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Recompression Using Deep Heliox Tables and Treatment Outcomes

In most cases decompression illness (DCI) in recreational divers resolves with recompression to 18 msw (2.8 bar pressure) while the patient is breathing oxygen. However, severe cases of DCI can be more resistant to treatment and may leave the diver disabled. To increase the chances of complete resolution, some physicians advocate the use of deeper tables combined with heliox. Their rationale is based on physics and animal studies. Recompression to a greater pressure can lead to a larger decrease in bubbles and quicker elimination. To avoid oxygen toxicity, oxygen should be diluted at greater pressures. Theoretically, If a diver acquires DCI while diving on air, using helium — which is slow to enter tissues — as a diluent in treatment gas may more quickly eliminate from the tissues the nitrogen and bubbles that cause injury.

This theory, however, had not been tested with divers. At the annual scientific meeting of the European Underwater and Baromedical Society in Amsterdam this August, Emmanuel Gempp presented experience with use of heliox tables at Sainte Anne’s Military Hospital in Toulon, France. Toulon is on the Mediterranean coast, where a lot of diving activities occur. The emergency medical services in the region are well organized. In 85 percent of DCI cases the time to recompression treatment in a hyperbaric chamber is less than three hours, and almost all injured divers receive first aid surface oxygen.

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Scuba Diving Participation in 2014

Each year the Sports and Fitness Industry Association (SFIA), formerly the Sporting Goods Manufacturers Association, releases a report based on a study about participation in 119 sports, recreation and fitness activities. One of the activities addressed in the study is scuba diving; those findings are published in “Scuba Diving Participation Report 2014.”

The 2014 study is based on 19,240 online interviews of a nationwide sample of both individuals (n=7,528) and households (n=11,712). Demographics of the survey participants included the following:

  • 49 percent male, 51 percent female
  • 15 percent < age 18, 29 percent > age 65
  • 65 percent Caucasian, 14 percent African American, 9 percent Asian/Pacific Islander, 9 percent Hispanic, 3 percent “other”

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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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Heart Attack Symptoms in Women

ImageHeart disease is the leading cause of death in women and heart attack is the leading cause of hospitalization. The characteristics of this disease in women may differ from those known in men; the age of onset, presence of risk factors, probability of aggressive diagnosis and treatment vary in men and women.

For example, heart disease develops 7 to 10 years later in women than in men (potentially because of a protective effect of estrogen). Heart attack (myocardial infarction, MI) is less frequent in young women than in men, but young women with heart attack are at greater risk of dying within 28 days of the attack. Common risk factors for heart disease have similar predicting value both for men and women; however, men more frequently have smoking as risk a factor, whereas women more frequently have hypertension, diabetes, hypercholesterolemia and angina. Although women typically smoke less, the relative risk for MI of women who smoke was 1.5 to 2 times greater than of men who smoked, especially in younger age (< 55 years). Higher prevalence of diabetes contributes to higher mortality rates of MI among women.

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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.

Placing the Risks and Benefits of Physical Activity Into Perspective

ImageGenerally, habitual physical activity reduces risk of death due to heart disease, but in susceptible persons vigorous activity can increase the risk of sudden cardiac death and acute myocardial infarction. Susceptible adult individuals are primarily those with atherosclerotic disease.

The incidence of both acute myocardial infarction and sudden death is greatest in habitually sedentary individuals. Habitually sedentary men are 56 times more likely to experience cardiac death during or after vigorous exercise than while resting; however, very physically active men are only five times more likely to die during or after vigorous exercise than at rest.2 Similarly acute myocardial infarction during or soon after vigorous physical exertion is 50 times more likely in least active than in most active subjects.3

Maintaining physical fitness through regular physical activity may help to reduce premature death because a disproportionate number of fatal cardiac events occur in the least physically active subjects performing unaccustomed physical activity. While sedentary people are advised to change their lifestyle and adopt regular physical exercise starting with low intensity and gradually increasing over time, they may need a preparticipation screening. Subjects with any health limitations need medical clearing and preferably a professional fitness coach. High-risk patients should be excluded from certain activities. For a brief set of guidelines, read “When to consult a health-care provider before engaging in physical activities.”

Even the most restrictive policies will never be able to completely prevent cardiovascular events associated with exercise. For individuals who exercise, it is important to recognize and report prodromal symptoms (symptoms preceding cardiac event). Prodromal symptoms were present in 50% of joggers, 75% of squash players, and 81% of distance runners who died during exercise. Prodromal symptoms may include chest pain/angina, increasing fatigue, indigestion/heartburn/gastrointestinal symptoms, excessive breathlessness, ear or neck pain, vague malaise, upper respiratory tract infection, dizziness/palpitations or severe headache. People who exercise have to be aware of this and physicians should inquire about exercise and these symptoms during exams.

