+ efflux was also inversely related to the membrane cholesterol and phospholipids content. In multiple regression analysis, the red blood cell Na+,Li(+)-countertransport activity was independently and negatively related to membrane cholesterol and free fatty acids content. Data show that an elevated level of erythrocyte membrane lipids in healthy men is accompanied by a lower Na+,Li(+)-countertransport, Na+,K(+)-cotransport, and Na+,K(+)-ATPase pump activity.

Adult↗
PubMed1994

Influence of cholesterol lowering on plasma membrane lipids and cationic transport systems.

BACKGROUND: In order to determine whether alterations in membrane lipids affect transmembrane cationic transport systems in erythrocytes and platelets, cationic fluxes and intracellular cationic concentrations were measured in hypercholesterolaemic patients before and during administration of an inhibitor of 3-hydroxy-3-methlglutaryl coenzyme A reductase. METHODS: After a 1-month run-in placebo period on a lipid-lowering diet the patients were treated, in a double-blind manner, with either placebo (n = 25) or pravastatin (n = 25) for 6 months. Placebo or pravastatin (10 mg during the first month, 20 mg during the second month and 40 mg during the remaining 4 months) was administered once a day in the evening. RESULTS: Compared with the placebo group, the erythrocyte and platelet membrane cholesterol content was reduced in the patients treated with pravastatin. The intra-erythrocyte and intraplatelet Na+ concentration was reduced during pravastatin administration, whereas the activity of the erythrocyte and platelet Na(+)-K+ pump was increased. However, the intra-erythrocyte and intraplatelet K+, Mg2+ and cytosolic Ca2+ concentrations, and water content, as well as the activities of the erythrocyte Na(+)-Li+ countertransporter and Na+,K+ cotransporter, and Na+ and K+ leakage, were not changed during pravastatin treatment. CONCLUSIONS: The present data show that cholesterol lowering in hypercholesterolaemic patients may result in a significant decrease in erythrocyte and platelet membrane cholesterol content. These changes in membrane cholesterol are accompanied by an increase in activity of the Na(+)-K+ pump and a decrease in intra-erythrocyte and intraplatelet Na+ concentrations.

Biological Transport↗
PubMed1994

Mechanical and other factors relating to left ventricular hypertrophy.

Although the development of left ventricular hypertrophy in hypertension is explained as a response to increases in pressure load and wall tension, the relationship between left ventricular mass and conventional blood pressure is usually weak. This may be due to the lack of standardization and the small number of blood pressure measurements in some studies. However, even 24-h blood pressure monitoring can explain only around 25% of the variation in left ventricular mass, and repeated blood pressure measurements over 30 years have not proved better in this respect. Therefore, other factors have been considered, including anthropometric and demographic characteristics; genetic influences; differences in salt intake, physical activity and alcohol consumption; neurohumoral factors; duration of hypertension; and previous antihypertensive treatment. Antihypertensive treatment may reduce left ventricular mass and a number of prospective, randomized, comparative studies have assessed whether some (classes of) drugs are more effective than others. A meta-analysis of such studies, comparing diuretics, beta-blockers, calcium antagonists and/or angiotensin-converting enzyme (ACE) inhibitors, suggests that the reduction of left ventricular mass with each of these classes is similar to the reduction obtained with the other three classes statistically combined. Of particular interest is the observation that the four studies which specifically compared an ACE inhibitor and a calcium antagonist concluded that their effects on left ventricular mass did not significantly differ. Furthermore, that agents such as minoxidil and hydralazine do not reduce left ventricular mass.

Antihypertensive Agents↗
PubMed1993

Fourier analysis of blood pressure profiles.

This short review deals with the use of the Fourier technique to analyze diurnal blood pressure (BP) profiles obtained by noninvasive ambulatory monitoring. A Fourier series with four harmonics strikes an acceptable balance between the accuracy and complexity required to model the diurnal profile accurately in most subjects. A weighting procedure makes it possible to allow for the varying time intervals between consecutive pressure readings. Studies based on a single recording are insufficient to characterize an individual with respect to the statistical parameters describing the diurnal BP profile, regardless of whether they are obtained by Fourier analysis or by other methods. The Fourier approach provides the means to translate 24 h BP profiles into interpretable statistical parameters, such as the amplitude and acrophase of the overall model and the harmonics. These parameters can subsequently be used in further statistical analyses. In conclusion, the Fourier approach makes the description of complex, asymmetrical, and multiphasic BP profiles possible. By using the procedures of linear multiple regression, commonly provided by software packages, the calculations can be readily implemented on microcomputers without requiring advanced skills in mathematics or programming techniques.

