Head down on deco =14% faster off gasing

mbelair · 16th December 2007, 16:47

Quote: (Originally Posted by caveseeker7)

Apollo.

Apparently, they still market the option.

http://www.apollosportsusa.com/docum...alog-12-13.pdf

UKSteve · 16th December 2007, 17:08

Quote: (Originally Posted by Freef)

Not a terribly accurate example as the bag is hardly rigid like the body. You might as well say fill a balloon with air under water and observe it's shape and then observe it again at the surface.

Actually I think you'll find that from a hydraulic pressure point of view the human body is not rigid at all.. the skeleton is on the inside and does not protect the body's liquids from pressure at all (except perhaps the brain to a limited extent) and this is the whole point.. the liquids are suddenly subjected to all round pressure rather than just the effects of gravity..

..but hey... I am not a doctor or scientist.. I make my living drilling holes in the ground ..or these days teaching others to do it so I might be talking a load of b0llocks

Was it not the Fastnet sailors who took a hammering when they were lifted vertically from the water after prolonged immersion and died from hypovoleamic (spelling??) shock?

Steve

Simon Mitchell · 16th December 2007, 19:04

Quote: (Originally Posted by Janos)

And of course there is immersion shock - the sad case of those North Sea oil rig workers who died after being lifted from the sea - they had been in the water so long that their veins had relaxed [1] and when they were winched out the blood pooled in their feet and insufficient blood got to the brain.

I've always wondered about this and long dives. How long do you have to be immersed before this becomes a problem?

Janos

PS - Simon - I've head rumours about your talk at the GUE conference - will you publishing / summarising it online anywhere (especially the exercise stuff).

Janos,

The reason for post immersion shock is a reversal of the process that Freef is expressing so much doubt about. There is a centralisation of blood volume during immersion as Dave T and I have pointed out. At the same time, over a prolonged period of immersion there is dehydration due to an immersion induced diuresis (Freef, you might want to ask yourself why that happens too) and other factors. If the victim is then hoiked out of the water in an upright position there is a sudden loss of (a now depleted) blood volume into the dependent vessels (mainly the large veins in the legs) and this can be sufficient to cause shock and cardiac arrest.

So, for Freef's sake, let me restate that another way: you can be upright in the water with no problem. Then you get removed from the water in an upright position and you die of hypotensive shock. Think about that.

There is no magical time at which this becomes an issue, but the longer the immersion the greater the risk. Frank Golden's definitive work on this issue, published in the Journal of the Royal Naval Medical Service (in 1992 IIRC) unequivocally recommends removal of prolonged immersion victims in the horizontal position.

I understand that GUE is making a DVD of all the talks, with the power point presentations included. There are bits of mine that might have to censored, but the important bits will be available.

Warm regards,

Simon M

dteubner · 16th December 2007, 19:21

Quote: (Originally Posted by Freef)

I'm no physiologist, but...

Is there really such a pressure difference?

Yes, of course there is. There is a essentially a column of blood from the head to the feet and so that blood exerts a pressure in the feet equal to the height of the column. The actual pressure at any point in the system is the sum of the pressure generated by the system (the heart in the ateries and the venous tone in the veins) and the hydrostatic prssure of the column.

Quote:

How does immersion cause this?

By getting rid of the pressure column effect because the external pressure at any point in the system is essentially equal to the column of blood. So the actual pressure in the circulation is simply the generated pressure alone.

Quote:

Blood may be the same density as water, but it is enclosed within the body and not mixing with the water [sharks permiting

]. The circulatory system is a liquid so there should me no [OK, minimal because it does contain dissolved gas] compression of the blood vessels and reduction in blood volume.

Blood is obviously incompressible but there is an important concept called venous capacitance. A vein will expand when the pressure of the blood in it rises. Immersion changes the distribution of venous blood by decreasing the pressure in the veins below the heart. This actually increases the venous pressure at the heart, increasing the venous return and the cardiac output. Increasing the cardiac output increases the blood fow to the kidneys which increases the urine output so the blood volume does fall (although indirectly).

The point is that, as Simon pointed out in his original post, effects of posture on blood flow and distribution in a dry environment will not happen when immersed.

**Freef** · 17th December 2007, 16:15

Well explained, green sent as promised.

With regard to the removal fromwater after prolonged immersion, how much does the water temperature play in the process? Does laying flat while floating about help reduce the risk?

