DI-5-CUFFS: Venoconstrictive Thigh Cuffs Limit Body Fluid Changes but Not Orthostatic Intolerance Induced by a 5-Day Dry Immersion

Abstract

Venoconstrictive thigh cuffs are used by cosmonauts to ameliorate symptoms associated with cephalad fluid shift. A ground simulation of microgravity, using the dry immersion (DI) model, was performed to assess the effects of thigh cuffs on body fluid changes and dynamics, as well as on cardiovascular deconditioning. Eighteen healthy men (25-43 years), randomly divided into two groups, (1) control group or (2) group with thigh cuffs worn 10 h/day, underwent 5-day DI. Cardiovascular responses to orthostatic challenge were evaluated using the lower body negative pressure (LBNP) test; body fluid changes were assessed by bio-impedance and hormonal assay; plasma volume evolution was estimated using hemoglobin-hematocrit; subjective tolerance was assessed by questionnaires. DI induced a decrease in plasma volume of 15-20%. Reduction in total body water of 3-6% stabilized toward the third day of DI. This reduction was derived mostly from the extracellular compartment. During the acute phase of DI, thigh cuffs limited the decrease in renin and the increase in N-terminal prohormone of brain natriuretic peptide (NT-proBNP), the loss in total body water, and tended to limit the loss in calf volume, extracellular volume and plasma volume. At the later stable phase of DI, a moderate protective effect of thigh cuffs remained evident on the body fluids. Orthostatic tolerance time dropped after DI without significant difference between groups. Thigh cuff countermeasure slowed down and limited the loss of body water and tended to limit plasma loss induced by DI. These observed physiological responses persisted during periods when thigh cuffs were removed. However, thigh cuffs did not counteract decreased tolerance to orthostatic challenge.

Effects of Venoconstrictive Thigh Cuffs on Dry Immersion-Induced Ophthalmological Changes

“…In a recent report, acute use of VTC during a 15 • tilt reversed tilt-induced increased IOP and subfoveal choroidal thickness (Balasubramanian et al, 2018). In this study, VTC is likely to tend to limit the reduction in IOP by preventing hypovolemia (previously demonstrated in this same study by Robin et al, 2020) thus diminishing ocular dehydration.…”

“…VTC have already been tested during short-term bed rest studies. Although their daily use proved their efficiency to limit hypovolemia and/or baroreflex impairment, VTC failed to prevent orthostatic intolerance (Arbeille et al, 1999;Custaud et al, 2000;Millet et al, 2000;Pavy-Le Traon et al, 2001;Robin et al, 2020); however, little is known about the impact of mechanical countermeasures on ocular changes. This study shows that VTC failed to prevent the increase in RNFLT in the temporal quadrant induced by DI.…”

“…The study was carried out at the Institut de Médecine et de Physiologie Spatiales (MEDES) in Toulouse, France, between November 2018 and March 2019. The detailed protocol was described by Robin et al (2020). The protocol included 4 days of ambulatory BDC before DI (BDC-4 to BDC-1), 5 days of DI (DI 1 to DI 5), and 2 days of ambulatory recovery (R 0 to R+1).…”

Reduced regional cerebral blood flow measured by 99mTc-HMPAO SPECT in microgravity simulated by 5-day dry immersion

“…The protocol did not include an assessment of post-biopsy pain, but no speci c events were reported during the muscle biopsies. The questionnaires on back pain and general discomfort only elicited signi cantly higher scores than in the pre-immersion period during the rst two days of immersion for both groups [35]. We believe that the most likely explanation for the increased CBF in the left thalamus at post-DI is the sensory stimulus generated by the muscle biopsy in the right thigh, the day before the brain SPECT.…”

“…According to the authors, the prolonged vasoconstriction and these histological changes could be responsible for an increase in CVR, thus contributing to the decrease in CBF [15]. During DI5-CUFFS, Robin et al observed a decrease in plasma volume across the 5 days [35]. Likewise, during 3-day DI, Ogoh et al demonstrated a correlation between the decrease in plasma volume and the decrease in blood ow velocity and conductance in the internal carotid artery [25], suggesting that the loss of plasma volume also contributes to the vasoconstriction of cerebral arteries.…”