Lung barotrauma risk

[TMHeimer]

A few things.

1) The epiglottis has nothing to do with closing the airway. It's a tissue flap that helps prevent aspiration of food and saliva, but a minor player. It's possible to learn techniques to swallow without it (such as with people who have had the supraglottic larynx removed for cancer). It occasionally can cause minor airway obstruction on inhalation in babies because it is soft and floppy in the first year of life, and curled on itself (laryngomalacia). This is rarely seen in adults, and usually only in patients with neurological disease.

2)The vocal cords (glottis) coming together (adduction) is what makes an airtight seal of the airway. From an evolutionary point of view, that's why we have a larynx to begin with - speech is a later benefit. Because non-cetacean mammals have crossed air and food passages, we need some fancy reflexes to shut the vocal cords and keep us from drowning in our own saliva, or every time we take a drink of water.

3) Forcefully adducting the vocal cords while ascending is what causes pulmonary barotrauma. If you aren't doing that, but are just pausing breathing, then the expanding gas in your lungs will vent on ascent.

4) Getting back to the OP, my understanding of "surge" is that the volume of water that you are suspended in is moving up and down. Therefore, surge should not change your actual depth at all, and you should be at no risk of barotrauma. There are stories of people doing deco in heavy seas, where the waves were big enough so that divers at their shallow stop could actually be seen at deck level, but inside a wave adjacent to the trough that the boat was in! Not sure if that is apocryphal, but you get the point...

Interesting point about surge. I always found it odd that it's just the water directly above you that matters. Ei.--if you're 100' down a water-filled hole the diameter of a manhole cover you are under the same pressure as if you were down 100' in the ocean. Seems weird, but apparently true.
As well, thanks for the medical info. I (and others?) tend to throw airway terms around without specific knowledge. I think we all agree that it's just best to always keep the airway(s) open.

 

[leadduck]

AFAIK, some medical conditions such as asthma or COPD significantly increase your risk of a lung barotrauma when ascending even from shallow depths and while exhaling, see for example
Parents sue Boy Scouts for 2011 negligence death

 

[doctormike]

AFAIK, some medical conditions such as asthma or COPD significantly increase your risk of a lung barotrauma when ascending even from shallow depths and while exhaling, see for example
Parents sue Boy Scouts for 2011 negligence death

That’s true, good point, although much less common, since you need pretty tight bronchospasm to cause a significant pressure gradient. The issue with reactive airway disease (AKA asthma) is that contraction of the muscles in the walls of the small airways far down in the lung cause local pockets of trapped gas, which causes damage on expansion. Same goes for other abnormalities or the lung that do the same thing like a congenital or aquired bleb, history of pneumothorax, etc...

All barotrauma (lung, ears, sinuses, teeth) is the result of poor ventilation of a gas filled space.

 

[jgttrey]

True about surge, but only if you are untethered and moving with the surge. If you are hanging on a fixed (to the bottom) mooring line, like on safety stop, then your "depth" will be changing as the water column over your head changes height.

 

[doctormike]

True about surge, but only if you are untethered and moving with the surge. If you are hanging on a fixed (to the bottom) mooring line, like on safety stop, then your "depth" will be changing as the water column over your head changes height.

Also true!

In rough seas it's pretty common to have the anchor line move up and down a good bit, even more than the actual ocean surge due to the pitching of the boat. That's why I usually try not to hang on to the line unless there is significant current. I either just use it as a visual reference or just loop my hand loosely around it, letting it ride up and down while I hold the stop. A Jon line is good in that situation as well. Keeps you from getting blown away but doesn't jerk you up and down, and makes the line less crowded.