Quote: (Originally Posted by dteubner)

Blood is obviously incompressible but there is an important concept called venous capacitance. A vein will expand when the pressure of the blood in it rises. Immersion changes the distribution of venous blood by decreasing the pressure in the veins below the heart. This actually increases the venous pressure at the heart, increasing the venous return and the cardiac output. Increasing the cardiac output increases the blood fow to the kidneys which increases the urine output so the blood volume does fall (although indirectly).

Janos · 17th December 2007, 20:51

Quote: (Originally Posted by Simon Mitchell)

The reason for post immersion shock is a reversal of the process that Freef is expressing so much doubt about. There is a centralisation of blood volume during immersion as Dave T and I have pointed out. At the same time, over a prolonged period of immersion there is dehydration due to an immersion induced diuresis (Freef, you might want to ask yourself why that happens too) and other factors. If the victim is then hoiked out of the water in an upright position there is a sudden loss of (a now depleted) blood volume into the dependent vessels (mainly the large veins in the legs) and this can be sufficient to cause shock and cardiac arrest.

So, for Freef's sake, let me restate that another way: you can be upright in the water with no problem. Then you get removed from the water in an upright position and you die of hypotensive shock. Think about that.

There is no magical time at which this becomes an issue, but the longer the immersion the greater the risk. Frank Golden's definitive work on this issue, published in the Journal of the Royal Naval Medical Service (in 1992 IIRC) unequivocally recommends removal of prolonged immersion victims in the horizontal position.

Thanks Simon, lifting a casualty horizontally was taught to me in my Rescue Management Course, I was just wondering if there were implications for people doing long (10+ hour) dives.

Quote: (Originally Posted by Simon Mitchell)

I understand that GUE is making a DVD of all the talks, with the power point presentations included. There are bits of mine that might have to censored, but the important bits will be available.

Great news

I've got some information secondhand from Clare, but it would be good to hear it, if not firsthand, then the next best thing

Janos

16th December 2007, 16:47	#31 (permalink)
mbelair New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jan 2006 Location: Montreal Posts: 81	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by caveseeker7) Apollo. Apparently, they still market the option. http://www.apollosportsusa.com/docum...alog-12-13.pdf __________________ Marc
(Online)

16th December 2007, 17:08	#32 (permalink)
UKSteve Still a novice... Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Jul 2005 Location: Weymouth, UK Posts: 557	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Freef) Not a terribly accurate example as the bag is hardly rigid like the body. You might as well say fill a balloon with air under water and observe it's shape and then observe it again at the surface. Actually I think you'll find that from a hydraulic pressure point of view the human body is not rigid at all.. the skeleton is on the inside and does not protect the body's liquids from pressure at all (except perhaps the brain to a limited extent) and this is the whole point.. the liquids are suddenly subjected to all round pressure rather than just the effects of gravity.. ..but hey... I am not a doctor or scientist.. I make my living drilling holes in the ground ..or these days teaching others to do it so I might be talking a load of b0llocks Was it not the Fastnet sailors who took a hammering when they were lifted vertically from the water after prolonged immersion and died from hypovoleamic (spelling??) shock? Steve
(Offline)

16th December 2007, 19:04	#33 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 156	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Janos) And of course there is immersion shock - the sad case of those North Sea oil rig workers who died after being lifted from the sea - they had been in the water so long that their veins had relaxed [1] and when they were winched out the blood pooled in their feet and insufficient blood got to the brain. I've always wondered about this and long dives. How long do you have to be immersed before this becomes a problem? Janos PS - Simon - I've head rumours about your talk at the GUE conference - will you publishing / summarising it online anywhere (especially the exercise stuff). Janos, The reason for post immersion shock is a reversal of the process that Freef is expressing so much doubt about. There is a centralisation of blood volume during immersion as Dave T and I have pointed out. At the same time, over a prolonged period of immersion there is dehydration due to an immersion induced diuresis (Freef, you might want to ask yourself why that happens too) and other factors. If the victim is then hoiked out of the water in an upright position there is a sudden loss of (a now depleted) blood volume into the dependent vessels (mainly the large veins in the legs) and this can be sufficient to cause shock and cardiac arrest. So, for Freef's sake, let me restate that another way: you can be upright in the water with no problem. Then you get removed from the water in an upright position and you die of hypotensive shock. Think about that. There is no magical time at which this becomes an issue, but the longer the immersion the greater the risk. Frank Golden's definitive work on this issue, published in the Journal of the Royal Naval Medical Service (in 1992 IIRC) unequivocally recommends removal of prolonged immersion victims in the horizontal position. I understand that GUE is making a DVD of all the talks, with the power point presentations included. There are bits of mine that might have to censored, but the important bits will be available. Warm regards, Simon M
(Offline)

