Decompression sickness

Venous gas bubbles in breath hold divers

Venous gas bubbles in breath hold divers remained a focus of researchers this year, with a notable presentation coming from Danilo Cialoni and his EDAN team1.  At EUBS 2017 they presented the extension of study previously reported and described in this blog. After discovering post-dive VGE in one breath hold diver, they studied VGE in 37 elite breath hold divers during their training in 42 meter deep pool with water temperature  of 32 oC.

Divers underwent echocardiographic Going downmonitoring before the series of dives, after a number of training dives, and every 15 minutes for up to 90 minutes after the last dive. Bubbles were detected in 39% of divers (28% low VGE grade and 11%  high VGE grade). Bubblers did significantly longer and deeper dives with shorter surface intervals. The data from this study will be used to correct the decompression algorithms for breath hold divers, which primarily means extending the time between the dives to prevent carrying over dissolved gas from one dive to another. Four divers did develop neurological symptoms of taravana during the study. All symptoms were mild and divers recovered after breathing oxygen at surface. Most notably, in one diver with taravana, bubbles were not discovered.

Another taravana case unrelated to this study was presented by another group2. A 39 year old diver performed about 30 dives over the course of 5 hours to depths between 29 and 32 meters, with dive times between 2 and 2.5 minutes each. A few minutes after his last dive the individual developed expressive aphasia (difficulty speaking and expressing thoughts) and a headache. The aphasia resolved shortly but the headache persisted and diver was admitted to an emergency department 48 hours post dive. The diagnostic workup included the brain MRI which revealed a brain injury. The patient was treated with one Table 6 and five HBO treatments at 2.5 ATA on the following days. His conditions significantly improved after the treatment and at 2 months follow up he was completely recovered.

Competitive breath hold divers should be aware that post-dive symptoms may be caused by brain injury and regardless of assumed cause (decompression or hypoxic) they need neurological examination and treatment in case of confirmed injury.


  1. Cialoni,D. et al. Prevalence of venous gas emboli in repetitive breath hold diving. Proposal for a new decompression algorithm. P 17
  2. Guerreiro F, et al. Decompression illness in extreme breath hold dive (Taravana syndrome) – A case report. P 47

What’s Left to Learn about Bubbles?



EUBS 2017 has left us with more questions than answers, on the topic of post-dive bubbles.

Ballestra presented the preliminary results of an exploratory study of the effects of sonic vibrations on post-dive venous gas emboli detected by transthoracic echocardiography1. Six divers performed dives to a depth of 33 meters depth for 20 minutes, in a fresh, warm water pool. Bubbles were detected in a standard way, with and without exposure to a sonic vibrations of 20 to 30 Hz. The amount of detected bubbles nearly doubled after sonic vibrations. If these preliminary result get confirmed, we will have to be concerned with post-dive exposure to a sonic noise from various sources, like music, helicopter vibrations and similar, and it is possible that we could find some convenient and fun ways to pre-condition our bodies before dives. This should be also considered in DCS cases in aircraft pilots.

In another study, the presenting author used contrast echocardiography, a standard clinical method, to monitor divers post-dive2. Unlike the more commonly used B-mode echocardiography,  which can detect circulating bubbles greater than 35 microns, the contrast echocardiography can detect much smaller bubbles (< 10 microns). Post-dive contrast echocardiography in seven divers did indeed show the presence of small bubbles in the right and left heart, even in absence of large bubbles detectable by standard B-mode echocardiography. Of particular note is the fact that the presence of small bubbles did not correlate with the amount of large bubbles detected.

The final study was a classical bubble study done by scientists from the Swedish Navy to evaluate the safety of the US Navy Diving Manual Revision 6 air decompression tables. Twenty-eight divers did 72 dives in controlled conditions with three different dive profiles at the no-D limit, or with one required decompression stop. Most dives resulted with VGE Spencer grade III or higher. Two divers were treated for limb DCS and four divers with high bubble load were given surface oxygen. This study confirms that high VGE grade correlates with the risk of DCS.

While the value of VGE monitoring for evaluation of decompression safety at the population level is not questionable, it does have clear limitations that are primarily reflected in great inter- and intra-individual variability. New technologies may help us to learn more about post-decompression bubbles dynamics and get closer to the personalized approach in prevention of DCS.


