Effects of Pre-Dive Exercise on Decompression Bubbles

Trial Review

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Registration number

ACTRN12626000511336 Ethics application status

Approved Date submitted

8/04/2026 Date registered

24/04/2026 Date last updated

24/04/2026 Date data sharing statement initially provided

24/04/2026 Type of registration

Prospectively registered
Titles & IDs Public title Effects of exercise, blood particles and the menstrual cycle on bubbles in divers Query! Scientific title Effects of pre-dive Exercise, Microparticles, and the Menstrual Cycle on Venous Gas Emboli in divers Query! Additional trial identifiers [1] 317047 0 Nil known Query! Universal Trial Number (UTN) U1111-1324-0457 Query! Trial acronym Query! Related trial records Query!
Health condition Health condition(s) studied: Decompression Sickness 341433 0 Query! Condition category Condition code Injuries and Accidents 337497 337497 0 0 Query! Other injuries and accidents Query!

Reproductive Health and Childbirth 337636 337636 0 0 Query! Menstruation and menopause Query!

Intervention/exposure Study type Interventional Query! Description of the intervention or exposure A randomized controlled, cross-over study will be conducted with 40 participants (see figure added). Each participant will complete five identical hyperbaric chamber dives. Three of the hyperbaric exposures will be conducted without prior exercise (dives 1, 3, and 5), and two will be preceded by a form of moderate exercise (cycling or brisk walking). For each participant, these two forms of exercise will be randomly allocated to their two 'prior exercise dives’.

Pre hyperbaric chamber dive visit
Before the first hyperbaric chamber exposure, digital written informed consent will be obtained during a site or digital meeting. Followed by a digital questionnaire, including dive history, age, gender, ethnicity, height, weight, and for women, if and which anticonception they use and their cycle length. Moreover, the Recreational Scuba Council screening questionnaire for fitness to dive will be completed. Subsequently, all participants will attend the University of Auckland exercise laboratory prior to starting the hyperbaric measurements to undertake the Astrand exercise test, which allows for an objective evaluation of maximal heart rate.

Pre-Dive Exercise
Prior to dives preceded by exercise (dives 2 and 4), participants will attend the University of Auckland Exercise Laboratory. Three hours prior to the scheduled dive, they will undertake the allocated supervised exercise regimen, treadmill walking or stationary bike cycling for 40 minutes. In both settings, exercise intensity will be adjusted to sustain 70% of the participant’s maximum heart rate estimated from the Astrand test, performed prior to starting the study.

Hyperbaric chamber dives
Each participant will complete five identical hyperbaric chamber dives to five atmospheres (equivalent to 40 metres of sea water) for 20 minutes at depth, with at least 5 days between each hyperbaric chamber dive. On arrival at five atmospheres, participants will exercise at 90 watts on a manually braked cycle ergometer. The hyperbaric chamber dives will take place in the Slark Hyperbaric Medicine Unit at North Shore Hospital. All dives will be undertaken in dry conditions, breathing hyperbaric chamber air with the participants accompanied by a member of the study team. Depending on the visit with or without pre-dive exercise the study visit will take 4-7 hours. Participants will be asked to refrain from other diving activities five days before each measurement and to avoid exercise (meaning purposive avoidance of any exercise other than necessary activities of daily living) for 48 hours prior to each experiment.

After exiting the chamber, participants will be monitored for Venous Gas Emboli (VGE) using TransThoracic Echocardiography (TTE) and standard quantitation protocols. VGE grades from the three dives without prior exercise will be used to assess VGE variability in individual participants performing identical dives. VGE grades following the dives preceded by exercise will be compared to those from the dives without prior exercise to evaluate the effect of pre-dive exercise on post-dive VGE formation.

Blood samples
Blood samples will be repeatedly taken for analyzing microparticles, CRP, serum cortisol and sex hormones.
At the beginning of each study visit an intravenous access will be placed for blood draws. Venous blood samples will be taken immediately prior to beginning exercising, directly after exercising and immediately prior to commencement of decompression. In the study visits where people will not exercise blood draws will take place prior to beginning hyperbaric exposure and again immediately prior to commencement of decompression.

