The effect of posture and of congestion of the head on sodium excretion in normal subjects

Effects of bleeding on electrolyte excretion and on glomerular filtration

Removal of small amounts of blood from sitting subjects caused reduction of sodium excretion without alterations in creatinine clearance, or in apparent cardiac output (electrokymographic method). This reduction could be prevented by compression of the neck. The experiments support the concept of an homeostatic central mechanism which regulates the volume of extracellular fluid by altering sodium excretion. If such a mechanism exists it is apparently activated by changes in the volume of body fluids rather than by changes in cardiac output.

Regulation of vasopressin release in moderately severe essential hypertension

Vasopressin plasma concentrations have been measured in two groups of subjects, 13 moderate essential hypertensive patients without target organ damage and eight control normotensive subjects, before and after the assumption of the upright position, and intravenous infusions of hypotonic saline (0.45% NaCl, 0.25 ml kg-1 min-1 for 1 h) and hypertonic saline (100 mmol NaCl in 50 ml). Plasma vasopressin in recumbent baseline conditions was not significantly different in the two groups. Upright posture and hypertonic challenge augmented, while hypotonic saline reduced plasma vasopressin levels, which were not significantly different between the two groups. Plasma renin activity increased in the upright position, was reduced by administration of hypotonic saline and unaffected by hypertonic saline, with no differences between the hypertensives and normotensives. After hypertonic saline, urinary flow rate and urinary sodium excretion in the hypertensive group increased to values significantly (p less than 0.05) higher than in normotensive subjects. In conclusion our study excludes significant alteration of vasopressin regulation in moderate uncomplicated hypertension. In hypertensives although the response of vasopressin to an osmotic load is preserved, the data suggest that the renal handling of the osmotic load may be altered.

Renin stimulation by passive tilting: the influence of an anti-gravity suit on postural changes in plasma renin activity, plasma noradrenaline concentration and kidney function in normal man

Plasma renin activity (PRA), plasma noradrenaline concentration, heart rate, blood pressure, and clearances of para-aminohippurate and inulin were measured in twelve normal subjects (clearances in only three subjects) before and after 40 min of 60 degrees upright tilting. The tilting experiments were repeated after inflation of an anti-gravity suit to 60 mmHg on the lower extremities. Inflation of the anti-gravity suit caused an abolition of the postural PRA increase, a marked reduction of the postural increases in plasma noradrenaline and heart rate, and elimination of the decreases in pulse pressure, inulin and para-aminohippurate clearances and sodium excretion. The results suggest a decisive role of the sympathetic nervous system for postural renin increase, probably mainly activated by stretch receptors in the low-pressure cardiopulmoanry area.

Studies on water excretion following intravenous hydration and the administration of pitressin or nicotine in congestive heart failure

The diuretic response to intravenous infusions of 5 per cent glucose in water and the antidiuretic response to intravenous injections of nicotine salicylate and aqueous Pitressin, during maximal water diuresis, were studied in normal subjects and patients in congestive failure of varying severity. Patients in moderately severe congestive failure exhibited normal diuretic responses during the periods of intravenous hydration and normal antidiuretic responses following nicotine or Pitressin injections. Patients in more severe congestive failure failed to achieve comparable diuretic responses, following intravenous hydration; in the course of this, signs of increasing congestive failure developed, which were associated with further decrease in urine flows, at times, without any further decrease in renal hemodynamics. These studies confirm the impression that patients in moderate congestive failure have neither increased sensitivity to, nor reduced ability to, inactivate endogenous or exogenous antidiuretic hormone. In addition, the observation, that patients in more severe failure do not achieve adequate water diuresis during intravenous hydration, suggests that sustained production of antidiuretic production, independent of normal osmoreceptor control, may be contributing to their fluid retention.

Long-range observations of sodium exchange in patients with congestive heart failure

Long-term studies of sodium balance were made in three patients with congestive failure. The data indicate exchange of water and sodium between the intracellular and extracellular spaces. They suggest that a portion of the intracellular cation exists in a form which is not osmotically active. The term "quantometer" is applied to the previously described intracranial volume-regulating mechanism. An hypothesis is offered in which it is assumed that exhaustion of this quantometer may contribute to the retention of sodium as heart failure becomes manifest.

Effects of posture on renal excretion of sodium and chloride in orthostatic hypotension

Large decreases in the rates of sodium excretion, chloride excretion, and glomerular filtration were observed in patients with orthostatic hypotension when they assumed the upright posture following a period of recumbency. When they returned to the recumbent position, sodium excretion typically was not restored immediately in spite of immediate restoration of filtered sodium load. The decreased sodium excretion found to occur in patients with orthostatic hypotension when they are in the upright posture is considered to be due in part to the decreased filtered sodium load and in part to changes in tubular reabsorption that are independent of filtered sodium load.

The effect of posture on the excretion of water and sodium by patients with congestive heart failure

Four patients with congestive heart failure were studied in the sitting and the recumbent positions. After hypotonic loading maximal diuresis set in at six hours, as compared with three hours in the normal subjects. Heart failure patients never excreted more than 50 per cent of water intake in either position. Likewise, these patients never equalled sodium intake with urinary excretion of sodium. Sodium excretion in the two positions was approximately the same. Increase in venous pressure, lengthening of circulation time, decline of vital capacity, and decline of serum sodium concentration were noted after each investigation period. These results are interpreted as indicating that the previously postulated intracranial volume regulating center is either inactive or over-powered by a more powerful mechanism in the patient with congestive heart failure.

Effect of neck compression on sodium excretion in subjects with congestive heart failure

Previous studies on normal subjects have shown that neck compression causes increased urinary excretion of sodium in the sitting position, but has little or no effect in the recumbent position. In the present study, patients with congestive heart failure have exhibited no increase in urinary sodium excretion after neck compression.

Further studies on the effects of changes in the distribution of extracellular fluid on sodium excretion; observations following compression of the legs

Bandaging of the legs of sitting subjects resulted in an increase in the renal excretion of sodium which declined after the bandages were removed. Consistent results were not obtained in recumbent subjects. The findings appear to constitute further evidence that the distribution, rather than the total volume of extracellular fluids, has a regulatory action on sodium excretion.

The Distribution of Body Fluids In Congestive Heart Failure

The pathogenesis of congestive heart failure is discussed. Experimental evidence is cited to support the thesis that abnormalities in the distribution of body fluids may affect circulatory and renal function, and hence may be a cause as well as an effect in the complex sequence of events leading to the congestive state. Emphasis is placed upon alterations in cellular metabolism which may lead to such disturbances in body fluids and so through various mechanisms, cellular, humoral, and circulatory, may modify the volume regulation of the body.