Bounce, repetitive diving question

floater · April 23rd, 2006, 09:01 PM

I've been reading George's deco articles at http://www.wkpp.org/decompression.htm and some of his other stuff.

I sort of see what he's getting at with the repetitive diving, but my understanding is far from solid, and I was hoping to get some more info here to make things more concrete.

1. He has said that the bubbles can grow up to 4 hours after surfacing (before they start to contract), but that he clears of them in under 30min. I'd like to know what the 4 hour figure is based on? How long does it take for the bubbles to then dissapear? How big are they (diameter?) and do they all grow more or less uniformly?

2. George recommends a deeper second dive because of the bounce dive problem, and I see why no bounce diving makes sense, but I'm not clear on why that implies that a deeper second dive is better. Namely the problem, as I understood it, was the rapid ascent associated with the bounce dive when there were still bubbles all over the system. But would it be any safer to make a deep bounce dive - say deeper than the first dive, as opposed to a second shallow bounce dive. I mean, if the bubbles have grown sufficiently big on the surface then going sufficiently deep would make them small enough to slip through into the brain and spine anyway, so going up fast would seem just as bad as doing it from a shallow depth. What am I missing?

NIMROD CHEN · April 23rd, 2006, 11:00 PM

Quote: (Originally Posted by floater)

I've been reading George's deco articles at http://www.wkpp.org/decompression.htm and some of his other stuff.

I sort of see what he's getting at with the repetitive diving, but my understanding is far from solid, and I was hoping to get some more info here to make things more concrete.

1. He has said that the bubbles can grow up to 4 hours after surfacing (before they start to contract), but that he clears of them in under 30min. I'd like to know what the 4 hour figure is based on? How long does it take for the bubbles to then dissapear? How big are they (diameter?) and do they all grow more or less uniformly?

2. George recommends a deeper second dive because of the bounce dive problem, and I see why no bounce diving makes sense, but I'm not clear on why that implies that a deeper second dive is better. Namely the problem, as I understood it, was the rapid ascent associated with the bounce dive when there were still bubbles all over the system. But would it be any safer to make a deep bounce dive - say deeper than the first dive, as opposed to a second shallow bounce dive. I mean, if the bubbles have grown sufficiently big on the surface then going sufficiently deep would make them small enough to slip through into the brain and spine anyway, so going up fast would seem just as bad as doing it from a shallow depth. What am I missing?

you are not going to go back up FAST , if you do your deco correctly - deep stops ,gas switch ...... , than you would not have any problems .

floater · April 23rd, 2006, 11:07 PM

Quote: (Originally Posted by NIMROD CHEN)

you are not going to go back up FAST , if you do your deco correctly - deep stops ,gas switch ...... , than you would not have any problems .

Sure, but I'm trying to ascertain why going shallwer than the first dive is not recommended even if you do your deco correctly.

lamont · April 24th, 2006, 05:11 AM

Quote: (Originally Posted by floater)

Sure, but I'm trying to ascertain why going shallwer than the first dive is not recommended even if you do your deco correctly.

i think the point is that you have to go sufficiently deep so that the volume of free phase gas in your system is compressed sufficiently so that the deco from the dive that you're doing will deco out the compressed free phase as well. "sufficiently deep" is not well defined. following up a 150 fsw dive with a 130 fsw one probably doesn't matter. following up a 350 fsw dive with a 70 fsw bounce to pickup bottles probably does....

floater · April 24th, 2006, 05:34 AM

Quote: (Originally Posted by lamont)

i think the point is that you have to go sufficiently deep so that the volume of free phase gas in your system is compressed sufficiently so that the deco from the dive that you're doing will deco out the compressed free phase as well. "sufficiently deep" is not well defined. following up a 150 fsw dive with a 130 fsw one probably doesn't matter. following up a 350 fsw dive with a 70 fsw bounce to pickup bottles probably does....

Thanks lamont, that's what i sort of figured, but i was unsure because:

1. to know how deep is deep enough you'd have to have some sense of the actual size of these bubbles, but i've never heard it quantified? (is this all just guessing? how did they find out about the bubbles anyway and their growth patterns?)

2. as long as the problem is not quantified, we can hypothesize that some of the bubbles might just reach sufficient compression during your max depth (even if deeper than the first dive) to slip past the lungs and after a 30 ft/min ascent to yout 80% of ATA depth may have grown too big again to come out, no?

mstroeck · April 24th, 2006, 09:25 AM

Quote: (Originally Posted by floater)

(is this all just guessing? how did they find out about the bubbles anyway and their growth patterns?)

As far as I've been able to ascertain, yes, it's mostly educated guesses backed up by some doppler testing. I have not been able to find any hard data, though, I would really appreciate if anybody could point me to it!

floater · April 24th, 2006, 04:27 PM

Quote: (Originally Posted by mstroeck)

As far as I've been able to ascertain, yes, it's mostly educated guesses backed up by some doppler testing. I have not been able to find any hard data, though, I would really appreciate if anybody could point me to it!

