Relationship between cardiac output and peripheral resistance in borderline hypertension

Oral saline consumption and pressor responses to acute physical stress

Sodium induced volume loading may alter pressor responses to physical stress, an early symptom of cardiovascular disease.

PURPOSE

Study 1: Determine the time point where total blood volume and serum sodium were elevated following saline consumption. Study 2: Examine the BP response to isometric handgrip (HG) and the cold pressor test (CPT) following saline consumption.

METHODS

Study 1: Eight participants drank 423 mL of normal saline (sodium 154 mmol/L) and had blood draws every 30 min for 3 h. Study 2: Sixteen participants underwent two randomized data collection visits; a control and experimental visit 90 min following saline consumption. Participants underwent 2 min of isometric HG, post exercise ischemia (PEI), and CPT.

RESULTS

Study 1: Total blood volume (3.8 ± 3.0 Δ%) and serum sodium (3.5 ± 3.6 Δ%) were elevated (P < 0.05) by the 90 min time point. Study 2: There were no differences in mean arterial pressure (MAP) during HG (EXP: 17.4 ± 8.2 ΔmmHg; CON: 19.1 ± 6.0 ΔmmHg), PEI (EXP: 16.9 ± 11.7 ΔmmHg; CON: 16.9 ± 7.8 ΔmmHg), or the CPT (EXP: 20.3 ± 10.8 ΔmmHg; CON: 20.9 ± 11.7 ΔmmHg) between conditions (P > 0.05). MAP recovery from the CPT was slower following saline consumption (1 min recovery: EXP; 15.7 ± 7.9 ΔmmHg, CON; 12.3 ± 8.9 ΔmmHg, P < 0.05).

CONCLUSION

Data showed no difference in cardiovascular responses during HG or the CPT between conditions. BP recovery was delayed by saline consumption following the CPT.

How Structure, Mechanics, and Function of the Vasculature Contribute to Blood Pressure Elevation in Hypertension

Large conduit arteries and the microcirculation participate in the mechanisms of elevation of blood pressure (BP). Large vessels play roles predominantly in older subjects, with stiffening progressing after middle age leading to increases in systolic BP found in most humans with aging. Systolic BP elevation and increased pulsatility penetrate deeper into the distal vasculature, leading to microcirculatory injury, remodelling, and associated endothelial dysfunction. The result is target organ damage in the heart, brain, and kidney. In younger individuals genetically predisposed to high BP, increased salt intake or other exogenous or endogenous risk factors for hypertension, including overweight and excess alcohol intake, lead to enhanced sympathetic activity and vasoconstriction. Enhanced vasoconstrictor responses and myogenic tone become persistent when embedded in an increased extracellular matrix, resulting in remodelling of resistance arteries with a narrowed lumen and increased media-lumen ratio. Stimulation of the renin-angiotensin-aldosterone and endothelin systems and inflammatory and immune activation, to which gut microbiome dysbiosis may contribute as a result of salt intake, also participate in the injury and remodelling of the microcirculation and endothelial dysfunction. Inflammation of perivascular fat and loss of anticontractile factors play roles as well in microvessel remodelling. Exaggerated myogenic tone leads to closure of terminal arterioles, collapse of capillaries and venules, functional rarefaction, and eventually to anatomic rarefaction, compromising tissue perfusion. The remodelling of the microcirculation raises resistance to flow, and accordingly raises BP in a feedback process that over years results in stiffening of conduit arteries and systo-diastolic or predominantly systolic hypertension and, more rarely, predominantly diastolic hypertension. Thus, at different stages of life and the evolution of hypertension, large vessels and the microcirculation interact to contribute to BP elevation.

Blood pressure predicts endothelial function and the effects of ethinyl estradiol exposure in young women

Hypertension, obesity, and endothelial function predict cardiovascular disease in women, and these factors are interrelated. We hypothesized that hypertension and obesity are associated with endothelial dysfunction in young women and that short-term ethinyl estradiol exposure mitigates this dysfunction. We examined flow-mediated dilation (FMD) responses before and during 7 days of oral ethinyl estradiol (30 µg/day) in 19 women (25 ± 5, 18-35 yr). We divided our sample into two groups based on two criteria: blood pressure and obesity. Women were divided into normal blood pressure (NBP; mean arterial pressure range: 78-91 mmHg, n = 7) and high blood pressure (HBP; mean arterial pressure range: 95-113 mmHg, n = 9) groups. We also stratified our subjects by body composition (lean: 18-31%, n = 8; obese: 38-59%, n = 9). We evaluated brachial FMD after two distinct shear stress stimuli: occlusion alone and occlusion with ischemic handgrip exercise. Obesity was unrelated to both FMD responses. Before ethinyl estradiol administration, the HBP group had blunted ischemic exercise responses relative to the NBP group (8.0 ± 3.5 vs. 12.3 ± 3.2%, respectively, P = 0.05). However, during ethinyl estradiol administration, ischemic exercise responses increased in the HBP group (12.8 ± 6.1%, P = 0.04) but decreased in the NBP group (5.6 ± 2.4%, P = 0.01). Standard FMD did not reveal differences between groups. In summary, 1) moderate HBP predicted endothelial impairment, 2) ethinyl estradiol administration had divergent effects on FMD in women with NBP versus HBP, and 3) enhanced FMD (ischemic handgrip exercise) revealed differences in endothelial function, whereas standard FMD (occlusion alone) did not. NEW & NOTEWORTHY We are the first to show that mild hypertension is a stronger predictor of endothelial dysfunction than obesity in healthy women without overt cardiovascular dysfunction. Importantly, the standard 5-min flow-mediated vasodilation stimulus did not detect endothelial dysfunction in our healthy population; only an enhanced ischemic handgrip exercise shear stress stimulus detected endothelial impairment. Estradiol administration increased flow-mediated dilation in women with high blood pressure, so it may be a therapeutic intervention to improve endothelial function.

