Head down on deco =14% faster off gasing

Mdemon · 15th December 2007, 17:10

Quote: (Originally Posted by Mark Chase)

Many thanks for the heads up on this...

Boom tish!

dteubner · 15th December 2007, 19:36

Quote: (Originally Posted by Freef)

No more than being horizontal in bed. If you were vertical in the water the blood would be in your legs to the same extent as if you were on dry land.

Sorry David but this isn't true.

When you are vertical in air then there is a big pressure difference between your head and your feet becasue the heart is pumping blood up to your head and down to your feet. So if your blood pressure is 120/80 (millimetres of mercury) then the pressure in your scalp is 45cm of water less than this (90/50) and your feet 135cm more (220/180). A similar effect happens in the veins.

If you are vertical in the water then there is an additional pressure gradient. Say you are standing in a pool with your head just under the water. The top of your head is experienceing 1ATA and your feet are at 1.18 ATA. Because blood has essentially the same density as water this gradient abolishes the blood pressure differences described above. So immersion casues a very significant effect on blood flow and blood distribution, as well as eliminating the effect of orientation (head up vs down or whatever).

Retardboy · 15th December 2007, 20:30

Quote: (Originally Posted by Simon Mitchell)

Hello Mark,

I don't think you can read much into this with respect to diving. The experiment was conducted dry. The centralisation of blood volume that is achieved with the head down position in a dry subject is already achieved by peripheral vasoconstriction and loss of gravitational effect in an immersed subject, no matter what position they are in - head up, head down, sideways etc. This is not to detract from the importance of their findings for dry subjects about to escape from a submarine, about to embark on a space walk or in a couple of other contexts I can think of. However, there is probably no relevance to divers.

Warm regards,

Simon Mitchell

Are you sure it has no relevance to us? What about DCI treatment? A slightly head-down position would also open the small vessels a bit more. Maybe a detuned reg would not be such a bad idea when laying on the boat sucking the O2-bottle... Just a thought

Simon Mitchell · 15th December 2007, 22:29

Quote: (Originally Posted by Freef)

In water you have no more loss of gravitational effect than you do in the basket of a helium balloon. You are still under the influence of the Earth's pull.

Quote: (Originally Posted by Freef)

No more than being horizontal in bed. If you were vertical in the water the blood would be in your legs to the same extent as if you were on dry land.

As David suggests, you are wrong about this in terms of haemodynamics and distribution of blood volume (the subject of my post). There is a significant effect of immersion which is well documented in all good physiology texts.

Warm regards,

Simon M

Simon Mitchell · 15th December 2007, 22:42

Quote: (Originally Posted by Retardboy)

Are you sure it has no relevance to us? What about DCI treatment? A slightly head-down position would also open the small vessels a bit more. Maybe a detuned reg would not be such a bad idea when laying on the boat sucking the O2-bottle... Just a thought

Hello,

I was referring to decompression in the water, which was the subject of Mark's original post. Treatment of DCS was one of the "other circumstances" that was running through my mind when I made my original post. However, I was reluctant to mention it for several reasons: first, because there is no data whatsoever describing benefit in treatment of DCS; and second, because there are potential disadvantages from putting DCS victims head down. It follows that it would be inappropriate to suggest this as a legitimate first aid strategy.

Warm regards,

Simon M

Retardboy · 16th December 2007, 04:36

Quote: (Originally Posted by Simon Mitchell)

Hello,

I was referring to decompression in the water, which was the subject of Mark's original post. Treatment of DCS was one of the "other circumstances" that was running through my mind when I made my original post. However, I was reluctant to mention it for several reasons: first, because there is no data whatsoever describing benefit in treatment of DCS; and second, because there are potential disadvantages from putting DCS victims head down. It follows that it would be inappropriate to suggest this as a legitimate first aid strategy.

Warm regards,

Simon M

Hehe, I understand that you have a bit different level of responsibility if making recommendations than me

I'll go get bent and check if it works

**Freef** · 16th December 2007, 09:00

I'm no physiologist, but...

Quote: (Originally Posted by dteubner)

When you are vertical in air then there is a big pressure difference between your head and your feet becasue the heart is pumping blood up to your head and down to your feet. So if your blood pressure is 120/80 (millimetres of mercury) then the pressure in your scalp is 45cm of water less than this (90/50) and your feet 135cm more (220/180). A similar effect happens in the veins.

Is there really such a pressure difference? I would have thought that in a closed system with a pump and a small variation in height above the pump the pressure would be more equalised. If it wasn't then the blood from the brain would have difficulty on the return journey as it is linked to the higher pressure blood vessels that are returning from the legs.

Quote: (Originally Posted by dteubner)

If you are vertical in the water then there is an additional pressure gradient. Say you are standing in a pool with your head just under the water. The top of your head is experienceing 1ATA and your feet are at 1.18 ATA. Because blood has essentially the same density as water this gradient abolishes the blood pressure differences described above. So immersion casues a very significant effect on blood flow and blood distribution, as well as eliminating the effect of orientation (head up vs down or whatever).

