Cardiac Autonomic Functions During Head-out Immersion and During Head Down Tilt

Study Overview
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Brief Summary
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Head down tilt (HDT) was widely used to simulate microgravity effects on cardiovascular system. HDT could be a suitable model of water immersion (WI) which is also used to simulate the cardiovascular effects of microgravity and which is not easy to study in laboratory. To define the possibility to simulate immersion by HDT, a comparison between these models is required. A comparison between WI and few angles during HDT seems necessary to understand which angle is more adapt. The immersion induces an increase of the central blood volume. This increase is caused by a redistribution of blood from peripheral portions of the body to the intrathoracic circulation. It seems to load cardiopulmonary and arterial baroreceptors. These baroreceptors bring into play autonomic nervous system (ANS) activation and induce a bradycardia. HDT induces an increase in central blood volume as supported by the central venous pressure and cardiac volume increase and in return, MSNA and heart rate decrease. These cardiovascular effects seem to be the same as the thermoneutral immersion and suggest that the ANS activation is the same during HDT and WI. Nevertheless, a few previous studies about ANS in HDT indicate some discordant results: a sympathetic decrease was reported but several results show an increase of parasympathetic activity linked with a trend of increase of arterial baroreflex. The aim of this study is to assess ANS activity in HDT on different angles (-6° and -15°) and WI. The investigators suppose an increase of parasympathetic activity during WI corresponding to parasympathetic activation during HDT especially at -6°.

Official Title
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Cardiac Autonomic Functions During Head-out Immersion and During Head Down Tilt

Conditions
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Healthy

Intervention / Treatment
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* Other: Head-down tilt and immersion


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Sportsman None coffee, alcohol, cigarettes 6 hours before the start of each visit Each meal must have been taken 4 hours before each visit No intensive sport 48 hours before ech visit Written inform consent Exclusion Criteria: Subject with cardiovascular,renal disease or with metabolic syndrome Subject with medication Subject who participated to an other medical research

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: 1<br> | Other: Head-down tilt and immersion<br>* Head-down tilt -6° at inclusion, head-down tilt -15° at week one and Water Immersion at week two<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| heart rate variability |  | inclusion, one week, two weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Blood pressure variability |  | inclusion, one week, two weeks | 
| Spontaneous baroreflex activity |  | inclusion, one week, two weeks | 
| Pulmonary diffusion |  | inclusion, one week, two weeks | 
| Upper limbs vascular resistance |  | inclusion, one week, two weeks | 
| post ischemic forearm hyperemia |  | inclusion, one week, two weeks | 
| Hematocrit rate |  | Inclusion, one week, two weeks | 
| Cardiac haemodynamic |  | Inclusion, one week, two weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Autonomic nervous system, Immersion, Heart rate variability, Head-down tilt, Healthy volunteers