Condition category
Injury, Occupational Diseases, Poisoning
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting

Plain English Summary

Background and study aims
Decompression sickness is an uncommon but serious complication of diving. It occurs when hyperbaric (high pressure) conditions during diving lead to bubbles of nitrogen forming in the blood vessels upon decompression (when the diver ascends from depth). Decompression sickness can produce many symptoms, ranging from joint pain and rashes to paralysis and death. Breathing gas mixtures with less nitrogen and higher oxygen content may decrease bubble formation after decompression. This study aims to investigate whether enriched air nitrox reduces bubble formation during simulated diving as compared to breathing normal air.

Who can participate?
Healthy volunteers aged over 18 with a diving license and without a history of a decompression accident.

What does the study involve?
Participants perform a simulated dive breathing air in the hyperbaric chamber of the CHU d’Angers. Intravascular bubble formation is assessed after the dive using cardiac (heart) ultrasound. Twelve participants prone to bubbling are then selected to perform two more simulated dives, one dive breathing air and the other dive breathing enriched air nitrox. Cardiac ultrasound is performed after each dive.

What are the possible benefits and risks of participating?
There are no benefits for the volunteers. Possible side-effects include decompression symptoms, similar to a non-simulated dive. All volunteers will be accompanied by a physician certified in hyperbaric medicine during a simulated dive.

Where is the study run from?
Centre Hospitalier Universitaire d'Angers (France)

When is the study starting and how long is it expected to run for?
January 2001 to August 2007

Who is funding the study?
Investigator initiated and funded (France)

Who is the main contact?
Prof Pierre Asfar

Trial website

Contact information



Primary contact

Prof Pierre Asfar


Contact details

Department of Medical Intensive Care and Hyperbaric Medicine
Centre Hospitalier Universitaire d'Angers
4 rue Larrey

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

Comparison of bubble formation after diving with air or nitrox using cardiac ultrasound (Comparaison par echocardiographie Doppler du phenomene bulleux a l’issue d’une plongee a l’air et au nitrox)



Study hypothesis

Enriched air nitrox reduces venous bubble scores as compared to air breathing during diving, and thereby the risk of decompression sickness in volunteers selected for high post-decompression bubble formation.

Ethics approval

Committee for protection of human subjects in biomedical research of Pays de la Loire (Comité consultatif de protection des personnes dans la recherche biomédical des Pays de la Loire), 23/11/2001, Protocol number 2001/17

Study design

Single-center prospective double-blind study with crossover design

Primary study design


Secondary study design

Randomised cross over trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please use the contact details below to request a patient information sheet


Decompression illness in hyperbaric medicine


The 47 divers underwent an initial simulated air dive to exclude subjects with low intravascular bubble production (Bubble score ≤ 1) in order to select divers with high bubble production (Bubble score ≥ 2). Twelve divers (10 men and two women) demonstrating high intravascular bubble production completed the study protocol in a randomized, double-blinded crossover setup. Divers were assigned to undergo one simulated dive while breathing air (Air; 21% oxygen) and one simulated dive breathing enriched air nitrox (EAN) with 36% oxygen in a randomized order.

Intervention type



Drug names

Primary outcome measure

Pulsed Doppler measurements of the trunk of the pulmonary artery in order to quantify intravascular bubble formation. Measurements of at least 1 minute duration were performed by a certified cardiologist, blinded for the FiO2 at 0, 30, 60 and 90 minutes after decompression. Images were recorded and analyzed for bubble scores offline. A modified bubble score was used, based on the Doppler score system of Spencer. Bubbles scores were analyzed independently by two blinded reviewers.

Secondary outcome measures

Decompression incidents by questionnaire 90 minutes after completion of the simulated dive.

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Forty-seven human volunteers
2. Age >18 years
3. Diving experience as confirmed by possession of a French recreational diver license
4. Absence of contraindication to dive

Participant type

Healthy volunteer

Age group




Target number of participants

18 per group in randomized phase. No specification for number of participants for test dive was indicated in the study protocol.

Participant exclusion criteria

1. History of decompression accident(s)
2. Oxygen administration or diving within 24 hours before simulated dive
3. Absent or low intravascular bubble production (Bubble score ≤ 1) after initial simulated test dive

Recruitment start date


Recruitment end date



Countries of recruitment


Trial participating centre

Centre Hospitalier Universitaire d'Angers
4 Rue Larrey

Sponsor information


Centre Hospitalier Universitaire d'Angers (France)

Sponsor details

4 Rue Larrey
+33 (0)241 353 637

Sponsor type

Hospital/treatment centre



Funder type


Funder name

Investigator initiated and funded (France)

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

The manuscript containing the trial results has been submitted for publication

Intention to publish date


Participant level data

Available on request

Basic results (scientific)

Publication list

2016 results in:

Publication citations

Additional files

Editorial Notes

11/05/2016: Publication reference added.