How does a doppler test work?

On the surface, do the bubbles pop once they reach a certain size? Or do they just contract again back out of existence? And in the latter case, could they not contract enough even on the surface to slip past the lungs (although that wouldn't be a problem I guess as they aren't about to re-expand again... on the surface that is...)?

mstroeck · April 24th, 2006, 04:41 PM

Quote: (Originally Posted by floater)

How does a doppler test work?

On the surface, do the bubbles pop once they reach a certain size? Or do they just contract again back out of existence? And in the latter case, could they not contract enough even on the surface to slip past the lungs (although that wouldn't be a problem I guess as they aren't about to re-expand again... on the surface that is...)?

A Doppler test is a method of using ultrasound to detect and measure bloodflow in blood vessels. A transducer is moved over the vessel, and sends out ultrasound which is reflected from solid components of the body. The sound is then made audible and fed into a speaker. From the change in pitch of this sound, the operator can deduce the speed of the blood flow.

The method makes use of the Doppler effect (best go to Wikipedia or so for an explanation) to measure the speed at which blood cells move to do this. Gas bubbles normally show up as annoying artifacts, but of course are the main interest when you are doing decompression research :-)

floater · April 24th, 2006, 05:04 PM

Quote: (Originally Posted by mstroeck)

A Doppler test is a method of using ultrasound to detect and measure bloodflow in blood vessels. A transducer is moved over the vessel, and sends out ultrasound which is reflected from solid components of the body. The sound is then made audible and fed into a speaker. From the change in pitch of this sound, the operator can deduce the speed of the blood flow.

The method makes use of the Doppler effect (best go to Wikipedia or so for an explanation) to measure the speed at which blood cells move to do this. Gas bubbles normally show up as annoying artifacts, but of course are the main interest when you are doing decompression research :-)

Does the test reveal the size distribution of the gas bubbles? What part of the body do they apply this test to?

mstroeck · April 24th, 2006, 05:40 PM

Quote: (Originally Posted by floater)

Does the test reveal the size distribution of the gas bubbles? What part of the body do they apply this test to?

Sorry, I have no idea :-) I'll try to find some information later today.

April 23rd, 2006, 09:01 PM	#1 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Bounce, repetitive diving question I've been reading George's deco articles at http://www.wkpp.org/decompression.htm and some of his other stuff. I sort of see what he's getting at with the repetitive diving, but my understanding is far from solid, and I was hoping to get some more info here to make things more concrete. 1. He has said that the bubbles can grow up to 4 hours after surfacing (before they start to contract), but that he clears of them in under 30min. I'd like to know what the 4 hour figure is based on? How long does it take for the bubbles to then dissapear? How big are they (diameter?) and do they all grow more or less uniformly? 2. George recommends a deeper second dive because of the bounce dive problem, and I see why no bounce diving makes sense, but I'm not clear on why that implies that a deeper second dive is better. Namely the problem, as I understood it, was the rapid ascent associated with the bounce dive when there were still bubbles all over the system. But would it be any safer to make a deep bounce dive - say deeper than the first dive, as opposed to a second shallow bounce dive. I mean, if the bubbles have grown sufficiently big on the surface then going sufficiently deep would make them small enough to slip through into the brain and spine anyway, so going up fast would seem just as bad as doing it from a shallow depth. What am I missing?

April 23rd, 2006, 11:00 PM	#2 (permalink)
NIMROD CHEN(Offline) New Member Join Date: Mar 2006 Location: ISRAEL Posts: 87	Quote: (Originally Posted by floater) I've been reading George's deco articles at http://www.wkpp.org/decompression.htm and some of his other stuff. I sort of see what he's getting at with the repetitive diving, but my understanding is far from solid, and I was hoping to get some more info here to make things more concrete. 1. He has said that the bubbles can grow up to 4 hours after surfacing (before they start to contract), but that he clears of them in under 30min. I'd like to know what the 4 hour figure is based on? How long does it take for the bubbles to then dissapear? How big are they (diameter?) and do they all grow more or less uniformly? 2. George recommends a deeper second dive because of the bounce dive problem, and I see why no bounce diving makes sense, but I'm not clear on why that implies that a deeper second dive is better. Namely the problem, as I understood it, was the rapid ascent associated with the bounce dive when there were still bubbles all over the system. But would it be any safer to make a deep bounce dive - say deeper than the first dive, as opposed to a second shallow bounce dive. I mean, if the bubbles have grown sufficiently big on the surface then going sufficiently deep would make them small enough to slip through into the brain and spine anyway, so going up fast would seem just as bad as doing it from a shallow depth. What am I missing? you are not going to go back up FAST , if you do your deco correctly - deep stops ,gas switch ...... , than you would not have any problems .

