Medical management of primary hypertension (first of three parts)

Endovascular renal denervation: a novel sympatholytic with relevance to chronic kidney disease

Endovascular renal denervation (sympathectomy) is a novel procedure developed for the treatment of resistant hypertension. Evidence suggests that it reduces both afferent and efferent sympathetic nerve activity, which may offer clinical benefit over and above any blood pressure-lowering effect. Studies have shown objective improvements in left ventricular mass, ventricular function, central arterial stiffness, central haemodynamics, baroreflex sensitivity and arrhythmia frequency. Benefits have also been seen in insulin resistance, microalbuminuria and glomerular filtration rate. In chronic kidney disease, elevated sympathetic activity has been causally linked to disease progression and cardiovascular sequelae. Effecting a marked reduction in sympathetic hyperactivity may herald a significant step in the management of this and other conditions. In this in-depth review, the pathophysiology and clinical significance of the sympatholytic effects of endovascular renal denervation are discussed.

Systolic hypertension in the elderly

Historically diastolic blood pressure (BP) rather than systolic BP has been regarded clinically as the more important component related to subsequent hypertensive morbidity and mortality, and treatment has thus been directed towards lowering the diastolic BP. Observational studies across many different populations have related cerebrovascular disease and death more to the systolic BP, which appears selectively to increase as the population ages. Isolated systolic hypertension (ISH), therefore, may be more prevalent as westernized societies become older. Those affected with ISH suffer a two- to fivefold increase in rates of stroke and ischemic heart disease compared to normotensives. Currently no clinical trials data exist for ISH showing the efficacy of antihypertensive therapy upon final morbidity and mortality, but a large-scale multicenter clinical trial, the Systolic Hypertension in the Elderly Program (SHEP), is currently underway in the United States. Results are expected in the early 1990s. If the results of this trial confirm the efficacy of treating ISH, the therapeutic challenge of ISH will be to selectively decrease systolic BP without undue side effects.

Effects of methylphenidate on cardiovascular responses in attention deficit hyperactivity disordered adolescents

The short-term dose effects of methylphenidate were examined on cardiovascular measures in 11 black male adolescents diagnosed as having attention deficit hyperactivity disorder (ADHD). In a double-blind, cross-over design with randomized order, the subjects received placebo and each of three methylphenidate doses (0.15, 0.3, and 0.5 mg/kg) for a period of 2 weeks per medication dosage. Significant main effects were found for diastolic and systolic blood pressure; however, pairwise comparisons revealed a significant linear increase in diastolic blood pressure only. Because of the unexpected increase in diastolic blood pressure, careful monitoring of black adolescents who are receiving methylphenidate is recommended.

Mortality associated with diastolic hypertension and isolated systolic hypertension among men screened for the Multiple Risk Factor Intervention Trial

The large cohort of white men (317,871) 35 to 57 years old at initial screening for possible enrollment into the Multiple Risk Factor Intervention Trial (MRFIT) was examined with regard to initial blood pressure levels and subsequent coronary heart disease (CHD), stroke, and all-cause mortality. The overall prevalence of isolated systolic hypertension (ISH), defined as systolic blood pressure (SBP) greater than or equal to 160 mm Hg and diastolic blood pressure (DBP) less than 90 mm Hg, was 0.67% among white men screened for MRFIT and increased with age (0.31% among 35- to 39-year-olds to 1.7% among 55- to 57-year-olds). The 6 year CHD and all-cause mortality rates in men over 50 were highest in those with ISH compared with both subjects with diastolic hypertension and those with normal pressure. The relative risk of death from stroke in those with ISH, compared with that in those with SBP less than 160 mm Hg and those with DBP less than 90 mm Hg, was 3.0 (95% confidence interval 1.3 to 6.8). In addition, at any level of DBP, the level of SBP appeared to be the major determinant of all-cause and CHD mortality. The determinants of ISH in individuals under 60 years of age as well as the possible efficacy of its treatment should be evaluated further.

