Kategorie: News
DCS study using detailed dive profiles
What can we learn from recorded dive profiles and their consequences about the possible occurrence of decompression sickness (DCS)? Actually quite a lot. This question was the main reason why DAN Europe started to create a database of dive profiles that recreational and technical divers had uploaded from their dive computers since 1994. And it was also the reason why the software was continuously improved and profiles with the corresponding background information were accumulated. Let's call it a homage to the diving community to large amounts of data!
Report by Michael Menduno (DAN - Divers Alert Network)
Therefore, DAN researchers were very interested in applying the latest analytical methods to this dive data in a unique study, examining nearly 40,000 profiles of recreational open water recreational dives collected from European divers along with detailed questionnaires. In almost 1000 dives, bubble measurements were also made with Doppler instruments after the dive and 320 dives resulted in a DCS. Note that technical dives with trimix and rebreather were excluded from the study. The results were published in 2017 in a scientific paper entitled Dive Risk Factors, Gas Bubble Formation, and Decompression Illness in Recreational SCUBA Diving: Analysis of DAN Europe DSL Data Base.
The study had three objectives: Firstly, it was intended to provide an accurate picture of the diving practices of European recreational divers compared to the recommended practices. Second, to investigate pressure-independent risk factors such as age, gender, physique and other environmental factors, including their possible impact on bubble formation. And third, the researchers hoped to identify risk factors that had been present in actual cases of DCS.
The DCS mystery
With the growing popularity of diving, more and more dives are made every year and accordingly more cases of DCS occur. Although the number of affected divers and the exact number of DCS cases is unknown, they are relatively rare with a probability of 0.01 - 0.1% per dive. The higher percentage refers to professional divers and the lower percentage to recreational divers. Nevertheless, the consequences can be dramatic.
Although the exact mechanism of DCS is still controversial [1], it is widely agreed that vascular gas emboli (VGE) are the main causes. However, divers may also have "silent" VGE, which is detected by a Doppler device but does not cause DCS symptoms.
The decompression methods used today are widely used and generally accepted. And it is precisely here that something is puzzling. The majority of DCS cases occur "unexpectedly", i.e. they cannot be explained by the decompression algorithms currently in use. So the diver does not "deserve" them, because he or she has contracted DCS even though he or she has properly followed the instructions of his or her dive computer.
"The problem is that today's decompression models only take into account saturation and desaturation of inert gas, but not the accumulation of microcores (precursor of a VGE), which we believe is primarily responsible for decompression bubbles," explains Costantino Balestra, DAN's Vice President of Research & Education, co-author of the study. According to Balestra, new research suggests that biological processes could interact with the micronuclei to form VGEs, making the diver's individual susceptibility and lifestyle all the more important in predicting DCS.
The results
Researchers have conducted a thorough statistical analysis of the divers' anthropometric data, risk factors and dive data, calculating the Body Mass Index (BMI) and also the respective Gradient Factor (GF) for each dive, which measures "nitrogen oversaturation" as a fraction of the maximum allowable value for each type of tissue. The tissue types were divided into fast, medium and slow. The researchers also determined the bubble stages during the dives, which also included Doppler monitoring for gas bubbles, in order to then compare them with the risk factors.
And this led to the following findings:
Most of the recreational dives were made in the "safe" area, i.e. they had an average depth of 27 m, an average dive time of 46 minutes and an average leading GF of 0.66. This means that the average tissue oversaturation was 66% of the maximum allowed limit. The average ascent speed was slower than the currently recommended speed of 9 - 10 m/min. And more importantly, very few deco stops were omitted. This indicates that divers tend to dive conservatively.
In addition, although divers had problems (including equipment problems) on 6.3% of the dives, they were really serious on less than 0.6%, i.e. on about 109 dives. The data also confirmed that the number of bubbles reached their maximum between 30 and 45 minutes after surfacing. This finding is very important and confirms that it is very important not to put too much physical strain on yourself during this time after a dive.
Risk factors and the impossibility to predict DCS
One focus of the study was to investigate how the different risk factors influence the formation of blisters and ultimately the occurrence of DCS. This should improve predictability. Interestingly, the analysis showed little or no correlation between bubble formation and the many risk factors that were considered. Only higher age and BMI seem to be associated with increased blistering.
Although researchers could not find a significant correlation between bubbles and risk factors not related to the dive profile (e.g. low visibility or high workload), they were able to conclude that many risk factors are likely to cause stress in divers. This led to the hypothesis that immunological-inflammatory factors, which are released in stress situations, could influence bubble formation. These possible variables are currently being investigated in a more in-depth follow-up study.
The analysis of the 320 DCS cases was fascinating and showed how difficult it is to predict DCS. In about 93% of the DCS cases, the divers correctly followed their decompression procedures. These cases were considered "undeserved". Only eight of 320 DCS cases had a GF that was >1, meaning that only 2.5% of the cases would have been "predicted" by the underlying algorithm. Interestingly, all eight involved either fast or slow tissue. These results show that more scientific investigation is needed and that the problem, as described above, needs to be approached more from a physiological point of view.
Next steps
More and more data is being collected and DAN Europe has planned a number of projects to continue the work started with this study. It is also planned to collect more "technical" data, including helium mixtures and rebreathers. Furthermore, the database will be expanded to include freediver data. DAN will soon launch new software tools that will make it easier for divers to participate in the collection of data.
1] The most recent hypotheses postulate that inert gas bubbles can trigger cell-mediated mechanisms that equate DCS with an inflammatory disease (Thom et al., 2015). These hypotheses suggest that the occurrence of "still bubbles" and other risk factors that may correlate with an increase in bubble formation and DCS are worth further scientific investigation.