Hemodynamic characteristics of primary aldosteronism

Hemodynamic responses to DOCA in young pigs

Hemodynamic variables were measured in 20 young pigs; thirteen received subcutaneous implantations of desoxycorticosterone acetate (DOCA) impregnated in Silastic strips, seven received implants of Silastic strips alone and served as controls. No salt was added to the standard diet of either group. Mean arterial pressure (MAP) rose in a regular pattern in the DOCA-treated pigs, reaching on the average a level significantly greater than that of the control group 48 hours after the implantation. Pressure continued to rise, reaching a plateau 38% above that of the preimplant value 2 weeks later. In some pigs the MAP elevation was caused by an increase in cardiac output (CO); in others it was caused by an increase in total peripheral resistance (TPR). An increase in central venous pressure occurred in many DOCA-treated pigs regardless of whether the increase in MAP was caused by an increase in CO or in TPR. The results indicate that it is arterial pressure per se that is the regulated variable in this model of mineralocorticoid hypertension. The regulating system, whether it resides in the kidney or in the central nervous system, elevates pressure by effecting increases in either CO or TPR.

Is arterial pressure the sole factor responsible for hypertensive cardiac hypertrophy?

Increased arterial pressure is obviously the major stimulus to cardiac hypertrophy in hypertension. However, different studies suggest that in addition to the pressure load, other factors could play participating roles in determining the degree of ventricular hypertrophy in response to the hypertensive disease as well as the degree of its reversal after control of arterial pressure. These other mechanisms include genetic factors and concimitant processes such as aging and the presence of cardiomyopathy or other disease. Two neurohumoral influences, namely, the adrenergic and the renin-angiotensin systems, may also participate, and the early evidence supporting these possible contributing factors is cited. Further studies are needed to determine the relative importance of each of these factors in different types of hypertension and in their response to different modes of antihypertensive therapy.

Mineralocorticoid-induced hypertension in patients with orthostatic hypotension

The mechanism of recumbent hypertension induced by fludrocortisone was studied in seven patients with orthostatic hypotension. All showed increases in blood pressure in the recumbent and standing positions, and hypertensive levels were achieved on recumbency in four of them. Hypertensive retinopathy developed in two patients and cardiomegaly in one. Initial blood-pressure elevations were associated with sodium retention and plasma-volume expansion. However, with long-term treatment, plasma volume decreased to control levels despite further blood-pressure increases. Treatment did not affect plasma levels of catecholamines but did enhance pressor responsiveness to infused norepinephrine in some subjects. Hemodynamic studies indicated that hypertension in the recumbent position was related to increases in total peripheral-vascular resistance and not to changes in cardiac output. Clinically, hypertension in the recumbent position is an important risk of fludrocortisone treatment in patients with orthostatic hypotension. This unusual model of chronic mineralocorticoid-induced hypertension is not volume dependent but is related to increased peripheral-vascular resistance.

The pressor response to angiotensin II in patients with low renin essential hypertension

The etiology of low renin essential hypertension (LREH) has not been established with certainty, but mineralocorticoid excess has been implicated frequently in its pathogenesis. The finding of several investigators of a normal exchangeable sodium space and extracellular fluid volume, however, does not support this hypothesis. To evaluate the possible role of sodium and water retention in LREH, the pressor response to infused angiotensin II (A II) was determined and compared to that of normal subjects and that of subjects with normal renin essential hypertension (NREH). This approach was based on the known suprasensitivity of vascular receptors to A II in situations in which sodium and water compartments are expanded as they are, for example, in proven hypermineralocorticoid states such as primary aldosteronism. In this study, we found that subjects with LREH demonstrated no increased pressor response to graded doses of A II; this suggests that LREH is not primarily mediated by sodium and water retention.

Altered blood volume regulation in sustained essential hypertension: a hemodynamic study

