Research Projects

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.

What is the Common Risk Faced by Recreation, Technical, and Breath Hold Divers?

Immersion pulmonary edema (IPE) continues to be a central focus of dive medicine researchers and clinicians. Late last week, at the 2017 EUBS Annual Meeting, four scientists presented five different studies on the subject.

It appears that IPE is significantly more common than previously reported. In a two year period (2014-16) one hyperbaric facility in Cozumel diagnosed 40 cases of IPE among recreational scuba divers­1. On the other side of the world, there were 21 cases of IPE reported among French military rebreather divers in a six year period2.

Pulmonary Edema - Water in Lungs

In the Cozumel study, an analysis of risk factors was attempted. For each case of IPE, there were two non-IPE recreational diving cases admitted to the same facility. Patients involved in the IPE cases in this series were found to be older than patients in the corresponding non-IPE cases. The non-IPE cases did more multi-day, repetitive, deeper and longer dives than IPE cases, and had a history of regular exercise more often. This could be interpreted as showing that IPE occurs more frequently in less fit divers, but more evidence is required to come to a definitive conclusion. Data from this study was presented in poster form, and we can only hope that this will be published as a full length paper at some point, with more details and data analysis.

Military divers involved in the French rebreather study were categorically both young and fit. The main factor that triggered the IPE in these cases was negative pressure breathing, which is present in back mounted rebreathers with lung centroid deeper than the breathing bag. In 30% of cases the situation was exaggerated by improper rebreather adjustment.

A third study report presented a case of pulmonary edema associated with Takotsubo syndrome in a 75-year old woman3. The woman had previously performed 100 dives. On the day of incident she performed a rapid ascent after 23 minutes at 84 feet. The reason for the ascent was not reported. Twenty minutes after surfacing, she started feeling the chest pain, pain in the bottom of the lungs, and difficulty breathing. Within an hour the patient reported further increased difficulty breathing was admitted to the emergency department. Initial evaluation with echocardiography revealed pulmonary edema, and further test found signs of pneumomediastinum with signs of acute coronary syndrome and dysfunction of the heart with characteristics of Takotsubo syndrome. The patient also underwent a coronarography which showed normal coronary arteries. Takotsubo syndrome is known as a stress induced cardiomyopathy and patients typically recover well, unless in case of aquatic activities, they drown. This patient probably decided to end the dive due to symptoms caused by this condition and associated pulmonary edema. During the ascent, she also experience a lung over-pressurization which resulted in the pneumomediastinum.

A fourth presentation showed that IPE may occur more often as the disabling condition preceding the drowning4. While at the surface in a vertical position, swimmers lungs are at a greater pressure than surface air, and they must breathe against negative pressure caused by their immersion. While this is occurring, their heart is additionally stressed due to a shift of blood from the extremities, to their chest cavity, also caused by immersion. It is expected that some water will seep into the lungs from the bloodstream in this situation, but in divers who are struggling due to panic or lack of buoyancy, this could develop into full pulmonary edema, flooding the alveoli completely and disabling a diver, who would then drown.

The final presentation on IPE covered risks involved in breath hold diving. While all activities that involve immersion in water have some risk of IPE, the risk involved in breath hold diving may be greater than previously understood. According to this presentation, 25% of elite breath hold divers have experienced IPE. The study used underwater echocardiography to study the mechanisms of IPE during breath hold diving, and preliminary reports indicate that IPE in breath hold diving is associated with hypoxia, pulmonary capillary congestion, and left ventricular dysfunction.



