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


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


  • 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.


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.

When to refer a diver for PFO screening?


Postdive occurrence of bubbles in divers venous blood (venous gas emboli or VGE) is quite common. VGE are usually filtered out of circulation by the pulmonary capillary filter. However, in the case of PFO, transpulmonary passage of venous blood or other rare causes of right-to-left shunt (RLS), VGE may pass to the arterial circulation and cause damage of vital tissues manifesting decompression illness (DCI). Note that DCI includes both decompression sickness and cerebral arterial gas embolism. Because of high prevalence of RLS, mainly as a result of PFO, and low incidence of DCI, there is a general agreement that screening for RLS should not be done routinely on all divers. While in some cases screening may be useful, there is no consensus about when the screening is justified. In a recent paper by Oliver Sykes and James E. Clark titled, “Patent foramen ovale and scuba diving: a practical guide for physicians on when to refer for screening,” the authors detail clear guidelines for physicians as well as their definitions of safe diving practices, provocative dive profiles and factors suggestive of PFO. Their recommendations are very useful. Do not miss this paper. It is available for free from the above link.

Their recommendations are summarized in Figure 8 of Sykes and Clark’s paper:


Figure 1. Flow chart on when to refer for screening by a cardiologist with an interest in diving. Courtesy of London Hyperbaric Medicine.

The findings in DAN’s PFO study coincide with most of the recommendations above. Retrospectively established incidence of various DCI manifestations in divers with PFO participating in our study is shown in following table:


Multiorgan DCI manifestations were a frequent finding and we suggest adding it to the indications for RLS screening. In this context, multiorgan means coincidental occurrence of symptoms from two or more of the following symptom groups: skin, neurological (brain, spinal cord, ocular or inner ear), pulmonary and constitutional.

Learn more: Read about the dive and DCS history in divers who tested positive for PFO and pursue closure. http://www.alertdiver.com/Study_Update_PFO

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

Primary Prevention of Cardiovascular Disease with a Mediterranean Diet

ImageIn a recent article published in New England Journal of Medicine, Ramón Estruch and his colleagues present results of a multicenter trial in Spain conducted to evaluate the effects of a Mediterranean diet on myocardial infarction, stroke or death from cardiovascular causes in subjects who were at high cardiovascular risk, but with no cardiovascular disease at enrollment. Participants were randomly assigned to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet (advised to reduce dietary fat). The results of an interim analysis were so overwhelming that the trial was stopped after a median follow-up of 4.8 years.

Study enrolled 7,447 persons with an age range of 55 to 80. Severe cardiovascular events occurred in 288 participants.  More severe events occurred in control group (109) then in the  group assigned to a Mediterranean diet with extra virgin olive oil (96 events) and the group assigned to a Mediterranean diet with nuts (83 events), respectively.  It represented a 30% reduction for the groups with Mediterranean diet in comparison to the control group.

Researchers concluded that “among persons at high cardiovascular risk, a Mediterranean diet supplemented with extra virgin olive oil or nuts reduced the incidence of major cardiovascular events.”

How your diet compares to Mediterranean-style diet? Check it here:


Estruch R, et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet.  NEJM, 2013; 368 (14):1279-1290

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

Obesity, The Heart & Diving


How does obesity affect your heart and why can obese divers develop heart trouble at apparently low level of exertion?

Obesity is an escalating problem and is linked to a spectrum of cardiac dysfunctions that affect feeling of wellbeing, physical fitness and longevity. In a recent review paper Rider O.J. et al, summarize current knowledge about how obesity affects the heart. The most notable fact is the change of source of the fuel from which the heart derives its energy. By excluding glucose and relying mostly on fatty acids, the energy process becomes less efficient and the heart needs more oxygen for the same level of work. In the long run, lipids become toxic for heart cells and lead to structural changes and weakening of the heart muscles, which is disabling and life threatening. In case of divers who feel fit enough to dive, however, the danger comes from the increased needs of heart for oxygen even at rest. In some cases, even a small increase in exercise level may cause a significant hypoxia of heart muscles which can lead to major troubles.

The good thing is that the problem can be improved by moderate weight loss. However, weight regulation should be started sooner rather than later when changes may become irreversible.