Vasodilators, antihypertensive therapy and the kidney

Both traditional and newer treatments of essential hypertension are discussed in relation to kidney function and renal perfusion. In essential hypertension, renal vascular resistance is routinely increased and renal blood flow is often decreased. Reduced sodium intake as a form of therapy will cause a decrease in both renal blood flow and glomerular filtration, most likely due to an angiotensin-induced renal vasoconstriction caused by the reactive increase in renin release. Treatment with diuretics produces the same effects, also angiotensin-mediated. The addition of a beta-adrenergic blocking agent to prevent renin release may be a good choice, but individual agents within this class must be examined for direct renal vasoconstriction. The effects of "nonspecific" vasodilators on renal perfusion and renal sodium handling vary with the patient but may produce antinatriuresis, sodium retention and decrease in glomerular filtration. Studies with calcium antagonists have shown promising results. Nifedipine studies show a substantial increase in renal plasma flow, a well-maintained glomerular filtration rate and a brisk diuresis and natriuresis. However, patients with the lowest baseline renal flow do not show these benefits. Diltiazem has shown a potentiated renal vascular response in normotensive patients of hypertensive parents. Angiotensin converting enzyme inhibitors such as captopril and enalapril have produced increased renal blood flow and well-maintained glomerular filtration in patients with essential hypertension. The agents available for treating hypertension have improved dramatically in the past decade. A salutary effect on the kidney will remain high on the list of important characteristics to be considered in choosing one of these agents.

Overview on atherosclerotic systolic hypertension

Hypertension in older atherosclerotic patients is characterised by a disproportionate elevation of systolic and pulse pressure contrasting with a subnormal diastolic level. Increased systolic pressure is strongly related to the excess of cerebrovascular complications and congestive heart failure observed in these patients. The physiopathological pattern is marked by a strong reduction in compliance of large arteries directly responsible for the predominant high systolic pressure because of the impairment of the buffering function of the arteries on the cardiac pulse wave. Clinical management is directed to the elevation of athero-arteriosclerotic changes of large arteries by means of appropriate non-invasive ultrasonic techniques and specific lowering in systolic pressure. Antihypertensive treatment must specifically decrease systolic pressure without superimposing adverse effects on the generalized and focalized atherosclerotic process. In this respect, new pharmacological agents capable of direct actions on large arteries might be suitable.

The kidney and antihypertensive therapy

To a large degree, modern antihypertensive therapy has evolved from the development of agents that act as vasodilators but, for one reason or another, avoid the disadvantages of the nonspecific vasodilators. This review examines the impact of antihypertensive agents on renal perfusion and function and relates it to their efficacy in reducing high blood pressure. Special attention is given to beta-adrenergic blocking agents that have a minimal impact on the kidney, converting enzyme inhibitors, calcium channel blockers and dopamine analogs. Also reviewed are the functional abnormalities involving the renal blood supply in essential hypertension, the role of newer pharmacologic agents in therapy and the nature and extent of reactive responses that often limit the response to therapeutic agents.

Strategies in antihypertensive therapy: implications of the kidney

Because we so rarely know the cause of hypertension, antihypertensive therapy remains empiric. However, certain principles of treatment are emerging; one of these concerns the critical role of the kidney in antihypertensive therapy. Whether or not the kidney is primarily responsible for hypertension in a patient, it is the patient's renal response to treatment that determines, to a major degree, an agent's efficacy. Vasodilators have been a conceptually attractive approach to the treatment of high blood pressure, because they decrease total peripheral resistance, which is considered to be the mechanism responsible for this condition in most patients. Nonspecific vasodilators exert a series of actions on the kidney--including profound sodium retention and reactive renin release--that limits therapeutic response. For reasons that are not yet clear, but are apparently related to specific action on calcium entry into vascular smooth muscle, endocrine function, and renal hemodynamics, calcium channel blocking agents, such as nifedipine, have an advantage in the treatment of hypertension. They cause little or no sodium retention; thus, the addition of a diuretic agent is not required. In fact, there is evidence that sodium loading in certain patients may potentiate the antihypertensive efficacy of these drugs. The renin-angiotensin system seems to be activated to a somewhat lesser degree by calcium channel blocking agents than it is by nonspecific vasodilators; in addition, these agents interfere with the actions of angiotensin on aldosterone release. Moreover, their dilator action on the renal blood supply favors sodium excretion. Nifedipine either has no effect on the renal blood supply or induces an increase in renal blood flow and maintains glomerular filtration rate, both of which combine to support the ensuing natriuresis.

