Efficacy of potassium and magnesium in essential hypertension: a double-blind,placebo controlled,crossover study.

OBJECTIVE--To evaluate the antihypertensive activity of potassium given alone or in combination with magnesium in patients with mild hypertension. DESIGN--A double blind, randomised, placebo controlled, crossover trial of 32 weeks'' duration. SETTINGS--Cardiology outpatient department, Sassoon General Hospitals, Pune, India. PATIENTS--37 Adults with mild hypertension (diastolic blood pressure less than 110 mm Hg). INTERVENTION--Patients received either placebo or potassium 60 mmol/day alone or in combination with magnesium 20 mmol/day in a crossover design. No other drug treatment was allowed. MEASUREMENTS--Blood pressure and heart rate assessed at weekly intervals and biochemical parameters at monthly intervals. RESULTS--Potassium alone or in combination with magnesium produced a significant reduction in systolic and diastolic blood pressures (p less than 0.001) and a significant reduction in serum cholesterol concentration (p less than 0.05); other biochemical variables did not change. Magnesium did not have an additional effect. Urinary potassium excretion increased significantly in the groups who received potassium alone or in combination with magnesium. The drug was well tolerated and compliance was satisfactory. CONCLUSION--Potassium 60 mmol/day lowers arterial blood pressure in patients with mild hypertension. Giving magnesium as well has no added advantage.     

Diagnosis and management of hypertension: the stated practices of family physicians.

Hypertension is an important and common problem in family practice, but there is no general agreement on the systolic and diastolic pressures at which it should be diagnosed and treated. Responses from 273 family physicians surveyed by mail in Metropolitan Toronto showed a wide variation in the pressures used as cut-off points. The probability that in a given patient hypertension would be diagnosed or treated at different systolic and diastolic pressures varied considerably among the physicians, the variation increasing with the age of the patient. There was also wide variation in opinion among the surveyed physicians about how often patients should be screened for hypertension; depending on the patient''s age, up to 35% of the physicians stated that the blood pressure should be measured at every visit. Only one third reported using any one or more methods to ensure that patients with hypertension were not lost to follow-up. The family physicians with an academic appointment used higher cut-off points for diagnosis and treatment, and they screened and scheduled follow-up visits less frequently than those without an academic appointment.     

Comparison of direct and indirect blood pressure measurement in anesthetized dogs.

This study was conducted to determine whether blood pressures and pulse rate could be determined accurately by indirect measurements from the front and hind legs of 15- to 40-kg dogs anesthetized with isoflurane. Indirect measurements from each animal were compared to direct measurements obtained from a catheter placed into the abdominal aorta via the femoral artery at four ranges of systolic pressure. When systolic pressure was above 80 mm Hg, indirect measurements were either the same as direct measurements or slightly lower. However, when systolic pressures were below 80 mm Hg, indirect systolic pressure measurements were 6 to 15% higher than direct measurements. Larger differences in diastolic pressures were found, which resulted in differences in mean pressure. The most accurate measurements were found when the cuff width-to-limb circumference ratio was between 0.4 and 0.6 and when systolic pressure was between 80 and 100 mm Hg.     

Relation between mortality and treated blood pressure in elderly patients with hypertension: report of the European Working Party on High Blood Pressure in the Elderly.

OBJECTIVE--To investigate the relation between mortality and treated systolic and diastolic blood pressures. DESIGN--Randomised double blind placebo controlled trial. Mortality in the two treatment groups was examined in thirds of treated systolic and diastolic blood pressures. PATIENTS--339 And 352 patients allocated to placebo and active treatment, respectively. The groups were similar at randomisation in sex ratio (70% women), mean age (71.5 years), blood pressure (182/101 mm Hg), and proportion of patients with cardiovascular complications (35%). MEASUREMENTS AND MAIN RESULTS--In the placebo group total mortality rose with increasing systolic pressure whereas it had a U shaped relation with diastolic pressure, the total lowest mortality being in patients in the middle third of the distribution of diastolic pressure. In the group given active treatment total mortality showed a U shaped relation with systolic pressure and an inverse association with treated diastolic pressure. In both groups cardiovascular and non-cardiovascular mortality followed the same trends as total mortality. The increased mortality in the lowest thirds of pressure was not associated with an increased proportion of patients with cardiovascular complications at randomisation or with a fall in diastolic pressure exceeding the median fall in pressure in each group. In contrast, patients in the lowest thirds of pressure showed greater decreases in body weight and haemoglobin concentration than those in the middle and upper thirds of pressure. CONCLUSIONS--In patients taking active treatment total mortality was increased in the lowest thirds of treated systolic and diastolic blood pressures. This increased mortality is not necessarily explained by an exaggerated reduction in pressure induced by drugs as for diastolic pressure a U shaped relation also existed during treatment with placebo. In addition, patients in the lowest thirds of systolic and diastolic pressures were characterised by decreases in body weight and haemoglobin concentration, and the patients in the lowest thirds of diastolic pressure taking active treatment also by an increased non-cardiovascular mortality, suggesting some deterioration of general health.     

