Does Pre-Dive Exercise Reduce DCS Risk?
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I'm not physiologist, but, IMHO, ANY physical activity may INCREASE the DCS chances. Why that? Short cardio will increase a) air demand b) lactic acid in your muscles. you need oxygen for lactic acid which will increase your oxygen consumption even more. By consuming more air after descending you will increase nytrogen consentration in you body, thus increasing DCS chances. This is how I see this machanism is working. Still it will be interesting to see if there is any studies.BigTuna:
CameronMartz
Fitness Instructor
Yes, there are several studies regarding pre-dive exercise, and the most recent ones find that at worst, pre-dive cardiovascular exercise has no effect on risk of DCS. At best, it might actually reduce risk of DCS. Note that as I have mentioned whenever this subject comes up, research is in its early stages, and there is much we do not know about the mechanism. The evidence is piling up, however, with yet another confirming study published in November. Here is a list of a few of the latest:
Hemodynamic changes induced by sub-maximal exercise prior to a dive and its consequences on bubble formation. Br J Sports Med. 2006 Nov 30; Blatteu J, et al.
"A single bout of strenuous exercise 2h before a dive significantly reduced the number of bubbles in the right heart of divers and could protect from decompression sickness."
http://www.ncbi.nlm.nih.gov/entrez/..._uids=17138641&query_hl=1&itool=pubmed_docsum
Aerobic exercise 2 hours before a dive to 30 msw decreases bubble formation after decompression. Aviat Space Environ Med. 2005 Jul;76(7):666-9; Blatteu J, et al.
"Like exercise 24 h ahead, 45 min of running 2 h before a dive decreases bubble formation after diving, suggesting a protective effect of aerobic exercise against DCS."
http://www.ncbi.nlm.nih.gov/entrez/...Retrieve&dopt=abstractplus&list_uids=16018350
Exercise ending 30 min pre-dive has no effect on bubble formation in the rat. Aviat Space Environ Med. 2005 Apr;76(4):326-8; Berge VJ, et al.
"The same type and intensity of exercise that reduces bubble formation when performed 20 h prior to a dive neither promotes nor reduces bubble formation if performed 30 min before a dive. The present data indicate that exercise completed 30 min before a dive does not increase the risk of developing decompression sickness in the rat."
http://www.ncbi.nlm.nih.gov/entrez/..._uids=15828630&query_hl=9&itool=pubmed_docsum
Exercise and nitric oxide prevent bubble formation: a novel approach to the prevention of decompression sickness? J Physiol. 2004 Mar 16;555(Pt 3):825-9. Epub 2004 Jan 14; Wisloff U, et al.
"Exercise 20 h before a dive suppressed bubble formation and prevented death, with no effect at any other time (48, 10, 5 and 0.5 h prior to the dive). Pre-dive activities have not been considered to influence the growth of bubbles and thus the risk of serious DCS."
http://www.ncbi.nlm.nih.gov/entrez/...Retrieve&dopt=abstractplus&list_uids=14724207
Aerobic exercise before diving reduces venous gas bubble formation in humans. J Physiol. 2004 Mar 16;555(Pt 3):637-42. Epub 2004 Jan 30; Dujic, et al.
"This is the first report to indicate that pre-dive exercise may form the basis for a new way of preventing serious decompression sickness."
http://www.ncbi.nlm.nih.gov/entrez/...uids=14755001&query_hl=10&itool=pubmed_docsum
One study recently published demonstrates how poorly understood this effect is:
Post-dive bubble formation in rats: effects of exercise 24 h ahead repeated 30 min before the dive. Aviat Space Environ Med. 2006 Sep;77(9):905-8; Loset A Jr, et al.
"This study demonstrated that acute exercise prior to a dive eliminated the protection against bubble formation found 24 h after high-intensity exercise in rats."
I would have liked to see a 3rd group of rats who performed no exercise to see what their bubble grades were on this protocol.
When looking at real world accident data, you will be hard pressed to find an incident of DCS attributed directly to pre-dive exercise. Though exertion at depth and after surfacing are known benders, there are no convincing cases of DCS caused by pre-dive exercise to my knowledge.