Microparticles
The blood specimens for analyzing microparticles will be stored prior to being sent for analysis to a collaborator in the USA for microparticle counting and typing. Query! Intervention code [1] 333714 0 Prevention Query! Description of the comparator or control The study is a randomized, controlled cross-over study. All the participants will be in the intervention and control group. Three of the dives will be conducted without prior exercise (control), and two will be preceded by a form of moderate exercise (cycling or brisk walking (intervention)). Query! Control group Active Query!
Outcomes Primary outcome [1] 345001 0 Venous Gas Emboli (VGE) Query! Timepoint [1] 345001 0 Within 15 minutes of arriving at surface pressure and every 20 minutes thereafter for at least 2 hours and until bubble grades are <= 1 Query! Secondary outcome [1] 460085 0 Microparticles; compound outcome of number and type of gas containing microparticles forming at depth, which might form micronuclei Query! Timepoint [1] 460085 0 Venous blood samples will be taken immediately prior to beginning exercising, immediately after exercising and immediately prior to commencement of decompression. In the study visits where people will not exercise, blood draws will take place prior to beginning hyperbaric exposure and again immediately prior to commencement of decompression. Query! Secondary outcome [2] 460086 0 Hormones; compound outcome of serum cortisol, C-reactive Proteine (CRP) and sex hormones Query! Timepoint [2] 460086 0 Venous blood samples will be taken immediately prior to beginning exercising, immediately after exercising and immediately prior to commencement of decompression. In the study visits where people will not exercise blood draws will take place prior to beginning hyperbaric exposure and again immediately prior to commencement of decompression Query!
Eligibility Key inclusion criteria • Age within the range of 18 to 60 years old
• Ability to read, write, and understand English
• Possession of a valid scuba diving certification
• ‘Fit to dive’ based on the current standard diver fitness assessment tools
• Provide written informed consent
Query! Minimum age 18 Years Query! Query! Maximum age 60 Years Query! Query! Sex Both males and females Query! Can healthy volunteers participate? Yes Query! Key exclusion criteria • Contraindication or impediment that prevents exercising
• Pregnant or trying to conceive a child during the study
• History of mental illness
• Current use of recreational drugs
• Excessive use of alcohol (more than 10 (female)/ 15 (for male) standard alcoholic drinks per week)
• Current smoker
Query!
Study design Purpose of the study Prevention Query! Allocation to intervention Randomised controlled trial Query! Procedure for enrolling a subject and allocating the treatment (allocation concealment
procedures) Allocation is not concealed Query! Methods used to generate the sequence in which subjects will be randomised (sequence
generation) This will be done by RedCap using a simple randomisation Query! Masking / blinding Open (masking not used) Query! Who is / are masked / blinded?

Query! Query! Query! Query! Intervention assignment Crossover Query! Other design features Query! Phase Not Applicable Query! Type of endpoint/s Efficacy Query! Statistical methods / analysis Sample size calculation
There is consensus that a downward shift of one grade in post-dive VGE formation is clinically relevant. A recent study providing guidance on power calculations for studies utilizing ordinal VGE grade data showed (for single participants performing single dives) that for 80% power in detecting a downward shift by one VGE grade with P < 0.05, a paired sample size of 40 participants was required (1). The present study meets this requirement even with the most austere approach to analysis. However, given that we will have 120 dives by 40 participants on one side of the comparison (admittedly not truly independent samples), and that combining the dives preceding the two forms of exercise may be legitimate (again, not truly independent), the study power would be greater.

Outcomes
First, we will compare peak movement bubble grades following the three identical dives (no prior exercise (120 dives in 40 participants)) in a summary graph similar to Doolette and Murphy to assess individual variability (2). Second, we will compare the median peak movement VGE grade following the no prior exercise dives (120 dives in 40 participants) to the median peak movement VGE grade following the walking and cycling prior exercise dives (two times 40 dives by 40 participants). In relationship to defining a meaningful change, a strategy that reduces median VGE by one grade is widely considered clinically significant. Third, we will compare the mean (or median – depending on normality) number of microparticles, particularly the gas-containing variant present pre-dive to immediately prior to decompression, to evaluate the previously reported phenomenon of formation of these microparticles during the period at depth. Then we will correlate the number of gas-containing microparticles present at depth immediately prior to decompression with peak movement VGE grades after decompression to evaluate the hypothesis that these microparticles are precursors to VGE formation. This correlation will be even more meaningful if we are able to use VGE counts derived from the newly developed UNC counting system mentioned above. Last, serum cortisol, CRP, sex hormones, and anticonception use will be correlated with post-dive VGE grades.