How does immersion cause this? 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 also still being pumped around, so there will be the pressure generated by the heart to circulate the blood which will still be the same pressure as the surface, surely?

Having said all that, I deco on the flat so there is a minimum pressure difference across my body.

UKSteve · 16th December 2007, 10:26

For the doubters of the effects of immersion ...try this....

Take a plastic bag and fill it with water. .... hold it and observe its shape.

Now immerse the bag in a bucket of water and observe its shape.. still bulging at the bottom???

Steve

Janos · 16th December 2007, 14:10

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).

[1] - Not physiologically true - something that does something to the somethings I think.

**Freef** · 16th December 2007, 16:21

Quote: (Originally Posted by UKSteve)

For the doubters of the effects of immersion ...try this....

Take a plastic bag and fill it with water. .... hold it and observe its shape.

Now immerse the bag in a bucket of water and observe its shape.. still bulging at the bottom???

Steve

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.

I'll have a go with a blood pressure cuff myself next week to see if there is a big difference between head and feet.

This will mean a cuff around my neck, but I don't want to hear any cheering at the back!

Can anyone can cite a reference to the changes in blood pressure that I can look up online?

Quote: (Originally Posted by dteubner)

If you are vertical in the water then there is an additional pressure gradient. Say you are standing in a pool with your head just under the water. The top of your head is experienceing 1ATA and your feet are at 1.18 ATA. Because blood has essentially the same density as water this gradient abolishes the blood pressure differences described above. So immersion casues a very significant effect on blood flow and blood distribution, as well as eliminating the effect of orientation (head up vs down or whatever).

Had another look at this, if it held true, wouldn't people get a massive rush of blood to the head if they were just under heart deep in a pool?

As I recall air pressure is about 760mmHg, with blood pressure at 130/90 or whatever it is, if the water pressure had too great effect then the lower pressure [systolic?] would be lowe than the water pressure if the heart was 1.2m or more above the feet.

If I'm missing something fine, but the examples given don't relate to the human body as far as I can see.

As with Mrs T and the Higgs boson, anyone able to demonstrate why this happens on a single side of A4 [or a post of no more than 25 lines!] wins a green.

