Im having trouble getting a plain English grasp on Haldane. Im just confused as hell by it and tissue compartments. Can anyone help or point me in the right direction?
Can someone put Haldane into plain English including compartments
- Thread starter Sharkdiver289
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Dr Deco
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Hello Sharkdiver:
I will put something understandable together for you - and others.:cool2: This will take a bit of time, but cetainly by Thursday [March 15th] afternoon.
I will put something understandable together for you - and others.:cool2: This will take a bit of time, but cetainly by Thursday [March 15th] afternoon.
Also, you might want to play a bit with divePAL (basic version is free) to see the compartments in action.
just draw a multilevel dive profile and see how the compartments react to it
Alberto (aka eDiver)
just draw a multilevel dive profile and see how the compartments react to it
Alberto (aka eDiver)
Another great source is Mark Powell's Deco for Divers. In plain easy to understand english he lays out deco theory and makes it seem easy.
I'm sure Dr. Deco will do a better and more thorough job of it, but here's a primer:
Haldane's big insight was that, if you kept the pressure changes small enough, people didn't get symptoms. He posited that if you went up slowly enough that the ratio of the pressure in your body to the pressure around you was never more than two to one, you would not get symptoms. This really WAS the big insight into decompression, and resulted in a huge reduction of cases of decompression sickness in caisson workers. We have refined this since, by recognizing that it's really the inert gas tensions that need to be considered, and by becoming aware that, even with controlled ascents, people will form bubbles, and bubble growth probably needs to be considered in creating ascent strategies that reduce the risk of symptoms.
Various people took Haldane's work and built on it. One of the refinements was to realize that not all the parts of the body absorb nitrogen at the same rate. Places with high solubility and high blood flow may absorb it faster (like blood and brain), and places with low perfusion and poor solubility may absorb very slowly (like bone). The attempt to model this variability resulted in the concept of "compartments". What a compartment is, is a mathematical construct of a space in the body that has an assigned rate of absorbing and washing out nitrogen. If you go to Alberto's website and play with the programs, you can see a graphical representation of nitrogen tensions in various "compartments", showing how, as you initially descend, nitrogen accumulates very quickly in the "fast" compartments, and over time, it accumulates in the slower ones. When you go up, the nitrogen washes out quickly from the "fast" compartments, and more slowly out of the "slow" ones. The final piece of the puzzle is that each "compartment" has an assigned maximum nitrogen tension (M value) that it can hold before it will cause symptoms. Keeping the nitrogen tension below that is what the ascent strategy is designed to do -- that's why you can only stay down so long, and go up so fast.
What's important to realize is that the body isn't divided into compartments, and the compartments in the mathematical model really do not correspond to specific tissues in the body very well. The whole compartment concept is a way to make it possible to represent mathematically a complex and continuous physiological process which is really not all that well understood. What we do know is that, if we follow the rules that develop when we run certain calculations through our compartment models, we reduce the risk of DCS in actual divers.
Haldane's big insight was that, if you kept the pressure changes small enough, people didn't get symptoms. He posited that if you went up slowly enough that the ratio of the pressure in your body to the pressure around you was never more than two to one, you would not get symptoms. This really WAS the big insight into decompression, and resulted in a huge reduction of cases of decompression sickness in caisson workers. We have refined this since, by recognizing that it's really the inert gas tensions that need to be considered, and by becoming aware that, even with controlled ascents, people will form bubbles, and bubble growth probably needs to be considered in creating ascent strategies that reduce the risk of symptoms.
Various people took Haldane's work and built on it. One of the refinements was to realize that not all the parts of the body absorb nitrogen at the same rate. Places with high solubility and high blood flow may absorb it faster (like blood and brain), and places with low perfusion and poor solubility may absorb very slowly (like bone). The attempt to model this variability resulted in the concept of "compartments". What a compartment is, is a mathematical construct of a space in the body that has an assigned rate of absorbing and washing out nitrogen. If you go to Alberto's website and play with the programs, you can see a graphical representation of nitrogen tensions in various "compartments", showing how, as you initially descend, nitrogen accumulates very quickly in the "fast" compartments, and over time, it accumulates in the slower ones. When you go up, the nitrogen washes out quickly from the "fast" compartments, and more slowly out of the "slow" ones. The final piece of the puzzle is that each "compartment" has an assigned maximum nitrogen tension (M value) that it can hold before it will cause symptoms. Keeping the nitrogen tension below that is what the ascent strategy is designed to do -- that's why you can only stay down so long, and go up so fast.
