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Biomedical subjects

A K Amery

Publications and source records attributed to A K Amery.

At least 19 recordsLinked to original sources
PubMed1995

The effect of gender on aerobic power and exercise hemodynamics in hypertensive adults.

To study the influence of gender on peak oxygen uptake and on the hemodynamic response to dynamic exercise in essential hypertension, 45 male and 45 female patients, matched for age and blood pressure, were studied. Blood pressure was measured intra-arterially and cardiac output by the direct oxygen Fick method. Anthropometric gender differences were accounted for by statistical adjustment for height and weight. The increase of absolute and adjusted stroke volume from sitting at rest to submaximal (50 W) and to peak bicycle exercise was smaller in women than in men (P < 0.05). At 50 W, oxygen uptake (0.96 vs 0.97 l.min-1) and cardiac output (10.9 vs 11.2 l.min-1) were not different between women and men, due to the steeper exercise-induced rises of heart rate (P < 0.001) and arteriovenous oxygen difference (P < 0.05) in the women. Women reached the same peak heart rate as men (168 vs 173 b.min-1), so that the lower (P < 0.001) stroke volume (77 vs 99 ml) and cardiac output (12.9 vs 17.0 l.min-1), together with the lower hemoglobin concentration, contributed to their impaired peak oxygen uptake (P < 0.001), both before (1.35 vs 2.17 l.min-1) and after adjustment for body size (1.44 vs 2.07 l.min-1). In conclusion, at fixed submaximal exercise, women achieve the same oxygen uptake and cardiac output as men despite a lower stroke volume, through adaptations of heart rate and peripheral oxygen extraction; their peak aerobic power and cardiac output are, however, substantially lower than in men.

Adolescent↗
PubMed1994

Efficacy of antihypertensive drugs given once a day: the calcium antagonists revisited.

BACKGROUND: A large number of antihypertensive drugs have been approved for administration once or twice a day, but no standardized evidence is required to demonstrate that the reduction in blood pressure is sustained over 24 h. AIM: To test the validity of claims of a long duration of action for second-generation calcium antagonists. METHOD: Literature search. FLAWS IN REPORTED STUDIES: Most studies relied on ambulatory blood pressure monitoring. However, several reports were difficult to interpret because (1) the study was not blinded or random; (2) the statistical analysis was inappropriate for the study design; (3) analyses were confined to the means of 24-h, daytime and night-time blood pressure; (4) there was no baseline adjustment or formal statistical testing; (5) patients were subdivided into responders and non-responders after treatment; (6) there was no specified time frame linking drug intake to the observed antihypertensive effects. CLAIMS NOT SUBSTANTIATED: The authors of the articles reviewed concluded that amlodipine, nitrendipine and modified (slow-release) formulations of diltiazem, isradipine, nifedipine and verapamil reduced both conventional (clinic) and the 24-h blood pressure levels. In some studies separate results were presented for the daytime (awake) and night-time (sleeping) periods; some investigated the reduction in blood pressure at the end of the dose interval; and some compared the diurnal blood pressure profiles with different drug treatments. However, these reports gave discrepant results, suggesting that at least under certain study conditions the effect of nitrendipine and of slow-release diltiazem, isradipine and nifedipine did not give full 24-h cover with a single daily dose. CONCLUSIONS: We conclude that the interpretation of studies on long-acting antihypertensive agents using ambulatory blood pressure monitoring would be easier if the same standards were applied as required in clinical studies using conventional blood pressure measurements.

Blood Pressure↗
PubMed1994

Ambulatory blood pressure in normotensive and hypertensive subjects: results from an international database.

