Thigh Cuffs to Prevent the Deconditioning Induced by 5 Days of Dry Immersion
Condition: Weightlessness; Weightlessness; Adverse Effect
Study type: Interventional

Summary: 
      The objective of the study is to investigate whether thigh cuffs help to prevent and/or
      reduce the deconditioning induced by 5 days of dry immersion and in particular the fluid
      shift and its related ophthalmological disorders. During a randomized 5 day dry-immersion
      study in 20 healthy male adults the two following aims will be undertaken:

        -  Ten scientific protocols will assess the changes in the cerebral, ocular,
           cardiovascular, metabolism, cognitive, muscle and bone systems.

        -  In the above mentioned systems, the potential beneficial effects of the countermeasure
           protocol will also be investigated.
    

Detailed description: 
      Space flights have shown the possibilities and limitations of human adaptation to space. For
      the last 50 years, results showed that the space environment and microgravity in particular,
      cause changes that may affect the performance of astronauts. These physiological changes are
      now better known: prolonged exposure to a weightlessness environment can lead to significant
      loss of bone, muscle mass, strength, cardiovascular and sensory-motor deconditioning, immune,
      hormonal and metabolism changes. Nevertheless, more recent missions have revealed a new suite
      of physiological adaptations and consequences of space flight. Indeed, astronauts exposed to
      prolonged weightlessness experience hyperopic shifts and structural alteration in the eye
      (e.g., choroidal folds and optic disc edema). This condition was defined by NASA as
      Spaceflight-Associated Neuro-ocular Syndrome (SANS). Some of these vision changes remain
      unresolved for years after flight. This phenomenon has most likely existed since the
      beginning of human space flight, but is just recently being recognized as a major consequence
      of adaptation to microgravity. Changes in vision and eye structure are thought to be the
      result of prolonged exposure to space flight-induced headward fluid shifts and elevated
      intracranial pressure. Loss of the hydrostatic pressure gradient during spaceflight leads to
      this redistribution of body fluids toward the head. To prepare for future manned missions
      beyond the low Earth Orbit, the mechanisms underlying SANS syndrome have to be investigated
      and countermeasures designed to reverse or prevent SANS are required. Venoconstrictive thigh
      cuffs (VTCs) represent one possible countermeasure to mitigate a headward fluid shift. The
      Russian Space Agency uses VTCs (bracelets) to sequester fluid in the lower limbs and mitigate
      the subjective sensation of head congestion during space-flight. Moreover, experiments on
      6-month Mir missions demonstrated that bracelets reduced jugular vein cross-sectional area in
      cosmonauts by 12% to 20%. However, it is unknown how VTCs (including bracelets) affect ocular
      physiologic features. The space agencies are actively engaged in studying the initiation and
      progression of SANS syndrome through studies on the International Space Station and on the
      ground. Indeed, considering the limited number of flight opportunities, the difficulties
      related to the performance of in-flight experiments (operational constraints for astronauts,
      limited capabilities of in-flight biomedical devices), ground-based experiments simulating
      the effects of weightlessness are used to better understand the mechanisms of physiological
      adaptation, design and validate the countermeasures. Different methods are used to simulate
      microgravity on Earth. However, two separate 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. Unlike bed rest, dry immersion
      provides a unique opportunity to study the physiological effects of the lack of a supporting
      structure for the body. Dry immersion means immersing into the thermoneutral water covered
      with special elastic free floating waterproof fabric. The subject, surrounded by film and
      "free suspended" in the water mass, remains dry. During horizontal immersion, pressure forces
      are distributed nearly equally around the entire surface of the body (only the head and neck
      are not entirely supported by water). The absence of mechanical support of specific zones
      during immersion creates a state akin to weightlessness that is called "supportlessness".
      Physiological changes under DI develop more rapidly and are more profound than under HDBR.
      This advanced ground-based model is extremely suited to test countermeasures for
      microgravity-induced deconditioning and physical inactivity-related pathologies.

      The present study is organized in this context by the French space agency (CNES) to assess on
      twenty healthy male volunteers the effects of thigh cuffs to prevent the deconditioning
      induced by 5 days of dry immersion and in particular the fluid shift and its related
      ophthalmological disorders. Using an integrated approach, the CNES has selected ten
      scientific protocols to assess the changes in the different physiological fields and the
      potential beneficial effects of the countermeasure to prevent and/or reduce these changes.
    

Intervention name(s): Dry immersion Control Group; Thigh cuffs intervention
Intervention type(s): Other; Other
Intervention description(s): Subjects are immersed up to the neck for 5 days in a specially designed bath filled with tap water.; Subjects are immersed up to the neck for 5 days in a specially designed bath filled with tap water. During the 5 days of dry immersion, the subjects will wear the thigh cuffs daily for 10 hours during the day (8 am to 6 pm). Thigh cuffs are strips of fabric with inserts of elastic fabric. Different sizes exist to adapt to different thighs. Each cuff has five tightening positions (from 1 to 5) and they will be tightened at the upper third of the thighs to create an occlusion pressure of about 30 mmHg.
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: A monocentric open parallel randomized and controlled study.
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Simulated Microgravity; Weightlessness; Countermeasure; Dry immersion; Supportlessness