October 2017

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

Steven De Abreu, Liubov Amirova, Ronan Murphy, Robert Wallace, Laura Twomey, Guillemette Gauquelin-Koch, Veronique Raverot, Françoise Larcher, Marc-Antoine Custaud and Nastassia Navasiolava
Mitovasc, UMR Institut National de la Santé et de la Recherche Médicale 1083, Centre National de la Recherche; Scientifique 6015, Université d’Angers, Angers, France; Russian Federation State Research Center, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia; Center for Preventive Medicine, School of Health and Human Performance, Dublin City University, Dublin, Ireland; Centre National d’Etudes Spatiales, Paris, France, 5 Hospices Civils de Lyon, Lyon, France; Laboratoire de Biochimie, Centre Hospitalier Universitaire d’Angers, Angers, France; Centre de Recherche Clinique, Centre Hospitalier Universitaire d’Angers, Angers, France
Frontiers in Physiology - October 2017, Volume 8, Article 799 (DOI: 10.3389/fphys.2017.00799)

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 ± 2min 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.

Keywords: modeled weightlessness, physical inactivity, supportlessness, cardiovascular deconditioning, glucose intolerance, muscle tone, day-night variations, kaliuresis

Dry immersion (DI) induces an accelerated model of cardiovascular deconditioning in response to microgravity. The “support unloading” induced by DI provides rapid and profound cardiovascular deconditioning. This is exemplified by increased plasma volume loss, orthostatic intolerance, pronounced autonomic changes, pronounced metabolic impairment, rapid and profound decreases in muscle tone, and influence on circadian rhythms. DI is tolerated well enough despite backache, and shows rather moderate stress effect. Such rapid, profound and quickly reversible gravitational deconditioning renders the strict DI model extremely significant to test countermeasures for microgravity-induced deconditioning and physical inactivity-related pathologies.