As an aside, lactic acid is unlikely to have any impact on risk of DCS, assuming any reasonable time separating exercise and immersion. It is rapidly metabolized, and blood levels in a healthy individual would likely return to baseline well before the boat pulled up to the dive site. I am unaware of any studies linking blood pH to risk of DCS, anyway, so I doubt it would be an issue.
Cameron
Hemodynamic changes induced by sub-maximal exercise prior to a dive and its consequences on bubble formation. Br J Sports Med. 2006 Nov 30; Blatteu J, et al.
"A single bout of strenuous exercise 2h before a dive significantly reduced the number of bubbles in the right heart of divers and could protect from decompression sickness."
http://www.ncbi.nlm.nih.gov/entrez/..._uids=17138641&query_hl=1&itool=pubmed_docsum
Aerobic exercise 2 hours before a dive to 30 msw decreases bubble formation after decompression. Aviat Space Environ Med. 2005 Jul;76(7):666-9; Blatteu J, et al.
"Like exercise 24 h ahead, 45 min of running 2 h before a dive decreases bubble formation after diving, suggesting a protective effect of aerobic exercise against DCS."
http://www.ncbi.nlm.nih.gov/entrez/...Retrieve&dopt=abstractplus&list_uids=16018350
Exercise ending 30 min pre-dive has no effect on bubble formation in the rat. Aviat Space Environ Med. 2005 Apr;76(4):326-8; Berge VJ, et al.
"The same type and intensity of exercise that reduces bubble formation when performed 20 h prior to a dive neither promotes nor reduces bubble formation if performed 30 min before a dive. The present data indicate that exercise completed 30 min before a dive does not increase the risk of developing decompression sickness in the rat."
http://www.ncbi.nlm.nih.gov/entrez/..._uids=15828630&query_hl=9&itool=pubmed_docsum
Exercise and nitric oxide prevent bubble formation: a novel approach to the prevention of decompression sickness? J Physiol. 2004 Mar 16;555(Pt 3):825-9. Epub 2004 Jan 14; Wisloff U, et al.
"Exercise 20 h before a dive suppressed bubble formation and prevented death, with no effect at any other time (48, 10, 5 and 0.5 h prior to the dive). Pre-dive activities have not been considered to influence the growth of bubbles and thus the risk of serious DCS."
http://www.ncbi.nlm.nih.gov/entrez/...Retrieve&dopt=abstractplus&list_uids=14724207
Aerobic exercise before diving reduces venous gas bubble formation in humans. J Physiol. 2004 Mar 16;555(Pt 3):637-42. Epub 2004 Jan 30; Dujic, et al.
"This is the first report to indicate that pre-dive exercise may form the basis for a new way of preventing serious decompression sickness."
http://www.ncbi.nlm.nih.gov/entrez/...uids=14755001&query_hl=10&itool=pubmed_docsum
One study recently published demonstrates how poorly understood this effect is:
Post-dive bubble formation in rats: effects of exercise 24 h ahead repeated 30 min before the dive. Aviat Space Environ Med. 2006 Sep;77(9):905-8; Loset A Jr, et al.
"This study demonstrated that acute exercise prior to a dive eliminated the protection against bubble formation found 24 h after high-intensity exercise in rats."
I would have liked to see a 3rd group of rats who performed no exercise to see what their bubble grades were on this protocol.
When looking at real world accident data, you will be hard pressed to find an incident of DCS attributed directly to pre-dive exercise. Though exertion at depth and after surfacing are known benders, there are no convincing cases of DCS caused by pre-dive exercise to my knowledge.
As an aside, lactic acid is unlikely to have any impact on risk of DCS, assuming any reasonable time separating exercise and immersion. It is rapidly metabolized, and blood levels in a healthy individual would likely return to baseline well before the boat pulled up to the dive site. I am unaware of any studies linking blood pH to risk of DCS, anyway, so I doubt it would be an issue.
Cameron
Thats the key, if you healty, in shape, doing regular cardio - it descreases the risk. So what the point of "pre-dive"? The whole year before you dive first time?
CameronMartz
Fitness Instructor
kreuzerkrieg:Thats the key, if you healty, in shape, doing regular cardio - it descreases the risk. So what the point of "pre-dive"? The whole year before you dive first time?
Actually, some of the rat studies looked at what a single bout of exercise did for an unconditioned rat (basically the rat version of a human couch potato), and they still found the exercise to be protective. Yes, general fitness seems to reduce risk of DCS, but the mechanism of pre-dive exercise may be independent of this.
