CompletedNot Applicable

A Comparison Study Between 10 Days of Dry Immersion Versus 10 Days of Head-down Bedrest on 20 Healthy Male Volunteers

France20 participantsStarted 2024-12-09

Plain-language summary

The space agencies are actively engaged in studying the physiological adaptation to space environment through studies on board the International Space Station (ISS) but also on the ground. Different methods are used to simulate weightlessness on Earth, including cellular models, animal models using hind-limb unloading, or on humans with unilateral lower limb suspension. However, two approaches, -6° head-down bed rest (HDBR) and dry immersion (DI) have provided possibilities for long-term exposures with findings closest to those seen with a weightless state. They produce changes in body composition (including body fluid redistribution), cardiovascular and skeletal muscle characteristics that resemble the effects of microgravity. The common physiological denominator is the combination of a cephalad shift of body fluids and reduced physical activity. Being similar in their effects on the human body, these models, however, differ in their specifics and acting factors. The Head-down Bedrest (HDBR) model has been widely used for this purpose and is considered one of the references for reproducing the physiological effects of weightlessness on Earth. During HDBR, subjects are lying down with an angle of -6° between the feet and head, on their side, their back or their front, but must keep one shoulder in contact with the mattress. All daily activities and tests are performed in this position. One of the advantages of the HDBR model is that it has now been used in a great number of studies internationally, and its effects have long been described and compared with those of microgravity and spaceflight. Long-term bedrest is the gold-standard method for studying the effects of weightlessness and to test countermeasures. Dry immersion involves immersing the subject in water covered with an elastic waterproof fabric. As a result, the immersed subject, who is freely suspended in the water mass, remains dry. Within a relatively short duration, the model can faithfully reproduce most physiological effects of actual microgravity, including centralization of body fluids, support unloading, and hypokinesia. The objective of the present study is to compare the physiological adaptations to10 days of dry immersion versus 10 days of head-down bedrest in 20 healthy male subjects. A set of measurements will assess the changes in the cardiovascular, neuro-ophthalmological, hematological, metabolic, sensorimotor, immune, muscle and bone systems as a result of both models. The most likely outcome of this study will not be to show a clear superiority of one model over the other. Rather, we expect to show differences in kinetics and intensity of adaptations, that should vary from one system to another. This will help future researchers choose the best model depending on the system they are investigating and the rapidity or intensity of the effect they are exploring. The two models, instead of competing with one another, are probably complementary.

Who can participate

Age range20 Years – 40 Years

SexMALE

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* Healthy male volunteer (see below the description of medical tests and laboratory analysis performed at the selection visit), * Age 20 to 40, * No overweight nor excessive thinness with BMI (weight kg/ height m2) between 20 and 26, * Height between 165cm and 180 cm, * Certified as healthy by a comprehensive clinical assessment (detailed medical history and complete physical examination): in particular, free from any chronic disease or any acute infectious disease or cardiovascular, neurological, ENT (especially orthostatic hypotension and vestibular disorders), orthopaedic or musculoskeletal disorders, * Fitness level assessment: 35 ml/min./kg \< VO2max \< 55 ml/min./kg, * Non active smokers, * No alcohol, or drug addiction, and no medical treatment, * Covered by a Health Insurance System, * Having signed the informed consent, * Free from any engagement during the study. Exclusion Criteria: * Any history or presence of clinically relevant cardiovascular, neurological or ENT (especially orthostatic hypotension and vestibular disorders), any chronic disease; any acute infectious disease. Particularly: * Symptomatic orthostatic hypotension whatever the decrease in blood pressure, or asymptomatic postural hypotension defined by a decrease in SBP equal to or greater than 20 mmHg within 3 minutes when changing from the supine to the standing position, * Cardiac rhythm disorders, * Hypertension, * Chronic back pains, * Vertebral fracture, scoliosis or herniated disc, * Glaucoma,…

What they're measuring

Changes in orthostatic tolerance

Timeframe: At baseline and first day of recovery

Changes in peak aerobic power (VO2max test)

Timeframe: At baseline and the first day of recovery

Change in plasma volume

Timeframe: At baseline and 3 days after the end of the intervention

Change in plasma volume percentage

Timeframe: At baseline and at day 1, day 3, day 7 and at the end of the intervention periods

Change in fluid shift distribution towards the cardiac and cephalic region

Timeframe: At baseline, the first day to quantify the short term effect, the fifth day and the tenth day of interventions to quantify the long term effect of fluid shift

Change in body fluid compartments by bioelectrical impedance analysis

Timeframe: At baseline, during the ten days of intervention and until 3 days after the end of the intervention

Change in calf and thigh circumferences

Timeframe: At baseline, during the intervention period and until 3 days after the intervention period

Trial details

NCT IDNCT06777329

SponsorCentre National d'Etudes Spatiales

Sponsor typeOTHER_GOV

Study typeINTERVENTIONAL

Primary completion2025-04-23

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