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.” (more…)
Between July 15-17, the Office of Naval Research (ONR) and the Naval Sea Systems Command (NAVSEA) hosted an undersea medicine progress review meeting in Durham, North Carolina. The presentations focused primarily on topics of interest for the Navy, but most of the research also benefits recreational and technical divers. One topic I found particularly interesting concerns the combined effect of increased carbon dioxide levels (CO2) in breathing gas and the breathing resistance that breathing apparatuses impose on divers.
If breathing is unimpeded, slightly increased levels of CO2 pose no problem. However, the more CO2 that is inhaled, the less CO2 can be added, and a larger breathing volume per unit of time will be required to wash out the same amount of CO2. This increase of breathing volumes occurs automatically, successfully washing out the metabolic CO2 and maintaining a nearly normal level of CO2 in arterial blood (even during exercise when the internal metabolic production of CO2 is increased).
On June 18, 2014 in collaboration with the Undersea Hyperbaric Medical Society, Divers Alert Network sponsored the Medical Examination of Diving Fatalities Symposium. The talks covered specifics of autopsy in scuba fatalities, field investigation of diving accidents, the complexity of rebreather accidents investigation, integration of various aspects of an investigation into final analysis and principles of the epidemiological approach.
Sudden Cardiac Death (SCD) while scuba diving was discussed extensively. While many cardiac-related deaths in scuba diving may be classified as “natural death” associated with preexisting cardiac conditions, the provocative role of diving could not be excluded in some cases. Cardiac causes were suspected in one-quarter to one-third of all recreational diving accidents in recent decades. Rates of cardiac-related deaths vary reflecting regional demographic differences and trends among divers. Current trends of the increasing age of divers are of concern, but on the other hand, cardiac-related deaths in the general population seem to be gradually decreasing thanks to preventive efforts to reduce exposure to lifestyle risk factors and to control involuntary risk factors. Thus, it is not possible to predict whether the current trends in scuba diving fatalities will continue, but cardiac issues will remain for a concern for divers in years to come. Effective trend monitoring requires reliable data including medical examination, and meetings like this one help to advance medical examination practice.
Acute breathing difficulty during swimming or diving may be associated with Immersion Pulmonary Edema (IPE). At SPUMS 2014, Peter Wilmshurst presented a summary of his rich clinical experience. In his opinion, IPE is an underestimated cause of fatalities. Problem with diagnosis of IPE in scuba diving is its rapid evolution. Divers may be overwhelmed with an internal lung flood before they realize the nature of their breathing difficulty and can safely exit the water.
Does the selective vulnerability of the inner ear to DCS help explain the disconnect between a prevalent risk factor and a rare disease?
In his presentation at SPUMS 2014, Dr. Simon Mitchell has summarized the work he and Dr. David Doolette have done regarding the pathophysiology of inner ear decompression sickness (IEDCS) as well as some recent publications from other authors.
Mitchell addressed the reservations some experts have when it comes to the causal relationship of patent foramen ovale (PFO)and decompression sickness (DCS). Some experts say there is a disconnect; PFO must be present in many divers (one quarter), but DCS occurs only in few. Wilmshurst responds to this disconnect asserting that only divers with a large PFO are at risk and this is generally in line with the DCS statistics.
Peter Wilmshurst’s series of cases shows that 79% of all skin DCS have PFO, 10% lung disease and only remaining cases occur in divers with closed PFO due to severe dive exposure. Similar statistics were provided for inner ear DCS and neurological DCS. Other authors dispute association of PFO with spinal form of DCS and say only cerebral DCS appears to be associated. Nevertheless, a large number of DCS cases could be avoided if the diver was aware of PFO and exercised caution.
How safe is the option of transcatheter closure?
Mark Turner, another cardiologist from the United Kingdom, provided a detailed presentation of the procedure, pitfalls and outcomes. The overall outcome: Successful with very low rate of adverse events.
At the 43rd Annual Scientific Meeting of South Pacific Underwater Medical Society going on May 18 – 25, 2014, a key theme is PFO and diving. The keynote speaker is Dr. Peter Wilmshurst, the cardiologist and diving physician who first described the association between PFO and decompression sickness in 1986. Here, he presented his findings in several hundred cases of DCS. His insight into this problem is most valuable and we are looking forward to the publication of a synthesis of his findings.
Obesity has been long considered a risk factor for decompression sickness (DCS). It has been based on findings in animal studies and epidemiological data in military diving. There was no data to confirm the same effects of obesity on incidence of DCS in recreational diving; however, there were some studies indicating a positive correlation between body mass index (BMI) and likelihood of venous gas emboli (circulating gas bubbles) after dive.
In a recent paper, Kaczerska D, et al. The influence of high-fat diets on the occurrence of decompression stress after air dives. UHM 2013;40(6):487-497, intended to test possible effects of high fat intake on risk of DCS.
The most feared manifestation of acute oxygen toxicity is a loss of consciousness and tonic-clonic convulsions (seizures). The threat of oxygen-induced seizures in scuba diving becomes real when the partial pressure of the breathing gas exceeds 1.6 bars. It is known that exercise, carbon dioxide and immersion increase risk of seizures; thus, the working diver should limit oxygen in their breathing gas to 1.2 bars.
The recent paper by Heather Held, “Female rats are more susceptible to central nervous system oxygen toxicity than male rats,” presents data of an experimental study on rats which shows that females have a lower threshold for oxygen convulsions. Age, weight and hormonal status did not show obvious effect on sensitivity to oxygen toxicity.
Long-distance air travel crossing several time zones in a short time causes jet lag syndrome (also called Rapid Time Zone Change Syndrome) upon arrival, because our circadian rhythm established at our origin is out of sync with the day-night cycle at our destination. Symptoms include feeling sleepy, hungry and alert at the wrong times. This affects our social life and ability to work or exercise. Fortunately within days our internal clock synchronizes with the environment. The more time zones we cross, the greater the expression of the syndrome and the longer it takes to overcome.
Divers often travel to faraway dive locations and may be affected by jet lag for the better part of their trip. The jet lag may affect one’s ability to dive safely; therefore, divers need to know how to minimize its effects.