Afterload and blood pressure amplitude in dilated cardiomyopathy]

The beat-to-beat variability of the diastolic blood pressure induces small variations in the afterload of the left ventricle. These variations influence myocardial contractility, and thus blood pressure amplitude. We assessed the interdependence of blood pressure and changes in the afterload. We continuously recorded blood pressure (duration 200 s, at rest) in 20 patients with dilated cardiomyopathy (ejection fraction 32 +/- 13%, left ventricular diameter 67 +/- 8 mm) and in 20 healthy volunteers. Interbeat intervals, diastolic pressures, systolic pressure amplitudes and mean slopes of systolic pressure amplitudes were measured. Correlation coefficients (r) were calculated to assess the interdependence of blood pressure amplitudes/mean systolic slopes and the preceding diastolic pressures/interbeat intervals, respectively. In healthy volunteers we found a strong interdependence between blood pressure amplitude and the preceding diastolic pressures (r = 0.62 +/- 0.21 and 0.47 +/- 0.22). Higher diastolic pressures were followed by higher blood pressure amplitudes, and by steeper slopes of the systolic peaks. In patients with dilated cardiomyopathy, such interdependence was significantly lower (r = 0.33 +/- 22 and r = 0.28 +/- 0.35), and in patients with severely reduced left ventricular function (ejection fraction < 32%) was only marginal (r = 0.23 +/- 0.27 and 0.21 +/- 0.44, respectively). The forces of the isovolumetric contraction necessary to initiate the ejection phase of the left ventricle depend on the afterload, i.e. on the diastolic pressure. The responses of amplitude and slope of the systolic blood pressure to small changes in the afterload make it possible to assess left ventricular contractility. The latter is impaired in dilated cardiomyopathy.     

Measuring blood pressure in the elderly: does atrial fibrillation increase observer variability?

OBJECTIVE--To compare the interobserver and intraobserver variability of blood pressure measurements in geriatric patients in atrial fibrillation and in sinus rhythm. DESIGN--Prospective assessment of blood pressure measurements carried out in random order in two groups of elderly patients by five doctors unaware of the aims of the study. SETTING--Acute assessment wards for geriatric medicine, Cardiff Royal Infirmary. PATIENTS--50 Elderly patients in sinus rhythm and 50 in atrial fibrillation. MAIN OUTCOME MEASURES--Interobserver and intraobserver variability of blood pressure measurements in the two groups expressed as the coefficient of variability and compared by the Mann-Whitney U test. RESULTS--Interobserver variability was significantly greater in the patients with atrial fibrillation for both systolic and diastolic pressures. Intraobserver variability was significantly greater in the atrial fibrillation group for diastolic pressures but the difference was not significant for systolic pressures. These differences were not related to pulse rate, age, or level of blood pressure. CONCLUSIONS--The findings suggest that in the presence of atrial fibrillation physicians'' interpretations of Korotkoff sounds are less uniform, which may have important clinical implications. Possibly a standardised methodology may overcome this problem.     

Sleep and blood pressure.

Direct arterial pressure was recorded continuously over 24 hours in 18 totally unrestricted people (six normotensives, four untreated hypertensives, and eight treated hypertensives). There was an almost equal fall of about 20% in both systolic and diastolic blood pressure during sleep in the three groups when compared with their waking pressures. This fall in pressure was greater than that observed previously in patients sleeping in a laboratory or hospital. Furthermore, it suggests that hypertensive subjects do not have a higher centrally-induced vasoactive component and that hypotensive drugs do not alter the pattern of blood pressure behaviour induced by sleep.     

Is exercise good for high blood pressure?

