Dr Deco
Contributor
- Messages
- 2,384
- Reaction score
- 97
- # of dives
- I just don't log dives
Hello Readers:
It has been clear over the years at this FORUM that many posters would really like to have a decompression meter that would indicate specific susceptibility to DCS. We again have a question on Customizable Table and Computers. This opportunity is as good as any to discuss this fascinating if not controversial - topic. [WetCell has several postings indicating he has thought about this at length.]
This is not a new goal, since individual differences amongst divers have been recognized for a considerable time. In fact, it was described by JS Haldane in his initial paper of 1908, and variation with time was noted by tunnel workers in the late 1800s. but for recreational divers, there are problems associated with a lengthening of the bottom times [longer NDLs].
This idea of customization is largely predicted on the postulates that DCS is
Both of these concepts have problems, as has been found over several decades. As far as point number 1 is concerned, tissue micronuclei would play no role. For point number 2, the largest percentage of DCS problems reported in recreational SCUBA are neurological and in situ bubbles might actually be secondary, arterialization of venous bubbles being the primary instigating factor.
There is considerable variance in opinion on these topics. They say that when ten scientists gather, there will be found eleven different opinions. There have been many decompression schemes and analysis methods in the past fifty years.
Making Individualized Meters
Such a meter would require considerable research effort and financial backing. Both are unlikely.
- Except for travel, there is not a lot of money in dive products and precious little to spend on real data. I never found any commercial group except PADI willing to put any money into research with humans. While divers may find this unfortunate, it is true.
- The US Navy currently has little to no programs in hyperbaric research similar to the ones it had until 1982. Very sad. I worked for many years under research grants from the US Navy. [The dearth of money in this field led to my retiring when I had the chance.]
- NASA and the US Air Force currently have virtually no research in basic studies in DCS physiology.
- Organizations such as NIH do not fund this work since diving is considered sport and avoidance is a matter of personal choice.
Nitrogen Uptake and Elimination
Research work in nitrogen exchange is decades old. The first to measure gas uptake was JS Haldane [1908]. He formed postulates regarding this in the body as a whole and it was from these that his Haldane Method of table calculation is based. That is a legacy correct or incorrect that it with us today. Exchange of any substance [gases or otherwise] is a whole body measurement, while DCS is very localized in certain tissues. These measurements have not yielded very useful data in elucidating the causes or mechanism of DCS. They are simply too gross a measure. Interesting work was first performed during WW II using the newly obtainable radioactive gases.
It is true that DCS does correlate, somewhat, with fat content but only in resting subjects. Human divers are, of course, active. The original Haldane model did have fat and aqueous tissues and, all most all models have fat/water compartments. Compartments are emphasized since few believe today that you get the bends from fat tissue. The model is only for gas exchange and is recognized as bookkeeping.
The models use many compartments to describe physiological situations; multiple halftimes cannot be occurring at one time in the same tissue. They attempt to describe uptake and elimination of nitrogen in tissue when this exchange is by blood flow. Unfortunately, perfusion varies and the change is not incorporated into any model or meter. An individualized meter would need to take into account perfusion-dependent nitrogen exchange for uptake and elimation. This is not dependent on biometric data derived predive, so simple body composition studies would be insufficient.
Hyperbaric researchers differ on to what degree inter-tissue diffusion gas loading occurs. A specific model would need to include this, if it is correct. Most models are parallel loading, but one is a series model. Both work quite well. [It is hard initially to build differences into a model when it is agreed that the model is specious.]
Many researchers disagree that bubbles play much of a role at all after the decompression process starts. Body habitus and gas exchange are not big players, they propose, but rather play a secondary role to pathophysiological processes. They say it is biochemical and biometrics would not address this at all. [I do not agree with this entire concept.] We also have the question of distortion vs. ischemia and what decompression bubbles do.
Tissue Micronuclei
Micronuclei are not included in most models and would not be addressed by biometric measurements of BMI or by hydrostatic weighing. No models change nuclei number [except the limited use NASA model.] No one has a method to measure nuclei concentration before a dive. It has been known for decades that bubble formation varies enormously from diver to diver, and this variation correlates with no variable that is known today. Nuclei concentration is highly inconsistent across the animal kingdom. Mammals have apparently many nuclei while bacterial have few; pressure changes of 2000 psi are required from bubble formation in unicellular organisms.
In actual DCS studies, physical activity is the biggest factor in a given individual [I believe] after gas loading. Activity is not an easy measure, although something might be accomplished with heart rate . Activity has long been recognized as a variable in DCS and bubble formation [though not necessarily by researchers today] See e.g., Ferris et al, 1943. The importance of straining maneuvers in selecting the site of the bends. DAN is just begun to mention this factor.