  1. Garcia-Magna E. Risk factors for scuba diving pulmonary edema in recreational divers. p. 78
  2. Gemp E et al. Immersion pulmonary edema with rebreather among French military divers from 2009 to 2015: role of hydrostatic imbalance. p 74.
  3. GArcia-Magna E. Takotsubo syndrome associated with scuba diving pulmonary edema (SDPE). p 79
  4. Castagna O, MacIver D. Is cardiogenic pulmonary edema a critical step in the pathophysiological mechanism of drowning? p. 20.
  5. Marabotti C. Breath hold diving-induced acute pulmonary edema. New pathophysiological insight from underwater Doppler echocardiography. p. 76

Bubble Production in Divers Who Have Had DCS

Venous gas embolism (VGE), or bubbles, in divers postdive indicates that their decompression was too fast, their bodies became supersaturated and free gas emerged from solution in tissues. The occurrence of free gas is considered a necessary condition for decompression sickness (DCS), which can happen even without VGE. However, the presence of VGE increases the number and types of possible harms to the body and thus the probability of DCS.

A number of studies indicate variability in proneness to DCS among divers; however, the question of whether divers who have suffered DCS produce bubbles more readily in general has not been answered yet. To answer this question, researchers would need to identify “bubblers” and “nonbubblers” and observe the outcomes of their dives over some period of time, which would require a lot of resources and time.

Can Crystalline Salt Reduce the Size of Scuba Equipment?

safe diver quiz

A popular article over last few days is one about crystalline salt that can uptake and store oxygen in high concentration. It was published in Chemical Science by Jonas Sundberg and coauthors from University of Southern Denmark.1 The article describes a synthetized crystalline containing cobalt combined with an organic compound, which has some properties of biological carriers of oxygen like iron-based hemoglobin in mammals or similar copper-based carriers in other animals.

The most significant property of this crystalline is that it binds oxygen reversibly – it can uptake oxygen and release it – and that this process may be controlled.  Professor Christine McKenzie, the leader of the team that synthetized the crystalline, told the Science Daily2 that among other applications:  “When the material is saturated with oxygen, it can be compared to an oxygen tank containing pure oxygen under pressure – the difference is that this material can hold three times as much oxygen. This could be valuable for lung patients who today must carry heavy oxygen tanks with them. But also divers may one day be able to leave the oxygen tanks at home and instead get oxygen from this material as it “filters” and concentrates oxygen from surrounding air or water. A few grains contain enough oxygen for one breath, and as the material can absorb oxygen from the water around the diver and supply the diver with it, the diver will not need to bring more than these few grains.”

Oil Particulate and Carbon Dioxide in Divers’ Breathing Gas

At the ONR-NAVSEA Undersea Medicine Program Review that took place this summer in Durham, North Carolina, two presentations pertained to monitoring Navy divers’ breathing gas for oil particulate contamination and carbon dioxide (CO2) levels.

Contamination of breathing gas may cause adverse health effects in divers. The type of injury depends on the contaminant. Impaired judgment and loss of consciousness, both of which may be deadly underwater, are among the most severe symptoms associated with CO2 and oil particulate contamination. The U.S. Navy bases their breathing air standards on CGA G-7.1 Grade D criteria, which lists a safety standard of 5 mg/m3 for oil mist and particulate and a maximum of 1,000 parts per million for CO2. So far, there is no convenient means of monitoring breathing gas for these contaminants outside of specialized laboratories.


Using the Selfie as a Telemedical Tool

isolated hand holding smartphone or phone
Last April, a Canadian woman named Stacey Yepes experienced stroke symptoms, but by the time she made it to the hospital her symptoms were gone. Because her physicians could not find any signs of stroke, they believed that she was displaying symptoms of stress and released her home. A few days later, she had a similar attack and used her phone to tape herself during an episode in which she suffered from facial drooping and slurred speech. The video helped her doctors diagnose her with TIA (transient ischemic attack).

In many cases of diseases with transitory symptoms, physicians are unable to diagnose patients and opportunities for early treatments are missed. In the case of TIA, it is especially important to establish an early diagnosis and provide treatment to prevent the progression of symptoms and permanent loss of brain tissue. TIA can lead to blood clotting in the brain, but early administration of thrombolytic medication can prevent clotting and brain damage. Because of the transitory nature of TIA symptoms, some hospitals offer stroke telemedical consultations to enhance diagnosis of and establish early eligibility for thrombolytic medication. By using video connections, they establish a correct diagnosis in 96% of cases, as compared with only 83% of cases in which symptoms are only reported by phone.