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

Area of Science:

• Space Physiology
• Gravitational Biology
• Human Adaptation

Background:

• Dry immersion (DI) is a validated ground-based model simulating microgravity's physiological effects.
• It replicates weightlessness conditions including inactivity, lack of hydrostatic pressure, and supportlessness.
• Understanding multi-system deconditioning is crucial for space exploration and terrestrial inactivity-related conditions.

Purpose of the Study:

• To investigate integrative physiological responses to a 3-day dry immersion protocol in healthy men.
• To assess the extent of multi-system deconditioning induced by dry immersion.
• To evaluate the suitability of dry immersion as a model for microgravity research.

Main Methods:

• A 3-day strict dry immersion protocol was applied to 12 healthy male participants.
• Physiological data collected included clinical and biological parameters, body fluid changes, cardiovascular function (orthostatic tolerance tests), metabolic state (oral glucose tolerance test), and muscle tone.
• Circadian rhythms, hormonal levels (cortisol, melatonin), and pain intensity were also monitored.

Main Results:

• Orthostatic tolerance significantly decreased post-DI (27±1 min to 9±2 min).
• Impaired glucose tolerance and a 72±23% increase in net insulin response were observed.
• Leg muscle tone reduced by ~10%, while circadian variations in temperature, heart rate, and blood pressure were maintained; urinary K+ variations diminished.

Conclusions:

• Dry immersion serves as an accurate and rapid model for gravitational deconditioning.
• Observed impairments in glucose tolerance and muscle tone are linked to inactivity and lack of support.
• DI induces moderate physiological stress, making it highly suitable for testing countermeasures against microgravity and inactivity.