Age-dependent sympathetic neural responses to ß1 selective beta-blockade in untreated hypertension-related tachycardia

BACKGROUND

Elevated heart rate (HR) increases cardiovascular morbidity and mortality in hypertension. The impact of beta-blockers on patient prognosis in hypertension is controversial. This study examined the age-related effects of betaxolol on HR, muscle sympathetic nerve activity (MSNA), blood pressure (BP) and sympathovagal balance in untreated males with hypertension and tachycardia.

METHODS

Ten young (age 26 ± 1 years) and seven older (age 50 ± 4 years) males underwent measurement of BP, HR, HR variability (Poincare plot) and MSNA before and after 8 weeks treatment with betaxolol at the initial starting dose of 10 mg/day, which was increased to 20 mg/day once daily after 4 weeks in all subjects.

RESULTS

In younger subjects, betaxolol decreased systolic BP (-13 ± 4 mm Hg, p = .01) and HR (-29 ± 4 bpm, p < .001) but not MSNA (3 ± 3 burst/min., p = 0.47) after 8 weeks. In older subjects a pronounced reduction in BP (-27 ± 7, p = .007) was accompanied by a significant decrease in MSNA (-13 ± 5 burst/min., p < .05) and HR (-17 ± 4 bpm, p = .002). SD1/SD2 ratio of Poincare plot increased in younger (0.36 ± 0.03 vs 0.51 ± 0.05, p = .004), but not in older (0.43 ± 0.08 vs 0.54 ± 0.12, p = .50) subjects.

CONCLUSION

Autonomic neural responses to betaxolol are age-dependent in hypertension-related tachycardia. Betaxolol reduces sympathetic drive to the heart, but not to the peripheral vessels confirming the contribution of augmented cardiac sympathetic activity to disease pathophysiology in younger adults. In older hypertensives, the sympathovagal balance is not influenced by betaxolol. The paradoxical reduction in MSNA despite lowering of BP and HR in older patients may suggest age-related functional decrements in autonomic control and/or inhibitory effects of betaxolol on the central nervous system.

High blood pressure: An obscuring misnomer?

High blood pressure (BP) has been identified as a major risk factor for cardiovascular complications. Although two-way association between BP and hypertensive complications makes hypertension a near-ideal biomarker, BP as “the cause” for the complications of HT per se still needs more evidence. Another entirely possible hemodynamic candidate for causing hypertensive cardiovascular adverse events can be flow or its iterations, which might have escaped the attention because of its perfect correlation with pressure and harder technical measurement. In this article, we analyze the evidence in hand to compare flow- and pressure-related phenomena to delineate which of the two is the dominant mediator of complications related to hypertension and should be the target for therapy. A “flow-” rather than a “pressure-” based factor, as the causative or major driving mediator of common hypertensive complications, may change our understanding of hypertension pathophysiology.

Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs

This review focuses on how blood flow to contracting skeletal muscles is regulated during exercise in humans. The idea is that blood flow to the contracting muscles links oxygen in the atmosphere with the contracting muscles where it is consumed. In this context, we take a top down approach and review the basics of oxygen consumption at rest and during exercise in humans, how these values change with training, and the systemic hemodynamic adaptations that support them. We highlight the very high muscle blood flow responses to exercise discovered in the 1980s. We also discuss the vasodilating factors in the contracting muscles responsible for these very high flows. Finally, the competition between demand for blood flow by contracting muscles and maximum systemic cardiac output is discussed as a potential challenge to blood pressure regulation during heavy large muscle mass or whole body exercise in humans. At this time, no one dominant dilator mechanism accounts for exercise hyperemia. Additionally, complex interactions between the sympathetic nervous system and the microcirculation facilitate high levels of systemic oxygen extraction and permit just enough sympathetic control of blood flow to contracting muscles to regulate blood pressure during large muscle mass exercise in humans.

Evidence of a hyperkinetic state in children with elevated blood pressure

BACKGROUND

Left ventricular hypertrophy (LVH) and elevated left ventricular mass index (LVMI) are important predictors of cardiovascular morbidity and mortality in adults. Children with hypertension and pre-hypertension demonstrate LVH and greater LVMI compared to normotensive children. The impact of blood pressure (BP) on early changes in left ventricular properties provides an opportunity to understand and identify cardiovascular risk early in childhood.

AIM

The aim of this study was to assess left ventricular structural and functional properties in a sample of children across a wide range of BP values.

SUBJECTS AND METHODS

Children aged 11-14-years were divided into BP groups: hypertensives (HTN; ≥95th percentile; n = 21) and normotensives (NTN; <90th percentile; n = 85) based on BP measures taken at two time points. Resting supine heart rate (HR), cardiac output (CO) and total peripheral resistance (TPR) were collected along with left ventricular structural and functional properties using ultrasound sonography.

