PADI medical clearance for diving includes a nice requirement that we should all meet. It's the 13 MET Bruce Protocol treadmill exercise test. It may weed out those of us who are not fit to dive and those with occult heart disease.
I apologize for not responding earlier but I have not been as active recently. My daily work activities as a general primary care doctor have been keeping me busy during the day. My fathering duties have kept me even busier with my kids afternoon and evening activities.
But as a board certified internal medicine MD I just wanted to clarify some comments. I don't mean to single out Hatul's post but it is the first one in this thread. There have been a few others in the same light and I just wanted to clarify the limitations of assessing a person's health.
First, the standard treadmill test is a poor test to assess the person's underlying risk of heart disease. It cannot reliably predict a person's underlying risk for having a heart attack. What it will tell a doctor is that the person does not have any "clinically significant reversible ischemia." Let me interpret that last quote. For a standard Bruce protocol treadmill test to be positive there must be a significant lesion that restricts the blood flow in a coronary artery to either produce symptoms and/or ischemic changes on the EKG while the test is in progress. Also, the heart rate must exceed a certain level of oxygen requirement from the heart muscle to produce either the symptoms and/or ischemic changes on the EKG.
For example. If the patient has an underlying blockage in a coronary artery of say 90 % and the heart rate exceeds the heart's demand for oxygen (say at 80% maximum effort for age) then the patient will start to complain of some fatigue or shortness of breath or chest pain. The EKG will show signs that the heart muscle is not receiving enough oxygen due to the restricted blood flow and the characteristic ischemic changes will be present on EKG (seen as ST segment depression of 2 mm or more). And by definition reversible so that during the rest and recovery phase the symptoms disappear and the ST segment depressions go back to normal. That would be a positive stress test.
But current theories for how a patient suffers from an acute coronary event (i.e. a heart attack) is that the victim suffers from an acute atherosclerotic plaque rupture. In other words, the build up of cholesterol plaque in the arteries and hardening of the arteries ruptures and then causes an immediate formation of a blood clot in the artery. This takes place over seconds if not minutes and the patient will immediately start experiencing the symptoms of a heart attack. Also by definition the heart muscle starts to die due to lack of blood flow and lack of oxygen caused by the blood clot. If the patient is lucky and gets to medical attention quickly and a cardiologist can restore blood flow in an emergency angiogram the patient may survive and have a good outcome. But even under the best of circumstances 1 out 3 patient's with their first heart attack will still die even with appropriate medical intervention. Because it is virtually impossible to get medical intervention while scuba diving the odds of surviving drop dramatically.
You will notice that I did not give a percentage of how blocked the artery was when the person suffered the heart attack. That is because the plaque can rupture at any level of atherosclerosis. You can have heart attack with minimum plaque build up say 10% or extensive plaque build up of 99% and any level in between. It just so happens you are more likely with stable coronary disease to have symptoms at some level and get diagnosed and subsequently treated before the plaque rupture and possible heart attack.
Bottom line is you can have a "normal" 13 MET treadmill and still have a heart attack. That is the way Jim Fixx died training for a marathon. He was the author of The Complete Book of Running and was by all accounts in great physical shape. He would have short circuited the treadmill and EKG machine for his stress test. But he suffered a catastrophic plaque rupture at age 52 while running. Autopsy confirmed significant underlying atherosclerosis with one artery as much as 95% blocked.
Essentially life is a terminal event. The only question for any individual is how and when will you die. You cannot legislate any number of rules and regulations that will prevent you from dying. Now, you can minimize your risks of having a heart attack by regular office visits to a doctor and taking aspirin, cholesterol medications, and blood pressure medications. You can minimize contributing risk factors by maintaining a healthy body weight, avoiding or quitting tobacco, regular exercise, and a having a healthy diet. But even with those measures there is always the possibility that under certain circumstances (say a genetic predisposition as in Jim Fixx's family history) you may still have an unfortunate medical event.
Being overweight is also not an immediate indication that the person is automatically at risk for a cardiac event or is inherently unhealthy. Weight in and of itself is not a maker of physical fitness. The body mass index (BMI) is simply a marker of how heavy you are relative to your weight. That is all it is. It is not a marker of your physical fitness or aerobic stamina. You cannot look at a person either overweight or "normal" weight and predict how long or how short they will last on a treadmill. Being overweight may increase your predictive value that you will perform at a shorter time but that is an association only and not an absolute. To use an analogy, speeding in the rain will increase the likelihood you will have a car accident but is not a guarantee that you will have an accident.
And what about older divers in general? If we are advocating limiting the personal rights of overweight people shouldn't we limit the rights of older people too? (this is a rhetorical statement people and not meant to be taken literally) After all, the biggest correlation to fatal diving accidents is age over 55. That is because age over 55 is a risk factor for heart attack and increased risk for underlying medical illness as the underlying cause of death in a scuba accident. You are more likely to die of a medical issue over the age 55 while participating in scuba diving than dying in a scuba related accident due to scuba itself. I'm almost 50. Should I consider quitting scuba diving because I statistically have a higher risk of dying while diving?
I am not trying to downplay the emotional impact having a diver die on a dive boat has for the witnesses and good Samaritans forced to help in an emergency. But at some point life itself is a risky proposition. Should we avoid skiing because a skier might have a heart attack on the slopes skiing. Should I not go to the gym this afternoon and work out because I might have a heart attack on the treadmill. Do I avoid going to the bathroom? Seriously, there is a very high correlation to passing out and being on the toilet. At what point do we stop worrying about trying to legislate and govern with rules and regulations to prevent emergencies? You might as well try and develop rules to stop the sun from rising tomorrow.
Personally I am not going to worry about having a heart attack. That doesn't mean I'm going to sit back and just let one happen. I'm trying to exercise and maintain a lean body weight as much as possible. With a personal family history of heart attacks and not being able to take Lipitor (makes my muscles ache) that's about all I can do for now. I still eat more fats and red meat than I should but that goes to my underlying philosophy of life as well. Life is meant to be enjoyed. I enjoy a good steak and a hamburger every once in a while. And I really, really enjoy both skiing and scuba diving. So I'll continue to do both as long as my age and physical activity will allow.
Fun and safe diving to all.
