raviepoo
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Is it dangerous to cough on scuba?
Coughing
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Dr Deco
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Dear Readers:
Coughing
Yes, in some cases, coughing can cause a problem. As readers of this FORUM will note, I am not a big advocate of supersaturation control to prevent DCS. By this I mean, I do not believe that the deco meters alone will eliminate problems for some divers. Without question, gas loading is the biggest factor in determining who will get DCS. Nobody gets the bends without a pressure change. As a research scientist, I have put numerous animal and human subjects on the same depressurization profile, and I know that more than gas loading is involved. Actually, everyone knows this, and we are advised to keep in shape and stay well hydrated. This is good advice, although quite general.
In most cases, it is not clear what causes the difference between bends resistant and bends susceptible individuals (or animals). In other cases, what the diver does is obvious and significant. Straining with the muscles of the arms and legs is a good way to generate micronuclei and to enlarge those already present. If bubbles are present in the veins, changes in blood flow to the heart, in the presence of a PFO, can make a difference.
Abstract concerning Valsalva-like maneuvers
Balestra C, Germonpré P, Marroni A. Intrathoracic pressure changes after Valsalva strain and other maneuvers: implications for divers with patent foramen ovale. Undersea Hyperb Med 1998; 25(3): 171-4
Scuba divers with patent foramen ovale (PFO) may be at risk for paradoxical nitrogen gas emboli when performing maneuvers that cause a rebound blood loading to the right atrium. We measured the rise and fall in intrathoracic pressure (ITP) during various maneuvers in 15 divers. The tests were standard isometric exercises (control), forceful coughing, knee bend (with and without respiration blocked), and Valsalva maneuver (maximal, gradually increased to reach control ITP, and as performed by divers to equalize middle ear pressure). All the maneuvers, as well as the downward slope of ITP at the release phase, were related to the control value. ITP levels were significantly higher than the standard isometric effort during a breath-hold knee bend (172%), cough (133%), and maximal Valsalva (136%) whereas "usual" Valsalva maneuvers produced ITPs significantly lower than the standard (28%). We conclude that maneuvers other than the usual divers' Valsalva are more likely to cause post-release central blood shift, both by the levels of ITP reached and by the time during which these ITPs are sustained. Divers (especially with PFO) should be advised to refrain from strenuous leg, arm, or abdominal exercise after decompression dives.
How to get DCS
On any give profile, if I were hypothetically to be given the task to produce neurological DCS in an individual, what would I do?
I liken these methods to drinking water. When water was free, hardly anyone drank it. Now people charge $2 a bottle, and folks buy it like crazy. These diving techniques described in these FORUMS cost nothing, but a deco meter costs hundreds of dollars. SO - - people continue to talk about deco meters. The meter is a road map to help you find your way in the world of pressure profiles.
But, it alone will not keep you safe.
Dr Deco :doctor:
Coughing
Yes, in some cases, coughing can cause a problem. As readers of this FORUM will note, I am not a big advocate of supersaturation control to prevent DCS. By this I mean, I do not believe that the deco meters alone will eliminate problems for some divers. Without question, gas loading is the biggest factor in determining who will get DCS. Nobody gets the bends without a pressure change. As a research scientist, I have put numerous animal and human subjects on the same depressurization profile, and I know that more than gas loading is involved. Actually, everyone knows this, and we are advised to keep in shape and stay well hydrated. This is good advice, although quite general.
In most cases, it is not clear what causes the difference between bends resistant and bends susceptible individuals (or animals). In other cases, what the diver does is obvious and significant. Straining with the muscles of the arms and legs is a good way to generate micronuclei and to enlarge those already present. If bubbles are present in the veins, changes in blood flow to the heart, in the presence of a PFO, can make a difference.
Abstract concerning Valsalva-like maneuvers
Balestra C, Germonpré P, Marroni A. Intrathoracic pressure changes after Valsalva strain and other maneuvers: implications for divers with patent foramen ovale. Undersea Hyperb Med 1998; 25(3): 171-4
Scuba divers with patent foramen ovale (PFO) may be at risk for paradoxical nitrogen gas emboli when performing maneuvers that cause a rebound blood loading to the right atrium. We measured the rise and fall in intrathoracic pressure (ITP) during various maneuvers in 15 divers. The tests were standard isometric exercises (control), forceful coughing, knee bend (with and without respiration blocked), and Valsalva maneuver (maximal, gradually increased to reach control ITP, and as performed by divers to equalize middle ear pressure). All the maneuvers, as well as the downward slope of ITP at the release phase, were related to the control value. ITP levels were significantly higher than the standard isometric effort during a breath-hold knee bend (172%), cough (133%), and maximal Valsalva (136%) whereas "usual" Valsalva maneuvers produced ITPs significantly lower than the standard (28%). We conclude that maneuvers other than the usual divers' Valsalva are more likely to cause post-release central blood shift, both by the levels of ITP reached and by the time during which these ITPs are sustained. Divers (especially with PFO) should be advised to refrain from strenuous leg, arm, or abdominal exercise after decompression dives.
How to get DCS
On any give profile, if I were hypothetically to be given the task to produce neurological DCS in an individual, what would I do?
- pick bubbles-prone individuals (you can not tell this about your self,
- test them to see who has a hemodynamically significant PFO
- have them exercise on the gas uptake potion of the dive,
- have them rest during the off gassing portion of the dive,
- have them perform deep knee-flexes shortly after reaching the surface,
- shortly thereafter, have them perform a Valsalva-like maneuver (preferably while lying down - - to increase the rebound flow)
I liken these methods to drinking water. When water was free, hardly anyone drank it. Now people charge $2 a bottle, and folks buy it like crazy. These diving techniques described in these FORUMS cost nothing, but a deco meter costs hundreds of dollars. SO - - people continue to talk about deco meters. The meter is a road map to help you find your way in the world of pressure profiles.
But, it alone will not keep you safe.
Dr Deco :doctor:
OP
raviepoo
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You say that forceful coughing can be a problem. What about a tiny, weak, little cough?
What should a diver do when confronted with an uncontrollable urge to cough under water? I have had this happen to me a few times. No, I was not ill at the time - no head cold, congestion, etc. But a wrong swallow or a little tickle in my throat provoked a cough under water. I have 100 dives and can count these episodes on the fingers of one hand. How can I ensure that I don't end up in the chamber?
What should a diver do when confronted with an uncontrollable urge to cough under water? I have had this happen to me a few times. No, I was not ill at the time - no head cold, congestion, etc. But a wrong swallow or a little tickle in my throat provoked a cough under water. I have 100 dives and can count these episodes on the fingers of one hand. How can I ensure that I don't end up in the chamber?
BillP
Senior Member
If you have to cough, you have to cough, don't you? Sometimes it just can't be helped.
You can't. Do what you can do to limit your risk, use your common sense to understand what you can't do, and hope for the best.
Bill
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