RESULTS

LVMI and TPR were not different between groups. CO, HR and left ventricular end-diastolic and end-systolic volumes were elevated in the HTN group. Furthermore, HR and body mass index were found to be independent predictors of BP group status in children.

CONCLUSION

These findings show that children with elevated BP are characterized by high HR and CO and normal TPR. Also, the results identify HR as a predictor of BP group status in early childhood.

Hemodynamic circulatory patterns in young patients with predominantly diastolic hypertension

To evaluate the spectrum of hemodynamic patterns in patients with isolated diastolic hypertension-predominantly diastolic hypertension, we re-analyzed a previously reported cohort of 189 non-medicated hypertensive individuals that were assessed by impedance cardiography. We selected 46 patients who were less than 50 years old and had pulse pressure less or equal than 45 mm Hg confirmed by ambulatory blood pressure monitoring. The selected cohort had a mean age of 39.7 years and was 47% men. Three distinct groups were identified: a high cardiac index (CI) "hyperdynamic" group, with normal to near normal systemic vascular resistance (SVR); an intermediate CI and SVR group; and a "vasotonic" group, with low CI and high SVR. Heart rate was similar among the three groups. Stroke volume index (SVI) was significantly higher in the hyperdynamic group (61.8, 49.7, and 39.7 mL/m(2) in the high, intermediate, and low CI groups, respectively). The hyperdynamic group had greater total arterial compliance index than the vasotonic group (1.3 ± 0.3 vs 0.92 ± 0.2 mL/m(2) mm Hg for high vs low CI, respectively; P < .001). In conclusion, isolated diastolic hypertension-predominantly diastolic hypertension patients can have diverse hemodynamic patterns that cannot be predicted based on peripherally measured blood pressure and heart rate alone. This hemodynamic complexity must be taken into account when considering the genetic and pathophysiologic mechanisms of hypertension.

The prognostic significance of heart rate for cardiovascular disease and hypertension

Five decades ago, hypertension was a debated risk factor for the development of cardiovascular disease. After further studies and the introduction of antihypertensive medications, few, if any, have doubted the important role hypertension plays as a cardiovascular risk factor. Today, a growing body of evidence emphasizes the relationship between heart rate and hypertension, and heart rate and cardiovascular disease, which makes the measurement of heart rate an important component of the cardiovascular risk assessment. Current European guidelines for managing arterial hypertension recommend the measurement of heart rate for risk stratification, but there still are no recommendations for treatment. This review discusses the evidence for a relationship between heart rate and cardiovascular mortality and morbidity and hypertension.

Small artery structure and function in hypertension

It has been known for some considerable time that sustained hypertension changes the circulatory architecture both in the heart and blood vessels. The histopathological alterations are of considerable interest because once they have developed they appear to carry an adverse prognostic risk. In the heart it is apparent that there is hypertrophy. This extends also to the large- and medium-sized blood vessels but at the level of the smaller arteries that contribute to vascular resistance, this is not the case: it is clear that the physiological response to higher pressures is a change in the positional conformation of the pre-existing tissue constituents and as a result of this the lumen is narrowed. This brief review looks at our knowledge in this area and attempts to clarify our understanding of how hypertension brings these about and what happens when these homeostatic mechanisms break down. From a therapeutic perspective it appears imperative to control blood pressure in an attempt to reverse or prevent such alterations to cardiovascular structure. Our knowledge is fast expanding in this field and it is only to be anticipated that as detection methodology improves everyday practice will alter as we profile our patients in terms of structural alterations in the ventricle and blood vessels.

Integrative mechanisms of blood pressure regulation in humans and rats: cross-species similarities

As our understanding of the importance of individualized medicine continues to grow, the clinical relevance of interindividual variability in hemodynamic variables is receiving increasing attention. However, it is not known whether the rat, which is often used for studies of cardiovascular regulation, exhibits similar interindividual variability. In the present study, we evaluated whether the magnitude of interindividual variability in cardiac output (CO) and total peripheral resistance (TPR) was similar in humans and in rats. We assessed interindividual variability of mean arterial pressure (MAP), CO, and TPR during control conditions in normotensive humans (n = 40) and during normotension and deoxycorticosterone acetate-salt hypertension in Sprague-Dawley rats (n = 16). Humans and rats showed marked interindividual variability in CO and TPR but low variability in MAP. During deoxycorticosterone acetate-salt hypertension, CO was maintained, but TPR was elevated compared with the baseline period. We conclude that the magnitudes of interindividual variability of MAP, CO, and TPR are quantitatively similar in humans and rats, providing support for the relevance of this variability in both species and suggesting that studies in rats could be designed to address questions specific to individualized medicine in hypertension.

Haemodynamics studies in young men with mild blood pressure elevation

The cardiac output at rest, and the intra-arterial blood pressure and hand blood flow at maximal vasodilation were determined in two groups of men aged 18-22 years. 44 patients were referred from a military enlistment centre because of mild blood pressure elevation, and 29 normotensive volunteers were mainly recruited from the same enlistment centre. In addition, in a majority of subjects in both groups the auscultatory blood pressure of both parents was determined. The patients were characterized by a significantly higher cardiac index at rest, and a significantly higher vascular resistance in the hand blood vessels at maximal vasodilation than the controls, indicating the presence of structural alterations in the resistance vessels of these subjects with only very mild blood pressure elevation. The tendency to increased vascular resistance in the hand blood vessels at maximal vasodilation was more prominent in patients with a normal cardiac index than in those with a high index. This suggests inclusion in the patient group of tense, anxious individuals with an elevated cardiac index but otherwise normal circulation, but does not exclude the possibility that these patients may develop structural vascular changes later on. The parents' blood pressure was higher in the group of patients, both for patients with a normal and those with a high cardiac index, compared to the parents of the controls.