What's important to realize is that the body isn't divided into compartments, and the compartments in the mathematical model really do not correspond to specific tissues in the body very well. The whole compartment concept is a way to make it possible to represent mathematically a complex and continuous physiological process which is really not all that well understood. What we do know is that, if we follow the rules that develop when we run certain calculations through our compartment models, we reduce the risk of DCS in actual divers.
Dr Deco
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Hello Sharkdiver:
Haldanes Method
My many thanks to TS and M for filling in until I could complete my piece. She always does agood job and is well informed on these decompression issues.
Historically,the Haldane method is based on two concepts, both of which are used in table design to this day, albeit with some modifications. This model was conceived byJohn Scot Haldane MD and published in the Journal of Hygiene in 1908. The overall ideais that gas bubbles form in any tissue, are distributed in the blood, become lodged in susceptible tissues, and cause the pain known as the bends. At the time, people were not convinced that gas bubbles played the major role in the bends.
Using the ideas briefly described below, Haldane developed a calculation algorithm. An algorithm is a term used to describe a calculation method. Some familiar short ones are long division and the extraction of square roots. Table calculation has a very long algorithm.
Haldane developedthis under a contract from the admiralty of the Royal Navy. Navy divers had problems with 100 fsw dives while Greek sponge divers were routinely making successful dives to 190 fsw. The Brits were miffed!
Metastable Supersaturation
This point most difficult too obtain was one of Haldanes big contributions. Haldane knew that divers were able to ascend from a relatively shallow depth directly to the surface without any decompression stops. This depth was about thirty three feet of seawater, and the residence time at that depth was many hours. The body was essentially saturated. Haldane believed that the body could sustain a certain degree of supersaturation of dissolved nitrogen without time limit. This supersaturation was (dissolved nitrogen pressure at depth)/(total pressure at surface). Later this was termed the metastable state. In other words, dissolved nitrogen stayed dissolved, and bubbles did not form if thesupersaturation was controlled.
Haldane performed experiments with small animals and found empirically that supersaturation was possible. He believed that this was related to an insufficient number of nucleation points in the body. [Today we would say that this was caused by an insufficient number of sufficiently large micronuclei.]
In his algorithm, Haldane set this supersaturation limit at two to one. This came from the empirical observation that 33 fsw to the surface was two atmospheres absolute pressure to one atmosphere absolute pressure. As tables were designed for deeper depths, it became clear that some tissues could sustain a greater supersaturation ratio and others required a smaller ratio. This depended on the tissue, a topic we will look at next.
Tissues
The other idea in his model related to the unequal flow of blood in the body. Haldane was well aware that some tissues hada very high blood supply; these were for example, the brain and muscle tissues.High blood-flow tissues were termed fast. Other tissues had a poor supply; these were fat and connective tissues. These were termed slow tissues.
These terms applied to the rate at which nitrogen was taken up or released by thetissue. A good blood supply allowed rapid loading and unloading, much like a loading dock with a railroad with many freight cars. A slow tissue had poor uptake and elimination. This might be compared to a loading dock with a single truck. Haldane knew that tissues picked up nitrogen more rapidly when exercising and recommended some activity during decompression.
In the past several decades, tissue has been changed to compartment to indicate that large volumes are not necessarily intended. A compartment might be but a very small piece of tissue.