April 23rd, 2006, 11:07 PM	#3 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Quote: (Originally Posted by NIMROD CHEN) you are not going to go back up FAST , if you do your deco correctly - deep stops ,gas switch ...... , than you would not have any problems . Sure, but I'm trying to ascertain why going shallwer than the first dive is not recommended even if you do your deco correctly.

April 24th, 2006, 05:11 AM	#4 (permalink)
lamont(Offline) APLP Join Date: Nov 2005 Location: Seattle, WA Posts: 181	Quote: (Originally Posted by floater) Sure, but I'm trying to ascertain why going shallwer than the first dive is not recommended even if you do your deco correctly. i think the point is that you have to go sufficiently deep so that the volume of free phase gas in your system is compressed sufficiently so that the deco from the dive that you're doing will deco out the compressed free phase as well. "sufficiently deep" is not well defined. following up a 150 fsw dive with a 130 fsw one probably doesn't matter. following up a 350 fsw dive with a 70 fsw bounce to pickup bottles probably does....

April 24th, 2006, 05:34 AM	#5 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Quote: (Originally Posted by lamont) i think the point is that you have to go sufficiently deep so that the volume of free phase gas in your system is compressed sufficiently so that the deco from the dive that you're doing will deco out the compressed free phase as well. "sufficiently deep" is not well defined. following up a 150 fsw dive with a 130 fsw one probably doesn't matter. following up a 350 fsw dive with a 70 fsw bounce to pickup bottles probably does.... Thanks lamont, that's what i sort of figured, but i was unsure because: 1. to know how deep is deep enough you'd have to have some sense of the actual size of these bubbles, but i've never heard it quantified? (is this all just guessing? how did they find out about the bubbles anyway and their growth patterns?) 2. as long as the problem is not quantified, we can hypothesize that some of the bubbles might just reach sufficient compression during your max depth (even if deeper than the first dive) to slip past the lungs and after a 30 ft/min ascent to yout 80% of ATA depth may have grown too big again to come out, no?

April 24th, 2006, 09:25 AM	#6 (permalink)
mstroeck(Offline) New Member Join Date: Nov 2005 Location: Vienna, Austria Posts: 156	Quote: (Originally Posted by floater) (is this all just guessing? how did they find out about the bubbles anyway and their growth patterns?) As far as I've been able to ascertain, yes, it's mostly educated guesses backed up by some doppler testing. I have not been able to find any hard data, though, I would really appreciate if anybody could point me to it!

April 24th, 2006, 04:27 PM	#7 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Quote: (Originally Posted by mstroeck) As far as I've been able to ascertain, yes, it's mostly educated guesses backed up by some doppler testing. I have not been able to find any hard data, though, I would really appreciate if anybody could point me to it! How does a doppler test work? On the surface, do the bubbles pop once they reach a certain size? Or do they just contract again back out of existence? And in the latter case, could they not contract enough even on the surface to slip past the lungs (although that wouldn't be a problem I guess as they aren't about to re-expand again... on the surface that is...)?

April 24th, 2006, 04:41 PM	#8 (permalink)
mstroeck(Offline) New Member Join Date: Nov 2005 Location: Vienna, Austria Posts: 156	Quote: (Originally Posted by floater) How does a doppler test work? On the surface, do the bubbles pop once they reach a certain size? Or do they just contract again back out of existence? And in the latter case, could they not contract enough even on the surface to slip past the lungs (although that wouldn't be a problem I guess as they aren't about to re-expand again... on the surface that is...)? A Doppler test is a method of using ultrasound to detect and measure bloodflow in blood vessels. A transducer is moved over the vessel, and sends out ultrasound which is reflected from solid components of the body. The sound is then made audible and fed into a speaker. From the change in pitch of this sound, the operator can deduce the speed of the blood flow. The method makes use of the Doppler effect (best go to Wikipedia or so for an explanation) to measure the speed at which blood cells move to do this. Gas bubbles normally show up as annoying artifacts, but of course are the main interest when you are doing decompression research :-)

April 24th, 2006, 05:04 PM	#9 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Quote: (Originally Posted by mstroeck) A Doppler test is a method of using ultrasound to detect and measure bloodflow in blood vessels. A transducer is moved over the vessel, and sends out ultrasound which is reflected from solid components of the body. The sound is then made audible and fed into a speaker. From the change in pitch of this sound, the operator can deduce the speed of the blood flow. The method makes use of the Doppler effect (best go to Wikipedia or so for an explanation) to measure the speed at which blood cells move to do this. Gas bubbles normally show up as annoying artifacts, but of course are the main interest when you are doing decompression research :-) Does the test reveal the size distribution of the gas bubbles? What part of the body do they apply this test to?

April 24th, 2006, 05:40 PM	#10 (permalink)
mstroeck(Offline) New Member Join Date: Nov 2005 Location: Vienna, Austria Posts: 156	Quote: (Originally Posted by floater) Does the test reveal the size distribution of the gas bubbles? What part of the body do they apply this test to? Sorry, I have no idea :-) I'll try to find some information later today.