Blood Pressure↗
PubMed1993

Response of ambulatory blood pressure to antihypertensive therapy guided by clinic pressure.

The objective of this prospective study was to define the limits below which ambulatory blood pressure (BP) does not decrease in patients with essential hypertension, when the decision to institute and intensify drug treatment is based on conventional blood pressure measurements. After a 1 month placebo run-in period, 30 patients were treated for 1 year with the converting enzyme inhibitor lisinopril or the calcium antagonist isradipine; dose adjustments and the decision to add hydrochlorothiazide were based on conventional blood pressure measurements in the clinic. Ambulatory blood pressure was recorded during 24 h in the run-in period and after 16, 24, and 52 weeks of active therapy. The baseline ambulatory blood pressure below which pressure does, on average, not decrease during active treatment was defined as the pressure at which the regression line between the on-treatment pressure and blood pressure in the run-in period intersects the line of identity. The systolic/diastolic blood pressure limits were similar for the three assessments during active treatment and averaged 128/88 mm Hg for daytime, 106/73 mm Hg for nighttime pressure, and 119/81 mm Hg for the whole 24 h, with upper 95% confidence limits of 137/93, 115/78, and 127/86 mm Hg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Erythrocyte cation transport systems and membrane lipids in insulin-dependent diabetes.

The relationship between erythrocyte cation transport systems and membrane and plasma lipids was examined in normal men and patients with insulin-dependent diabetes mellitus (IDDM). Different measurements of erythrocyte transport systems were obtained in patients with IDDM and in age- and weight-matched healthy men: Na+:Li+ countertransport activity or Li(+)-stimulated Na+ efflux, Na+:K+ cotransport activity or bumetanide-sensitive Na+ efflux, Na+:K+ pump activity or ouabain-sensitive Na+ efflux, and the ouabain- and bumetanide-resistant Na+ and K+ fluxes or the ground membrane permeability for Na+ and K+ as well as the intraerythrocyte Na+, K+, and Mg2+ concentrations. Plasma cholesterol, triglycerides, phospholipids, low- and high- density lipoprotein cholesterol, and erythrocyte membrane cholesterol and phospholipid content were obtained from the fasting subjects. The patients with IDDM had an elevated (P < .05 or less) erythrocyte Na+:Li+ countertransport activity, ground membrane leak for K+, intraerythrocyte K+ concentration, and erythrocyte membrane cholesterol content, but a lower red blood cell phospholipid content. In single regression analysis, the erythrocyte Na+:Li+ countertransport, Na+:K+ cotransport, and Na+:K+ pump activity and ground membrane leak for Na+ and K+ were inversely related to the red blood cell membrane lipid content. Our data in patients with IDDM show that a decreased erythrocyte membrane lipid content was accompanied by a higher erythrocyte Na+:Li+ countertransport, Na+:K+ cotransport, and Na+:K+ pump activity.

Adult↗
PubMed1993

Relationship between blood pressure measured in the clinic and by ambulatory monitoring and left ventricular size as measured by electrocardiogram in elderly patients with isolated systolic hypertension.

OBJECTIVE: To assess the additional diagnostic precision conferred by ambulatory blood pressure monitoring on clinic blood pressure measurement in evaluating the severity of isolated systolic hypertension. METHODS: The association between left ventricular size as determined by ECG voltages [R-wave voltages in lead V5 (RV5) and S-wave voltages in lead V1 (SV1)] and blood pressure as assessed by clinic measurements and ambulatory blood pressure monitoring was studied in 97 elderly patients included in the placebo run-in phase of the Syst-Eur trial. The additional diagnostic precision conferred by ambulatory monitoring on clinic blood pressure measurements was assessed by relating the residual ambulatory blood pressure level to the ECG-left ventricular size. The residual ambulatory blood pressure level was calculated by subtracting the predicted ambulatory blood pressure level for each patient (using the linear regression equation relating both techniques for the group) from the observed ambulatory blood pressure. RESULTS: Clinic systolic blood pressure was on average 20 mmHg higher (P < 0.001) than daytime ambulatory blood pressure while diastolic blood pressure was similar with both techniques. The sum of SV1 + RV5 was significantly related to clinic systolic pressure (r = 0.25), and 24-h (systolic, r = 0.37; diastolic, r = 0.29), daytime (systolic, r = 0.30; diastolic, r = 0.19) and night-time (systolic, r = 0.33; diastolic, r = 0.28) ambulatory blood pressure levels. These findings were not affected by adjustment for gender, age and the body mass index. The sum of SV1 + RV5 was significantly related to the residual 24-h (systolic, r = 0.30; diastolic, r = 0.31), daytime systolic (r = 0.20) and night-time (systolic, r = 0.31; diastolic, r = 0.29) ambulatory blood pressure monitoring levels. CONCLUSION: Ambulatory blood pressure monitoring adds to the diagnostic precision of clinic blood pressure measurement in assessing the severity of hypertension in this population. The ongoing side project on ambulatory blood pressure monitoring in the Syst-Eur study should establish whether these findings hold true for morbidity and mortality.