Body Habitus
It seems highly logical that visible variations in the human body would contribute to DCS likelihood. They, in fact, do not surprising as this may be. You would think that a couple of, for example, decompressions in a hyperbaric chamber would determine resistance or susceptibility to DCS. Gray (Gray JS. Constitutional factors affecting susceptibility to decompression sickness. Chap. VII in Fulton JF. Decompression Sickness ,1951) wrote, The only direct and reliable method of individual susceptibility consists of determining the percentage of a large number (usually several hundred) of repeated standard decompressions in which the individual develops symptoms. Individual susceptibility is not determinable in a useable manner. [Now, that was in 1951, and I believe that more can be done. I, in fact, have demonstrated some predictive capacity if individuals in my work at NASA. It has limited utility in the real world. ]
Much has been done with constitutional factors over the years. While bioelectrical impedance analysis (BIA) was not available during WW II, hydrostatic weighing was and proved to be not particularly useful. (Nims, LF. Environmental factors affecting decompression sickness. Chap, VIII. In Fulton JF, Decompression Sickness ,1951).
Preselection tests
Possibly most telling is the failure of body composition analysis during WW II for preselection tests for high altitude bombing crews. [The use of WW II data appears here so often as it was a time when considerable financial resources were available, many human test subjects were available, there was considerable impetus to conduct the research, and there were fewer restrictions on human subject safety.] Actual chamber depressurizations of the potential crewmembers were required. Additionally, in order to acquire any degree of accuracy, it was found that exercise was needed during the decompression phase.
Neurologic DCS
Recreational divers report a higher fraction of dives ending with neurologic involvement when DCS presents as compared to laboratory studies. This often is the result of arterialization that is promoted by exercise [I believe]. Arterialization has an etiology [cause] that is a very difficult to determine. There are routs through a PFO and through intrapulmonary shunts. Laboratory studies of this by me and others have yielded inconsistent results. You do not know what will occur.
To be safe, it is best to avoid situations where many venous bubbles will be produced. Longer NDLs promote bubbles prior to the appearance of DCS. This early appearance is the basis of the utility of Doppler bubble detection. As a diver, you really want to avoid,as much as possible, any schedules that produce venous bubbles.
Dr Deco :doctor:
It has been clear over the years at this FORUM that many posters would really like to have a decompression meter that would indicate specific susceptibility to DCS. We again have a question on Customizable Table and Computers. This opportunity is as good as any to discuss this fascinating if not controversial - topic. [WetCell has several postings indicating he has thought about this at length.]
This is not a new goal, since individual differences amongst divers have been recognized for a considerable time. In fact, it was described by JS Haldane in his initial paper of 1908, and variation with time was noted by tunnel workers in the late 1800s. but for recreational divers, there are problems associated with a lengthening of the bottom times [longer NDLs].
This idea of customization is largely predicted on the postulates that DCS is
[1] the result of nitrogen supersaturation in many tissues and,
[2] bubbles formed in tissues are the causative agent.
Both of these concepts have problems, as has been found over several decades. As far as point number 1 is concerned, tissue micronuclei would play no role. For point number 2, the largest percentage of DCS problems reported in recreational SCUBA are neurological and in situ bubbles might actually be secondary, arterialization of venous bubbles being the primary instigating factor.
There is considerable variance in opinion on these topics. They say that when ten scientists gather, there will be found eleven different opinions. There have been many decompression schemes and analysis methods in the past fifty years.
Making Individualized Meters
Such a meter would require considerable research effort and financial backing. Both are unlikely.
- Except for travel, there is not a lot of money in dive products and precious little to spend on real data. I never found any commercial group except PADI willing to put any money into research with humans. While divers may find this unfortunate, it is true.
- The US Navy currently has little to no programs in hyperbaric research similar to the ones it had until 1982. Very sad. I worked for many years under research grants from the US Navy. [The dearth of money in this field led to my retiring when I had the chance.]
- NASA and the US Air Force currently have virtually no research in basic studies in DCS physiology.
- Organizations such as NIH do not fund this work since diving is considered sport and avoidance is a matter of personal choice.
Nitrogen Uptake and Elimination
Research work in nitrogen exchange is decades old. The first to measure gas uptake was JS Haldane [1908]. He formed postulates regarding this in the body as a whole and it was from these that his Haldane Method of table calculation is based. That is a legacy correct or incorrect that it with us today. Exchange of any substance [gases or otherwise] is a whole body measurement, while DCS is very localized in certain tissues. These measurements have not yielded very useful data in elucidating the causes or mechanism of DCS. They are simply too gross a measure. Interesting work was first performed during WW II using the newly obtainable radioactive gases.
