Decompression sickness (DCS) is often covered in open-water courses but then mentioned only briefly in continuing education. While it’s true that our understanding of the condition has been mostly stagnant for the past two decades, that is beginning to change, and it’s time to start updating divers and students as researchers discover new information.
A recent big-data study performed by a DAN Europe research team used modern statistical analysis techniques to dig into a sample of nearly 40,000 open-circuit recreation dives and look for patterns and clues about DCS risk factors in real-world cases. Some of what they’ve found confirms our previous knowledge and opens entirely new avenues for research into the factors that contribute to DCS risk. Here’s what we’ve learned.
The Good News
Most divers are safe and well trained. Bulk analysis of the data set showed that the average dive had a depth of approximately 89 feet (27.1 meters), a run time of 46.4 minutes and a maximum gradient factor of 0.66 — a gradient factor of 1 represents pure Buhlmann (zero conservatism).
Ultrasound bubble counts confirmed previous research showing that bubble formation peaked 30 to 45 minutes post-dive, although prior issues with directly linking bubble count and DCS symptoms did arise.
Work at depth has long been one of the primary risk factors on which technical and advanced divers alike have focused. Whether that work is due to current at depth or significant exercise (scalloping, artifact removal, etc.), it is going to stay on the list of likely but unproven risk factors. Researchers theorized that work at depth could increase stress in divers, which could increase risk, but workload alone does not correlate directly to DCS risk.
Stress and Hormones
While many specific factors (like workload at depth) didn’t correlate directly with DCS risk, researchers theorized that stress and the resulting hormone release could affect bubble formation. This theory brings to light some interesting concepts and has been the focal point of a new study focusing on hormone production and DCS risk.
Some studies have shown that women may be at slightly greater risk for DCS despite the few physiological differences between the sexes, and a small number of studies have linked menstrual cycle peaks with higher DCS risk (and, conversely, the use of oral contraceptives with decreased risk).
These factors combined seem to indicate a connection between both exogenous and naturally-produced hormones and DCS. This potential link will require further investigation in the coming year.
The beauty of working with huge data sets and modern statistical analysis techniques is the ability to reveal results you would previously never consider. Analysis of the DAN database seems to show that DCS prevalence increases as visibility decreases.
This relates to the study of stress and hormone production mentioned above, but it’s interesting to see that even with significant data, more concrete risk factors like workload do not correlate with DCS risk.
Age and BMI
BMI and age have long been theorized to increase DCS risk; this study confirmed the increased risk. Both factors appeared to contribute directly to increased bubble formation, while physiological metrics like height and weight individually could not be correlated (indicating that BMI, rather than a direct function of height or weight, increases the risk of DCS). Analysis of diver fat mass, which also correlated with DCS risk, further confirmed the results.
The study is ongoing, and this work and the offshoot studies will continue in 2020 and the years to come. Keep an eye out here and at DAN.org for more information. Contact the DAN medical department directly with any questions about how these risk factors may pertain to your diving.
For more information, visit: DAN.org