Excess catecholamine syndrome. Pathophysiology and therapy

In addition to genetic factors, lifestyle has a predominant influence on primary hypertension and noninsulin-dependent diabetic mellitus (NIDDM). We initiated studies using radiotelemetry for characterizing molecular events linked with excess calorie intake and psychologic stress. An increased calorie intake was associated with raised (p < 0.05) systolic and diastolic blood pressure as well as heart rate independent of day-night cycle. Sympathetic activity was in excess when related to the unchanged motility. The hyperkinetic hypertension is expected to result in adverse remodeling of resistance vessels and to aggravate insulin resistance. To examine adverse effects of psychological stress, rats were subjected to intermittent food pellet feeding. Urinary catecholamines and cardiac norepinephrine stores were increased (p < 0.05). The depressed (p < 0.05) rate of Ca2+ uptake of sarcoplasmic reticulum is expected to contribute to cellular Ca2+ overload. These lifestyle influences strengthen the notion of an excess catecholamine syndrome which requires selective reduction of sympathetic outflow of the brain by I1-receptor agonists.

Pathophysiologic and prognostic implications of measuring arterial compliance in hypertensive disease

Structural alterations of the arterial wall precede atherosclerosis and cardiovascular events. Endothelial dysfunction appears to be the earliest marker for this structural change that makes the vasculature sensitive to the adverse effects of pressure, lipids, diabetes, smoking and other so-called risk factors. Reduced arterial compliance or elasticity provides an index to the structural abnormalities associated with aging and disease states. Preliminary studies suggest that an alteration in pulsewave oscillations induced at small artery branch points serves as a guide to endothelial dysfunction and reduced nitric oxide bioactivity. Additional studies are urgently needed to document the usefulness of clinical measurement of arterial compliance as a marker for the vascular abnormality that leads to cardiovascular disease and as a guide to efficacy of therapeutic interventions.

Cardiovascular responses during effortful active coping and acute experience of anger in women

This study addresses the question of whether effortful active coping and anger provocation add in their effects on cardiovascular responses. Heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) responses of 64 female students were collected during an active versus nonactive coping task with and without provocation. After a baseline period, women did mental arithmetic (active coping) or read numbers aloud (nonactive coping). Half of each group was then additionally provoked. Ratings of the emotional states (Positive and Negative Affect Scale) indicate that provocation led to an increase in anger, but not in fear or negative or positive affect. Effortful active coping and provocation elevated cardiovascular activity. Although active coping enhanced all cardiovascular variables, provocation particularly affected HR and DBP. The effects of active coping and provocation on HR and DBP but not on SBP were additive and probably were produced by different physiological mechanisms.

The evidence for a pathophysiologic significance of the sympathetic overactivity in hypertension

Interest for the role of the sympathetics in the genesis of hypertension has come full circle from early enthusiasm, through a period of neglect, to present understanding that strong evidence cannot be ignored. Sympathetic overactivity starts in childhood and is easily evident in 30% of patients with incipient hypertension. Later, in advanced hypertension, altered cardiovascular responsiveness obscures the obvious signs of sympathetic overactivity but the brain maintains its decisive pathophysiologic role. The early onset, the bimodal distribution of the neurogenic "hyperkinetic" pattern and familial aggregation suggest a genetic component in sympathetic overactivity. Patients with hypertension are at high risk for coronary disease and some of that risk is not directly related to blood pressure elevation. High sympathetic tone explains the pathophysiology of "pressure-independent" risk for premature coronary atherosclerosis in hypertension and for excess mortality/morbidity in patients who had already developed coronary heart disease.

Cardiac adaptation to increased systemic blood pressure in borderline hypertensive men

The present study examined cardiac characteristics of borderline hypertensive men with a positive parental history of hypertension. Hemodynamics in relation to left ventricular function and structure were evaluated in 15 borderline hypertensive men with a parental history of hypertension and in 20 normotensive control subjects with a negative parental history. Groups were matched in age, height, weight and percent body fat. Left ventricular mass and dimensions were measured by M-mode echocardiography, and left ventricular function was assessed by radionuclide ventriculography. Both groups had similar left ventricular mass, dimensions and wall thicknesses. In relation to control subjects, borderline hypertensive men had a significantly higher heart rate and blood pressure (BP) (p < 0.001), but a similar cardiac index. Borderline hypertensive men had a higher peripheral resistance index (p < 0.02), longer time to peak filling rate, and reduced cardiac efficiency, whereas they had higher contractility, minute and stroke work indexes than did control subjects (all p < 0.05); they also had higher diastolic BP (p < 0.03) during exercise, and sustained higher BP during recovery than did controls. Although this group of borderline hypertensive men did not have an altered cardiac anatomy, they had an increased vascular resistance, an altered diastolic function and a reduced cardiac efficiency while undergoing a greater work load. These cardiodynamic profiles are consistent with functional vascular changes and a parallel compensation by the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial and peripheral vascular responses to behavioral challenges and their stability in black and white Americans

The purpose of this study was to assess the short term stability of myocardial and peripheral vascular responses to behavioral challenges, and to compare the response patterns of Black and White men. Blood pressure and heart rate, as well as stroke volume, cardiac output, total peripheral resistance, and systolic time interval measures derived from the impedance cardiogram were obtained in 12 Black and 12 White men. These measures were taken prior to and during an evaluative speech stressor, a mirror star tracing task, and a forehead cold pressor test presented during two laboratory sessions scheduled two weeks apart. In general, total peripheral resistance and impedance-derived baseline measures showed acceptable reproducibility (G greater than .85). With a few exceptions, adequate reliability was also demonstrated for change (delta) scores. All tasks raised blood pressure responses above resting levels. Blacks demonstrated significantly greater increases in total peripheral resistance responses across tasks. Whites but not Blacks also revealed increases above baseline in cardiac output and contractility as estimated by the Heather Index. These findings are consistent with the view that Blacks show greater vascular responsiveness than Whites across a variety of tasks, but reveal less myocardial responsiveness.

Impact of age, race, and obesity on hypertensive mechanisms and therapy

Despite the demonstrated efficacy of traditional antihypertensive therapy in reducing blood pressure, hypertension continues to be a major cause of cardiovascular disease morbidity and mortality. Stepped-care therapy is a nonphysiologic approach that, due to potential metabolic derangements and stimulation of undesirable reflex responses, may not substantially reduce the cardiovascular and renal complications associated with hypertension or improve long-term survival in many hypertensive patients. Because of fundamental hemodynamic differences related to the age, race, and weight of hypertensive patients, drug treatment often elicits varying responses. Certain classes of drugs are not only more effective but also more appropriate from a physiologic standpoint in specific types of patients. Therapy selection based in part on hemodynamic mechanisms and demographic patterns is a more rational approach to patient management and may contribute to a better overall outcome than has been observed with conventional treatment.

Disease entities, mixed multi-normal distributions, and the role of the hyperkinetic state in the pathogenesis of hypertension

This paper concerns the theory and relevance of finite mixtures of univariate and multivariate normal distributions in medical research and suggests that multivariate normal mixture analysis, hitherto not extensively explored, is an appealing approach to the investigation of etiologically obscure, multifactorial diseases such as hypertension. We elaborate a statistical strategy to resolve and test for a normal mixture distribution in a seemingly heterogenous population actually comprising homogenous subpopulations. We use this strategy to validate the hypothesis that in the population at large there is a subgroup of individuals with the characteristic of a hyperkinetic circulatory state, defined as the association of an elevated cardiac index or heart rate with high blood pressure. This subgroup may have implications for the pathogenesis of hypertension. We discuss directions and implications for future research into the pathogenesis of hypertension.

Management of mild hypertension

The benefits of blood pressure reduction have been clearly established for diastolic pressures of more than 100 mm Hg. For patients with a diastolic pressure between 90 and 99 mm Hg on repeated measurements, treatment should be initiated if other risk factors are present--for example, a family history of coronary risk, increased cholesterol level, male sex, smoking, or diabetes mellitus. When the pressure seems to be labile or exaggerated in the office, home or ambulatory readings may provide confirmatory information. For persons with diastolic pressures in the range of 90 to 94 mm Hg, it may be suitable to initiate therapy with nonpharmacologic maneuvers such as sodium restriction, weight reduction, and physical conditioning. In such cases, careful follow-up of blood pressure is particularly important because it may increase later. The initial therapy for mild hypertension should be selected to minimize adverse effects and should be tailored to the individual patient. Management of all levels of hypertension must be considered in light of the associated risk factors and a concomitant effort to minimize cardiovascular risk.

Initial assessment of the patient with hypertension

The initial assessment of a patient with hypertension can easily be done in a primary-care setting. The goals of the examination are to determine whether the patient is truly hypertensive and, if so, the severity of the hypertension, the degree of target-organ involvement, the presence of curable causes of hypertension, the patient's overall cardiovascular risk profile, and the patient's understanding and willingness to adopt necessary life-style changes and comply with treatment.

New insights and new approaches for the treatment of essential hypertension: selection of therapy based on coronary heart disease risk factor analysis, hemodynamic profiles, quality of life, and subsets of hypertension

The pharmacologic therapy of mild primary hypertension (diastolic blood pressure less than 105 mm Hg) has effectively reduced hypertensive arteriolar end organ disease such as cerebrovascular accidents, congestive heart failure, and nephropathy, but there has been no convincing evidence that coronary heart disease (CHD) or its complications, acute myocardial infarction or angina, have been reduced. The risks of therapy with certain antihypertensive drugs may outweigh their treatment benefits as it relates to CHD. The optimal treatment strategy should be to reduce all CHD risk factors, reverse the hemodynamic abnormalities present by lowering the systemic vascular resistance (SVR), preserving cardiac output (CO) and perfusion, and to select the best antihypertensive drug for concomitant medical diseases or problems while maintaining a good quality of life. Antihypertensive drugs that have favorable or neutral effects on CHD risk factors include alpha blockers, calcium channel blockers, central alpha agonists, and angiotensin-converting enzyme inhibitors. On the other hand, diuretics and beta blockers without intrinsic sympathomimetic activity have unfavorable effects on many CHD risk factors. Baseline and serial evaluation of the effects of these drugs on serum lipids, lipid subfractions, glucose, uric acid, electrolytes, exercise tolerance, left ventricular hypertrophy, blood pressure, SVR, CO, perfusion, concomitant diseases, and side effects is necessary to evaluate overall cardiovascular risk.

Brain and the regulation of blood pressure: a hemodynamic perspective

The central nervous system subserves the homeostasis of the circulation and is organized as a negative feedback system. The following properties of such a feedback system are of interest: a) the setting; b) the range of the regulation; and c) the nature of the feedback (regulated) variable. In this review we show that in hypertension blood pressure is set at a higher level, but regulation of blood pressure in hypertension is normal. The central nervous system is involved in maintaining a higher set point in early human hypertension as well as in many forms of experimental hypertension. Results from trials of antihypertensive drugs suggest that setting of the baseline level of blood pressure and regulation of blood pressure variability are independent properties and are probably regulated by different areas of the central nervous system. It is, therefore, unlikely that research on blood pressure "reactivity" will elucidate the pathophysiology of the central resetting of baseline blood pressure level in hypertension. We present evidence that in subserving the circulation, the central nervous system regulates and senses blood pressure and not flow. Pathophysiologic implications of this concept are discussed particularly in regards to the apparent decrease of sympathetic tone during the evolution of hypertension.

University of California, Davis, conference: Mild hypertension

Prevalence of "higher than normal" blood pressures in a community is inversely related to the magnitude of the elevation; the milder grades of elevation are far more prevalent. A multifactorially inherited tendency to develop hypertension is modulated by multiple environmental influences. Autonomic nervous and behavioral factors plausibly appear to contribute to the initiating mechanisms of hypertension; the associated hemodynamic changes and the resulting cardiovascular structural changes interact to perpetuate the process. The complex interaction of hypertension and atherosclerosis is further complicated by direct as well as secondary effects of antihypertensive drugs on atherogenesis. Attributable cardiovascular risk is generally proportional to the degree of hypertension across the entire range of elevated blood pressure; this kind of relationship holds also for normal versus subnormal blood pressure values. Pharmacologic lowering of blood pressure, however, does not confer proportional benefit. Thus, such lowering of blood pressure to normotensive levels does not reduce the risk level to that in the normotensive population. Therapeutic outcome is influenced by the interaction of blood pressure lowering, type of antihypertensive agents used, existing risk factors, and target organ damage. Benefits of lowering blood pressure in established mild hypertension (diastolic blood pressure greater than 95 mm Hg) are confirmed. Drug treatment of patients with lower diastolic blood pressure or with isolated elevations of systolic blood pressures continues to be controversial as does the choice of initial therapeutic agent(s). The large-scale experience of clinical trials encompassing the long-term risks and benefits of the drug treatment of mild hypertension is limited to the use of diuretics and adrenergic beta blockers. A variety of new and promising therapeutic agents for use as alternate choices for initial therapy needs to undergo comparative evaluation.

Sodium sensitivity in normotensive and borderline hypertensive humans

The responses to sodium depletion and repletion were studied in subgroups of 92 normotensive and 65 borderline hypertensive individuals. The borderline hypertensives were characterized by significantly higher blood pressure, weight, cardiac output, hematocrit and decreased density of conjunctival capillaries and venules. Sodium-sensitivity was defined as an increase in mean arterial blood pressure exceeding 5% during sodium repletion. The prevalence of sodium-sensitivity was higher in blacks than in whites and greater in hypertensives than in normotensives. Sodium-sensitive individuals were characterized by significantly increased forearm vascular resistance and decreased plasma renin activity and aldosterone concentration. The resemblance of these changes to those reported in the Dahl salt-sensitive rat suggests a genetic basis for the response to sodium.

Essential hypertension: neural considerations

Current evidence suggests that the sympathetic nervous system plays a predominant role in some fraction of essential hypertension. Patients in whom such mechanisms are likely to be operative are young people with mild or labile hypertension. These mechanisms are expressed clinically through orthostatic hypertension, rapid heart rate, modestly elevated cardiac output, and normal or slightly elevated peripheral vascular resistance. The vascular resistance is inappropriately high for the level of cardiac output, and this is reflected in a mildly elevated blood pressure. This evidence carries therapeutic implications and suggests that sympatholytic drugs should be the first line of therapy. An additional pressor mechanism may arise from increased sympathetic activity along renal efferent nerves that impairs sodium excretion and another possible mechanism is stimulation of brain centers through impulses from the kidneys carried in renal afferent nerves.

Obesity hypertension

Obesity and hypertension are two major risk factors for the cardiovascular system. Whereas arterial hypertension increases afterload to the left ventricle, obesity produces an increase in stroke volume and increases preload. As a result of this double burden, the heart adapts with eccentric left ventricular hypertrophy. Contractility becomes impaired early in the course of obesity hypertension, and ventricular ectopy is observed. As a consequence, the obese hypertensive patient is at a high risk for congestive heart failure and sudden death. Despite the synergistic effects of obesity and hypertension on the heart, patients appear to be relatively protected from nephrosclerosis and coronary artery disease. These epidemiologic observations are supported by the pathophysiologic changes that take place in obesity hypertension. At any given level of arterial pressure, cardiac output and renal blood flow are elevated in obese hypertensive patients, whereas systemic and renal vascular resistance are decreased when compared to lean hypertensive patients. Because total peripheral resistance is considered the hemodynamic hallmark of arterial hypertension, systemic vascular complications may be less pronounced in obesity hypertension. Weight loss decreases preload, afterload to the left ventricle, and the sympathetic drive to the heart. Protecting the heart from these hypertrophic stimuli should be a major goal of preventive cardiology.