Table Algorithm
Haldane usedan exponential expression for the uptake and elimination. This is similar to half-life in decay ofradioactive elements. Thus after onehalftime, 50% of the isotope has changed. After another halftime, an additional 50% has decayed and only 25% ofthe original remains, and so on. Elimination of dissolved nitrogen has the samepattern. Uptake is the processedreversed with 50% taken up, then 75% etc. Important is that the nitrogen be dissolved or the elimination rate isskewed very skewed. Gaseous nitrogenis hardly eliminated at all! This can beimportant when calculating the remaining tissue nitrogen at the end of asurface interval.
This processis quite simple and allows for small computes to be made for the diver to carryalong on the dive. Most dive computers have this single-pase system. They take the values for the allowablesupersaturation for the published data of Rogers and Powell, and they tracetheir pedigree to the PADI Recreational Dive Planner. [This is found in thesmall print in the owners manual.]
The dual-phasemodels [e.g., the RGBM of Dr Bruce Weinke] assume that small microbubbles [micronuclei]are present and these nuclei grow with the influx of dissolved nitrogen duringthe ascent portion of the dive. The computerprograms for these models are much more complicated.
Failure of Tables
The Haldane method did notassume that micronuclei were present in tissues or that bubbles formed during asafe dive [or only a few, at most].
Now, one thing is important tobear in mind and that is this Haldane scheme is an algorithm, and it is not particularly useful for analyzing why a particular dive fails. Thus, a diver might say that my buddy and I made the identical dive and I was hit and he was not. Why? Was not everything the same? No, everthing was not. Divers havediffering amounts of micronuclei. These differwhen resting and differ with activity. No two divers are identical in this respect.
Dr Deco :doctor:
Haldanes Method
My many thanks to TS and M for filling in until I could complete my piece. She always does agood job and is well informed on these decompression issues.
Historically,the Haldane method is based on two concepts, both of which are used in table design to this day, albeit with some modifications. This model was conceived byJohn Scot Haldane MD and published in the Journal of Hygiene in 1908. The overall ideais that gas bubbles form in any tissue, are distributed in the blood, become lodged in susceptible tissues, and cause the pain known as the bends. At the time, people were not convinced that gas bubbles played the major role in the bends.
Using the ideas briefly described below, Haldane developed a calculation algorithm. An algorithm is a term used to describe a calculation method. Some familiar short ones are long division and the extraction of square roots. Table calculation has a very long algorithm.
Haldane developedthis under a contract from the admiralty of the Royal Navy. Navy divers had problems with 100 fsw dives while Greek sponge divers were routinely making successful dives to 190 fsw. The Brits were miffed!
Metastable Supersaturation
The longer the workmen remain in the caissons, the more slowly theyshould undergo decompression, for they must allow not only time for thenitrogen of the blood to escape, but also allow the nitrogen of the tissue time to pass into the blood....this last point is the most difficult to obtain...
- Paul Bert,Barometric Pressure, 1878.
- Paul Bert,Barometric Pressure, 1878.
This point most difficult too obtain was one of Haldanes big contributions. Haldane knew that divers were able to ascend from a relatively shallow depth directly to the surface without any decompression stops. This depth was about thirty three feet of seawater, and the residence time at that depth was many hours. The body was essentially saturated. Haldane believed that the body could sustain a certain degree of supersaturation of dissolved nitrogen without time limit. This supersaturation was (dissolved nitrogen pressure at depth)/(total pressure at surface). Later this was termed the metastable state. In other words, dissolved nitrogen stayed dissolved, and bubbles did not form if thesupersaturation was controlled.
Haldane performed experiments with small animals and found empirically that supersaturation was possible. He believed that this was related to an insufficient number of nucleation points in the body. [Today we would say that this was caused by an insufficient number of sufficiently large micronuclei.]
We have evidence here that the phenomenon must be due to supersaturation and the absence of points, since we have very frequently observed goats pass urine after decompression which frothed freely on cominginto contact with foreign surfaces.