Links to abstracts:
http://www.ncbi.nlm.nih.gov/entrez/...Retrieve&dopt=abstractplus&list_uids=11731590
http://www.ncbi.nlm.nih.gov/entrez/..._uids=12527743&query_hl=2&itool=pubmed_docsum
This is not to suggest that a human diver who is unconditioned would benefit from 45 minutes (or 90 minutes, as in one study) of intense cardio 2 hours before diving. <g> The rats did not actually have to do anything other than take a ride in a chamber. Thus, it is only logical that if you wanted to take advantage of some protective effect of pre-dive exercise, a diver should have a regular conditioning program to be able to function after said exercise.
Latent vasodilation, cardiovascular activation, presence of certain biochemicals- these are all related theories for the cause that are being examined. A long-term fitness program has other benefits- better vascularity, better body composition, better efficiency of gas transfer into and out of the body...
Cameron
The question is how it will affect human in case of non-sport dive, for example technical diving. 45 minute cardio may be pretty ehausting, can it endanger human subject if he has to perform physical work at depth?
Well, I guess we have to wait a couple of years before sufficient data will be gathered and analyzed...
Well, I guess we have to wait a couple of years before sufficient data will be gathered and analyzed...
Dr Deco
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Hello BigTuna:
Pressure Workers
This question is of current interest. It has been known for more than a century that individuals who work at pressure are more resistant to DCS than new workers are. These were referred to in the past as seasoned men. The explanation was sought in reduction of the tendency to form bubbles. It is possible that seasoned men are those that work daily in the hyperbaric environments. While men were involved in physical labor more than a century ago, those that went into pressure environments might have been unemployed for some period prior to getting a job in pressure environments, a well-paying but dangerous occupation.
Recent Studies
While studying some data of a colleague at NASA in 1991, I noticed that test subjects who were active for several days prior to their chamber exposure had lower Doppler bubble scores than when sedentary [reference 1]. The meaning of this result was not pursued further at that time.
Because exercise, other that that performed while at depth, has now become an issue, several studies have been reported. These have indicated that activity before a dive is not a factor to increase the incidence of DCS [2]. I suspect that this is because any nuclei formed by the musculoskeletal activity are compressed and eliminated during the dive that follows the activity. This is in contradistinction to activity prior to altitude decompression (as with astronauts during spacewalks) which is exacerbating if DCS if performed within the first few hours [3].
Exercise performed a few hours before diving, even up to 24 hours prior, actually appears to reduce DCS and Doppler-detectable bubbles [ref 4 7]. The authors of these articles attribute the effect to the production of nitric oxide, a substance that modifies capillary behavior. This is surmised because blocking the enzyme responsible for nitric oxide production removes the protection from bubble formation.
Oxygen Effect
Recent work [ref 10] by Bruce Butler and I indicated that predive oxygen appears to act like a drug also mitigating the formation of gas bubbles from diving.
How much more information will be gathered in the near future is difficult to say. There are few research dollars for diving physiology and medicine.
Dr Deco :doctor:
The next class in Decompression Physiology for 2007 is August 18-19. :1book:
This class is at the USC campus in Los Angeles.
http://wrigley.usc.edu/hyperbaric/advdeco.htm
References :book3:
[1] MR Powell. Exercise and physical fitness decrease gas phase formation during hypobaric decompression. Undersea Biomed. Res., 18 (Suppl.), 61, (1991).
[2] Berge VJ, Jorgensen A, Loset A, Wisloff U, Brubakk AO. Exercise ending 30 min pre-dive has no effect on bubble formation in the rat. Aviat Space Environ Med. 2005 Apr;76(4):326-8.
[3] Dervay JP, Powell MR, Butler B, Fife CE. The effect of exercise and rest duration on the generation of venous gas bubbles at altitude. Aviat Space Environ Med. 2002 Jan;73(1):22-7.
[4] Wisloff U, Brubakk AO. Aerobic endurance training reduces bubble formation and increases survival in rats exposed to hyperbaric pressure. J Physiol. 2001 Dec 1;537(Pt 2):607-11Dujic Z, Duplancic D,
[5] Marinovic-Terzic I, Bakovic D, Ivancev V, Valic Z, Eterovic D, Petri NM, Wisloff U, Brubakk AO. Aerobic exercise before diving reduces venous gas bubble formation in humans. J Physiol. 2004 Mar 16;555(Pt 3):637-42. Epub 2004 Jan 30.
