barb
Contributor
I'm looking to learn more about what causes air embolism - I know a too fast ascent increases risk but I recently read of a death where the diver was at depth and died from an air embolism. How could that happen?
air embolism - Information on?
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The Iceni
Medical Moderator
Hi Barb,
Please do not be put off diving by this post. You asked . I trust the medical regulators will forgive my impertinence in answering!
It is now thought that small bubbles form in the veins of all divers on ascent but these are mopped up by the lungs causing little or no damage. On the other hand air emobism, or more properly arterial gas embolism;- AGE, which is relatively uncommon, will occur whenever gas finds it's way into the arterial tree. As the diver ascends from any depth the pressure changes increase the size of the gas bubble and, even if it is not large enough to start with, it will eventually grow to sufficent size to obstruct blood flow further down that artery, arteriole or capillary.
Obviously the most dangerous are those bubbles that find their way into the cerebral or coronary arteries. (Because of gravity and the relative size of those arteries the former is more likely.) Bubbles of inert gas in the cerebral arteries will cause a stroke, (an uncommon feature of type II DCI.), those in the coronary arteries a genuine heart attack (myocardial infarction) in an ortherwise healthy individual.
What causes AGE?
1) Any situation where the integrity of the pulmonary capilliaries (or veins) is damaged. This tear allows bubbles of gas into the pulmonary veins whence they go directly though the heart and then to the arterial circulation.
This can occur with a rapid ascent, particularly when breath holding, also resulting in a burst lung or pneumothorax. In a pneumothorax the intrathoracic pressure can be considerable and may exceed that of a car tyre. The gas trapped between the lungs and the chest wall has nowhere to go except into the pulmonary veins. The pressure can often be high enough to stop venous return to the heart and cause a cardiac arrest.
This is why "asthma" or any chronic obstructive pulmonary disease COPD is a relative contraindication to scuba diving. Asthma, emphysema or any COPD is characterised by an obstruction to exhalation at the level of the smaller airways, resulting in the trapping of gas in lung tissue. This gas expands on ascent and can rupture the alveolar sacs or bronchioles to cause the enivitable pneumothorax and/or AGE.
2) This is also why those divers with a congenital defect known as patent foramen ovale can suffer unexpected DCI since the numerous small bubbles can cross from the right atrium into the left atrium through such a "shunt" to bypass the lung filter.
Now you know why we are all advised to practice slow ascents and not to hold our breath on ascent, even from the shallowest of dives.
However, you can be reassured, barb, that for adequatly trained and healthy divers air embolism is very rare.
About as common as a shark attack, I suppose! :shark:
Please do not be put off diving by this post. You asked . I trust the medical regulators will forgive my impertinence in answering!
It is now thought that small bubbles form in the veins of all divers on ascent but these are mopped up by the lungs causing little or no damage. On the other hand air emobism, or more properly arterial gas embolism;- AGE, which is relatively uncommon, will occur whenever gas finds it's way into the arterial tree. As the diver ascends from any depth the pressure changes increase the size of the gas bubble and, even if it is not large enough to start with, it will eventually grow to sufficent size to obstruct blood flow further down that artery, arteriole or capillary.
Obviously the most dangerous are those bubbles that find their way into the cerebral or coronary arteries. (Because of gravity and the relative size of those arteries the former is more likely.) Bubbles of inert gas in the cerebral arteries will cause a stroke, (an uncommon feature of type II DCI.), those in the coronary arteries a genuine heart attack (myocardial infarction) in an ortherwise healthy individual.
What causes AGE?
1) Any situation where the integrity of the pulmonary capilliaries (or veins) is damaged. This tear allows bubbles of gas into the pulmonary veins whence they go directly though the heart and then to the arterial circulation.
This can occur with a rapid ascent, particularly when breath holding, also resulting in a burst lung or pneumothorax. In a pneumothorax the intrathoracic pressure can be considerable and may exceed that of a car tyre. The gas trapped between the lungs and the chest wall has nowhere to go except into the pulmonary veins. The pressure can often be high enough to stop venous return to the heart and cause a cardiac arrest.
This is why "asthma" or any chronic obstructive pulmonary disease COPD is a relative contraindication to scuba diving. Asthma, emphysema or any COPD is characterised by an obstruction to exhalation at the level of the smaller airways, resulting in the trapping of gas in lung tissue. This gas expands on ascent and can rupture the alveolar sacs or bronchioles to cause the enivitable pneumothorax and/or AGE.
2) This is also why those divers with a congenital defect known as patent foramen ovale can suffer unexpected DCI since the numerous small bubbles can cross from the right atrium into the left atrium through such a "shunt" to bypass the lung filter.
Now you know why we are all advised to practice slow ascents and not to hold our breath on ascent, even from the shallowest of dives.
However, you can be reassured, barb, that for adequatly trained and healthy divers air embolism is very rare.
About as common as a shark attack, I suppose! :shark:
Thanks for answering Paul
I have a better understanding now but still wonder why this diver in Tobermory developed an AGE?
According to his buddy they were together ascending sharing air when he started to sink - pulling her down with him. She had to make the hardest decision of her life - she pushed him away and ascended. My heart goes out to her for having been in that position but I still wonder why he died of AGE? They were ascending together - same speed.
I want to understand to protect myself and my future buddies
I have a better understanding now but still wonder why this diver in Tobermory developed an AGE?
According to his buddy they were together ascending sharing air when he started to sink - pulling her down with him. She had to make the hardest decision of her life - she pushed him away and ascended. My heart goes out to her for having been in that position but I still wonder why he died of AGE? They were ascending together - same speed.
I want to understand to protect myself and my future buddies
AGE while sharing used to be common in the days when sharing was routinely taught and before octipi and reserve DV's were thought of
Reciever holds breath while he hasn't got the DV in mouth and the pair are ascending (quite fast if they are panicing or near panicing). POP!
Thats why you are taught to dribble air outg while sharing and its not your turn to breathe
The BSAC analyse all the UK accident statisteics and yearly there are examples of folks that share succesfully from deep to shallow depth and then they separate and one sinks. Its always been assumed they went pop. thats why the BSAC no longer teach normal single DV sharing and teach the use of an octopus or second reg.
Personally I would teach both, but require all divers to have at least 2 independant air sources. Personally I dive a long hose round my neck and my spare on a bungy round my neck as well. ie DIR style. I dont agree on everything the DIR bigots preach but thats one thing they have got right. Oh, I also have an Air2, as a backup to the backup and because I prefer it over a normal BC inflator (Chunkier and easier to operate with 5mm gloves on). As an instructor taking in novices I am always diving solo, so I also have at least 2 independant air sources (normally isolation manifold twin 12's) or at min a single with a pony.
Reciever holds breath while he hasn't got the DV in mouth and the pair are ascending (quite fast if they are panicing or near panicing). POP!
Thats why you are taught to dribble air outg while sharing and its not your turn to breathe
The BSAC analyse all the UK accident statisteics and yearly there are examples of folks that share succesfully from deep to shallow depth and then they separate and one sinks. Its always been assumed they went pop. thats why the BSAC no longer teach normal single DV sharing and teach the use of an octopus or second reg.
Personally I would teach both, but require all divers to have at least 2 independant air sources. Personally I dive a long hose round my neck and my spare on a bungy round my neck as well. ie DIR style. I dont agree on everything the DIR bigots preach but thats one thing they have got right. Oh, I also have an Air2, as a backup to the backup and because I prefer it over a normal BC inflator (Chunkier and easier to operate with 5mm gloves on). As an instructor taking in novices I am always diving solo, so I also have at least 2 independant air sources (normally isolation manifold twin 12's) or at min a single with a pony.
Dr Deco
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Dear Readers:
Arterial gas embolism is definitely something a diver wishes to avoid. Thus we have the Prime Directive, always keep an open airway up to the surface. Never move from higher to lower pressure with your airway closed. I suspect from the replies that this closed-airway scenario is what occurred at Tobermory.
Venous bubbles are also present in many recreational divers during decompression. Remember that decompression is the ascent phase of the dive PLUS the surface portion of the dive. If you have a PFO and perform a Valsalva-like maneuver (holding your breath while straining, climbing the boat ladder, lifting, etc), then it is possible that the normal left-to-right pressure gradient in the atria of you heart will reverse. This [abnormal] right-to-left gradient can appear for a couple of heartbeats and allow gas bubbles to pass into the arterial circulation.
Dr Deco :doctor:
Arterial gas embolism is definitely something a diver wishes to avoid. Thus we have the Prime Directive, always keep an open airway up to the surface. Never move from higher to lower pressure with your airway closed. I suspect from the replies that this closed-airway scenario is what occurred at Tobermory.