Aged↗
PubMed1993

The relationship between blood pressure and sodium and potassium excretion during the day and at night.

OBJECTIVE: The relationships between blood pressure and the urinary excretion rates of sodium and potassium during the day and at night were investigated. METHODS: A total of 160 participants (135 normotensive subjects and 25 untreated patients with essential hypertension) were examined using ambulatory blood pressure monitoring and timed urine collections during waking and sleeping hours. RESULTS: Blood pressure averaged 126/79 mmHg during waking hours and 107/62 mmHg during sleep. More sodium, potassium and aldosterone were excreted during the daytime, but the natriuretic substance kallikrein was excreted at a fixed rate throughout the 24 h. During waking hours there was poor correlation between blood pressure and urinary sodium and potassium excretion. By contrast, at night when the aldosterone: kallikrein ratio fell, the sodium and potassium excretion rates were positively correlated with blood pressure. CONCLUSIONS: Pressure natriuresis, not apparent during waking hours, may be unmasked at night when the balance between sodium-retaining and sodium-losing mechanisms favours natriuresis. Thus, the relationship between blood pressure and 24-h sodium excretion, usually considered to show the influence of salt intake on blood pressure, may also reflect pressure-induced natriuresis, if urine is more completely collected at night than during the day, and in circumstances favouring sodium retention during the day and sodium loss during sleep.

Adult↗
PubMed1993

Short report: low-level lead exposure does not increase the blood pressure in the general population. Cadmibel Study Group.

OBJECTIVE: Long-term exposure to high concentrations of lead may adversely affect several organ systems, but the possible influence of low-level lead exposure on blood pressure remains debatable. The present study examined this relationship in a cross-sectional population survey. METHODS: Blood pressure and lead exposure were measured in 1648 subjects (827 males, 821 females; mean age 45 years), drawn at random from the general population, but not being treated for hypertension. RESULTS: Systolic/diastolic blood pressure averaged 131/77 mmHg in the males and 124/74 mmHg in the females. Blood lead was higher in males than in females (0.5 versus 0.3 mumol/l), but the opposite was observed for zinc protoporphyrin (1.0 versus 1.1 micrograms/g haemoglobin). After adjustment for significant covariates (age, body mass index, pulse rate, serum creatinine and serum calcium, and for contraceptive pill intake and menopause in females), systolic pressure was negatively correlated with blood lead in males; the partial correlations with blood lead were not significant for systolic pressure in females nor for diastolic pressure in either sex. Neither males nor females showed a significant relationship between blood pressure and lead exposure assessed from the zinc protoporphyrin level in blood. CONCLUSIONS: This study does not support the hypothesis that exposure to lead is associated with increased blood pressure in the population at large.

Adult↗
PubMed1993

Does isradipine modified release 5 mg once daily reduce blood pressure for 24 hours?

Twelve patients with essential hypertension were randomized in a double-blind cross-over study to investigate the blood pressure BP-lowering activity of isradipine regular formulation (RF) 2.5 mg twice daily (between 7 and 8 a.m. and at approximately 6 p.m.), and isradipine modified release (MR), 5 mg once daily (between 7 and 8 a.m.). The two randomized treatment periods were separated by a placebo period. Patient compliance was similar between placebo and isradipine RF and MR treatment. As compared with placebo, isradipine RF decreased daytime BP by 10 mm Hg systolic (SBP, p < 0.001) and by 6 mm Hg diastolic (DBP, p < 0.01), and night SBP and DBP by 7 (p < 0.05) and 3 mm Hg (P = NS), respectively. Isradipine MR reduced the daytime SBP 8 mm Hg (p < 0.05) and DBP by 3 mm Hg (p = NS), and the night SBP by 1 mm Hg (p = NS) and DBP by < 1 mm Hg (P = NS). Analysis of variance showed that the interaction terms between the effects of treatment and time of day were not significant for SBP (F = 1.56, p = 0.24) or DBP (F = 1.40, p = 0.26) with isradipine RF treatment, but they were significant for SBP (F = 6.33, p = 0.03) and DBP (F = 5.12, p = 0.04) with isradipine MR treatment. Therefore, the BP-lowering effect of isradipine MR 5 mg once daily appears to weaken as the day progresses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Influence of antihypertensive drugs on exercise capacity.