[6] Blatteau JE, Gempp E, Galland FM, Pontier JM, Sainty JM, Robinet C. Aerobic exercise 2 hours before a dive to 30 msw decreases bubble formation after decompression. Aviat Space Environ Med. 2005 Jul;76(7):666-9.
[7] Loset A Jr, Mollerlokken A, Berge V, Wisloff U, Brubakk AO. Post-dive bubble formation in rats: effects of exercise 24 h ahead repeated 30 min before the dive. Aviat Space Environ Med. 2006 Sep;77(9):905-8.
[8] Wisloff U, Richardson RS, Brubakk AO. NOS inhibition increases bubble formation and reduces survival in sedentary but not exercised rats. J Physiol. 2003 Jan 15;546(Pt 2):577-82.
[9] Wisloff U, Richardson RS, Brubakk AO. Exercise and nitric oxide prevent bubble formation: a novel approach to the prevention of decompression sickness? J Physiol. 2004 Mar 16;555(Pt 3):825-9. Epub 2004 Jan 14.
[10] Butler BD, Little T, Cogan V, Powell MR. Hyperbaric oxygen pre-breathe modifies the outcome of decompression sickness.Undersea Hyperb Med. 2006 Nov-Dec;33(6):407-17.
Pressure Workers
This question is of current interest. It has been known for more than a century that individuals who work at pressure are more resistant to DCS than new workers are. These were referred to in the past as seasoned men. The explanation was sought in reduction of the tendency to form bubbles. It is possible that seasoned men are those that work daily in the hyperbaric environments. While men were involved in physical labor more than a century ago, those that went into pressure environments might have been unemployed for some period prior to getting a job in pressure environments, a well-paying but dangerous occupation.
Recent Studies
While studying some data of a colleague at NASA in 1991, I noticed that test subjects who were active for several days prior to their chamber exposure had lower Doppler bubble scores than when sedentary [reference 1]. The meaning of this result was not pursued further at that time.
Because exercise, other that that performed while at depth, has now become an issue, several studies have been reported. These have indicated that activity before a dive is not a factor to increase the incidence of DCS [2]. I suspect that this is because any nuclei formed by the musculoskeletal activity are compressed and eliminated during the dive that follows the activity. This is in contradistinction to activity prior to altitude decompression (as with astronauts during spacewalks) which is exacerbating if DCS if performed within the first few hours [3].
Exercise performed a few hours before diving, even up to 24 hours prior, actually appears to reduce DCS and Doppler-detectable bubbles [ref 4 7]. The authors of these articles attribute the effect to the production of nitric oxide, a substance that modifies capillary behavior. This is surmised because blocking the enzyme responsible for nitric oxide production removes the protection from bubble formation.
Oxygen Effect
Recent work [ref 10] by Bruce Butler and I indicated that predive oxygen appears to act like a drug also mitigating the formation of gas bubbles from diving.
How much more information will be gathered in the near future is difficult to say. There are few research dollars for diving physiology and medicine.
Dr Deco :doctor:
The next class in Decompression Physiology for 2007 is August 18-19. :1book:
This class is at the USC campus in Los Angeles.
http://wrigley.usc.edu/hyperbaric/advdeco.htm
References :book3:
[1] MR Powell. Exercise and physical fitness decrease gas phase formation during hypobaric decompression. Undersea Biomed. Res., 18 (Suppl.), 61, (1991).
[2] Berge VJ, Jorgensen A, Loset A, Wisloff U, Brubakk AO. Exercise ending 30 min pre-dive has no effect on bubble formation in the rat. Aviat Space Environ Med. 2005 Apr;76(4):326-8.
[3] Dervay JP, Powell MR, Butler B, Fife CE. The effect of exercise and rest duration on the generation of venous gas bubbles at altitude. Aviat Space Environ Med. 2002 Jan;73(1):22-7.
