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.
While vacationing in Croatia, I heard a story about a diver who fits the description of people I sometimes call “robo-divers.” The story’s hero is a famous Croatian sponge diver, with whom I share an acquaintance. My friend, who is one of his teammates, described this robo-diver’s practice, which is similar to previously described empirical dive practices of other local sponge divers: Reportedly, he does four descents per day to extreme depths, after each of which he ascends very slowly without decompression stops. After the last dive of the day, he quickly takes his boat to shallow waters (within approximately 10 minutes) and descends for about two hours of decompression, split between stops at nine, six and three meters (30, 20 and 10 feet).
I don’t know about his decompression sickness history, but I do know that he is 64 years old now, and the fact that he has survived this long following those types of dive practices make me think of him more as a robot than as a man of flesh and bone. At very least, it is unlikely that this diver has a PFO.
Immersion pulmonary edema (IPE) or swimming-induced pulmonary edema (SIPE) manifests with coughing, blood in sputum, difficulty breathing and a drop in the oxygen content of arterial blood. It may occur during surface swimming or diving, and can affect subjects of all ages and levels of health. Risk factors include exaggerated vasoconstriction in cold water, strenuous exercise, negative static lung load caused by immersion, fluid overload and low vital capacity.
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.
During the ONR-NAVSEA Progress Review Meeting that took place in Durham from July 15-17 this summer, Stephen Thom summarized the current status of his research on circulating microparticles (MPs), which are small fragments shed by various cells that have been exposed to stress. These MPs can be found in subjects with inflammation or injury and in divers after diving.
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).
Eating a Mediterranean diet has been reported as beneficial in preventing metabolic syndrome, slowing down the progression of atherosclerosis and decreasing risk of myocardial infarction and stroke. Metabolic syndrome (MS) is a disorder of energy utilization and storage, which according to the American Heart Association, is characterized by at least three of the following five signs:
Abdominal obesity: (excess body fat around the waist) waist circumference greater than 102 cm (40 inches) in men and greater than 88 cm (35 inches) in women
High serum triglycerides level: equal to or greater than 150 mg/dl (1.7 mmol/L)
Reduced high density lipoprotein (HDL): less than 40 mg/dL (1.03 mmol/L) in men and less than 50 mg/dL (1.29 mmol/L) in women
Increased blood pressure: equal to or greater than 130/85 mmHg or use of medication for hypertension.
Elevated fasting blood glucose level: equal to or greater than 100 mg/dL (5.6 mmol/L) or use of medication for hyperglycemia
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.