The cardiovascular, endocrine and renal response of tetraplegic and paraplegic subjects to dietary sodium restriction.

Abstract

SUMMARY1. The effects of change from a high to low sodium diet upon renal sodium and water excretion and hormone responses were studied in patients with dissociated sympathetic control (DS, tetraplegic) and controls with sympathetic control largely intact (IS, paraplegic).2. Total and fractional urinary sodium excretion fell in response to sodium restriction in both groups, but the fall in fractional sodium excretion was greater in the DS group compared with the IS group (DS, 1-34+0-12 to 0-42+0-05%; IS, 0-96+0-08 to 0-52+0-06%).3. Supine mean arterial pressure fell during the low salt period in the DS group (80-2 + 2-7 to 74-4 + 2-3 mmHg) but was unaffected by salt restriction in the IS group (101 + 2-3 to 98-8 + 27 mmHg). In the DS group, creatinine clearance remained constant throughout the low salt period (103-7 + 79 to 98-3 + 97 ml min-), but fell during salt restriction in the IS group (1014 + 8-5 to 832 + 5 ml min-).4. Plasma renin activity was lower during salt loading in DS subjects but increased more rapidly and to higher levels in response to salt restriction (DS, 1021+142 to 4439+355; IS, 1765+269 to 3683+465pg angiotensinIml-1h-1). Plasma atrial natriuretic peptide concentration was higher in the DS group during salt loading and salt restriction (DS, 37-6 + 5-6 to 22 + 3-8; IS, 20-2 + 2-3 to 11 + 1-6 pg ml-').5. These results are consistent with the view that direct sympathetic control of the kidney is not essential for renal sodium conservation in response to dietary salt restriction but is likely to be involved in the haemodynamic and hormonal responses.

Reduced sodium output following acute spinal injury

“…This is supported by our previous findings 11 and by the increased levels of atrial natriuretic peptides in tetraplegic patients. 20 We believe that we have demonstrated that there is a problem particularly in tetraplegic patients that warrants further investigation. We hope that this study will point the way.…”

A sound night's rest may do no good in autonomic failure!

“…However, neurogenic orthostatic hypotension may be associated with, or complicate, a number of disorders where the primary disease process may help or hinder fluid balance. Thus, in patients with high spinal cord injuries, their brisk neuroendocrine and renin-angiotensin-aldosterone system responses may aid retention of salt and water [11], whereas in diabetic autonomic neuropathy, renal impairment may influence nocturnal and recumbency-induced polyuria. The studies of Omboni et al [6] therefore should be the stimulus to determining further, in a variety of other autonomic disorders causing orthostatic hypotension, if a sound night's rest may do good, or even harm !…”