Heart Attacks

nigelh

And divers like me who both dive a rebreather and have had a heart attack really seeth at seeing that again and again. Once might be funny, twice bad taste, more.... We are talking about dead divers here.

I asked "What could have predicted this?" "Nothing but an Angeiogram" said the consultant. "And the risk on them is such that we never do them without other symptoms."

__________________
nigelh

ROB DAVIE

Nigel,

Thank you for your frankness, and for reporting your own personal case history!

Your last two sentences make an extremely important point!

Rob

__________________
[SIZE=2]"CC Rebreathers will become a viable part of tech diving [U]WHEN PIGS FLY[/U]!!"--GI3[/SIZE]

dteubner

There are some quite separate issues here.

1. Does diving increase the risk of heart attacks? - Yes for a number of different reasons

2. Does diving with a rebreather increase the risk of heart attack over open circuit? - I can't see how it would.

3. Can you tell (by doing a medical or whatever) who is going to have a heart attack? - Sometimes but as Nigel points out not always. The best way to be sure about the presence of heart disease is by doing a coronary angiogram. Angiograms have risks in and of themselves so if you do them on everyone you will kill more people than you save.

4. How do you determine the cause of death in a diver who dies? I guess this is really tricky and you can rarely be absolutely certain. The degree of confidence in the cause of death is going to vary depending on the circumstances (especially the evidence) and who was involved in the investigation. Stefan makes a number of really excellent points about unit analysis. At the end of the day, a lot of the time the cause of death is not much more than someone saying "I reckon this".

5. What do you do with cause of death information? Sometimes there may be really valuable lessons to learn (it may be that the David Shaw accident is an example of this). It may be nothing more than saying "shit happens". Forums like this are an excellent way of disseminating information to the rebreather community. But for the information to be useful it has to be accurate, and there is little way to feed good information from local coroner's juristrictions to the forums where in needs to be. I would really like to see a forum (even if it were heavily moderated) where formal coroner's reports about rebreather accidents are posted. I think there is real potential for us to learn a lot from this.

Dave T

decoweenie

Could you please elaborate on these 2 points for my own education ?

Thanks!

dteubner

Diving and heart attacks.

What happens when you have a heart attack is a narrowed blood vessel supplying the heart muscle suddenly blocks completely and the muscle dies. The reasons the vessel suddenly blocks are sort of complicated but things which make the heart work harder can contibute. The things that are encountered in diving are:
- exercise
- immersion. when you get in the water you eliminate the effects of gravity on the circulation and move blood to the central circulation which increases the amount of blood getting back to the heart which makes it pump harder
- dehydration may contibute the sudden blockages
- cold

Risks of angiograms
When you have an angiogram a catheter is put in the big arterty in your groin (ususally) and fed up to the heart. Intravenous contrast (xray die) is then injected into the coronary arteries allowing pictures to be taken. The risks are
- bleeding form the insertion site
- bleeding from damage to the aorta
- strokes - the catheter can knock off a bit of crud from the walls of the aorta which then go to your head and block off arteries there
- heart attacks for reasons similar to the above
- allergic reactions to the contrast
I am an emergency physician, not a cardiologist, so I don't have the exact numbers in my head, but the risk of significant problems is probably about 1:100 and death 1:5000 to 1:10000 or so.

Dave T

decoweenie

Dave T., thanks!

iain-hsm

High C02 OR C02 breakout can cause a heart attack. As interested party in these matters I would offer the following explanation as to how a rebreather diver dies with the autopsy conclusion cause of death being a heart attack.

Exercise needs an amount of oxygen and the cells in turn produce an amount of C02. As cardiovascular rate increases blood flow and lung breathing rate and volume increases. This with the addition of stress and increased excitement this in turn releases stress hormones and adrenalin.

The rebreather all this time with the help of your lung power is pushing the expired C02 laden gas around the breathing tube, through the scrubber and through the loop. Work enough to be called work of breathing WOB. Increased C02 production levels relative to C02 elimination in the scrubber material stimulates the nervous system to increase heart rate, increasing blood volume and blood pressure. The diver is now experiencing the onset of Hypercapnia.

With continued high C02 loadings in the breathing bag then peripheral blood vessel dilation will occur. This will have the effect of increasing heart rate even further culminating in massive myocardial contractions or heart attack.

The second important point is the equipment examination. After a death (in the UK) the equipment (if recovered) is examined by an expert witness. Of most reports I have read, the equipment on examination has show normal operation, the gas analysis (if available) has also been normal within limits. The expert witness would therefore conclude that the equipment was working correctly at the time of death. So as the cause of death is on the coroner to conclude and with a normal autopsy this is routinely shown to be a heart attack. Remember a diver is only a diver while he is alive. At death he is classified as a corpse.

So conclude equipment tested and found to be working OK. Therefore cause of death heart attack. The reason and cause of the heart attack was C02 in the loop. Iain Middlebrook

AD_ward9

Since observing the higher than expected number of apparent heart attacks in the rebreather fatal accident list, we have been trying to get some research done in this area.

There are various mechanisms by which rebreathers can cause events likely to precipitate a heart attack in someone who is poor cardiac health.

The key issue seems to be CO2 retention. It is well documented that high CO2 levels cause high blood pressures. This well known in anaesthesia.

The WOB of some rebreathers is far beyond known safe limits, and this translates to increased CO2 retention. On top of that, is the risk of inhaled CO2 being high.

As I said, it needs further research, but the smoking gun is there: there is a known cause, a known effect, and known result.

Alex

PCDiver

CO2 retention .... So there could be some truth in this thread: http://www.rebreatherworld.com/gener...le-killer.html

__________________
>>>>> www.submergeproductions.com dedicated to promoting technical diving
>>>>> Check out our dive show video interviews at http://www.submergeproductions.com/A...nterviews.aspx
>>>>> Wreck dive videos http://www.submergeproductions.com/A...omthedeep.aspx

AD_ward9

Possibly.

All we know for sure is that the observed mortality for rebreather divers from heart attacks is about 500 times higher than for a similar population of O.C. divers.

The average age of Rebreather divers is 5 years older, but this does in no way account for such a large difference.

The numbers of incidents are still low, but there are many papers on anaesthesia describing blood pressures increases very dramatically with increased CO2 (this is while a person is not conscious). When conscious a person with high CO2 levels is likely to be under much more stress.

What this needs is some proper research. Meanwhile we need to ensure WOB is within recommended or regulated limits and all means possible are used to avoid tunneling or premature breakthrough.

Alex