OBJECTIVE: To delineate more precisely an operational threshold for making clinical decisions based on ambulatory blood pressure (ABP) measurement by studying the ABP in subjects who were diagnosed as either normotensive or hypertensive by conventional blood pressure (CBP) measurement. SUBJECTS: Twenty-four research groups recruited 7069 subjects. Of these, 4577 were normotensive (CBP < or = 140/90 mmHg), 719 were borderline hypertensive (systolic CBP 141-159 mmHg or diastolic CBP 91-94 mmHg) and 1773 were definitely hypertensive. Of the subjects in the last of these categories, 1324 had systolic hypertension (systolic CBP > or = 160 mmHg) and 1310 had diastolic hypertension (diastolic CBP > or = 95 mmHg). Combined systolic and diastolic hypertension was present in 861 subjects. Hypertension had been diagnosed from the mean of two to nine (median two) CBP measurements obtained at one to three (median two) visits. RESULTS: The 95th centiles of the ABP distributions in the normotensive subjects were (systolic and diastolic, respectively) 133 and 82 mmHg for 24-h ABP, 140 and 88 mmHg for daytime ABP and 125 and 76 mmHg for night-time ABP, respectively. Of the subjects with systolic hypertension, 24% had 24-h systolic ABP < 133 mmHg. Similarly, 30% of those with diastolic hypertension had 24-h diastolic ABP < 82 mmHg. The probability that hypertensive subjects had 24-h ABP below these thresholds tended to increase with age and was two- to fourfold greater if the CBP of the subject had been measured at only one visit and if fewer than three CBP measurements had been averaged for establishing the diagnosis of hypertension. By contrast, for each 10-mmHg increment in systolic CBP, this probability decreased by 54% for 24-h systolic ABP and by 26% for 24-h diastolic ABP, and for each 5-mmHg increment in diastolic CBP it decreased by 6 and 9%, respectively. In comparison with 24-h ABP, the overlap in the daytime and night-time ABP between normotensive and hypertensive subjects was of similar magnitude and was influenced by the same factors. CONCLUSIONS: The ABP distributions of the normotensive subjects included in the present international database were not materially different from those in previous reports in the literature. One-fifth to more than one-third of hypertensive subjects had an ABP which was below the 95th centile of the ABP of normotensive subjects, but this proportion decreased if the hypertensive subjects had shown a higher CBP upon repeated measurement. The prognostic implications of elevated CBP in the presence of normal ABP remain to be determined.

Adolescent↗
PubMed1993

Short report: ambulatory blood pressure in normotensive compared with hypertensive subjects. The Ad-Hoc Working Group.

OBJECTIVE: To delineate more precisely an operational threshold for making clinical decisions based on ambulatory blood pressure (ABP) measurement by studying the ABP in subjects who were diagnosed as either normotensive or hypertensive by conventional blood pressure (CBP) measurement. SUBJECTS: Twenty-four research groups recruited 7069 subjects. Of these, 4577 were normotensive (CBP < or = 140/90 mmHg), 719 were borderline hypertensive (systolic CBP 141-159 mmHg or diastolic CBP 91-94 mmHg) and 1773 were definitely hypertensive. Of the subjects in the last of these categories, 1324 had systolic hypertension (systolic CBP > or = 160 mmHg) and 1310 had diastolic hypertension (diastolic CBP > or = 95 mmHg). Hypertension had been diagnosed from the mean of two to nine (median two) CBP measurements obtained at one to three (median two) visits. RESULTS: The 95th centiles of the 24-h ABP distributions in the normotensive subjects were (systolic and diastolic, respectively) 133 and 82 mmHg. Of the subjects with systolic hypertension, 24% had 24-h systolic ABP < 133 mmHg. Similarly, 30% of those with diastolic hypertension had 24-h diastolic ABP < 82 mmHg. The probability that hypertensive subjects had 24-h ABP below these thresholds tended to increase with age and was two- to fourfold greater if the CBP of the subject had been measured at only one visit and if fewer than three CBP measurements had been averaged for establishing the diagnosis of hypertension. By contrast, for each 10-mmHg increment in systolic CBP, this probability decreased by 54% for 24-h systolic ABP and by 26% for 24-h diastolic ABP, and for each 5-mmHg increment in diastolic CBP it decreased by 6 and 9%, respectively. CONCLUSIONS: The ABP distributions of the normotensive subjects included in the present international database were not materially different from those in previous reports in the literature. One-fifth to more than one-third of hypertensive subjects had an ABP which was below the 95th centile of the ABP of normotensive subjects, but this proportion decreased if the hypertensive subjects had shown a higher CBP upon repeated measurement. The prognostic implications of elevated CBP in the presence of normal ABP remain to be determined.