The kidney and effective antihypertensive therapy

Whether or not the kidney is involved in the genesis of hypertension in an individual patient, it becomes a major determinant of the response to antihypertensive therapy once a treatment strategy is adopted. The major mechanisms through which the kidney influences blood pressure are renin release and sodium retention, either together or separately, but additional mechanisms may also contribute. When sodium intake is restricted or a diuretic is used, the reactive increase in plasma renin activity makes a substantial contribution to limiting the blood pressure fall. When vasodilators or agents that block the sympathetic nervous system are used, sodium retention plays an important role. Among newer agents, the effectiveness of calcium channel blockers, converting enzyme inhibitors and perhaps dopamine analogs reflects, for reasons that differ from 1 class of agent to another, a special action on the kidney that limits the reactive renal response to the reduction in blood pressure. Treatment strategies that address the problem of the renal response are more likely to be effective than approaches that avoid or ignore it.

The kidney and strategies for the treatment of hypertension

Renal compensatory mechanisms are a chief consideration when selecting an antihypertensive agent. The relationships, therefore, between renal blood flow and glomerular filtration rate, sodium handling by the kidney, and release of renin require particular attention. We shall examine therapeutic measures such as beta adrenergic blockers, vasodilators, calcium entry blockers, and converting enzyme inhibitors in light of their effects on renal blood flow.

Diuretics in the management of hypertension

Diuretics-especially the thiazide type-are the cornerstone of antihypertensive therapy. Practitioners need to be familiar with one or two of each type to use them effectively with full knowledge of possible side effects. Chronic use demands periodic monitoring of electrolyte levels.

Pulse pressure-III. Prognostic significance in four Chicago epidemiologic studies

This report, the third in a series on pulse pressure and pure systolic hypertension, examines the associations between blood pressure and the cardiovascular diseases and coronary heart disease, both cross-sectionally and prospectively, utilizing data from four Chicago epidemiologic studies, in an effort to determine whether or not a widened pulse pressure, or pure systolic hypertension, is an independent risk factor. In these analyses, blood pressure is divided into two components, one related to level and the other to pulse pressure, with pulse pressure redefined so that the association between pulse pressure and the prevalence of ECG abnormalities or mortality, indicates whether the endpoint is more strongly related to systolic or diastolic blood pressure. In these studies, blood pressure level is significantly related to both ECG abnormalities and mortality. In the cross-sectional analyses, pulse pressure is generally positively related to the prevalence of ECG abnormalities, indicating a stronger association for systolic blood pressure, and thus a possible association with pure systolic hypertension. However, in the prospective analyses, pulse pressure is generally not related to mortality, indicating an equal association with mortality for systolic and diastolic blood pressure in these studies. Thus, although the cross-sectional analyses generally support the hypothesis that a widened pulse pressure, or pure systolic hypertension, is an independent risk factor for the cardiovascular diseases and coronary heart disease, the prospective analyses do not.