Ten men with uncomplicated essential hypertension (mean standing blood pressure 165/109 mm Hg) and 10 normal controls matched for age and weight were studied for the hypotensive potential of moderate exercise. Tests were conducted on a treadmill set to induce a steady heart rate of 120 beats/min and performed over five 10-minute periods separated by three minutes'' rest and finishing with 30 minutes'' sitting quietly in a chair.During exercise the mean systolic pressures were identical in the hypertensive patients and controls (175±SEM 5 mm Hg), the controls therefore sustaining an appreciably greater increase in pressure. During the 30-minute rest period after the tests both the control and hypertensive groups showed a significant and sustained fall in absolute systolic pressures as compared with pre-exercise values (p <0·001), the mean percentage reductions being 22% and 25% respectively.If a fall in blood pressure after exercise is maintained for four to 10 hours, then a “good walk” twice a day might be reasonable treatment for mild hypertension. Studies are continuing to determine the amount of exercise needed and the duration for which the reduction in blood pressure is maintained.     

Seasonal variation in arterial blood pressure.

Blood pressure measurements recorded during the medical Research Council''s treatment trial for mild hypertension have been analysed according to the calendar month in which the readings were made. For each age, sex, and treatment group systolic and diastolic pressures were higher in winter than in summer. The seasonal variation in blood pressure was greater in older than in younger subjects and was highly significantly related to maximum and minimum daily air temperature measurements but not to rainfall.     

Auscultatory indirect measurement of blood pressure in dogs

An indirect method of measuring blood pressure (cuff plus stethoscope) was evaluated in 70 dogs weighing 15 to 30 kg (17.5 +/- 8.8 kg; mean +/- standard deviation). A cuff 12 cm wide was used. The measurements were most audible with the cuff on the upper foreleg of the dog and with the stethoscope placed in the medial epicondylar region just distal to the cuff. The cuff was inflated to greater than systolic pressure and allowed to deflate slowly. In 70 lightly sedated dogs, systolic blood pressures averaged 145 +/- 25 mmHg (mean +/- standard deviation) and diastolic blood pressures averaged 84 +/- 14 mmHg. Indirect measurements were compared to direct measurements (femoral arterial catheter). Systolic pressures obtained by this direct method averaged 138 +/- 29 mmHg (mean +/- standard deviation) and diastolic pressures averaged 84 +/- 17 mmHg. The correlation coefficient for systolic pressure was 0.96 and for diastolic pressure 0.97.     

Blood pressure and five year survival in the very old

During 1977-8 we measured blood pressure in 561 old people (83% of those aged 85 or more living in Tampere) and analysed their five year survival according to their blood pressure group. The subjects were divided into six groups on the basis of their blood pressures (from <120 to >200 mm Hg systolic, from <70 to >110 diastolic). The greatest mortality was observed in those in the lowest systolic and lowest diastolic groups. Mortality was least in subjects with systolic pressures of 160 mm Hg or more and diastolic pressures of 90 mm Hg or more.The most essential finding in this series of the very old was an increased mortality in the lowest blood pressure groups.     

Further steps toward a neonatal chronocardiology

The study of 53 series of blood pressures at half-hour intervals from clinically healthy full-term newborns during the first days of life reveals various classifiers correlating with a history of high blood pressure: the circadian amplitude of diastolic blood pressure, the 50% range of systolic blood pressure and the standard deviation of heart rate.     

Maternal blood pressure and fetal ultrasonography in normal baboon pregnancies

Pregnancy in baboons is characterized by lower systolic, diastolic, and mean blood pressures than in the nonpregnant state. As pregnancy progresses, diastolic and mean pressures tend to increase whereas systolic pressure remains low. Sonographic measurements of fetal growth follow a sigmoid pattern, but their increase in relation to length of gestation approximates a straight line between 6 and 21 weeks of gestation (23 to 84% of term).     

