Why don't we emphasize cesa more??

[jbd]

I am not advocating taking new divers down to 30 feet and having them blow and go--it is a recipe for a fatality. Under a controlled condition starting in the shallow end of the pool should not be a problem but the insurance is not going to cover the instructor I betcha even there.

N

I'm an instructor and have insurance and have the requirement to teach CESA. It must be OK with the insurance company.

 

[jbd]

fisherdvm,

gas embolisms can occur in any part of the body with respect to diving and will generally involve ascending too quickly for the current level of gas loading. Not all embolisms will be fatal. The fatal ones will typically be the brain, the heart or the lungs.

CESA is a last ditch attempt at self resuce when all else has gone wrong and is typically most sucessful for the person involved if they are very relaxed while performing the CESA.

The problem with teaching the CESA horzontally in a pool is that one is forced to exhale the air to make the required bubbles which evidence an open airway. So we come up with this goofy humming, ahhing and whatever other contrived methods to keep enough air in the lungs to travel the required horizontal distance.

The reality is that all one needs to do is relax the airway and allow the air to expand naturally from the lungs as the ambient pressure decreases. No humming or ahhing is needed and in som cases may even be detrimental by restricting the flow of air from the lungs.

The aforementioned relaxation comes from either passing out UW once one is OOA. I know this to have happened to one person. The other way is through proper practice of the method.

 

[H2Andy]

The reality is that all one needs to do is relax the airway and allow the air to expand naturally from the lungs as the ambient pressure decreases. No humming or ahhing is needed

true alas... but...

they had to come up with a way to know whether Dive Student A had his airway really open and wasn't going to rupture a lung or worse ...

what do you do? explain the crap out of CESA and make them memorize the mantra: "if i don't keep my airway open on the way up I'll die" but not have them demonstrate the skill?

"if under any circumstances you find yourself in an uncontrolled ascent, or must for some reason ascend really fast, MAKE SURE YOUR AIRWAY IS OPEN."

spend about half an hour teaching why, with pictures. make them write it down 100 times. make them promise you and each other they will do it this way?

 

[fisherdvm]

fisherdvm,
gas embolisms can occur in any part of the body with respect to diving and will generally involve ascending too quickly for the current level of gas loading.

Respecfully disagree. "Current level of gas loading" suggests diffused air in the blood stream. And what you really mean is nitrogen. And the illness you are talking about is DCS or decompression sickness.

When you say "ascending too quickly for the level of gas loading", you totally missed the point of air embolism. It has little to do with rate of ascent, but has to do with a closed epiglottis and a non-compliant, non-distensible pulmonary system. If one's epiglottis is closed, it doesn't matter if he ascend at 1 ft per minute or 100 ft per minute, his lung is going to explode and send air bubble into the blood stream.

Decompression "illness" encompasses both DCS, and air embolism (a type of barotrauma). Gas embolism occurs from real air, not dissolved nitrogen, in the lung. It expands exponentially depending of the depth. This rapid expanding air can cause embolism even with a slight change in in atmospheric pressure, as little as 6 ft of water.

Gas embolism does not occur in "any part of the body". It occurs within the alveoli of the lungs. Gas bubbles are forced into the pulmonary vein, through the left atrium, into the left ventricle, into the aorta, then to the brain, arms, legs, kidneys and organs. The deadly ones are to the brain, and the debilitating ones are to the spinal cords.

 

[fisherdvm]

The reality is that all one needs to do is relax the airway and allow the air to expand naturally from the lungs as the ambient pressure decreases. No humming or ahhing is needed and in som cases may even be detrimental by restricting the flow of air from the lungs.

Also disagree. Breathholding reflex is an instinct that we must overcome. As one poster noted before, if water enter the larynx, it would reflexly close. As it is a part of the swallowing reflex, to allow food to criss-cross the air passage way. God created a funky system where food enter posterior to the airway, or trachea.

To block this reflex from occurring, especially if your regulator flooded or is pulled out of your mouth, you have to consciously force it to open. That is why you whistle, say "ahhhhhhhh".

 

[Adobo]

Respecfully disagree. "Current level of gas loading" suggests diffused air in the blood stream. And what you really mean is nitrogen. And the illness you are talking about is DCS or decompression sickness.

Gas embolism occurs from real air, not dissolved nitrogen, in the lung. It expands exponentially depending of the depth. This rapid expanding air can cause embolism even with a slight change in in atmospheric pressure, as little as 6 ft of water.

Gas embolism does not occur in "any part of the body". It occurs within the alveoli of the lungs. Gas bubbles are forced into the pulmonary vein, through the left atrium, into the left ventricle, into the aorta, then to the brain, arms, legs, kidneys and organs. The deadly ones are to the brain, and the debilitating ones are to the spinal cords.

To me, the most interesting aspect of this discussion is that people are spending an inordinate amount of time talking about how to be proficient at CESA when really, the thing to do is figure out what practices to have in place so that you don't wind up underwater with no breathing gas.

Whenever you are in a situation that you are down to your last option, it usually means you flowered up several things leading up to that situation.

We can talk about the biology behind DCS and embolisms. But ultimately, there isn't much you can to do mitigate the risks to either other than doing a slow/proper ascent. (Or in the case of a PFO, have the proper treatment prior to diving.) And in the case of your SPG reading zero (I would bet that this is the most common cause of OOG situations), a slow ascent is contradictory to what your instincts are telling you.

 

[fisherdvm]

One earlier poster, a free diver, suggests that because he could hold his breath and dive to 60 ft, that he should be able to ascend 60 ft with SCUBA. I would wonder if his reflex breath holding is more of a liability rather than an asset when compressed air is in your lung, rather than an near empty lung of a free diver.

 

[fisherdvm]

I thought PFOs also may allow blood contain gas bubbles to go from the venous side to the arterial side. In this case, would we not be talking about a gas embolism also?

Patent foramen ovale may allow bubbles of DCS to pass from one side to another, but you are confusing the physiology of decompression sickness (where slow ascend, staying below your decompression limit, and the safety stop will prevent).

You might have no nitrogen gas loading, and still have lung barotrauma (or pulmonary emboli), as the factor here is not dissolved gas, but the air that is in your lung is 4 times the density of air at the surface. When you ascend, this air needs a way out, and if your epiglottis is close, it will seek the route of least resistance, which is the pulmonary circulation. As blood flow from the pulmonary vein into the pulmonary artery, the direction it will flow is to the left atrium and left ventricle. PFO will not change the path of the flow of these mega sized bubbles.

 

[H2Andy]

when really, the thing to do is figure out what practices to have in place so that you don't wind up underwater with no breathing gas.

i agree...

but what if you somehow work yourself into that corner, and haven't thought about or conditioned yourself mentally for an emergency OOA ascent?

my thought is, you teach someone everything to be done in order to avoid a CESA, and then you say, and if it all fails, here's how you do a CESA

 

[fisherdvm]

To me, the most interesting aspect of this discussion is that people are spending an inordinate amount of time talking about how to be proficient at CESA when really, the thing to do is figure out what practices to have in place so that you don't wind up underwater with no breathing gas.

It is kind of saying, why we need seat belts and air bags, if we should just teach people to drive better.