Now I can see why everyone was waiting for Dr. Ebersole's reply, as his answer is most helpful in making a good risk assessment!! I've managing risk fairly well most of my life, and I think that learning the art of managing risk is a life skill that should be taught throughout all formal and informal schooling. However, there's usually a dearth of reliable and useful information available from which to make much more than a guess, unless you want to devote more time than it is sometimes worth. Why so hard? Those without this skill are usually the ones offering up the advice, which often is either deficient, misleading, irrelevant, and obscures true gems like this one post. I have a few questions though to expand this answer just a bit, and then some background and opinions from me. But first, why his answer was significantly correct:
I found three articles that cover the METS requirements:
Achieving an Exercise Workload of =10 METS Predicts a Very Low Risk of Inducible Ischemia
This first full article covers just how important this is, in predicting the risks and also in improving your METS
Determining Heart Rates from MET Intensities
This covers a way to do the work so that you can use the heart rate to determine what your useful METS is in training.
Just from these articles and a few more, it is obvious to me that you should be able to KNOW that you can meet the guidelines he laid out. METS is extremely important, diving or not. I'd still like to know the effects of depth on cardiac health when virtually at rest, albeit at 90 feet.
Q - What are the reduction ratios various functionalities at different depths? Obviously, there's a huge difference in an experienced diver on a drift dive, trying to relax enough to end the dive with more air than the divemaster (>50 minutes w/reserve), vs. a new diver, scared close to panic, hunting for lobsters, actively fighting a current, or being actively chased. Yes, you want reserve capacity when you need it. But even at 50% o2 efficiency, an athlete is going to deplete most of his air in 15 minutes or less if swimming fast at depth. And since it take 4x the energy to go twice as fast, I'd get there half as fast, or use just twice the air. I guess I'm asking for the fitness aspect importance for CAD patients, and what aspects are at risk, if less fit.
Q - OTOH, how much less efficient are the cardiac arteries at 90ft? With a very low use of o2 at 90 ft, totally relaxed, ejection fraction shouldn't be much of a factor. ? But If stung badly, or a moray eel reaches for your hand or face, your going to panic for at least a few seconds, which adds a lot of stress and constriction, along with a good dose of adrenaline. Those that handle stress well, (and didn't get bitten), will likely be relatively unaffected. Those that don't relax though, are not going to have a good day and obviously would be stressing their hearts.
SCUBA vs snorkeling: I got into SCUBA after many years of snorkeling, mostly with NO partner. I'd do the stupid, worthless and dangerous hyperventilate to get my co2 higher, and o2 from 99% to 99.5%. Then I'd dive to 20-30 feet, and surface quickly when the urge to breath was too much. When in Cozumel once when I couldn't get to a good snorkeling site, they convinced me to do a shore dive. I quickly found that it was so much easier than the type of snorkeling I was doing, I'd never choose to free-dive again. In a few years, about 50 dives and certified open water, I'm now expert enough to think that know all I need to, and get myself into serious difficulty. Luckily I will likely always have a divemaster to try to limit that risk. Although I'm not stupid, my freediving by myself without understanding the co2 / o2 saturation factors, far exceed the risks I now take, SCUBA diving with heart disease.
In my case, although I've had two drug eluting stents, the two MI's I had, did minimal damage. I'm 71, my EF is still 55%-60, and slight occlusions haven't changed in over a decade. OTOH, I'm slightly out of shape right now, which could be remedied in a few months. So, I'd really like to know what effect that has, physiologically when diving. How much does being "out of shape", affect the risk for CAD patients? I think the METS articles I've included cover just how important this is--KNOW what your METS are, before you or I dive.