Read the full paper: OJ Rider, P Cox, D Tyler, K Clarke and S Neubauer. Myocardial substrate metabolism in obesity. International Journal of Obesity (2013) 37, 972–979; doi:10.1038/ijo.2012.170; published online 16 October 2012

Learn more from DAN FAQs: Healthy But Overweight

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

Four Healthy Lifestyle Behaviors Slow Down Progression of Atherosclerosis and Lower Risk of Death

Gabriella FabbriThe Multi-Ethnic Study of Atherosclerosis (MESA) included 6,229 US adults aged 44 to 84. All patients were given one point for each of four behaviors they had option to follow: a Mediterranean-style diet, 150 minutes of moderate-intensity physical activity per week, maintaining a healthy body-mass index (BMI), and not smoking. All participants also underwent coronary artery calcium screening at baseline and three years later.

People with higher score (healthier lifestyle) had slower progression of atherosclerosis and 80% less risk of death in the observed period. Each of the healthy behaviors contributed independently to better outcome.

Of the behaviors investigated, however, smoking was the most devastating. Subjects who exercised, ate healthily and maintained normal weight, but smoked, were still worse off than people who did nothing else right but stayed away from cigarettes. Not smoking is the best individual thing people (including scuba divers) can do for their health.

Read full paper: Ahmed HM, Blaha MJ, Nasir K, et al. Low-risk lifestyle, coronary calcium, cardiovascular events, and mortality: results from MESA. Am J Epidemiol 2013; DOI:10.1093/aje/kws453. Available at: http://aje.oxfordjournals.org.

Learn more about cardiovascular health.

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

DAN Investigates Implanted Cardiac Devices: Volunteers Needed

ImageIn a recent divers’ health survey that DAN conducted, 25 participants, or one in 200, reported having an implanted pacemaker device. The median age of divers with implanted devices was 64 (39 to 90) years and 95% were male. We did not anticipate this and the survey did not ask about reasons for pacemaker implants, but we have learned something about their health status.

  • About 64% active divers with pacemakers were either overweight or obese.
  • 22 reported that they regularly participate in vigorous exercise such as running, biking, swimming, weightlifting, etc.
  • Half were diagnosed with hypercholesterolemia, 9 with hypertension and 4 with diabetes.
  •  Few still indulge in some high risk habits such as heavy drinking and tobacco smoking.
  • When asked to describe their general health, one participant answered it was excellent, 12 very good, 10 good, and one diver said that his health was fair or poor.

Five of the respondents with implanted pacemakers had basic certifications, 16 had advanced and four held instructor-level diving certifications. In terms of diving habits, the respondents with implanted pacemakers reported they:

  • Perform about 30 dives per year (median)
  • Have been active divers for an average of 20 years
  • Have logged a median of 460 total lifetime dives per diver.

Divers with pacemakers don’t seem to be less active than other divers, but we did not explore the circumstances and severity of their dives. We did not ask about specific symptoms or manifestations related to underlying conditions for which they received the pacemaker nor about possible unwanted side effects of pacemakers.

 Volunteers with Pacemakers Needed

This is why DAN designed a new study to learn about specific issues experienced by divers with pacemakers choosing to dive with or without medical clearance. DAN is looking for volunteers to participate in the “Diving Experience of Divers with Implanted Cardiac Devices” study, which consists of an online survey that takes approximately 10 minutes to complete, in addition to a possible follow-up interview if clarification is needed. If you would like to participate in this investigative study, ongoing through August* 2013, please contact DAN Research (919-684-2948 or research@dan.org). Participants will not be compensated for participation.

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

*NOTE: This study has been extended through November 2013.

Exercise and Acute Cardiovascular Events: Placing the Risks Into Perspective


Do not ignore possible warning symptoms!

The American Heart Association’s Scientific Statement published in 2007 is still valid when it comes to exercise and acute cardiovascular events. While many sudden cardiac deaths related to exercise occur in subjects without obvious symptoms of heart disease, in many cases warning symptoms preceded death but were ignored by victims or their physician. Specifically, 50% of joggers, 75% of squash players, and 81% of distance runners who died during exercise had probable cardiac symptoms before death. Most reported these symptoms only to relatives and few sought medical attention. We have seen this also in scuba divers although not in such high percentages. Recommendation is that exercising adults should be aware of the nature of warning cardiac symptoms and the need for prompt medical attention.

