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Getting Closer to A Complete Understanding of Decompression Sickness

Decompression sickness is a major risk for subjects exposed to a significant decrease of ambient pressure, like what occurs in underwater diving, tunneling, flying at high altitude or in space exploration. While we know that there is an association between post-decompression occurrences of gas bubbles in body tissues and DCS, we still do not know where the bubbles originate, why they do not occur in all divers on the same dive, and how they lead to DCS. An increasing number of studies are focusing on possible role of micro particles in DCS.

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Microparticles are particles with diameters of 0.1

to 1 micrometer that various cells shed when exposed to noxious factors or various stimulations, and they play role in many biological processes and diseases. Microparticles are also elevated in divers after dive, and they seem to be related to bubbles. Some interventions that decrease number of post-dive bubbles, have been shown to diminish elevation of microparticles. It has also been shown that if animals not previously exposed to decompression receive microparticles from animal that were decompressed, they will develop symptoms of DCS. In blood samples from human divers who were admitted to recompression chambers for treatment of DCS, more microparticles were found than in a blood samples of the control group of divers who did not develop DCS.

A group of scientists led by Steven R. Thom of University of Maryland, previously University of Pennsylvania, did pioneering work in this area. They are identifying specific groups of microparticles involved, and biological processes through which they can contribute to occurrence or severity of DCS.

A group from Second Military Medical University in Shanghai led by Weighang Xu, recently published a series of articles describing their studies of how MPs may be related to DCS. Specifically, they studied a subgroup of endothelial microparticles (EMPs). The endothelium is a single cell layer that lines the inner surface of our blood and lymphatic vessels. There are more than a trillion endothelial cells in the body covering 3000 square meters area — they are involved in the control of vasomotor tonus, maintenance of structure and integrity of blood vessels, growth of new blood vessels, maintenance of blood fluidity, repair of tissue damage, regulation of blood clotting and prevention of hemorrhage, initiation and control of inflammation. It was shown previously that diving affects endothelial function and that it may be related to DCS.

In a series of in-vivo and in-vitro studies, Xu and his coworkers demonstrated how contact with bubbles changes endothelial cells and their function, described some of the mechanism and demonstrated how the adverse effects of bubbles may be prevented by various pre-treatments.

The progress of science is never smooth and straightforward and we cannot predict how long will it take to learn enough about bubbles, endothelium and DCS to be able to produce efficient prevention of DCS, but we know that science is making significant inroads into this matter and that we are every day closer to the ideals of precision medicine and individualized medical solutions.

Author: Petar J. Denoble

References
Yu X, Xu J, Huang G, Zhang K, Qing L, Liu W, et al. (2017) Bubble-Induced Endothelial Microparticles Promote Endothelial Dysfunction. PLoS ONE 12(1): e0168881. doi:10.1371/journal.pone.0168881.
Zhang, K. et al. Endothelia-Targeting Protection by Escin in Decompression Sickness
Rats. Sci. Rep. 7, 41288; doi: 10.1038/srep41288 (2017).
Yu  X,  Xu J,  Liu W,  Xu W. (2018): Bubbles Induce Endothelial Microparticle Formation via a Calcium-Dependent Pathway Involving Flippase Inactivation and Rho Kinase Activation. Cell Physiol Biochem 2018;46:965-974. DOI: 10.1159/000488825
Published online: April 17, 2018

Elite Breath Hold Divers and Short Term Memory

Author: Dr. Petar J. Denoble

 

The question about possible damages to the brain in breath-hold (BH) diving has been around for a long time. While the average people may hold their breath at rest (static apnea) for less than two minutes, trained BH divers easily double that time and elite BH divers can triple that to over six minutes. The top BH athletes regularly exceed 8 minutes and are close to ten. The world record in static apnea time without breathing oxygen in 2014 was set by Serbian Branko Petrovic at 11 minutes and 54 seconds. By now that record too has been exceeded. The superior performance of elite BH athletes could be attributed to their inherited biophysical characteristics, and some metabolic enhancement induced by training, but above all with the ability to postpone the break-through of apnea and sustain profound hypoxia. Inevitably, the longer the apnea lasts the worse hypoxia becomes, and it does affect the brain. The loss of motor control and consciousness during static BH competitions occurs at rates of 9.6% and 1.1% respectively. Negative acute effects of hypoxia on brain functions have been documented at high altitude in mountain climbers and in pilots. Studies of chronic effects of hypoxia in BH divers were less conclusive. Some previous psychometric studies did not find chronic effects that could be correlated to the years of practicing or to the number of negative neurological events. However, other studies using brain imaging and biochemical markers in elite BH divers have shown brain function abnormalities.

Recent study (1) involved 36 subjects divided in three groups: 12 Elite BH divers (EBHD), 12 novice BH divers (NBHD) and 12 participants without experience with BH diving (CTRL). The EBHD could perform static apnea longer freediver-free-diver_iStock-626817232_WEB.jpgthan 6 minutes (mean BH time 371 seconds) and practiced BH for at least two years. The NBHD could perform apnea longer than 3 minutes (mean BH time 245 seconds) and practiced BH for at less 5 months and less than one year. All subjects were subjected to a battery of psychometric tests. The EBHD group showed statistically lower performance on most tests, especially on tests measuring the short-term memory. The decrease in function was correlated to the length of static apnea. It was characterized as a mild short-term memory impairment not amounting to a pathological score except in one case. The diver with the pathological score was the one with the longest static apnea (436 seconds) and the longest diving career (19 years). There was no difference in psychometric performance between NBHD and CTRL.

The paper provides a review of previous testing and findings and it appears that positive findings of this study reflect the longer static BH times of EBHD group in comparison to BH divers studied previously. It appears that extreme apnea comes at price as it would be expected.

The conclusion of this study is that elite divers who practice for years are at risk of short-term memory impairment.

 

 

References

 

  1. Billaut FGueit PFaure SCostalat GLemaître F. Do elite breath-hold divers suffer from mild short-term memory impairments? Appl Physiol Nutr Metab.2018 Mar;43(3):247-251. doi: 10.1139/apnm-2017-0245. Epub 2017

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.

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What’s Left to Learn about Bubbles?

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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. (more…)

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. (more…)

New Decompression Model Based on Occurrence of Gas Bubbles in Small Arteries

Decompression sickness is caused by gas bubbles that form in the body during and after decompression. The current thought is that gas bubbles originate on the venous side and pass to the arterial side either through intra-cardiac (PFO) or intra-pulmonary shunt (arteriovenous anastomoses). A group of scientists proposed recently a third mechanisms: the evolution of bubbles in the distal arteries, independent of venous gas bubbles.(1) They presented their work at the EUBS 2017 meeting (2) in Ravenna. (more…)

Repeated DCS and the Efficacy of Counselling

Released this year, an interesting study on Belgian DCS cases looked at PFO presence, patency of present PFOs, and personality traits in divers who suffered cerebral DCS one or more times. Over the studies 20.5 year period (1993-2013) there were a total of 595 DCS cases treated in three major centers in Belgium. Among them 286 were identified as cerebral DCS and 209 had all necessary information for the analysis. Out of those 209 cases, 125 involved a patient experiencing a 1st episode of DCS, 70 involved 2nd episodes, and 14 involved patients experiencing a 3rd episode of DCS. (more…)