Adolescent↗
PubMed1992

Comparison of the effects of isradipine and lisinopril on left ventricular structure and function in essential hypertension.

The effects on cardiac structure and function of antihypertensive regimens with different effects on the renin-angiotensin system were compared. In a 1-year study, 32 patients with essential hypertension were randomized to treatment with either the converting enzyme inhibitor lisinopril or the calcium antagonist isradipine; hydrochlorothiazide could be added. Blood pressure (BP) decreased significantly (p less than 0.001) and similarly in the 2 treatment groups. Left ventricular (LV) mass was already significantly reduced after 16 weeks of treatment (p less than 0.001) and remained decreased thereafter, with no difference in the response to the 2 treatment regimens. The change in LV mass was related to the decrease in systolic BP for the total study group (p less than 0.001) and for each treatment group separately. During the 3-week run-out period on placebo, BP and LV mass increased again (p less than 0.01). Afterload decreased during active treatment (p less than 0.001), and fractional shortening of the LV internal diameter was significantly increased (p less than 0.01) to a similar extent in both groups. The ratio of peak mitral flow velocities during atrial contraction and early filling was reduced after 1 year of active treatment in the total study group (p less than 0.01); this change was similar in both groups. The data suggest that the regression of LV mass during antihypertensive therapy is mainly related to the decrease in systolic BP.

Adult↗
PubMed1991

Mean and range of the ambulatory pressure in normotensive subjects from a meta-analysis of 23 studies.

To perform a meta-analysis of published reports in an attempt to determine the mean and range of normal ambulatory blood pressure (BP), 23 studies including a total of 3,476 normal subjects were reviewed. Most studies were compatible with a mean 24-hour BP in the range of 115 to 120/70 to 75 mm Hg, a mean daytime BP of 120 to 125/75 to 80 mm Hg, and a mean nighttime BP of 105 to 110/60 to 65 mm Hg. With weighting for the number of subjects included in the individual studies, the 24-hour BP averaged 118/72 mm Hg, the daytime BP 123/76 mm Hg, and the nighttime BP 106/64 mm Hg. The night/day pressure ratio averaged 0.87 for systolic and 0.83 for diastolic BP, with ranges across the individual studies from 0.79 to 0.92 and from 0.75 to 0.90, respectively. If the mean +/- 2 standard deviation interval in the various studies was considered normal, the range of normality was on average 97 to 139/57 to 87 mm Hg for the 24-hour BP, 101 to 146/61 to 91 mm Hg for the daytime BP, and 86 to 127/48 to 79 mm Hg for the nighttime BP. Until the results of prospective studies on the relation between the ambulatory BP and the incidence of cardiovascular morbidity and mortality become available, the aforementioned intervals, which summarize the experience of 23 investigators, could serve as a temporary reference for clinical practice.

Adolescent↗
PubMed1991

Inheritance of blood pressure and haemodynamic phenotypes measured at rest and during supine dynamic exercise.

Thirty-two pairs of monozygotic and 21 pairs of dizygotic male twins aged between 18 and 31 years were studied. Blood pressure was measured and Doppler echocardiography at the level of the aorta was performed in resting conditions and at two levels of supine submaximal bicycle exercise (at a fixed work load of 60 W and at a work load corresponding to a heart rate of 110 beats/min). In resting conditions, a genetic component in the variability of systolic and diastolic blood pressure was found; during submaximal supine exercise only a minor genetic effect was observed. At rest, genetic variance was shown for left ventricular outflow haemodynamics and for peripheral vascular resistance. However, during exercise, the transmissible effect on haemodynamics and peripheral resistance was small.

Adult↗
PubMed1991

Inheritance of acute cardiac changes during bicycle exercise: an echocardiographic study in twins.

