Fluid and electrolyte shifts during bed rest with isometric and isotonic exercise

Abstract

Fluid and electrolyte shifts were measured in seven men (19-21 yr) during three 2-wk bed rest (BR) periods, each of which was separated by a 3-wk ambulatory recovery period. During two of the three BR periods they performed isometric exercise and isotonic exercise. No prescribed exercise was given during the other BR period. On day 4 of BR, plasma volume decreased (P less than 0.05) 441 ml (-12.6%) with no exercise, 396 ml (-11.3%) with isometric, and 262 ml (-7.8%) with isotonic exercise; the decreases (NS) of extracellular volume were -4.4%, -2.6%, and -2.7%, respectively. By day 13 of BR, plasma volume stabilized at the lower level with isometric and isotonic exercise and continued to decline with no exercise; but the extracellular volume returned to or above control levels due to an overshoot of the interstitial volume of +320 to +430 ml (2.0-2.7%) that was about equal to the plasma volume loss. During BR there were isocontent losses from the plasma of protein, albumin, globulin, urea N2, uric acid, creatinine, Na, Cl, osmolarity, P, and glucose that were not influenced by either exercise regimen. However, the blood, red blood cell, and plasma volumes, and the Ca and K contents were stabilized during BR by both exercise regimens. The results suggest that during BR, preservation of the extracellular volume takes precedence over maintenance of the plasma volume, and this mechanism is independent of the effects of isometric or isotonic exercise.

Prevention of bedrest-induced physical deconditioning by daily dobutamine infusions. Implications for drug-induced physical conditioning.

“…In addition, pharmacologic interruption of deconditioning has major relevance in a number ofhuman con- 1638 Sullivan et al ditions associated with physical inactivity (e.g., major illness, fractures, paralysis, space travel). Bedrest deconditioning elicits a number of pathophysiologic events and adaptations (7)(8)(9)(10)(11)(22)(23)(24), many of which were pro- duced in the bedrest-saline control group of this study. Exercise capacity, as assessed by duration, workload, and oxygen consumption at maximal exercise, decreased.…”

“…Orthostatic intolerance occurs after prolonged bedrest (8,10,24). We attempted to alleviate or minimize this response by allowing all subjects to sit in bed as desired and to sit in a dependent position (bedside chair or bicycle) for 2 h/d.…”

“…The 24 subjects were randomized (random number system) into three treatment groups: (a) saline control (n = 8), (b) dobutamine (n = 8), and (c) maintenance exercise control (n = 8). The treatments, administered on days 3-19 by the nursing personnel of the research center in conjunction with one ofthe investigators (Dr. Sullivan), lasted 2 h each day (8:00 to 10:00 a.m.).…”

Does resistance exercise prevent body fluid changes after a 90-day bed rest?

“…To prevent these perturbations in fluid homeostasis, several countermeasures have been tested during actual and simulated weightlessness. Many of these, such as lower body negative pressure (LBNP) (Gharib et al 1992) and ''thighcuff'' devices (Millet et al 2000), as well as various exercise regimens (Convertino 1996;Engelke et al 1996;Greenleaf et al 1977Greenleaf et al , 1989Maillet et al 1996), tend to have a beneficial effect on PV and thus on the orthostatic tolerance. Nevertheless, even though a normal PV is required to prevent orthostatic intolerance it should be associated with greater circulating levels of norepinephrine, efficient vasoconstrictor mechanisms and the baroreflex (Engelke et al 1996).…”

Effect of fludrocortisone acetate in patients with subarachnoid hemorrhage.

“…22 We expressed the results as total plasma volume and calculated the percentage change between the second (Day 6) and the first measurements and between the third (Day 12) and the first measurements. Because bed rest alone may cause a certain decrease in plasma volume after 1 week, 23 we considered only a drop in plasma volumes of >10% relevant, and we referred only to this as "decreased plasma volume. "…”