 The most commons warning symptoms are:

  • Chest pain/angina                                                                        
  • Increasing fatigue                                                         
  • Indigestion/heartburn/gastrointestinal symptoms        
  • Excessive breathlessness                                           
  • Ear or neck pain                                                                         
  • Vague malaise                                                                                  
  • Upper respiratory tract infection                                         
  • Dizziness/palpitations                                                                     
  • Severe headache                                                                              

Suggestions for prudent risk mitigation measures brought forth in the same article could be modified and applied to diving as follows:

  • If your health changed recently, you are healthy and over 45, or you have two or more risks for heart disease, take your annual medical exam before resuming physical activities in preparation for diving.
  • If you have a known cardiac condition, you should be evaluated for diving according to published guidelines
  • Prepare physically for your dive trip by gradually increasing your exercise level and refreshing your skills in preceding months.
  • Know the nature of warning symptoms for heart disease and seek prompt medical care if such symptoms develop.
  • Modify your dive plan in response to variations in the environmental and general diving conditions. Learn to when to call a dive (this may be even before the dive starts).
  • Ask your dive provider where their staff is trained and equipped for resuscitation and if they conduct periodic drills.

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

Scuba diving related or circumstantial deaths?

“The number of water-related deaths in Cayman this year has already exceeded the annual average, with only half the year gone,” stated Cayman Island News in an article titled “Ocean claims another diver” posted on July 12, 2013.

 It further specifies that one victim died in swimming pool, one fell overboard and one competitive swimmer died during swimming in ocean. The remaining seven were attributed to snorkeling and scuba diving. As the title suggested, this seemed mostly to be scuba divers.

 We checked DAN database and found 20 scuba fatalities in Caymans during the last five years, or an average four per year. For 2013 we found only two scuba fatalities. However, there were other fatalities in water-related activities. Here are the details:



The findings reflect general pattern of water activity related deaths.

  • Drowning in a swimming pool most often affects children as in this case.
  • Falling overboard from the cruiser happens most frequently to young males.
  • Competition-related deaths generally occur in younger athletes, while death during leisurely activities in water regardless whether it is beach going, surface snorkeling or scuba diving occur mainly in older people. Average age in this series was 69.5 years old and all victims in this sample were male.

 Only in two cases was a possible trigger identified: one swimmer succumbed in rough waters and one snorkeler had pulmonary fibrosis that may have contributed to his demise. In all seven cases the death occurred swiftly and fits the definition of sudden cardiac death, which is most often caused by heart disease. In some cases victims may have been diagnosed with cardiac disease previously and in other they felt pretty healthy until their death. Most sudden deaths occur in people with moderate atherosclerotic changes that do not cause any symptoms and may not be detected on annual medical exam, thus call for more strict medical criteria for scuba divers seem unjustified. Besides, neither snorkeling nor beach going requires any certifications or medical approval. With older population staying longer active, it is unavoidable that some deaths occur in public, most of them unrelated to the specific activity.  One could not speculate whether any of these seven deaths could have been prevented without unnecessarily denying older people right to enjoy active life. 

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

Mild traumatic brain injury and hyperbaric oxygen treatment


On the hyperbaric medicine side, two studies looked at effects of hyperbaric oxygen treatment (HBOT) on mild traumatic brain injury (mTBI). As you may remember, a few years ago some people started promoting HBOT for this condition, based on wrong assumptions. The hopes of those suffering and of their families skyrocketed. Based on the same wave, diving for mTBI was promoted. One paper (Scorza KA) from U.S. Army Medical material Development Activity, and the other (Wolf EG) from the hyperbaric medicine clinic on  Lackland Air Force Base, both indicate that there is no improvement of specific mTBI symptoms. It remains to be tested whether some particular subgroup of injured may benefit.

This summer, DAN is planning to evaluate an already ongoing dive training program offered to subjects with mTBI. We will look at this program as an occupational therapy and will try to evaluate possible effects on executive brain functions.

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

Deep capability or deep trouble?


Dr. Simon Mitchell gave an outstanding plenary presentation at the UHMS Annual Scientific Meeting. As a current rebreather diver, he recognizes how much he can do using rebreather, as well as the risks associated with such complex, high-maintenance machine. Divers must be knowledgeable, skilled and disciplined. With new models of rebreathers that target average diver (“recreational rebreathers”) we must do more to prevent injuries, some of which are caused by unsafe human behavior, errors and omissions and other by lack of recognizing predictable machine failure (oxygen cell failure, for example). Simon stressed the conclusions of Rebreather Forum 3.0 (RF3) and the need to use checklists. Checklists should be cleverly designed and printed out, not just mnemonics. It is essential for proper dive leadership to foster a culture of safety in the diving community. I hope you will have opportunity to attend Simon’s presentation at some of dive shows scheduled in the future. In the meantime, here are a few of his lectures from RF3.

CCR Physiology

Anatomy of a CCR Dive

Discussion and Consensus

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