Blood pressure and contraceptive use

In a survey of 461 women routinely attending family planning clinics those taking oral contraceptives had significantly higher mean systolic and diastolic blood pressures than those using non-hormonal contraception. There appeared to be a dose-response relation of blood pressure to the progestogen component of two oral contraceptives with an identical 30 μg ethinyloestradiol component. This supports the idea that the progestogen as well as the oestrogen component has an aetiological role in the rise in blood pressure. There was a significant correlation of blood pressure with duration of current use of oral contraceptive but not with total duration of use. There was also a significant negative correlation of blood pressure with time since oral contraceptives were last taken, and women who had stopped using oral contraceptives over a month previously had similar blood pressures to those who had never taken them. In women taking oral contraceptives those who had either a history of hypertension in pregnancy or a family history of hypertension had significantly higher mean blood pressures than those who did not. Both systolic and diastolic blood pressures correlated independently with weight and body mass index, but controlling for the effect of this and age did not affect the above relations. No significant differences in mean blood pressures were found between different ethnic groups, and there was no relation of blood pressure to reported marital state, social class, parity, smoking, or alcohol use.Any oral contraceptive that has a less adverse effect on blood pressure has implications for general prescribing policy; thus even small differences in the progestogen contents of low-dose oestrogen pills may be important.     

Mechanics of left ventricular relaxation, early diastolic lengthening, and suction investigated in a mathematical model

We investigated the determinants of ventricular early diastolic lengthening and mechanics of suction using a mathematical model of the left ventricle (LV). The model was based on a force balance between the force represented by LV pressure (LVP) and active and passive myocardial forces. The predicted lengthening velocity (e') from the model agreed well with measurements from 10 dogs during 5 different interventions (R = 0.69, P < 0.001). The model showed that e' was increased when relaxation rate and systolic shortening increased, when passive stiffness was decreased, and when the rate of fall of LVP during early filling was decreased relative to the rate of fall of active stress. We first defined suction as the work the myocardium performed to pull blood into the ventricle. This occurred when contractile active forces decayed below and became weaker than restoring forces, producing a negative LVP. An alternative definition of suction is filling during falling pressure, commonly believed to be caused by release of restoring forces. However, the model showed that this phenomenon also occurred when there had been no systolic compression below unstressed length and therefore in the absence of restoring forces. In conclusion, relaxation rate, LVP, systolic shortening, and passive stiffness were all independent determinants of e'. The model generated a suction effect seen as lengthening occurring during falling pressure. However, this was not equivalent with the myocardium performing pulling work on the blood, which was performed only when restoring forces were higher than remaining active fiber force, corresponding to a negative transmural pressure.     

Blood pressure characteristics of a select group of North American males,followed for 20 years

This report describes the 20-year blood pressure behaviour of 3869 selected young North American males.Initial mean systolic and diastolic pressures were higher than those recorded five years later; after that pressures increased progressively. The effect of initial selection was evident for the first 10 years of exposure.A significant relationship was demonstrated between all initial systolic and diastolic levels and the 20-year blood pressure behaviour. Systolic pressure was not affected by age until age 50 and diastolic until age 45. After that a significant relationship was demonstrated.In 20 years multiple readings ≥ 140 and/or ≥ 90 mm. Hg were recorded in 26% of the population. Increases in pressure usually extended over many years. Commonly they were labile, fluctuating above and below 140/90 mm. Hg. In a small, clearly defined group, accelerated increases reached high levels in three to 10 years.     

Community care compared with hospital outpatient care for hypertensive patients.

Three hundred and seventy-six patients with treated diastolic blood pressures of less than 105 mm Hg and no history of accelerated hypertension or renal failure were selected from among those attending the Hammersmith Hospital hypertension clinic. Their average lying treated blood pressure was 146 mm Hg systolic and 90 mm Hg diastolic and average age 56 years; 18% were black, 6% Asian, and 76% white. The patients were mostly having multiple treatment, 90% receiving a diuretic, 35% methyldopa, 33% propranolol, 18% atenolol, 9% hydrallazine, and 7% bethanidine. They were randomly allocated to either two years of further hospital outpatient care or referred back to their general practitioners. During the two years 19 (10%) of the 187 patients followed up in hospital defaulted and three had their treatment discontinued. Twelve (6%) of the 189 followed up by their general practitioners defaulted from follow-up and nine had their treatment discontinued. At the end of the trial the average lying blood pressure was 148 mm Hg systolic and 88 mm Hg diastolic in the hospital group and 149 mm Hg systolic and 90 mm Hg diastolic in the general practice group. The change in blood pressure was calculated for each individual and showed an average fall of 1.6 mm Hg in standing diastolic pressure in the hospital group and a rise of 1.4 mm Hg in the general practice group (p less than 0.05). The 90% confidence limits for a difference in standing diastolic pressure between the groups were 1 and 5 mm Hg with the pressure lower in the hospital group. General practice care was not quite as effective in controlling blood pressure as continued specialist supervision over two years in this selected group of treated outpatients with mild or moderate hypertension, but these results show that the discharge back to general practitioners of patients who are well controlled after hospital treatment is a sensible policy.     

