research

Who got it wrong, reporter or scientists?

meddietEating 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:

  1. 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
  2. High serum triglycerides level: equal to or greater than 150 mg/dl (1.7 mmol/L)
  3. 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
  4. Increased blood pressure: equal to or greater than 130/85 mmHg or use of medication for hypertension.
  5. Elevated fasting blood glucose level: equal to or greater than 100 mg/dL (5.6 mmol/L) or use of medication for hyperglycemia

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Medical Examination of Diving Fatalities Symposium 2014

03A39050On 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.

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Immersion Pulmonary Edema Discussions at SPUMS

ipeAcute 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.

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PFO and Inner Ear DCS

Does the selective vulnerability of the inner ear to DCS help explain the disconnect between a prevalent risk factor and a rare disease?

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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.

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PFO: Is It Time to Change the Course?

wooden pointerPresentations at SPUMS continue…

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.

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Review of PFO and Diving at SPUMS Meeting 2014

PFO_HeartArt_Final2At 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.

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High-Fat Diet and Risk of Decompression Illness

dietObesity 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.

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Sex and Sensitivity to Oxygen Toxicity

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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.

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A Look at Crowdsourcing for Research Funding

financial

Crowdsourcing is a means to raise funds through public contributions in a manner which allows a large number of small contributions to make a difference. Originally started in technology areas where considerable upfront capital was required to make the project viable, SciFund and Experiment.com have taken this into the research arena to allow small research projects to gain support. As those in research know, it is notoriously difficult to raise funds for small research projects and crowdsourcing provides that opportunity. As an example of how well it can work, Experiment has raised $600,000 over the last 4 years.

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Medicinal nicotine and diving

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Smoking has been recognized as a major health problem, which decreases physical fitness and increases risk of serious illness and premature death.  The surgeon general’s “Smoking and Health” report released in 1964  launched the anti-smoking campaign in United States. Back then, 42 percent of adult population smoked in comparison to today’s 18 percent. The government set the goal to reduce this to about 12 percent of the adult population by 2020. While the public awareness is there, individuals still struggle with the habit mostly due to the addictive nature of nicotine. Smoking is less prevalent among divers, but it is still a problem because its acute and chronic effects may contribute to scuba diving fatalities.

(Learn more about the current state of smoking in America, with this PBS NewsHour Interview with Acting Surgeon General Boris Lushniak)

Acute effects of  smoking

Nicotine affects the body in many ways. It increases blood pressure and heart rate frequency. The mechanism of blood pressure and heart rate elevation by nicotine occurs via activation of the sympathetic nervous system with release of norepinephrine and epinephrine (adrenaline).  Cigarette smoking results in sympathetic neural arousal that lasts for 24 hours. This is reflected in a loss of natural heart rate variability and an increased risk of arrhythmia. Narrowing of blood vessels requires the heart to work harder and use more oxygen, while the simultaneous narrowing of the coronary arteries diminishes the blood and oxygen supply to the heart muscle, which can contribute to myocardial infarction. Carbon monoxide reduces availability of oxygen in blood and may exaggerate hypoxia of heart muscles. Nicotine also induces endothelial dysfunction and increased tendency to clotting. Besides that, cigarette smoke contains many toxins other than nicotine (for example, carbon monoxide and oxidant gases) that might contribute to cardiovascular toxicity. Chronic smoking contributes to development of atherosclerosis, heart disease, cancer and premature death.

Major health damage related to smoking is caused by various components of the smoke, but nicotine has its own adverse effects. In an attempt to reduce risks while satisfying the cravings for nicotine, several products that deliver nicotine without smoke have been brought to the market. They are in form of skin patches, nasal spray, chewing gums and inhalers. The most recent, the e-cigarette,  is generating a lot of public discussion. It is important to note that while administering nicotine without smoke may reduce health damage caused by smoke components, it does not reduce effects of nicotine.

Divers are encouraged to cease smoking. Any effective help is welcomed. Medicinal nicotine may be the way to go for those who have failed in their previous attempts, but medical supervision is advised. Some means of delivery of medicinal nicotine, like chewing gums, nasal sprays, dermal patches and inhalers have been approved or tolerated by FDA which summarizes mainstream medical judgement. However some methods raise concerns about propagating the addiction, such as the more elaborate deliveries like the e-cigarette. Divers on a cessation program using medicinal nicotine must be aware of the side effects of nicotine use, nicotine overdose and nicotine withdrawal symptoms.

Side effects

Adverse effects of medicinal nicotine depend on dose and method of administration. Using nicotine inhalers  may cause local irritation in mouth and throat, coughing and rhinitis, change of taste, pain in jaw and neck, tooth disorders and sinusitis. Lozenge and chewing gums may cause dyspepsia. Other adverse events occurring in greater than 3% of patients on active drug include nausea, headache, influenza-like symptoms, pain, back pain, allergy, paresthesia, flatulence and fever.

Nicotine overdose

The overdose of nicotine among adult smokers is not very likely; however, a person can overdose on nicotine through a combination of nicotine patches, nicotine gum, nicotine inhaler cartridges and/or tobacco smoking at the same time. Intoxications with nicotine have been reported and causes include ingestion of nicotine pharmaceuticals, tobacco products, and prolonged skin contacts with nicotine containing plants or accidental ingestion of pesticides containing nicotine. The initial symptoms are caused by stimulatory effects and include nausea and vomiting, excessive salivation, abdominal pain, pallor, sweating, hypertension, tachycardia, ataxia, tremor, headache, dizziness, muscle twitching, and seizures. This may be later followed by depressor effects including low blood pressure and slow heart rate, central nervous system depression, coma, muscular weakness and/or paralysis, with difficulty breathing or respiratory failure.

Withdrawal

Symptoms of withdrawal may occur early on in the smoking cessation process and while on medicinal nicotine. Common withdrawal symptoms include dizziness, anxiety, sleep disorder, depression, drug dependence, fatigue and myalgia.

Diving and medicinal nicotine

Divers are encouraged to quit smoking using any possible help they need with due medical supervision. However, use of medicinal nicotine as a convenient replacement or addition to smoking may be unsafe and is not advised. While on a cessation program, divers must be aware of potential adverse effects which may be confused for dive related symptoms. As with all  medical interventions, it is wise to abstain from diving for a while to weather out possible adverse events and their interaction with dive safety.

Post written by: Petar Denoble, MD, D.Sc.