Effect of Hyperbaric Oxygen Therapy on Microcirculation

Study Overview
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Brief Summary
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Previous studies shoes that hyperoxia alters microcirculation.The investigators hypothesize that hyperbaric may restore microcirculation integrity. This hypothesis is supported by a recent study in rabbits, but no data exists for humans. The study will expose fifteen healthy volunteers to a succession of different fraction of inspired oxygen and barometric pressure and assess microcirculatory and macrocirculatory changes via sidestream dark field videomicroscopy, near-infrared spectroscopy, Laser Doppler, transthoracic echocardiography and bio-impedancemetry at every step.

Detailed Description
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Microcirculation alterations and hyperoxia are known to alter ICU-patients' prognostic. Studies have shown that hyperoxia alters healthy volunteers' microcirculation, whereas hyperbaric oxygen therapy is commonly used to facilitate cicatrization. There seems to be a paradox. A recent study in rabbits has given some evidences that hyperbaria may restore microcirculation integrity, but to date, there is no such evidences in human. To study hyperoxia and hyperbaric induced changes in micro and macrocirculation, fifteen healthy volunteers will be exposed to successive variations of inspired oxygen fraction and barometric pressure according to a predefine sequence so that only one parameter will change from a condition to the next one : FiO2 0.21 - 1 ATA FiO2 1 - 1 ATA FiO2 1 - 2.5 ATA FiO2 0.21 - 2.5 ATA FiO2 0.21 - 1 ATA At each time, and after a 30 minutes period of exposure, measures will be made using SDF-microscopy, Laser Doppler and NIRS to assess microcirculation. As previously described, macrocirculation can modify microcirculation due to a mechanism called hemodynamic coherence. Hence, the investigators planned to assess macrocirculation changes at every step of the protocol using bioimpedancemetry and transthoracic echocardiography. Each volunteer will be his own control, using the first measurements (condition 1. FiO2 0.21 - 1 ATA) as reference.

Official Title
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Effect of Hyperbaric Oxygen Therapy on Healthy Volunteers Microcirculation

Conditions
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Hyperbaric Oxygen Therapy

Intervention / Treatment
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* Procedure: Hyperbaric oxygen therapy


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: To provide a medical certificate of fitness to dive (< 1 year) Consent given for study participation French health insurance affiliated Exclusion Criteria: Temporary or definitive contra-indication to dive Pregnancy or < 18 years of age Precedent dive < 24 hours Under a legal protection measure Medical history of a disease known to alter microcirculation

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 64 Years

Sexes Eligible for Study
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All

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: Hyperbaric oxygen therapy<br>Successive changes in fraction of inspired oxygen and barometric pressure (ATA: Atmosphere absolute) Five successive steps: FiO2 0.21 - 1 ATA FiO2 1 - 1 ATA FiO2 1 - 2.5 ATA FiO2 0.21 - 2.5 ATA FiO2 0.21 - 1 ATA | Procedure: Hyperbaric oxygen therapy<br>* FiO2 0.21 - 1 ATA FiO2 1 - 1 ATA FiO2 1 - 2.5 ATA FiO2 0.21 - 2.5 ATA FiO2 0.21 - 1 ATA<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in proportion of perfused vessel (PPV) | Proportion of perfused vessel assessed by Sidestream dark field microscopy on the sublingual mucosa | 30 minutes after hyperbaric hyperoxia exposure (FiO2 1 - 2.5 ATA) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in proportion of perfused vessel (PPV) | Proportion of perfused vessel assessed by Sidestream dark field microscopy on the sublingual mucosa | 30 minutes after FiO2 1 - 1 ATA exposure | 
| Changes in proportion of perfused vessel (PPV) | Proportion of perfused vessel assessed by Sidestream dark field microscopy on the sublingual mucosa | 30 minutes after FiO2 0.21 - 2.5 ATA exposure | 
| Changes in hyperemic reaction after a vaso-occlusion test | Area under curve assessed by near-infrared spectroscopy | 30 minutes after FiO2 1 - 2.5 ATA exposure | 
| Changes in area of hyperaemia after a vaso-occlusion test | Area under curve assessed by Laser-Doppler | 30 minutes after FiO2 1 - 2.5 ATA exposure | 
| Validation of cardiac output assessed by bioimpedancemetry under hyperbaric condition | Comparison with transthoracic echocardiography | 30 minutes after FiO2 1 - 2.5 ATA exposure | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Hyperbaric oxygen therapy, Normobaric oxygen therapy, Hyperoxia, Sidestream dark field videomicroscopy, Microcirculation