15th December 2007, 17:10	#21 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,888	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Mark Chase) Many thanks for the heads up on this... Boom tish! __________________ www.southwestmafia.com It's as easy as abc; a) "Carry adequate bailout" b) "If in doubt, bail out" c) "Always know your PO2" If you find that hard, stick to crochet. "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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15th December 2007, 19:36	#22 (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) No more than being horizontal in bed. If you were vertical in the water the blood would be in your legs to the same extent as if you were on dry land. Sorry David but this isn't true. When you are vertical in air then there is a big pressure difference between your head and your feet becasue the heart is pumping blood up to your head and down to your feet. So if your blood pressure is 120/80 (millimetres of mercury) then the pressure in your scalp is 45cm of water less than this (90/50) and your feet 135cm more (220/180). A similar effect happens in the veins. If you are vertical in the water then there is an additional pressure gradient. Say you are standing in a pool with your head just under the water. The top of your head is experienceing 1ATA and your feet are at 1.18 ATA. Because blood has essentially the same density as water this gradient abolishes the blood pressure differences described above. So immersion casues a very significant effect on blood flow and blood distribution, as well as eliminating the effect of orientation (head up vs down or whatever). __________________ Dave T Hanlon's Razor - Never attribute to malice that which can be adequately explained by stupidity.
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15th December 2007, 20:30	#23 (permalink)
Retardboy New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Mar 2006 Location: Norway Posts: 16	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Simon Mitchell) Hello Mark, I don't think you can read much into this with respect to diving. The experiment was conducted dry. The centralisation of blood volume that is achieved with the head down position in a dry subject is already achieved by peripheral vasoconstriction and loss of gravitational effect in an immersed subject, no matter what position they are in - head up, head down, sideways etc. This is not to detract from the importance of their findings for dry subjects about to escape from a submarine, about to embark on a space walk or in a couple of other contexts I can think of. However, there is probably no relevance to divers. Warm regards, Simon Mitchell Are you sure it has no relevance to us? What about DCI treatment? A slightly head-down position would also open the small vessels a bit more. Maybe a detuned reg would not be such a bad idea when laying on the boat sucking the O2-bottle... Just a thought
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15th December 2007, 22:29	#24 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 157	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Freef) In water you have no more loss of gravitational effect than you do in the basket of a helium balloon. You are still under the influence of the Earth's pull. Quote: (Originally Posted by Freef) No more than being horizontal in bed. If you were vertical in the water the blood would be in your legs to the same extent as if you were on dry land. As David suggests, you are wrong about this in terms of haemodynamics and distribution of blood volume (the subject of my post). There is a significant effect of immersion which is well documented in all good physiology texts. Warm regards, Simon M Last edited by Simon Mitchell : 15th December 2007 at 22:54.
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15th December 2007, 22:42	#25 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 157	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Retardboy) Are you sure it has no relevance to us? What about DCI treatment? A slightly head-down position would also open the small vessels a bit more. Maybe a detuned reg would not be such a bad idea when laying on the boat sucking the O2-bottle... Just a thought Hello, I was referring to decompression in the water, which was the subject of Mark's original post. Treatment of DCS was one of the "other circumstances" that was running through my mind when I made my original post. However, I was reluctant to mention it for several reasons: first, because there is no data whatsoever describing benefit in treatment of DCS; and second, because there are potential disadvantages from putting DCS victims head down. It follows that it would be inappropriate to suggest this as a legitimate first aid strategy. Warm regards, Simon M
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16th December 2007, 04:36	#26 (permalink)
Retardboy New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Mar 2006 Location: Norway Posts: 16	Re: Head down on deco =14% faster off gasing Quote: (Originally Posted by Simon Mitchell) Hello, I was referring to decompression in the water, which was the subject of Mark's original post. Treatment of DCS was one of the "other circumstances" that was running through my mind when I made my original post. However, I was reluctant to mention it for several reasons: first, because there is no data whatsoever describing benefit in treatment of DCS; and second, because there are potential disadvantages from putting DCS victims head down. It follows that it would be inappropriate to suggest this as a legitimate first aid strategy. Warm regards, Simon M Hehe, I understand that you have a bit different level of responsibility if making recommendations than me I'll go get bent and check if it works
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16th December 2007, 09:00	#27 (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 I'm no physiologist, but... Quote: (Originally Posted by dteubner) When you are vertical in air then there is a big pressure difference between your head and your feet becasue the heart is pumping blood up to your head and down to your feet. So if your blood pressure is 120/80 (millimetres of mercury) then the pressure in your scalp is 45cm of water less than this (90/50) and your feet 135cm more (220/180). A similar effect happens in the veins. Is there really such a pressure difference? I would have thought that in a closed system with a pump and a small variation in height above the pump the pressure would be more equalised. If it wasn't then the blood from the brain would have difficulty on the return journey as it is linked to the higher pressure blood vessels that are returning from the legs. Quote: (Originally Posted by dteubner) If you are vertical in the water then there is an additional pressure gradient. Say you are standing in a pool with your head just under the water. The top of your head is experienceing 1ATA and your feet are at 1.18 ATA. Because blood has essentially the same density as water this gradient abolishes the blood pressure differences described above. So immersion casues a very significant effect on blood flow and blood distribution, as well as eliminating the effect of orientation (head up vs down or whatever). How does immersion cause this? 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 also still being pumped around, so there will be the pressure generated by the heart to circulate the blood which will still be the same pressure as the surface, surely? Having said all that, I deco on the flat so there is a minimum pressure difference across my body. __________________ David. Currently owner of two differently sized ankles.
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16th December 2007, 10:26	#28 (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 For the doubters of the effects of immersion ...try this.... Take a plastic bag and fill it with water. .... hold it and observe its shape. Now immerse the bag in a bucket of water and observe its shape.. still bulging at the bottom??? Steve
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16th December 2007, 14:10	#29 (permalink)
Janos "Two Sheds" Current Rebreather/s: Classic Kiss Other Rebreather/s: Classic Kiss Join Date: Feb 2005 Location: East Surrey Posts: 580	Re: Head down on deco =14% faster off gasing 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). [1] - Not physiologically true - something that does something to the somethings I think. __________________ 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
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16th December 2007, 16:21	#30 (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 Quote: (Originally Posted by UKSteve) For the doubters of the effects of immersion ...try this.... Take a plastic bag and fill it with water. .... hold it and observe its shape. Now immerse the bag in a bucket of water and observe its shape.. still bulging at the bottom??? Steve 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. I'll have a go with a blood pressure cuff myself next week to see if there is a big difference between head and feet. This will mean a cuff around my neck, but I don't want to hear any cheering at the back! Can anyone can cite a reference to the changes in blood pressure that I can look up online? Quote: (Originally Posted by dteubner) If you are vertical in the water then there is an additional pressure gradient. Say you are standing in a pool with your head just under the water. The top of your head is experienceing 1ATA and your feet are at 1.18 ATA. Because blood has essentially the same density as water this gradient abolishes the blood pressure differences described above. So immersion casues a very significant effect on blood flow and blood distribution, as well as eliminating the effect of orientation (head up vs down or whatever). Had another look at this, if it held true, wouldn't people get a massive rush of blood to the head if they were just under heart deep in a pool? As I recall air pressure is about 760mmHg, with blood pressure at 130/90 or whatever it is, if the water pressure had too great effect then the lower pressure [systolic?] would be lowe than the water pressure if the heart was 1.2m or more above the feet. If I'm missing something fine, but the examples given don't relate to the human body as far as I can see. As with Mrs T and the Higgs boson, anyone able to demonstrate why this happens on a single side of A4 [or a post of no more than 25 lines!] wins a green. __________________ David. Currently owner of two differently sized ankles.
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