The inheritance of cardiac changes during acute dynamic physical exercise was studied in 21 pairs of monozygotic and 12 pairs of dizygotic male twins, ages 18-31 yr. Echocardiography was performed in resting conditions and at submaximal supine bicycle exercise at a heart rate of 110 bpm. In resting conditions significant heritability could be demonstrated for end-diastolic mean wall thickness, but not for left ventricular diameter and fractional shortening. Also for the change of mean wall thickness from rest to exercise, no significant heritability could be demonstrated. The increase of end-diastolic left ventricular internal dimension from rest to exercise showed a genetic component of 24% (P less than 0.05). Inheritance accounted for 47% (P less than 0.001) of the total phenotypic variance of the increase of fractional shortening from rest to exercise. In conclusion, the data suggest that the capacity of increasing end-diastolic left ventricular internal dimension and increasing fractional shortening during submaximal exercise has, unlike findings at rest, a significant genetic component.

Adolescent↗
PubMed1989

Short-term morphologic results of percutaneous transluminal renal angioplasty as determined with angiography.

Short-term follow-up angiographic evaluation of renal artery stenoses treated by means of percutaneous transluminal renal angioplasty was performed in 89 patients with 108 treated stenoses, at a mean of 5.9 months +/- 6.7 after the procedure. In 72 patients intravenous digital subtraction angiography was performed; in 17 patients intraarterial digital subtraction angiography was performed. Indications for the study were (a) routine follow-up in 31 patients, (b) residual hypertension in 16, (c) residual stenosis on the postdilation angiogram (with residual hypertension) in 17, and (d) relapse of hypertension in 25. In 16 of the 25 patients (64%) with relapse of hypertension, angiography showed relapse of stenosis or occlusion of the vessel. In nine of the 17 patients (53%) with residual stenosis on the postdilation angiogram, an improvement in the angiographic appearance of the lesion was noted. Residual stenosis was noted in one normotensive patient, in three patients with residual hypertension, and in eight patients with residual stenosis on the postdilation angiogram.

Angiography↗
PubMed1986

Renal artery stenosis: evaluation with intravenous digital subtraction angiography.

The ability of diagnostic intravenous digital subtraction angiography (IVDSA) to demonstrate the degree of renal artery stenosis was compared with that of intraarterial angiography in 45 patients with 92 arteries. Stenotic lesions on both IVDSA and intraarterial studies were classified as normal (0% stenosis), minor (less than 50%), low grade (50%-80%), and high grade (80%-99%). There was agreement about the degree of stenosis in 90% of the cases. IVDSA grading was correct in 94% of atheromatous lesions and in 56% of the fibromuscular dysplastic lesions. In the high-grade atheromatous lesions, the degree of stenosis was slightly overestimated on IVDSA studies in 22.5% of the cases. In fibromuscular dysplasia, stenosis was underestimated in 33% of the cases.

Angiography↗
PubMed1984

Intracellular concentration and transmembrane fluxes of sodium and potassium in erythrocytes of white normal male subjects with and without a family history of hypertension.

Compared with white normal males without a family history of hypertension (n = 43), red blood cells of white normal males with such a family history (n = 17) had a higher (P less than 0.01) intracellular sodium concentration (8.07 +/- 0.30 versus 7.33 +/- 0.17 mmol/l cells). This could be at least partly due to their lower (P less than 0.001) frusemide-sensitive sodium efflux rate (250 +/- 19 versus 424 +/- 23 mumol/l cells/h). Also their ouabain-resistant 86Rb-uptake (0.81 +/- 0.06 versus 0.97 +/- 0.03 mumol/l cells/h) was lower (P less than 0.05). Potassium concentration in the red blood cells was similar in both groups.

Aldosterone↗
PubMed1983

Comparative study of active and inactive plasma renin in healthy infants and adults.

