The overarching aim of this work is to improve underwater diving safety by improving understanding of decompression sickness pathophysiology and exploring whether the primary harmful event (bubble formation) could be ameliorated with a simple intervention (pre-dive exercise).
Decompression sickness (DCS) may arise when bubbles form after a diver ascends to the surface following a compressed gas dive. Researchers use venous bubble (‘venous gas emboli’ - VGE) detection as a marker of post-dive decompression stress (more VGE = greater risk of DCS). Studies have shown marked unexplained intra-individual variability in VGE formation between identical dives. One unconfirmed explanation for this is differences in pre-dive physical activity and pre-dive exercise has been identified as one possible strategy to reduce bubble formation. Another unconfirmed explanation is variability in the numbers of blood borne microparticles that form during the dive may act as precursors for bubble formation after surfacing. Confirming that these microparticles can contribute to VGE formation and confirming that a simple exercise regimen prior to diving might reduce VGE would be significant steps in understanding DCS pathophysiology and improving dive safety.
We aim to confirm (or refute) the potential for intra-individual variability in VGE formation after diving when the same individual performs identical dives multiple times. We will also evaluate the effect of two forms of pre-dive exercise (walking and cycling) on post-dive VGE formation, and determine whether the number of gas-containing intravascular microparticles formed at depth during a dive correlates with the number of VGE that subsequently form after surfacing. This will also allow us to evaluate whether any effect of pre-dive exercise on post-dive VGE results from an influence on microparticle numbers.
The study will involve 40 participants who will each perform five identical hyperbaric chamber dives to five atmospheres (equivalent to 40 meters [132’] sea water) for 20 minutes duration at depth. Three of these dives with be conducted without prior exercise and two will be preceded by a form of moderate exercise (cycling, or brisk walking) completed approximately two hours prior to the dive. Immediately prior to every dive a blood sample for microparticle assay will be taken and this will be repeated in the chamber just prior to depressurization at the end of the time at five atmospheres. After exiting the chamber subjects will be monitored for VGE arriving in the right heart using transthoracic echocardiography and standard quantitation protocols. VGE grades from the three dives without prior exercise will be used to assess VGE variability in individual subjects 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. Numbers and types of microparticles measured in blood taken immediately prior to decompression will be correlated with post dive VGE numbers to evaluate the role of gas-containing microparticles formed at depth as precursors for post-dive bubble formation.
The study has a strong potential for findings that could enhance diving safety and that are only one degree of separation from operational implementation (for example, if exercise prior to diving reduces VGE, exercising prior to diving would not be difficult to promote to divers or do). A better understanding of decompression sickness and its prevention would positively enhance safety for everyone who dives. The work will also help maintain our region’s high profile in the underwater medicine space, and will provide an opportunity for a senior research fellow and PhD student to progress their careers.
Professor Simon Mitchell, The University of Auckland
The project was awarded A$99,622 funding through the ANZCA research grants program for 2026.