Essential hypertension. Matching pathophysiology and pharmacology

The underlying pathophysiologic mechanisms that elevate arterial pressure differ according to the patient's age, adipose body mass, and race. However, these mechanisms represent the extremes of a continuum, and overlap among them can be encountered in some patients. A few simple clinical clues allow the physician to identify whether an increase in cardiac output, total peripheral resistance, or both is the predominant mechanism in a given patient. Antihypertensive therapy should be aimed not only at lowering arterial pressure but also, more importantly, at ameliorating the concomitant pathophysiologic abnormality. A beta-adrenoreceptor blocker is the initial drug of choice in young patients with "cardiogenic hypertension." In middle-aged patients, cardiac output is usually normal and elevated total peripheral resistance becomes the hemodynamic culprit. In these patients, an angiotensin-converting enzyme (ACE) inhibitor, antiadrenergic drug, or calcium channel blocker should be given to lower total peripheral resistance without affecting cardiac output. In elderly patients, the burden on the heart should be lessened by use of an agent that lowers preload and afterload, such as an ACE inhibitor or certain of the calcium blockers. In obese patients in whom intravascular volume is expanded and in most black patients, the initial antihypertensive agent of choice remains a thiazide diuretic unless left ventricular hypertrophy is present.

Relative tachycardia in ambulant children with borderline hypertension

Borderline hypertensives who demonstrate tachycardia have a tendency toward the development of essential hypertension. However, the documentation of tachycardia in previous studies has been generally based on brief periods of observation. In the present study, we measured heart rates through a 24-hour period in 16 ambulatory mildly hypertensive subjects (ages 5 to 23 years). When compared with normal matched controls, significantly (p less than 0.05) higher heart rates were observed during the waking periods (99 +/- 9 vs 90 +/- 11) and sleep periods (72 +/- 12 vs 62 +/- 7). Similar observations were also made for 24 hours (90 +/- 8 vs 79 +/- 8). In addition, hypertensives also demonstrated thickened (during diastole) left ventricular posterior wall (0.96 +/- 0.17 vs 0.85 +/- 0.13 cm; p less than 0.05) and interventricular septum (0.98 +/- 0.17 vs 0.84 +/- 0.19 cm; p less than 0.05). It is suggested that tachycardia may be an early manifestation of borderline hypertension in children.

Use of diuretic agents in obese or black patients with systemic hypertension

Any increase in arterial pressure is the result of either an increase in cardiac output, an increase in total peripheral resistance or a combination of the two. Hypertension is not a homogeneous disease, however, and different mechanisms may be operative during the life span of the patient. Hypertension in the young, nonobese patient is usually hemodynamically characterized by high cardiac output, normal to slightly contracted intravascular volume and numerically normal total peripheral resistance. In contrast, hypertension in the middle-aged or elderly patient is usually hemodynamically characterized by normal to low cardiac output, contracted intravascular volume and high total peripheral resistance. Two further subgroups of hypertensive patients can be identified: obese patients, whose hypertension is characterized by high cardiac output, expanded intravascular volume and normal or low total peripheral resistance, and black patients, whose hemodynamic and fluid volume findings are similar to those of their white counterparts, but who tend to have lower heart rates and greater responsiveness to intravascular volume depletion than white hypertensive subjects. A rational therapeutic approach to essential hypertension should take into account these variable pathophysiologic features. Thiazide diuretics continue to be appropriate and generally well-tolerated choices for initial antihypertensive therapy in obese or in black patients. Many obese patients or black patients, however, are likely to develop early left ventricular (LV) hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular pathophysiology of essential hypertension: a clue to therapy

Arterial hypertension is by definition a haemodynamic disorder. At least 3 different subsets of cardiovascular pathophysiological features can be identified in so-called essential hypertension: The young lean patient characterised by an elevated cardiac output and renal blood flow, elevated plasma renin activity and circulating catecholamine levels, as well as symptoms and signs of hyperadrenergic hypertension. The elderly patient characterised by a low cardiac output often with left ventricular hypertrophy, elevated total peripheral resistance, nephrosclerosis, and symptoms and signs of target organ disease. The obese patient (and to a lesser degree the black patient) characterised by expanded fluid volume state, elevated cardiac output, a normal to low total peripheral resistance, and symptoms and signs of volume overload. To initiate antihypertensive therapy, the drug of choice in the young patient is a beta-adrenergic receptor blocker; in the elderly it is a haemodynamic vasodilator (anti-adrenergic drug, slow channel calcium blocker, or converting enzyme (ACE) inhibitor), and in black or obese patients it remains a thiazide diuretic. Enalapril, a new ACE inhibitor is indicated as a first-step agent in the great majority of hypertensive patients in whom the elevated arterial pressure should be reduced by a decrease in total peripheral resistance, without compromising systemic or regional blood flow. In contrast to other antihypertensive agents, enalapril will lower preload and afterload to the left ventricle while improving systemic and regional flow in elderly patients with latent or manifest congestive heart failure.

