Effect of leg exercise training on vascular volumes during 30 days of 6 degrees head-down bed rest

Abstract

Plasma and red cell volumes, body density, and water balance were measured in 19 men (32-42 yr) confined to bed rest (BR). One group (n = 5) had no exercise training (NOE), another near-maximal variable-intensity isotonic exercise for 60 min/day (ITE; n = 7), and the third near-maximal intermittent isokinetic exercise for 60 min/day (IKE; n = 7). Caloric intake was 2,678-2,840 kcal/day; mean body weight (n = 19) decreased by 0.58 +/- 0.35 (SE) kg during BR due to a negative fluid balance (diuresis) on day 1. Mean energy costs for the NOE, and IKE, and ITE regimens were 83 (3.6 +/- 0.2 ml O2.min-1.kg-1), 214 (8.9 +/- 0.5 ml.min-1.kg-1), and 446 kcal/h (18.8 +/- 1.6 ml.min-1.kg-1), respectively. Body densities within groups and mean urine volumes (1,752-1,846 ml/day) between groups were unchanged during BR. Resting changes in plasma volume (ml/kg) after BR were -1.5 +/- 2.3% (NS) in ITE, -14.7 +/- 2.8% (P less than 0.05) in NOE, and -16.8 +/- 2.9% (P less than 0.05) in IKE, and mean water balances during BR were +295, -106, and +169 ml/24 h, respectively. Changes in red cell volume followed changes in plasma volume. The significant chronic decreases in plasma volume in the IKE and NOE groups and its maintenance in the ITE group could not be accounted for by water balance or by responses of the plasma osmotic, protein, vasopressin, or aldosterone concentrations or plasma renin activity. There was close coupling between resting plasma volume and plasma protein and osmotic content.(ABSTRACT TRUNCATED AT 250 WORDS)

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

“…Contrary to actual or simulated microgravity studies testing isotonic, isokinetic and endurance exercise, thighcuffs or LBNP, using the FED (Convertino 1996;Engelke et al 1996;Gharib et al 1992;Greenleaf et al 1989Greenleaf et al , 1992Maillet et al 2000;Millet et al 2000) did not lessen the hypovolemia. The frequency of the exercise regimen and the exertion it required might be responsible for this lack of effect.…”

“…The frequency of the exercise regimen and the exertion it required might be responsible for this lack of effect. Indeed, the PV loss was mitigated either with daily isotonic leg exercise training of 1 h per day, 5 days per week (Greenleaf et al 1992) or with a multistage graded exercise bout to exhaustion, using a Quinton supine cycle ergometer applied 24 h before the end of a 16-day exposure to HDT (Engelke et al 1996).…”

“…The inefficiency of this countermeasure could not be attributed solely to its lack of effect on PV. Efficient counter-measures known to prevent PV loss have previously been shown to either improve orthostatic tolerance (Engelke et al 1996) or have little effect (Greenleaf et al 1992). To efficiently prevent post-HDT orthostatic intolerance, PV improvement should be associated with other improvements in vasoconstrictive capacity, baroreflex sensitivity, venous compliance, vestibular system alterations and cerebral perfusion.…”

Isovolemic Hemodilution Alters the Ratio of Whole-Body to Large-Vessel Hematocrit (F-Cell Ratio)

“…Since in most studies total blood vol ume is calculated from either plasma or red-cell volume and the peripheral hematocrit, these authors correct the hema tocrit for the f-cell phenomenon by applying a correction fac tor of 0.89-0.91 (e.g. [5][6][7]). However, this correction factor is an average value derived from measurements using both red cell and plasma markers [8,9], As stated in the 'Recommend ed methods for measurement of red-cell and plasma volume' by the International Committee for Standardization in Hae matology.…”

Cardiovascular Disorders

“…Moreover, performing higher-level exercise during flight seemed to have had a protective effect on the increase in heart rate and the fall in pulse pressure that are experienced by all crewmembers upon return (Figure 16.6). Further research is needed to determine whether this effect was due to a change in the carotid-cardiac baroreflex set point [275,318], altered splanchnic vasoconstriction [319], increased plasma volume [315,320], or decreased venous capacitance caused by increases in lower-extremity muscle tone and interstitial volume [321,322]. Regardless, these results suggest that inflight exercise [317,323] may be an important component of a comprehensive orthostatic countermeasures program for both long-and short-duration missions [324].…”