Venous bubbles are also present in many recreational divers during decompression. Remember that decompression is the ascent phase of the dive PLUS the surface portion of the dive. If you have a PFO and perform a Valsalva-like maneuver (holding your breath while straining, climbing the boat ladder, lifting, etc), then it is possible that the normal left-to-right pressure gradient in the atria of you heart will reverse. This [abnormal] right-to-left gradient can appear for a couple of heartbeats and allow gas bubbles to pass into the arterial circulation.
Dr Deco :doctor:
landlocked
Contributor
Geeze doc, your scarring me here. If I hold my breath while I'm climbing the ladder I could suffer an embolism?
The Iceni
Medical Moderator
Landlocked, I do not believe that was what Dr Deco said or meant.
He was confirming that such post-dive exercise will cause the development of yet more micronucleii and straining, to lift heavy kit, may cause a valsalva-like manoeuvre and some of those bubbles that are always present in the venous system to find their way via a right-to-left shunt into the arterial tree causing DCI.
In addition, I remember three years ago, when on holiday in Cornwall with my wife, I decided to do a dive for the first time in far too many years. This was a shore dive which went very well and got me hooked again.
After the dive we had to carry the kit up the cliffs to the van and I remember feeling decidely unwell for a few minutes after this. I now know that was very foolish thing to do - OK I was not very fit but generating all those micronucleii probably caused me to suffer mild DCI.
The problem as I see it is that repetetive dives over a number of days results in the gradual topping up of the slower tissue compartments with nitrogen because even an overnight surface interval is insufficient to eliminate all the nitrogen from the body.
It takes at least two and a half days for all the nitrogen to be excreted and there is less evidence to support the safety of currently used alorithms for multiple dives over multiple days because of this.
In consequence I now never plan to do more than two dives per day over more than three consecutive days.
Playing ultra safe? perhaps.
Madmole.
I wondered why BSAC had abandonned air sharing. What you say makes a lot of sense. I always use a manifolded twinset so I have access to all of my gas, even after a first stage failure. To my mind a 3 litre pony is not adequate (and it is clumbsy and assymetrical) but admit that this is matter of personal choice.
The recurring problem all instructors face is the need to do multiple dives.
He was confirming that such post-dive exercise will cause the development of yet more micronucleii and straining, to lift heavy kit, may cause a valsalva-like manoeuvre and some of those bubbles that are always present in the venous system to find their way via a right-to-left shunt into the arterial tree causing DCI.
In addition, I remember three years ago, when on holiday in Cornwall with my wife, I decided to do a dive for the first time in far too many years. This was a shore dive which went very well and got me hooked again.
After the dive we had to carry the kit up the cliffs to the van and I remember feeling decidely unwell for a few minutes after this. I now know that was very foolish thing to do - OK I was not very fit but generating all those micronucleii probably caused me to suffer mild DCI.
The problem as I see it is that repetetive dives over a number of days results in the gradual topping up of the slower tissue compartments with nitrogen because even an overnight surface interval is insufficient to eliminate all the nitrogen from the body.
It takes at least two and a half days for all the nitrogen to be excreted and there is less evidence to support the safety of currently used alorithms for multiple dives over multiple days because of this.
In consequence I now never plan to do more than two dives per day over more than three consecutive days.
Playing ultra safe? perhaps.
Madmole.
I wondered why BSAC had abandonned air sharing. What you say makes a lot of sense. I always use a manifolded twinset so I have access to all of my gas, even after a first stage failure. To my mind a 3 litre pony is not adequate (and it is clumbsy and assymetrical) but admit that this is matter of personal choice.
The recurring problem all instructors face is the need to do multiple dives.
Dr Deco
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Dear Readers:
This Valsalva-like maneuver is the hold and release breathing that keeps blood from entering the thoracic vena cava and then suddenly entering in one big slug. This type of maneuver is what is performed to determine if one has a PFO. What is done is this:
Now you have one reason.
Dr Deco :doctor:
This Valsalva-like maneuver is the hold and release breathing that keeps blood from entering the thoracic vena cava and then suddenly entering in one big slug. This type of maneuver is what is performed to determine if one has a PFO. What is done is this:
- hold breath after a full inspiration
- inject bubbles in shaken saline into the arm vein
- release breath (Valsalva maneuver)
- look with echo ultrasound to see if the gas bubbles appear in left side of heart.
Now you have one reason.
Dr Deco :doctor:
I reread the information on the Tobermory death and according to the divers buddy - They went from 110' to 93' together. The diver that died was using her octo so he would have been breathing fine. According to her he was looking her in the face when he suddently started to descend again - took her down to 139' before she had to push him away as she only had 500 psi left. So now tell me how could this diver have an embolism going form 110' to 93' ?
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