Cardiac and renal hemodynamics and total blood volume were determined in 28 normal subjects and 60 patients with untreated essential well-established hypertension. Endogenous creatinine clearance was within normal ranges and sodium intake was 110 mEq/day. A significant negative volume-resistance relationship was observed both in normal subjects (P less than 0.005) and hypertensive patients (P less than 0.001). In comparison with the normal curve, the hypertensive curve has two characteristics: 1) the curve was reset on the right-hand side and, 2) the slope was significantly shallower, indicating a reduced ability to decrease the volume per unit rise in resistance. By using the normal curve as a reference system, a quantitative evaluation of the blood volume disturbance was proposed. In hypertensives, the value of the total peripheral resistance could correspond to two different values of the total blood volume: the real value and the theoretical value extrapolated from the normal curve. The difference between the two values was called "relative variation in blood volume" and was used as a mathematical model. In hypertensives, the real blood volume was significantly reduced (P less than 0.001) while a significant "relative increase" in total blood volume was observed (P less than 0.001). This "relative increase" was directly correlated with the diastolic arterial pressure (r=0.064; P less than 0.00001) and was inversely related to the renal blood flow (r=-0.54; P less than 0.0001) and the creatinine clearance. Such correlations were not observed with the real blood volume. In agreement with Guyton's theory, this study highly suggests that sustained hypertension is related to an increase in blood volume relative to the capacity of the circulatory system and that a renal defect is necessary for the blood pressure elevation mechanism.

Hyperkinetic heart in severe hypertension: a separate clinical hemodynamic entity

A long-term study of established hypertension helped identify a well defined group of 10 patients who differed both clinically and hemodynamically from 59 patients with the more frequent form of this disease. Their cardiac output was significantly increased (P less than 0.001) despite a severe elevation of arterial pressure (average 212/125 mm Hg plus or minus 13.5/7.3[standard error[). All had labile hypertension of long standing (16.2 years average) that was difficult to control and always symptomatic; in all, the diagnosis of pheochromocytoma had to be specifically excluded. Increased myocardial contractility was suggested by (1) significant elevation of the rate of rise of isovolumic pressure (P less than 0.001), and (2) high ratio of cardiac output to cardiopulmonary volume (P less than 0.005). Beta adrenergic blockade with propranolol helped to alleviate symptoms and to control tachycardia but failed by itself to reduce arterial pressure.

Mechanism of immediate hemodynamic effects of chlorothiazide

The mechanism of the immediate hemodynamic effects of intravenous chlorothiazide (25 mg. per kilogram) was studied in 22 anesthetized open-chest dogs. Within 20 minutes after administration, cardiac output and stroke volume significantly fell; this was associated with decreased central venous and left ventricular end-diastolic pressures. That these hemodynamic effects were caused by, and dependent upon, volume loss through diuresis (eightfold increase in urine volume) was shown: by a return of these measurements to control levels when the volume loss (by diuresis) was corrected with 6 per cent Dextran; by prevention of the hemodynamic changes in chlorthiazide-treated dogs previously prepared with ureterocaval anastomosis; and by confirming these same hemodynamic effects by quantitatively equivalent hemorrhage. Thus, the immediate diuresis produced by chlorothiazide resulted in a contracted plasma volume (increased hematocrit and serum protein concentration) which, in turn, diminished cardiac venous return, central filling pressures, stroke volume, and cardiac output. There was no evidence demonstrated to indicate any direct myocardial effect or peripheral venodilation induced by thiazide.

Cardiac hypertrophy in spontaneously hypertensive rats

Ventricular weight in spontaneously hypertensive rats (F26 generation, Okamoto-Aoki strain) was significantly higher ( P < 0.001) than that in body weight-matched American Wistar and Kyoto-Wistar normotensive rats, not only among older groups of rats but also among younger groups that had not developed significant hypertension. Deoxyribonucleic acid (DNA) concentration in ventricular muscle was not different from normal in the youngest group ( P < 0.4) but was significantly reduced in the older spontaneously hypertensive rats ( P < 0.01). Plasma renin activity was significantly increased in younger spontaneously hypertensive rats before the development of established hypertension; moreover, ventricular weight and plasma renin activity were significantly correlated in younger rats ( r = 0.788, P < 0.005 for all rats, r = 0.644, P < 0.01 for spontaneously hypertensive rats). Antihypertensive therapy with either α-methyldopa or hydralazine reduced blood pressure, especially in hypertensive rats; however, ventricular weight was reduced by methyldopa ( P < 0.01) but not by hydralazine. Plasma renin activity was reduced by methyldopa but increased by hydralazine ( P < 0.01). DNA concentration was reversed toward normal by methyldopa but not by hydralazine. Similar results were obtained when methyldopa and hydralazine were given to younger rats to prevent hypertension. The changes in ventricular weight with the onset of hypertension and with its reversal or its prevention suggest that blood pressure might not be the sole factor contributing to cardiac hypertrophy in the spontaneously hypertensive rat and that the renin-angiotensin system might play a permissive role enhancing myocardial hypertrophy.