Obesity in hypertension: how innocent a bystander?

Hypertension and obesity frequently coexist in the same patient. However, the two disorders disparately affect cardiovascular function and structure. The presence of obesity significantly affects hypertensive target organ involvement. On one hand, obesity may tend to mitigate the harmful effects of a chronically elevated total peripheral and renal vascular resistance and lessen end-organ damage such as nephrosclerosis in essential hypertension. However, since both obesity and hypertension increase cardiac workload, although by different mechanisms, their presence in the same patient results in a double burden to the left ventricle. Congestive heart failure, sudden death, and coronary heart disease are common sequelae of obesity hypertension. Weight loss reduces arterial pressure by a decrease in intravascular volume and cardiac output associated with a fall in sympathetic activity. Intervention in obesity hypertension diminishes the dual hemodynamic burden imposed on the heart and becomes therefore a major objective in the prevention and treatment of heart disease.

Evidence for altered vascular reactivity in sodium-sensitive young subjects with borderline hypertension

To assess mechanisms associated with the pressor effects of a high sodium diet in susceptible individuals, the hemodynamic and hormonal effects of sodium depletion and repletion were studied in 33 normal subjects and 30 subjects with borderline hypertension. The hypertensive group had significantly higher mean arterial pressure, weight, hematocrit, and upright plasma renin activity. Forearm hemodynamics were measured during periods of ad lib diet, 10 mEq, and 200 mEq sodium diet. The fall in forearm resistance during reactive hyperemia was inversely related to mean arterial pressure at rest (R = .400, p less than .005) and rose significantly in hypertensive subjects during salt depletion, 39 +/- 3.6 to 61 +/- 6.1 mmHg/ml/min/100 g (p less than .05). Sodium sensitivity in either normotensive or borderline hypertensive subjects was defined as an increase in mean blood pressure of more than 5% when sodium repleted. The individuals who were sodium sensitive had a higher forearm vascular resistance during sodium depletion than those who were sodium resistant, 67 +/- 10.5 versus 45 +/- 4.1 mm/ml/min/100 g (p less than .03). We conclude that young individuals with borderline hypertension already have alterations in vascular reactivity. This trait is shared by normotensive individuals whose blood pressure rises in response to sodium.

Natural history of borderline hypertension in the Hisayama community, Japan--I. The relative prognostic importance of transient variability in blood pressure

Long-term prognosis of borderline hypertensives was studied in a prospective population survey carried on since 1961 in the town of Hisayama, Japan. Five consecutive BP recordings on 1621 subjects aged 40 and over were obtained at entry, and the variability in BP between the first and fifth readings was taken into account when classifying the subject into categorical groups. Even with an estimated variability in BP in several measurements on one occasion, a large fluctuation in BP was observed in both the borderline hypertensives and the normotensives. Borderline hypertensives with a transient elevation in BP more frequently died from cardiovascular disease than did those without BP elevation, as estimated by the long-term cumulative mortality. However, there was no difference in the frequency of hypertension-related organ damage between these two groups at entry.

R-wave amplitude change during aerobic exercise in hypertensive adolescents after treatment

This study attempts to determine whether the blunted reduction in R-wave amplitude during progressive aerobic exercise observed in adolescents with systemic hypertension could be altered by pharmacologic therapy to reduce blood pressure. Twenty-nine hypertensive adolescents were randomly assigned to treatment with either a diuretic, hydrochlorothiazide, or a centrally acting agent, clonidine. After 16 weeks of therapy, casual blood pressure was significantly reduced in both groups. Repeat exercise stress testing on therapy demonstrated a significant change in R-wave response. In both treatment groups the change in R-wave amplitude during exercise corresponded with the R-wave response pattern observed in normotensive control subjects. These observations indicate that the altered R-wave amplitude response to exercise observed in young hypertensive subjects is reversible and suggest that the altered R-wave response before treatment is related to a higher vascular resistance.

Changes in R wave amplitude during aerobic exercise stress testing in hypertensive adolescents

The change in R wave amplitude during progressive aerobic exercise was studied in hypertensive adolescent boys. A comparable control group consisted of normotensive adolescent boys matched for age, body size and race. Twenty-four normotensive and 22 hypertensive subjects exercised to exhaustion on a treadmill utilizing the Bruce protocol. Blood pressure and heart rate were monitored during exercise and recovery. The change in R wave amplitude in a lead V5 electrocardiogram was determined at each level of exercise. The normotensive group demonstrated a progressive increase in systolic pressure, heart rate and rate-pressure product (heart rate x systolic pressure) during exercise and a progressive decrease in R wave amplitude with a significant correlation of R wave change versus the cardiac response variable (p less than 0.001). Hypertensive subjects manifested a greater increase in systolic pressure, heart rate and rate-pressure product during exercise with no decrease in R wave amplitude until the exercise end point. The difference in R wave response to progressive exercise in the two groups was significant (p less than 0.01). A variation in myocardial function in hypertensive adolescents as demonstrated by a difference in R wave response to exercise may reflect a level of peripheral vascular resistance greater than that of normotensive control subjects.