For more details about risk/benefit and strategies to mitigate risks see the paper of Thompson PD et al.

References

  1. Thompson PD et al. Scientific Statement From the American Heart Association Council on Nutrition, Physical Exercise and Acute Cardiovascular Events: Placing the Risks Into Perspective: Physical Activity, and Metabolism and the Council on Clinical Cardiology. Circulation. 2007;115:2358-2368; originally published online April 27, 2007; http://circ.ahajournals.org/content/115/17/2358
  2. Siscovick DS, Weiss NS, Fletcher RH, Lasky T. The incidence of primary cardiac arrest during vigorous exercise. N Engl J Med. 1984;311: 874–877.
  3.  Mittleman MA, Maclure M, Tofler GH, Sherwood JB, Goldberg RJ, Muller JE. Triggering of acute myocardial infarction by heavy physical exertion: protection against triggering by regular exertion: Determinants of Myocardial Infarction Onset Study Investigators. N Engl J Med. 1993;329:1677–1683.

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

When to consult a health-care provider before engaging in physical activities

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Physical activity (PA) is beneficial for health, but the transition from a sedentary lifestyle to PA or a change in the level of habitual PA may be associated with risks, especially in subjects with preexisting heart disease. The position paper of the European Association of Cardiovascular Prevention and Rehabilitation provides in-depth guidelines for preparticipation evaluation that is useful for recreational scuba divers, too. According to the classification of PA levels referred to in this article, scuba diving  falls under moderate-intensity PA, while some situations can emerge in diving that would correspond to high-intensity PA.

Classification of PA levels

  1. Low intensity intended PA, corresponding to 1.8-2.9 METS
  2. Moderate intensity intended PA, corresponding to 3-6 METS
  3. High intensity intended PA, including individuals participating/willing to participate in masters events such as long-distance cycling, city marathons, long-distance cross-country skiing and triathlons, corresponding to greater than 6 METS.

For more details about METS, take a moment to review the Compendium of Physical Activities page.

For a quick orientation to assess your need for medical evaluation, use the Preparticipation Screening Questionnaire below. It is of utmost importance to be honest with yourself when it comes to conditions and symptoms asked in the questionnaire. Remember, you keep the keys to your safe participation in PA and in scuba diving.

American Heart Association/American College of Sport Medicine Health/Fitness Facility Preparticipation Screening Questionnaire:

Section I: History

You have had:

  • A heart attack
  • Heart surgery
  • Cardiac catherization
  • Coronary angioplasty (PCI)
  • Pacemaker/implantable cardiac defibrillator/rhythm disturbance
  • Heart valve disease
  • Heart failure
  • Heart transplantation
  • Congenital heart disease

Symptoms:

  • You experience chest discomfort with exertion
  • You experience unreasonable breathlessness
  • You experience dizziness, fainting, blackouts
  • You take heart medications

Other health issues:

  • You have musculoskeletal problems
  • You have concerns about the safety of exercise
  • You take prescription medication(s)
  • You are pregnant

If you have marked any of the statements in Section I, consult your healthcare provider before engaging in exercise. You may need to use a facility with a medically qualified staff.

Section II: Cardiovascular risk factors

  • You are a man older than 45 years
  • You are a woman older than 55 years or you have had a hysterectomy or you are postmenopausal
  • You smoke
  • Your blood pressure is>140/90 or you do not know your blood pressure
  • You take blood pressure medication
  • Your cholesterol level is >240mg/dl or you do not know your cholesterol level
  • You have a close relative who had a heart attack before the age of 55 (father or brother) or 65 years (mother or sister)
  • You are diabetic or take medicine to control your blood sugar
  • You are physically inactive (i.e. you get <30min of physical activity at least 3 days/week)
  • You are >20 pounds overweight

If you have marked 2 or more of the statements in Section 2, consult your health-care provider before engaging in exercise. You might benefit from using a facility with a professionally qualified exercise staff to guide your exercise program.

If none of the above statements in Section 1 and 2 were true, you should be able to exercise safely without consulting your health-care provider in almost any facility that meets your exercise program needs

Adopted from Balady. Circulation 1998; 97:2283-2293. PCI, percutaneous coronary intervention.

 References

Borjesson M, Urhausen A, Kouidi E, et al. Cardiovascular evaluation of middle-aged/senior individuals engaged in leisure-time sport activities: position stand from the sections of exercise physiology and sports cardiology of the European Association of Cardiovascular Prevention and Rehabilitation. Eur J Cardiovasc Prev Rehabil 2010; June 19 (http://cpr.sagepub.com/content/early/2011/01/14/HJR.0b013e32833bo969.full.pdf)

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