  1. Ballestra C., et al. Can sonic vibrations increase the number of decompression vascular gas emboli? P 12.
  2. Papadopoulou V., et al. Can current contrast mode echocardiography help estimate bubble opulation dynamics post-dive? P 18.
  3. Genser M., et al. Incdence of ost-dive bubbles and DCS usingthe US Navy Revison 6 ait tables. P 34


Outcomes of Decompression Illness

Recompression treatment and hyperbaric oxygen (HBOT) are standard treatment for decompression illness. While it is generally accepted that sooner recompression is associated with better outcomes, the urgency of treatment may not be same for all cases. Looking for practical guidelines we regularly consult published case series. Three case series presented at EUBS 2017 may be used to illustrate problems with such approach.

In the first paper1, authors compare outcomes in 24 mild cases of DCS treated in an on-site facility with an average delay to treatment 7.8 hours, to outcomes of 29 mild cases treated at an off-site facility with an averaged delay of 42 hours. Cases treated on-site almost all resolved completely after a single recompression (US Navy Table 6 or US Navy Table 5) and only one case needed an additional treatment. Of 29 cases treated off-site, only 17 resolved after first recompression, eight resolved after additional 1 to 5 tailing treatments, and four were left with some residual symptoms after tailing treatments. The authors suggest that this data supports rapid on-site treatment for all cases. In my opinion, there are two issues with this data.


First, the two datasets may not be comparable. Diagnostic criteria and outcome evaluation methods were not explicitly reported and may have been different in two facilities. Cases treated off-site may have left the site before symptom onset and travel may have contributed to the DCS. Second, the sample size is small enough that apparent differences may have been effected by chance.

The second reported case series2 includes 31 divers treated for DCS or AGE. Patients were thoroughly evaluated after the treatment and two to three months later. The evaluation included explicit inquiry about 20 separate symptoms and overall quality of life (VAS scale 1 – 100). At discharge and follow up 45% and 46% of patients respectively were free of symptoms. The most frequent persisting symptoms were tiredness, tingling, difficulty concentrating, and ear ringing.

The third presented series included 12 cases of inner ear DCS3. All patient were harvester divers and most dives included some omitted decompression time. The average time to treatment was 11 hours (5 – 72). Some cases received an on-site in-water recompression but still needed repeated HBOT. Patients received between 1 and 25 HBOT sessions. Eight cases recovered completely, three had residual symptoms and one was lost to follow up. Interestingly, the outcome was not apparently affected by the time to treatment.

These three case series with different case mixes could not be compared directly to each other, but they are a good reminder that the ability to generalize findings from small case series is questionable, particularly when it comes to the question of how the delay to treatment affects the outcome. This research also supports the call for a more standard and thorough description of case series, so we can better compare case studies, and evaluate the data.


  1. Wang Z. Efficacy of early treatment of decompression sickness in an on-site facility vs. delayed treatment of decompression sickness in an off-site facility. P 49.
  2. Johnsson J, et al. Recompression treated decompression illness signs and symptoms – initial findings and 2-3 months follow-up. P 72.
  3. Calderon J. et all. 12 cases of vestibular decompression sickness with clinical monitoring and recording of video. Hospital Ancud, Chile.

Can drinking wine provide benefits for divers?

Historically, alcohol was used to treat bends in Greek sponge divers. In the late 1980s attempts to verify the possible beneficial effects of ethanol on prevention of DCS led to prevailing opinions that there was no proven benefit and that divers should not drink and dive. On the other hand, the assumption that wine drinking has beneficial effects on general health is still propagated.

wine_shutterstock_85339912The so called “French paradox” fueled a search for possible healthful components in wine that, as some researchers posted, protect French people from heart disease despite their fat rich diet and high blood cholesterol levels. Tannins and phenolics, a large group of substances that together make up to 0.1% of wine mass and determine the color and the taste of wine, were identified as beneficial substances. The most intriguing and studied phenolic is resveratrol which is now also sold as a dietary supplement.

Studies of resveratrol in vitro (on cellular cultures or in various models of biochemical systems) have shown anti-oxidant and other effects that with basic biological processes may provide protection against aging, various diseases and death. Further animal studies appeared to confirm beneficial effects. Some of the suspected mechanisms involving resveratrol included functions of endothelial cells (inner lining of blood vessels) and platelets which are also affected in diving. If resveratrol could prevent endothelial cell dysfunction and platelet aggregation, it may help to avoid decompression sickness. Recent resveratrol studies claimed several additional health benefits that could be appealing to divers.