1. Doolette DJ, Gault KA, Gutvik CR. Sample size requirement for comparison of decompression outcomes using ultrasonically detected venous gas emboli (VGE): power calculations using Monte Carlo resampling from real data. Diving Hyperb Med. 2014;44(1):14-9. Epub 2014/04/02. PubMed PMID: 24687480.

(2) Doolette DJ, Murphy FG. Within-diver variability in venous gas emboli (VGE) following repeated dives. Diving Hyperb Med. 2023;53(4):333-9. Epub 2023/12/13. doi: 10.28920/dhm53.4.333-339. PubMed PMID: 38091593; PubMed Central PMCID: PMCPMC10944664. Query!
Recruitment Recruitment status Not yet recruiting Query! Date of first participant enrolment Anticipated 1/06/2026 Query! Actual Query! Date of last participant enrolment Anticipated 1/06/2027 Query! Actual Query! Date of last data collection Anticipated 31/12/2027 Query! Actual Query! Sample size Target 40 Query! Accrual to date Query! Final Query! Recruitment outside Australia Country [1] 28014 0 New Zealand Query! State/province [1] 28014 0 Auckland Query!
Funding & Sponsors Funding source category [1] 321569 0 Charities/Societies/Foundations Query! Name [1] 321569 0 Divers Alert Network (DAN) Query! Country [1] 321569 0 United States of America Query! Funding source category [2] 321570 0 Charities/Societies/Foundations Query! Name [2] 321570 0 Australian New Zealand College of Anaesthetists Query! Country [2] 321570 0 Australia Query! Funding source category [3] 321571 0 Charities/Societies/Foundations Query! Name [3] 321571 0 Australian Dive Safety Foundation Query! Country [3] 321571 0 Australia Query! Primary sponsor type University Query! Name University of Auckland Query! Address Query! Country New Zealand Query! Secondary sponsor category [1] 324363 0 None Query! Name [1] 324363 0 Query! Address [1] 324363 0 Query! Country [1] 324363 0 Query! Other collaborator category [1] 283896 0 Hospital Query! Name [1] 283896 0 Te Whatu Ora Waitemata Query! Address [1] 283896 0 Query! Country [1] 283896 0 New Zealand Query!
Ethics approval Ethics application status Approved Query! Ethics committee name [1] 320102 0 Central Health and Disability Ethics Committee Query! Ethics committee address [1] 320102 0 https://ethics.health.govt.nz/about/central-health-and-disability-ethics-committee/ Query! Ethics committee country [1] 320102 0 New Zealand Query! Date submitted for ethics approval [1] 320102 0 14/07/2025 Query! Approval date [1] 320102 0 07/10/2025 Query! Ethics approval number [1] 320102 0 Query!
Summary Brief summary The purpose of this study is to investigate three questions. The main purpose is to investigate whether exercising before diving reduces the risk of decompression sickness. We can detect an increased or reduced risk of decompression stress by looking at small bubbles in the bloodstream (more bubbles = more risk). Additionally, we would like to investigate if microparticles formed during a dive cause bubble formation after surfacing. Microparticles are tiny fragments of membranes from active cells. There are more microparticles in your body when you are sick, for example. These small particles may play a role in decompression sickness by acting as bubble ‘micronuclei’. Lastly, we want to observe any effect of the menstrual cycle and contraception use on bubble formation in women. Query! Trial website Query! Trial related presentations / publications Query! Public notes Query!
Contacts Principal investigator Name 149434 0 Prof Simon Mitchell Query! Address 149434 0 University of Auckland. Private Bag 92019 Auckland 1142 New Zealand Query! Country 149434 0 New Zealand Query! Phone 149434 0 +64 27 4141212 Query! Fax 149434 0 Query! Email 149434 0 [email protected] Query! Contact person for public queries Name 149435 0 Xavier Vrijdag Query! Address 149435 0 University of Auckland. Private Bag 92019 Auckland 1142 New Zealand Query! Country 149435 0 New Zealand Query! Phone 149435 0 +64 21 023 04558 Query! Fax 149435 0 Query! Email 149435 0 [email protected] Query! Contact person for scientific queries Name 149436 0 Xavier Vrijdag Query! Address 149436 0 University of Auckland. Private Bag 92019 Auckland 1142 New Zealand Query! Country 149436 0 New Zealand Query! Phone 149436 0 +64 21 023 04558 Query! Fax 149436 0 Query! Email 149436 0 [email protected] Query!
Data sharing statement Will the study consider sharing individual participant data? No

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