16th December 2007, 19:21	#34 (permalink)
dteubner Pedant Current Rebreather/s: Sport Kiss Classic Kiss Other Rebreather/s: Join Date: Mar 2005 Location: Adelaide, Australia Posts: 216	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Freef) I'm no physiologist, but... Is there really such a pressure difference? Yes, of course there is. There is a essentially a column of blood from the head to the feet and so that blood exerts a pressure in the feet equal to the height of the column. The actual pressure at any point in the system is the sum of the pressure generated by the system (the heart in the ateries and the venous tone in the veins) and the hydrostatic prssure of the column. Quote: How does immersion cause this? By getting rid of the pressure column effect because the external pressure at any point in the system is essentially equal to the column of blood. So the actual pressure in the circulation is simply the generated pressure alone. Quote: Blood may be the same density as water, but it is enclosed within the body and not mixing with the water [sharks permiting ]. The circulatory system is a liquid so there should me no [OK, minimal because it does contain dissolved gas] compression of the blood vessels and reduction in blood volume. Blood is obviously incompressible but there is an important concept called venous capacitance. A vein will expand when the pressure of the blood in it rises. Immersion changes the distribution of venous blood by decreasing the pressure in the veins below the heart. This actually increases the venous pressure at the heart, increasing the venous return and the cardiac output. Increasing the cardiac output increases the blood fow to the kidneys which increases the urine output so the blood volume does fall (although indirectly). The point is that, as Simon pointed out in his original post, effects of posture on blood flow and distribution in a dry environment will not happen when immersed. __________________ Dave T Hanlon's Razor - Never attribute to malice that which can be adequately explained by stupidity. Last edited by dteubner : 16th December 2007 at 19:46.
(Offline)

17th December 2007, 16:15	#35 (permalink)
Freef Custom Title Disallowed! Current Rebreather/s: Dolphin Other Rebreather/s: Dolphin Join Date: Jan 2006 Location: Land of the Freef, UK. Posts: 1,356	Re: Head down on deco =14% faster off gasing Well explained, green sent as promised. With regard to the removal fromwater after prolonged immersion, how much does the water temperature play in the process? Does laying flat while floating about help reduce the risk? Quote: (Originally Posted by dteubner) Blood is obviously incompressible but there is an important concept called venous capacitance. A vein will expand when the pressure of the blood in it rises. Immersion changes the distribution of venous blood by decreasing the pressure in the veins below the heart. This actually increases the venous pressure at the heart, increasing the venous return and the cardiac output. Increasing the cardiac output increases the blood fow to the kidneys which increases the urine output so the blood volume does fall (although indirectly). __________________ David. Currently owner of two differently sized ankles.
(Offline)

17th December 2007, 20:51	#36 (permalink)
Janos "Two Sheds" Current Rebreather/s: Classic Kiss Other Rebreather/s: Classic Kiss Join Date: Feb 2005 Location: East Surrey Posts: 579	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Simon Mitchell) The reason for post immersion shock is a reversal of the process that Freef is expressing so much doubt about. There is a centralisation of blood volume during immersion as Dave T and I have pointed out. At the same time, over a prolonged period of immersion there is dehydration due to an immersion induced diuresis (Freef, you might want to ask yourself why that happens too) and other factors. If the victim is then hoiked out of the water in an upright position there is a sudden loss of (a now depleted) blood volume into the dependent vessels (mainly the large veins in the legs) and this can be sufficient to cause shock and cardiac arrest. So, for Freef's sake, let me restate that another way: you can be upright in the water with no problem. Then you get removed from the water in an upright position and you die of hypotensive shock. Think about that. There is no magical time at which this becomes an issue, but the longer the immersion the greater the risk. Frank Golden's definitive work on this issue, published in the Journal of the Royal Naval Medical Service (in 1992 IIRC) unequivocally recommends removal of prolonged immersion victims in the horizontal position. Thanks Simon, lifting a casualty horizontally was taught to me in my Rescue Management Course, I was just wondering if there were implications for people doing long (10+ hour) dives. Quote: (Originally Posted by Simon Mitchell) I understand that GUE is making a DVD of all the talks, with the power point presentations included. There are bits of mine that might have to censored, but the important bits will be available. Great news I've got some information secondhand from Clare, but it would be good to hear it, if not firsthand, then the next best thing Janos __________________ You can lead a horse to water but you can't climb a ladder with a large bell in both hands - Vic Reeves www.hellfins.com/shed
(Offline)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode