Multi-System Deconditioning in 3-Day Dry Immersion without Daily Raise

Abstract

Dry immersion (DI) is a Russian-developed, ground-based model to study the physiological effects of microgravity. It accurately reproduces environmental conditions of weightlessness, such as enhanced physical inactivity, suppression of hydrostatic pressure and supportlessness. We aimed to study the integrative physiological responses to a 3-day strict DI protocol in 12 healthy men, and to assess the extent of multi-system deconditioning. We recorded general clinical data, biological data and evaluated body fluid changes. Cardiovascular deconditioning was evaluated using orthostatic tolerance tests (Lower Body Negative Pressure + tilt and progressive tilt). Metabolic state was tested with oral glucose tolerance test. Muscular deconditioning was assessed via muscle tone measurement.Results: Orthostatic tolerance time dropped from 27 ± 1 to 9 ± 2 min after DI. Significant impairment in glucose tolerance was observed. Net insulin response increased by 72 ± 23% on the third day of DI compared to baseline. Global leg muscle tone was approximately 10% reduced under immersion. Day-night changes in temperature, heart rate and blood pressure were preserved on the third day of DI. Day-night variations of urinary K+ diminished, beginning at the second day of immersion, while 24-h K+ excretion remained stable throughout. Urinary cortisol and melatonin metabolite increased with DI, although within normal limits. A positive correlation was observed between lumbar pain intensity, estimated on the second day of DI, and mean 24-h urinary cortisol under DI. In conclusion, DI represents an accurate and rapid model of gravitational deconditioning. The extent of glucose tolerance impairment may be linked to constant enhanced muscle inactivity. Muscle tone reduction may reflect the reaction of postural muscles to withdrawal of support. Relatively modest increases in cortisol suggest that DI induces a moderate stress effect. In prospect, this advanced ground-based model is extremely suited to test countermeasures for microgravity-induced deconditioning and physical inactivity-related pathologies.

Phase Coupling Between Baroreflex Oscillations of Blood Pressure and Heart Rate Changes in 21-Day Dry Immersion

“…Of note, the second model, in comparison with the first, better reproduces the effects of real space flight on most body systems (Tomilovskaya et al, 2019). Cardiovascular effects of dry immersion that last no more than 7 days are relatively well described (Iwase et al, 2000;Vinogradova et al, 2002;Navasiolava et al, 2011;de Abreu et al, 2017). In general, post-immersion changes in the cardiovascular system are similar to those observed after space flight.…”

Bed Rest, Exercise Countermeasure and Reconditioning Effects on the Human Resting Muscle Tone System

“…Another method to document biomechanical properties in stiffness and plasticity of disused tendons and myotendinous junctions was used previously in the knee extensors (rectus femoris of the Quadriceps) and plantar flexors (Triceps surae) following 20 days of bed rest ( Kawakami et al, 2000 ; Lapole and Pérot, 2011 ) as well as adaptation and maladaptation following muscle disuse/unloading and resistive exercise thus underlining the viscoelastic function of the muscle-tendon-bone interface in muscle physiology and its obvious maladaptation during extended disuse in bed rest. Data from a short-term (3–5 days) “dry water immersion” study noted a decrease in muscle stiffness of the calf triceps surae ( Koryak, 2014 ) and rectus femoris ( Demangel et al, 2017 ; De Abreu et al, 2017 ), whilst earlier work proposed that muscle stiffness was decreased throughout global muscle groups during real microgravity ( Gallasch and Kozlovskaya, 1998 ; Lambertz et al, 2001 ; Lambertz et al, 2003 ). As expected, the shoulder muscles showed little change over the bed rest period.…”

Ground-Based Analogs for Human Spaceflight

“…The fluid shift in the head and neck occurs to lesser degree than strict HDT. It also requires that subjects leave the apparatus for hygienic purposes, impacting the study, and simulated effects (Abreu et al, 2017). Because the subject is not focused upon or supported by any structure, dry immersion allows for the observation of the effects of "supportlessness."…”