Both single dose and short term diuretic treatment adversely affect maximal exercise capacity and the duration of prolonged submaximal exercise. However, insufficient data are available to establish the effect of long term diuretic treatment on exercise capacity. beta-Blockade reduces maximal aerobic power by approximately 7%. In addition, the capacity for prolonged submaximal exercise appears to be markedly impaired in normotensive and hypertensive patients, particularly when nonselective beta-blockers are prescribed. Fewer data are available for other drugs, but, whatever the mechanism of vasodilation, drugs that reduce systemic vascular resistance do not seem to have any effect on exercise capacity.

Antihypertensive Agents↗
PubMed1993

Antihypertensive therapy in elderly patients with isolated systolic hypertension: third progress report of the Syst-Eur trial.

The Syst-Eur trial is a randomised, double-blind, placebo-controlled trial that examines the hypothesis that antihypertensive treatment can prevent or delay cardiovascular complications in elderly patients (> 60 years) with isolated systolic hypertension. On March, 1st 1993 a total of 1395 patients with a sitting systolic blood pressure on placebo averaging 160-219 mmHg and a diastolic blood pressure < 95 mmHg were randomised into this trial. The placebo and active treatment groups were similar at randomisation with respect to age (72 +/- 7 years, mean +/- SD), percentage of women (68%), percentage of patients with cardiovascular complications (30%) and sitting blood pressures (175 +/- 12/85 +/- 6 mmHg). The fall in sitting systolic and diastolic blood pressures from baseline to 2 years was significantly more pronounced (p < 0.001) in the actively treated (-22 +/- 18/-6 +/- 9 mmHg) as compared with the placebo treated Syst-Eur patients (-10 +/- 20/-1 +/- 9 mmHg). Active treatment consists of nitrendipine if necessary associated with a converting-enzyme inhibitor and a thiazide. Whether treatment with these antihypertensive agents results in a clinically meaningful reduction of cardiovascular morbidity and mortality is the subject of investigation in this trial.

Aged↗
PubMed1993

Erythrocyte and platelet cationic concentrations and transport systems in normal volunteers treated with carmoxirole.

The effect of carmoxirole, a presynaptic dopamine (DA2) receptor agonist, on blood pressure, plasma catecholamines, renin-aldosterone and atrial natriuretic peptide and the intracellular concentration and transmembrane fluxes of Na+ and K+, in erythrocytes and platelets was studied in 24 normal men, using a double-blind, parallel study design. After a run-in period of 1 week, the subjects were treated with either placebo (n = 8) or 0.5 mg carmoxirole (n = 16) once daily for 1 week. Blood pressure and heart rate were not changed during carmoxirole administration in these normal men. Surprisingly, no significant effect of carmoxirole was found on the circulating plasma concentration of noradrenaline, adrenaline or dopamine. Other hormones such as renin, aldosterone and atrial natriuretic peptide were also not changed during carmoxirole administration. No significant effect of carmoxirole could be demonstrated on the intracellular concentration of Na+, K+, Mg2+ and Ca2+ and on the transmembrane fluxes of Na+ and K+ in erythrocytes and platelets. In the carmoxirole-treated subjects (n = 16), 6 subjects reported spontaneously adverse events such as syncope, dizziness and vomiting tendencies and/or fatigue.

Adult↗
PubMed1993

The older hypertensive. Assessment and treatment.

A meta-analysis is presented of 8 therapeutic trials in elderly hypertensive patients. In an intention-to-treat analysis, cardiovascular mortality was decreased on average by 22% (95% confidence interval ranging from -32% to -10%). This decrease was explained by both a reduction in coronary mortality by 26% (-40% to -9%) and in cerebrovascular mortality by 33% (-50% to -9%). The effectiveness of therapy in terms of reducing cardiovascular mortality is not established with confidence in those trials where the diastolic blood pressure at randomization is below 95 mmHg or in the patients above 75 years of age. A goal blood pressure is not definitively established, but a reduction of the systolic blood pressure to about 150 mmHg may be optimal. Extrapolation of the trial results to the elderly population with systolo-diastolic hypertension at large seems acceptable for the western population, but may be premature for the Asian and African elderly. Beta-blockers and especially diuretics are recommended as first-line drugs in elderly patients with symptomless, uncomplicated hypertension, since the effectiveness of other drugs in reducing morbidity and mortality is not yet established. Recommendation for treatment of symptomless patients with isolated systolic hypertension may be premature. The ongoing Syst-Eur and Syst-Chin trials may provide further information.

Aged↗