The first claim is that resveratrol has beneficial effects on
skeletal and cardiac muscle functions similar to what is seen with endurance exercise training.1  Wouldn’t it be nice to work on your fitness by relaxing and sipping wine after a long workday rather than going to the gym and sweating?

The second claim is that resveratrol improves brain perfusion and provides neuroprotection2, both of which may be helpful in reducing risk of decompression sickness. Why not drink wine before or after diving?

Unfortunately, there is only one problem with all these studies; the amount of resveratrolDelicious  portion of  fresh salmon fillet  with aromatic herbs, used is equivalent to drinking 50 to 3000 liters of wine per day. It is far more than is needed to get drunk. It’s enough to dive in. Thus, drinking red wine does not seem to be a practical prophylaxis of decompression sickness.

But don’t despair. Even French Paradox is not due to wine drinking as was believed forty years ago. Most population studies indicate that health and longevity may be associated with overall diet. The benefits of French diets appear to come from plenty of fresh vegetables, moderate caloric intake and physical activity rather than just from wine. The French diet has a lot in common with the so called Mediterranean Diet which is widely considered most favorable. In fact, in 2010 it was acknowledged by UNESCO as an Intangible Cultural Heritage of Humanity. (

This story illustrates a common wisdom that there is no one single dietary supplement that could provide what mortals want. To stay healthy and fit for diving, adopt a healthy diet3 and, if you drink wine, limit yourself to one glass with your meal. More importantly, do not drink before the dive.

For quick orientation about healthy meal check MyPlate



  1. Dolinsky VW, Kelvin E. Jones EJ, Robinder S. Sidhu SS, Mark Haykowsky M, Michael P. Czubryt MP, Tessa Gordon T, and Jason Dyck   Improvements in skeletal muscle strength and cardiac function induced by resveratrol during exercise training contribute to enhanced exercise performance in rats. J Physiol 590.11 (2012) pp 2783–2799
  2. Otto MA. Resveratrol improves cerebral perfusion in type 2 diabetes. Clinical Endocrinology News Digital Network. January 17, 2016
  3. US Department of Health and Human Services and US Department of Agriculture 2005 – 2020 Dietary Guidelines for Americans. 8th December 2015. Available at

Skin Mottling after Diving May Be Result of Brain Lesions Caused by Gas Bubbles

Cutaneous decompression sickness (DCS), or “skin bends,” most often manifests as skin mottling on the torso, upper arms and buttocks to various degrees. An associated marbled look to the skin is sometimes referred to as cutis marmorata. While cutaneous DCS is most likely related to gas occurring in body — after decompression or due to lung barotrauma or some medical procedures — there generally is no accepted explanation how the free gas is related to skin changes.

Possible explanations include the occurrence of gas bubbles in subcutaneous tissues, occlusion of subcutaneous arteries with circulating bubbles bypassing the lung filter (as with a patent foramen ovale), inflammatory reaction bubbles present locally or bubbles causing endothelial injury at remote locations.


Can a Test Identify Divers Who May Be More Susceptible to DCS?

Are some divers prone — or resistant — to gas bubbles after diving?

Decompression sickness (DCS), which may occur in divers after decompression from a dive, is dependent on the combined dose of gas saturation during the dive and the rate and magnitude of decompression. However, there is a great variability of outcomes in subjects exposed to the same dive profiles. The variability decreases as the severity of exposure increases.

DCS is correlated with the degree of venous gas emboli (VGE), or “bubbles”, in circulation after a dive. Generally, the higher the VGE grade (more bubbles) the greater the probability of DCS, and vice versa. Similar to DCS, there is a great variance in the probability of VGE appearing postdive. Some researchers who practice VGE detection have hinted that some divers bubble after most dives and may exhibit a high bubble grade (HBG) and others tend not to bubble at all or rarely exhibit HBG. The former are often labeled as bubblers (or high bubblers), while the latter are labeled as nonbubblers (or low bubblers).


Do Viagra and other PDE5 Inhibitors Increase the Risk of DCS in Humans?

Phosphodiesterase type 5 (PDE5) inhibitors — such as Viagra, Cialis, Levitra, Vivanza, Mvix and Lodenafil — are a class of popular drugs prescribed to treat erectile dysfunction and are often sold on the black market as sexual-function enhancers. It is reasonable to assume that many divers use PDE5 inhibitors while on a diving vacation, although the drugs’ possible effects on decompression safety have not been studied previously. In a recent paper, Blatteau et al.1 presented the results of a study on rats treated with sildenafil (Viagra) and then exposed to a simulated dive.