It is true that DCS does correlate, somewhat, with fat content but only in resting subjects. Human divers are, of course, active. The original Haldane model did have fat and aqueous tissues and, all most all models have fat/water compartments. Compartments are emphasized since few believe today that you get the bends from fat tissue. The model is only for gas exchange and is recognized as bookkeeping.
The models use many compartments to describe physiological situations; multiple halftimes cannot be occurring at one time in the same tissue. They attempt to describe uptake and elimination of nitrogen in tissue when this exchange is by blood flow. Unfortunately, perfusion varies and the change is not incorporated into any model or meter. An individualized meter would need to take into account perfusion-dependent nitrogen exchange for uptake and elimation. This is not dependent on biometric data derived predive, so simple body composition studies would be insufficient.
Hyperbaric researchers differ on to what degree inter-tissue diffusion gas loading occurs. A specific model would need to include this, if it is correct. Most models are parallel loading, but one is a series model. Both work quite well. [It is hard initially to build differences into a model when it is agreed that the model is specious.]
Many researchers disagree that bubbles play much of a role at all after the decompression process starts. Body habitus and gas exchange are not big players, they propose, but rather play a secondary role to pathophysiological processes. They say it is biochemical and biometrics would not address this at all. [I do not agree with this entire concept.] We also have the question of distortion vs. ischemia and what decompression bubbles do.
Tissue Micronuclei
Micronuclei are not included in most models and would not be addressed by biometric measurements of BMI or by hydrostatic weighing. No models change nuclei number [except the limited use NASA model.] No one has a method to measure nuclei concentration before a dive. It has been known for decades that bubble formation varies enormously from diver to diver, and this variation correlates with no variable that is known today. Nuclei concentration is highly inconsistent across the animal kingdom. Mammals have apparently many nuclei while bacterial have few; pressure changes of 2000 psi are required from bubble formation in unicellular organisms.
In actual DCS studies, physical activity is the biggest factor in a given individual [I believe] after gas loading. Activity is not an easy measure, although something might be accomplished with heart rate . Activity has long been recognized as a variable in DCS and bubble formation [though not necessarily by researchers today] See e.g., Ferris et al, 1943. The importance of straining maneuvers in selecting the site of the bends. DAN is just begun to mention this factor.
Body Habitus
It seems highly logical that visible variations in the human body would contribute to DCS likelihood. They, in fact, do not surprising as this may be. You would think that a couple of, for example, decompressions in a hyperbaric chamber would determine resistance or susceptibility to DCS. Gray (Gray JS. Constitutional factors affecting susceptibility to decompression sickness. Chap. VII in Fulton JF. Decompression Sickness ,1951) wrote, The only direct and reliable method of individual susceptibility consists of determining the percentage of a large number (usually several hundred) of repeated standard decompressions in which the individual develops symptoms. Individual susceptibility is not determinable in a useable manner. [Now, that was in 1951, and I believe that more can be done. I, in fact, have demonstrated some predictive capacity if individuals in my work at NASA. It has limited utility in the real world. ]
Much has been done with constitutional factors over the years. While bioelectrical impedance analysis (BIA) was not available during WW II, hydrostatic weighing was and proved to be not particularly useful. (Nims, LF. Environmental factors affecting decompression sickness. Chap, VIII. In Fulton JF, Decompression Sickness ,1951).
Preselection tests
Possibly most telling is the failure of body composition analysis during WW II for preselection tests for high altitude bombing crews. [The use of WW II data appears here so often as it was a time when considerable financial resources were available, many human test subjects were available, there was considerable impetus to conduct the research, and there were fewer restrictions on human subject safety.] Actual chamber depressurizations of the potential crewmembers were required. Additionally, in order to acquire any degree of accuracy, it was found that exercise was needed during the decompression phase.
Neurologic DCS
Recreational divers report a higher fraction of dives ending with neurologic involvement when DCS presents as compared to laboratory studies. This often is the result of arterialization that is promoted by exercise [I believe]. Arterialization has an etiology [cause] that is a very difficult to determine. There are routs through a PFO and through intrapulmonary shunts. Laboratory studies of this by me and others have yielded inconsistent results. You do not know what will occur.
To be safe, it is best to avoid situations where many venous bubbles will be produced. Longer NDLs promote bubbles prior to the appearance of DCS. This early appearance is the basis of the utility of Doppler bubble detection. As a diver, you really want to avoid,as much as possible, any schedules that produce venous bubbles.
Dr Deco :doctor:
