Hemodynamic lesions in hypertension

Effects of voluntary exercise on blood pressure, angiotensin II, aldosterone, and renal function in two-kidney, one-clip hypertensive rats

Spontaneous dynamic exercise promotes sympathoinhibition and decreases arterial pressure in two-kidney, one-clip (2K-1C) hypertensive rats. Renal sympathetic nerves stimulate renin secretion and increase renal tubular sodium reabsorption. We hypothesized that daily voluntary wheel running exercise by 2K-1C rats will decrease mean arterial pressure (MAP), plasma angiotensin II (Ang II), and aldosterone as well as normalize urinary sodium and potassium excretion independent of changes in glomerular filtration rate (GFR). Five-week-old male Sprague Dawley rats underwent sham clipping (Sham) or right renal artery clipping (2K-1C). Rats were randomized to standard caging (SED) or cages with running wheels (EX). After 12 weeks, rats were assigned to either collection of aortic blood for measurement of Ang II and aldosterone or assessment of inulin clearances and excretory function. Running distances were comparable in both EX groups. MAP was lower in 2K-1C EX vs 2K-1C SED rats (P<0.05). Plasma Ang II and aldosterone were significantly higher in 2K-1C SED rats and decreased in 2K-1C EX rats to levels similar to Sham SED or Sham EX rats. Clipped kidney weights were significantly lower in both 2K-1C groups, but GFR and urine flow rates were no different from right and left kidneys among the four groups. Total and fractional sodium excretion rates from the unclipped kidney of 2K-1C SED rats were higher vs either Sham group (P<0.05). Values in 2K-1C EX rats were similar to the Sham groups. Potassium excretion paralleled sodium excretion. These studies show that voluntary dynamic exercise in 2K-1C rats decreases plasma Ang II and aldosterone, which contribute to the lower arterial pressure without deleterious effects on GFR. The effects on sodium excretion underscore the impact of pressure natriuresis despite elevated plasma Ang II and aldosterone in sedentary 2K-1C rats. In contrast, potassium excretion is primarily regulated by circulating aldosterone and distal sodium delivery.

Preeclamptic pregnancy is associated with increased sympathetic and decreased parasympathetic control of HR

Previous work from our laboratory using heart rate variability (HRV) has demonstrated that women before menopause have a more dominant parasympathetic and less effective sympathetic regulations of heart rate compared with men. Because it is still not clear whether normal or preeclamptic pregnancy coincides with alternations in the autonomic functions, we evaluated the changes of HRV in 17 nonpregnant, 17 normotensive pregnant, and 11 preeclamptic women who were clinically diagnosed without history of diabetic neuropathy, cardiac arrhythmia, and other cardiovascular diseases. Frequency-domain analysis of short-term, stationary R-R intervals was performed to evaluate the total variance, low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF; 0.15-0.40 Hz), ratio of LF to HF (LF/HF), and LF in normalized units (LF%). Natural logarithm transformation was applied to variance, LF, HF, and LF/HF for the adjustment of the skewness of distribution. We found that the normal pregnant group had a lower R-R value and HF but had a higher LF/HF and LF% compared with the nonpregnant group. The preeclamptic group had lower HF but higher LF/HF compared with either the normal pregnant or nonpregnant group. Our results suggest that normal pregnancy is associated with a facilitation of sympathetic regulation and an attenuation of parasympathetic influence of heart rate, and such alterations are enhanced in preeclamptic pregnancy.

Differential therapy of hypertensive heart disease

Hypertensive damage to the target organ "heart" comprises the sum and interactions of the cardiac organ manifestations of arterial hypertension such as myocardial hypertrophy and disease of large and small coronary arteries. Because the prognosis of arterial hypertension is determined to a considerable extent by these cardiac complications, the aim of treatment of hypertensive heart disease is reversal of the myocardial hypertrophy in order to prevent later progression to hypertensive heart failure. A further goal of therapy is reversal of the hypertensive small coronary disease in order to improve the coronary reserve. Once the stage of hypertensive heart failure is reached, the principles of medical management of heart failure with digitalis, diuretics and angiotensin-converting enzyme inhibitors apply. Whereas the evidence that regression of hypertrophy can be induced by suitable antihypertensive drugs (calcium channel blockers of the dihydropyridine type, angiotensin-converting enzyme inhibitors and sympathicolytic substances) is practically conclusive, clinical evidence of reversal of the hypertensive disease of small coronary arteries has yet to be provided. Moreover, to what extent the prognosis of hypertensive heart disease can be improved by reversal of hypertrophy is still unknown.

Hypertension

An estimated 58 million Americans are at increased risk of morbidity and premature death due to high blood pressure (BP) and require some type of therapy or systematic monitoring. This article focuses on recent advances in our understanding of the pathogenesis of hypertension, new approaches to the diagnosis and treatment of secondary hypertension, and current views of the most appropriate nonpharmacologic and pharmacologic therapy for essential hypertension. In view of the extremely high prevalence of the disorder, emphasis is placed on efficient and cost-effective strategies for diagnosing and managing the hypertensive patient. Recent evidence indicates that nonpharmacologic therapy, including dietary potassium and calcium supplements, reduction of salt intake, weight loss for the obese patient, regular exercise, a diet high in fiber and low in cholesterol and saturated fats, smoking cessation, and moderation of alcohol consumption produces significant sustained reductions in BP while reducing overall cardiovascular risk. Accordingly, nonpharmacologic antihypertensive therapy should be included in the treatment of all hypertensive patients. In persons with mild hypertension, nonpharmacologic approaches may adequately reduce BP, thereby avoiding the expense and potential side effects of drug therapy. In patients with more severe hypertension, nonpharmacologic therapy, used in conjunction with pharmacologic therapy, can reduce the dosage of antihypertensive medications necessary for BP control. Patients treated with nonpharmacologic therapy only should be followed closely, and if BP control is not satisfactory, drug therapy should be added. The large number of drugs available for use in hypertension treatment, coupled with our rapidly expanding knowledge of the pathophysiology of hypertension and of the adverse effects of these drugs in individual patient groups, make it possible to individualize antihypertensive treatment. When used as monotherapy, most agents effectively lower BP in the majority of patients with mild or moderate essential hypertension. Thus, a single agent from one of four classes: diuretics, angiotensin-converting enzyme inhibitors, calcium channel blockers, and beta-adrenergic blockers, usually provides effective BP control with minimal side effects in most patients. Therapy should be initiated with the agent most likely to be effective in BP lowering and best tolerated. If the initial agent is ineffective at maximal recommended therapeutic doses or has undue side effects, an alternative agent from another class should be tried. When monotherapy is unsuccessful, a second agent, usually of a different mechanism of action, should be

Hyperkinetic hemodynamic pattern in some borderline hypertension: differential responses to alpha and beta agonists

Twenty eight male borderline hypertensive patients(BH), mean age of 19.72 +/- 2.80 years, were studied and matched with 28 normal controls (NC). Alpha-adrenergic responsiveness was estimated with DPD15 (the dosage of neosynephrine required for an increase of diastolic pressure of 15mmHg); beta-adrenergic responsiveness with CD25 (the dosage of isoproterenol required for an increase of heart rate of 25 beats/minute). Using CD25 of 1.0ug (mean of the NC), the BH could be subdivided into two specific types: 13 patients (46%) whose CD25 less than 1.0 ug, 0.50 +/- 0.24 (m +/- SD) had a hyperkinetic pattern; the remaining 15 patients (54%) whose CD25 greater than 1.0ug, 1.76 +/- 0.32 (m +/- SD), had a normokinetic one. Values of DPD15 of the two types were comparable. Cardiac index (CI, L/min/M2) and total peripheral resistance (TPR, dynes/sec/cm-5) of the two types manifested significant differences, both p less than 0.001. When plotting CI and TPR versus CD25, good correlations were obtained. In the BH group, the coefficient r was -0.73 between CI and CD25, + 0.70 between TPR and CD25; correlations were poor when plotting versus DPD15. Similar correlations also happened in the NC. The present study suggests that coexistence of two different hemodynamic patterns may be due to the imbalance resulted from the interaction between alpha-adrenergic responsiveness and beta-adrenergic responsiveness.

Autonomic nervous dysfunction in severe pre-eclampsia

We evaluated autonomic nervous function in 14 subjects with severe pre-eclampsia and 11 subjects with normal third-trimester pregnancies using standard cardiovascular tests, i.e. heart rate responses to deep breathing and standing up, and blood pressure response to standing up. Both of the heart rate responses were lower in subjects with severe pre-eclampsia than in the control group (P less than 0.01 and P less than 0.001, respectively). Four subjects with severe pre-eclampsia had postural hypotension, defined as a systolic blood pressure fall of at least 30 mmHg on standing. Our results show that severe pre-eclampsia may be associated with autonomic nervous dysfunction. The inability to regulate heart rate and blood pressure in response to postural alterations may compromise the placental and renal blood flow in certain conditions, emphasising the importance of bed rest in severe pre-eclampsia.

The abnormal heart rate response to a deep breath in borderline labile hypertension: a sign of autonomic nervous system dysfunction

A group of patients with borderline or labile hypertension were prospectively recruited and asked to take a deep breath while lying supine and being monitored by electrocardiography. Their attenuated heart rate responses were sharply abnormal, demonstrating an excessively rapid rate throughout but without quickening on inspiration nor slowing with expiration. It is suggested that this further demonstrates inadequate autonomic control, sympathetic and parasympathetic, of the heart in labile hypertension and even at a moment when the patient's blood pressure is normal.

Erythrocyte acetylcholinesterase in essential hypertension

Red cell acetylcholinesterase activity (AChE) has been studied in 58 patients suffering from essential hypertension; diastolic blood pressure values were about 130 mm or higher in 45 patients (group A) and lower in 13 (group B). The very significant increase (p < 0.001) of AChE activity in group A has been forced by the severity of systemic lesions. Meanwhile, the AChE values have been slightly increased, but not statistically significant in the patients of group B. These results are supporting the hypothesis that the blood pressure control can be mediated or normalized, at least in part, by cholinergic mechanisms.

Total effective compliance, cardiac output and fluid volumes in essential hypertension

Total effective compliance, hemodynamic parameters, extracellular fluid volume, cardiopulmonary (CPBV) and total blood (TBV) volumes were determined in 32 men, including 14 normotensive controls and 18 sustained essential hypertensive patients. The effective compliance was calculated from the changes in central venous pressure recorded simultaneously with the changes in blood volume obtained after a rapid Dextran infusion. In normotensive controls, compliance was 2.08 +/- 0.09 ml/mm Hg/kg and was positively correlated with plasma (r = 0.79) and extracellular fluid (r = 0.84) volumes. In hypertensives, compliance was significantly reduced (1.49 +/- 0.06 ml/mm Hg/kg; P is less than 0.001) and was correlated negatively with the CPBV/TBV ratio (r = -0.75) and positively with the plasma volume/interstitial fluid volume ratio (r = 0.84). These results suggest that in normotensives, there is a regulatory mechanism between volume and compliance and that this contributes to maintaining filling pressure and cardiac output within normal ranges. In hypertensives, the reduced compliance could participate in the maintenance of normal values of cardiac output and extracellular fluid volume by influencing the partition of intravascular and extracellular fluid volumes.