[4] Wisloff U, Brubakk AO. Aerobic endurance training reduces bubble formation and increases survival in rats exposed to hyperbaric pressure. J Physiol. 2001 Dec 1;537(Pt 2):607-11Dujic Z, Duplancic D,
[5] Marinovic-Terzic I, Bakovic D, Ivancev V, Valic Z, Eterovic D, Petri NM, Wisloff U, Brubakk AO. Aerobic exercise before diving reduces venous gas bubble formation in humans. J Physiol. 2004 Mar 16;555(Pt 3):637-42. Epub 2004 Jan 30.
[6] Blatteau JE, Gempp E, Galland FM, Pontier JM, Sainty JM, Robinet C. Aerobic exercise 2 hours before a dive to 30 msw decreases bubble formation after decompression. Aviat Space Environ Med. 2005 Jul;76(7):666-9.
[7] Loset A Jr, Mollerlokken A, Berge V, Wisloff U, Brubakk AO. Post-dive bubble formation in rats: effects of exercise 24 h ahead repeated 30 min before the dive. Aviat Space Environ Med. 2006 Sep;77(9):905-8.
[8] Wisloff U, Richardson RS, Brubakk AO. NOS inhibition increases bubble formation and reduces survival in sedentary but not exercised rats. J Physiol. 2003 Jan 15;546(Pt 2):577-82.
[9] Wisloff U, Richardson RS, Brubakk AO. Exercise and nitric oxide prevent bubble formation: a novel approach to the prevention of decompression sickness? J Physiol. 2004 Mar 16;555(Pt 3):825-9. Epub 2004 Jan 14.
[10] Butler BD, Little T, Cogan V, Powell MR. Hyperbaric oxygen pre-breathe modifies the outcome of decompression sickness.Undersea Hyperb Med. 2006 Nov-Dec;33(6):407-17.
Big Tuna,
As you may or may not know there are "minor" risk factors such as predive fatigue, stress, alcohol consumption, or possibility of predive dehydration (inadequate fluid intake), physical exertion, or feeling of cold during the dive, and postdive exercise can contribute to DCS.
So, that said, I would elect not to do any pre-dive exercise thinking that it may reduce the risk.
In fact, I would wear my seatbelt and drive sober back home from the dive site. Statistically, those two habits in themselves would more greatly increase your safety than worrying about how to reduce the risk of getting DCS. IMO
Safe diving....
As you may or may not know there are "minor" risk factors such as predive fatigue, stress, alcohol consumption, or possibility of predive dehydration (inadequate fluid intake), physical exertion, or feeling of cold during the dive, and postdive exercise can contribute to DCS.
So, that said, I would elect not to do any pre-dive exercise thinking that it may reduce the risk.
In fact, I would wear my seatbelt and drive sober back home from the dive site. Statistically, those two habits in themselves would more greatly increase your safety than worrying about how to reduce the risk of getting DCS. IMO
Safe diving....
Dr Deco
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Hello Big Tuna:
I am assuming that your inquiry about DCS and predive exercise was only of academic interest. My reply was prepared with that as an assumption. I do not advocate this as a means of mitigating decompression sickness risk.
In addition to gas loading, the next action would be the reduction of post dive activity. While the readers of “Ask Dr Deco” on SCUBA BOARD are aware that this is a risk, that does not appear to be true in the general population of divers. For example, the May issue of SCUBA DIVING carried a story concerning neurological DCS. It mentioned that none of the gas loadings were abnormal, but it said nothing about physical activity before the “hit” nor anything about Valsalva-like maneuvers (coughing, straining, etc) that might have provoked bubble arterialization.
This type of omission is common.
Dr Deco :doctor:
I am assuming that your inquiry about DCS and predive exercise was only of academic interest. My reply was prepared with that as an assumption. I do not advocate this as a means of mitigating decompression sickness risk.
In addition to gas loading, the next action would be the reduction of post dive activity. While the readers of “Ask Dr Deco” on SCUBA BOARD are aware that this is a risk, that does not appear to be true in the general population of divers. For example, the May issue of SCUBA DIVING carried a story concerning neurological DCS. It mentioned that none of the gas loadings were abnormal, but it said nothing about physical activity before the “hit” nor anything about Valsalva-like maneuvers (coughing, straining, etc) that might have provoked bubble arterialization.
This type of omission is common.
Dr Deco :doctor:
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Hi Michael,
Yes, those were important omissions.
Regards,
Doc
Yes, those were important omissions.
Regards,
Doc
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