Active, inactive and total plasma renin activity (obtained after cryoactivation), active, inactive and total plasma renin concentration (obtained after acid activation) and plasma angiotensin II were measured in 20 healthy infants and in 20 healthy adults. Active plasma renin activity but not active plasma renin concentration or plasma angiotensin II were significantly higher in the infants. In the latter both cryoactivation and acid activation resulted in a nearly 100% increase of the mean active plasma renin activity or active plasma renin concentration. Therefore the active fraction represented 0.5 of total renin with both methods. This was different in adults, where acid activation was more effective than cryoactivation. In adults, plasma angiotensin II was correlated only with active plasma renin activity and active plasma renin concentration; in contrast, plasma angiotensin II of infants was correlated with both active plasma renin activity, and with inactive plasma renin activity.

Adult↗
PubMed1980

Comparative study of an angiotensin-II analog and a converting enzyme inhibitor.

The effects of an angiotensin-II analog (saralasin, i.v.) and of a converting enzyme inhibitor (captopril, oral) were compared in 12 sodium-depleted patients with hypertension. The decrease of the mean intraarterial pressure (MAP) with captopril (-21.5 +/- [SEM] 4.3 mm Hg) was more pronounced (P < 0.001) than the change of MAP during saralasin (-10.5 +/- 4.0 mm Hg). The pretreatment arterial plasma renin activity (log PRA) was closely related to the change of MAP during saralasin (r = -0.94; P < 0.001) and also to the captopril-induced change of MAP (r = -0.82; P < 0.001); similar results were obtained for the log plasma angiotensin (PA) I and II levels. The change of MAP was more pronounced, however, with captopril than during saralasin at any level of pretreatment PRA, PAI or PAII. Saralasin did not affect heart rate (P > 0.4), but during captopril the heart rate increased by 5.1 beats/min (P < 0.001). Captopril produced a 70% decrease of PAII, but the change of MAP was poorly related to the changes of PAII (r = -0.57; P < 0.05); PRA and PAI rose threefold to fourfold. PRA, PAI, and PAII all increased during saralasin. These observations may suggest that the antihypertensive action of captopril is not based solely on the inhibition of AII formation, but also the agonistic effect of saralasin has to be considered.

Adult↗
PubMed1979

Active and inactive renin in normal human plasma. Comparison between acid activation and cryoactivation.

Inactive renin in human plasma is converted to active renin in vitro by acid activation or by cryoactivation. Renin activity was measured at pH 5.5 and renin concentration at pH 7.4. The plasma renin activity before and after cryo-treatment is termed active (APRA) and total (TPRA) plasma renin activity; the plasma renin concentration before and after acid treatment active (APRC) and total (TPRC) plasma renin concentration. In this study we demonstrated that in normal subjects the proportion of active to total renin after cryo-treatment averaged 61%, which was significantly (p less than 0.001) higher than the mean percentage active renin of 34 found with the acid activation procedure. Plasma angiotensin II correlated significantly with APRA, TPRA, TPRC and plasma angiotensin I (PA I), but not with inactive renin, which suggests that inactive renin does not produce angiotensin II in vivo. Cold treatment after acid activation and acid treatment after cryoactivation did not provoke a significant change in the measured renin concentration. Our data support the view that acidification of the plasma activates more than does cryo-treatment, and that inactive renin does not contribute to plasma angiotensin II.

Acids↗
PubMed1979

The effects of beta-adrenoceptor blockade on renin, angiotensin, aldosterone and catecholamines at rest and during exercise.

1 beta-adrenoceptor blockade with metoprolol provoked, both at rest and during exercise, a decrease of 'active' renin and angiotensin II together with an increase of 'inactive' renin and unchanged 'total' renin. The significant exercise-provoked increases in angiotensin II, plasma renin activity and 'active', 'inactive' and 'total' renin when on placebo, were reduced by metoprolol. 2 No significant change in serum sodium and potassium and in plasma aldosterone was found during beta-adrenoceptor blockade at rest. During exercise plasma aldosterone dropped significantly without any change in serum sodium or potassium. 3 Plasma noradrenaline increased significantly at rest on metoprolol. The increase in plasma noradrenaline and adrenaline during exercise was similar on placebo and on metoprolol.

Adult↗