Systolic and diastolic blood pressures as predictors of coronary heart disease in middle aged Norwegian men.

Systolic and diastolic blood pressures were compared as predictors of mortality from coronary heart disease in Norwegian men aged 35-49. A total of 39,207 men were followed up for an average of 8.9 years; 385 died of coronary heart disease. Diastolic blood pressure seemed to be the better predictor, the difference being most pronounced in the age group 35-39. At this age 26% more deaths from coronary heart disease were found in the upper quintile of diastolic blood pressure compared with the upper quintile of systolic blood pressure. At ages 45-49 there were almost the same numbers of deaths from coronary heart disease in the upper quintiles of systolic and diastolic pressures. These findings suggest that the relative predictive strength of systolic and diastolic blood pressure may be dependent on age. Furthermore, for very obese men the association between blood pressure and death from coronary heart disease is much weaker.     

Oscillometric measurement of systolic and diastolic blood pressures validated in a physiologic mathematical model

ABSTRACT: BACKGROUND: The oscillometric method of measuring blood pressure with an automated cuff yields valid estimates of mean pressure but questionable estimates of systolic and diastolic pressures. Existing algorithms are sensitive to differences in pulse pressure and artery stiffness. Some are closely guarded trade secrets. Accurate extraction of systolic and diastolic pressures from the envelope of cuff pressure oscillations remains an open problem in biomedical engineering. METHODS: A new analysis of relevant anatomy, physiology and physics reveals the mechanisms underlying the production of cuff pressure oscillations as well as a way to extract systolic and diastolic pressures from the envelope of oscillations in any individual subject. Stiffness characteristics of the compressed artery segment can be extracted from the envelope shape to create an individualized mathematical model. The model is tested with a matrix of possible systolic and diastolic pressure values, and the minimum least squares difference between observed and predicted envelope functions indicates the best fit choices of systolic and diastolic pressure within the test matrix. RESULTS: The model reproduces realistic cuff pressure oscillations. The regression procedure extracts systolic and diastolic pressures accurately in the face of varying pulse pressure and arterial stiffness. The root mean squared error in extracted systolic and diastolic pressures over a range of challenging test scenarios is 0.3 mmHg. CONCLUSIONS: A new algorithm based on physics and physiology allows accurate extraction of systolic and diastolic pressures from cuff pressure oscillations in a way that can be validated, criticized, and updated in the public domain.     

Comparison of simultaneous measurement of mouse systolic arterial blood pressure by radiotelemetry and tail-cuff methods

Radiotelemetry of mouse blood pressure accurately monitors systolic pressure, diastolic pressure, heart rate, and locomotor activity but requires surgical implantation. Noninvasive measurements of indirect systolic blood pressure have long been available for larger rodents and now are being reported more frequently for mice. This study compared mouse systolic arterial blood pressure measurements using implanted radiotelemetry pressure transducer with simultaneous tail-cuff measurements in the same unanesthetized mice. The pressure range for comparison was extended by inducing experimental hypertension or by observations of circadian elevations between 3 AM and 6 AM. Both trained and untrained tail-cuff operators used both instruments. Every effort was made to follow recommended manufacturer's instructions. With the initial flow-based tail-cuff instrument, we made 671 comparisons (89 sessions) and found the slope of the linear regression to be 0.118, suggesting poor agreement. In an independent assessment, 277 comparisons (35 sessions) of radiotelemetry measurements with the pulse based tail-cuff instrument were made. The slope of the linear regression of the simultaneous measurements of systolic pressures was 0.98, suggesting agreement. Bland-Altman analysis also supported our interpretation of the linear regression. Thus although reliable systolic pressure measurements are possible with either tail-cuff or radiotelemetry techniques, in our hands some tail-cuff instruments fail to accurately detect elevated blood pressures. These data, however, do not distinguish whether this instrument-specific tail-cuff failure was due to operator or instrument inadequacies. We strongly advise investigators to obtain an independent and simultaneous validation of tail-cuff determinations of mouse blood pressure before making critical genotyping determinations.