Management of hypertension newly detected by health screening

An attempt was made, through a hospital-based health screening service, to ensure proper longterm care of clients with hypertension and other cardiovascular risk factors. Of 8755 subjects screened on one occasion, 1274 (14.6%) had a blood pressure reading above defined limits; of these, 1058 were not receiving antihypertensive drugs. Apparently hypertensive subjects were rescreened within one week or were referred to their local doctors. At their second visits, over half of the 716 rescreened subjects had reading consistently below the defined limits. Those with intermittent blood pressure elevation (89 patients) were designated as having labile hypertension, and were reviewed regularly. The remainder, with persisting hypertension, were sent to their local doctors or to the hospital's hypertension clinic. After six months, the group ith labile hypertension showed no change in mean left cardiac ventricular voltage, and more than 50% the group had normal blood pressure; 14 patients were receiving antihypertensive drugs. Subjects referred to the hypertension clinic had a high prevalence of cardiovascular risk factors and a low prevalence of clinically evident organ damage. Only half of this group were deemed to require drug therapy. In a postal survey of clients referred to private doctors, 35% of respondents reported that they had started taking anti-hypertensive drugs. Thorough rescreening of blood pressure is essential in preventing the unnecessary use of antihypertensive drugs, and this can be facilitated by providing management streams appropriate to the needs of the individual subject.

Effects of intermittent pressure loading on the development of ventricular hypertrophy in the cat

Although the effects of persistent pressure loading on the development of ventricular hypertrophy have been studied extensively, the effects of intermittent pressure loading have not been examined. To study the effects of intermittent pressure loading we subjected the right ventricle of cats to intermittent pulmonary artery constriction over a 2-week period. Two intermittent pressure loading schedules were employed. The first consisted of a right ventricular systolic pressure of 60 mm Hg for 3.5 days and normal right ventricular pressure for 3.5 days; and the second consisted of a right ventricular systolic pressure of 60 mm Hg for 2.3 days and normal right ventricular pressure for 4.7 days. The intermittent pressure-loaded cats were compared with normal unoperated controls, sham-operated controls, and cats with persistent right ventricular pressure load for either 1-week or 1- to 2-month duration. The data indicate that intermittent pressure loading caused significant right ventricular hypertrophy. Since significant residual ventricular hypertrophy was present in both intermittent pressure loading groups, regression of ventricular hypertrophy involves a slower process than the progression of hypertrophy.

A study of comparative blood pressure measures in predicting risk of coronary heart disease

The Western Collaborative Group Study is a prospective study of 3,154 employed men, aged 39-59 years. Coronary heart disease (CHD) occurred in 257 subjects during 8.5 years of follow-up. The multiple logistic risk model was used to assess the comparative strength of systolic, diastolic, mean arterial and pulse pressure for the prediction of CHD in two age decades after adjustment for age, serum cholesterol, cigarette smoking, behavior pattern and weight. The risk of CHD was more strongly associated with the systolic than the diastolic pressure. The general practice of assessing the importance of blood pressure based only on the diastolic component should be reassessed.

Beta-adrenoreceptor blockade in hypertension

There is good evidence from many sources that beta-adrenoreceptor blockade is an effective form of therapy in mild, moderate and severe hypertension either alone or in combination with other antihypertensive agents. Although a number os such beta blocking compounds are now available, they appear to have a hypotensive effect of approximately equal magnitude. This hypotensive effect is obtained in both the supine and standing positions thus avoiding postural hypotension. The maximum hypotensive effect may take some time to become apparent. Despite considerable work the mode of action remains uncertain, reduction in cardiac output, resetting of baroreceptors, reduction in plasma renin and a central nervous system effect have been suggested but remain unproved. There is evidence to suggest that these compounds can control, to some degree, the surges in blood pressure resulting from either mental or physical stress. A low incidence of serious side effects has been reported by many workers. Only the long-term use of these compounds in comparison with other antihypertensive agents will determine their place in the management of hypertension.

Hypertension as a disease of modern society

About 50 per cent of people in modern societies have blood pressure sufficiently elevated to result in increased mortality. This proportion is much smaller in undisrupted societies of hunter-gatherers. In most cases the elevated blood pressure in modern societies is associated with physiological changes characteristic of chronic stress. The difference between blood pressure in modern populations and that in undisrupted hunter-gatherer societies cannot be accounted for by genetic differences or differences in salt consumption. Two primary features of modern society which contribute to the elevation of blood pressure are community disruption and increased work pressure. Drug therapy and relaxation therapies for hypertension attempt to counteract the physiological effects of social stress. However, it is more appropriate to use the occurrence of hypertension as an indicator of fundamental social problems which need to be solved.