- J. S. Haldane. The prevention of compressed air
illness. J. Hygiene Camb. 1908 p. 415
- J. S. Haldane. The prevention of compressed air
illness. J. Hygiene Camb. 1908 p. 415
This is well seen on watching under the microscope a stream ofbubbles coming off some point in soda water. It follows that if the concentration if dissolved molecules of gas isnot higher than some unknown point [we would call this partial pressure today],bubbles will not be formed. It ispossible that the absence of bubbles from most of the solid tissues is to be explainedby this non-existence of very small bubbles and the mechanical difficulties ofthe rapid aggregation of a sufficient number of molecules to produce largebubbles.
- J. S. Haldane. The prevention ofcompressed airillness. J. Hygiene Camb. 1908 p. 422
- J. S. Haldane. The prevention ofcompressed airillness. J. Hygiene Camb. 1908 p. 422
There are reasons for supposing that the living body presents nothing in the way of points or surfaces on which bubbles might arise in theblood or tissues as they do upon the glass and dust in soda-water.
- J. S. Haldane. The prevention of compressed air illness. J. Hygiene Camb. 1908 p. 410
- J. S. Haldane. The prevention of compressed air illness. J. Hygiene Camb. 1908 p. 410
In his algorithm, Haldane set this supersaturation limit at two to one. This came from the empirical observation that 33 fsw to the surface was two atmospheres absolute pressure to one atmosphere absolute pressure. As tables were designed for deeper depths, it became clear that some tissues could sustain a greater supersaturation ratio and others required a smaller ratio. This depended on the tissue, a topic we will look at next.
It is a fact well known to those practically acquainted with work incompressed air that even with very rapid decompression there is no risk ofcaisson disease unless the pressure has exceeded a certain amount. It seems perfectly clear that no symptomsoccur with less than one atmosphere of excess pressure, however long the exposure may be.
- J. S. Haldane, The prevention of compressed air illness J. Hygiene Camb.1908 p.355
- J. S. Haldane, The prevention of compressed air illness J. Hygiene Camb.1908 p.355
Tissues
These terms applied to the rate at which nitrogen was taken up or released by thetissue. A good blood supply allowed rapid loading and unloading, much like a loading dock with a railroad with many freight cars. A slow tissue had poor uptake and elimination. This might be compared to a loading dock with a single truck. Haldane knew that tissues picked up nitrogen more rapidly when exercising and recommended some activity during decompression.
In the past several decades, tissue has been changed to compartment to indicate that large volumes are not necessarily intended. A compartment might be but a very small piece of tissue.
Table Algorithm
Haldane usedan exponential expression for the uptake and elimination. This is similar to half-life in decay ofradioactive elements. Thus after onehalftime, 50% of the isotope has changed. After another halftime, an additional 50% has decayed and only 25% ofthe original remains, and so on. Elimination of dissolved nitrogen has the samepattern. Uptake is the processedreversed with 50% taken up, then 75% etc. Important is that the nitrogen be dissolved or the elimination rate isskewed very skewed. Gaseous nitrogenis hardly eliminated at all! This can beimportant when calculating the remaining tissue nitrogen at the end of asurface interval.
This processis quite simple and allows for small computes to be made for the diver to carryalong on the dive. Most dive computers have this single-pase system. They take the values for the allowablesupersaturation for the published data of Rogers and Powell, and they tracetheir pedigree to the PADI Recreational Dive Planner. [This is found in thesmall print in the owners manual.]
The dual-phasemodels [e.g., the RGBM of Dr Bruce Weinke] assume that small microbubbles [micronuclei]are present and these nuclei grow with the influx of dissolved nitrogen duringthe ascent portion of the dive. The computerprograms for these models are much more complicated.
Failure of Tables
The Haldane method did notassume that micronuclei were present in tissues or that bubbles formed during asafe dive [or only a few, at most].
Now, one thing is important tobear in mind and that is this Haldane scheme is an algorithm, and it is not particularly useful for analyzing why a particular dive fails. Thus, a diver might say that my buddy and I made the identical dive and I was hit and he was not. Why? Was not everything the same? No, everthing was not. Divers havediffering amounts of micronuclei. These differwhen resting and differ with activity. No two divers are identical in this respect.
Dr Deco :doctor:
We were lucky enough to have Dr. Deco come and speak to our dive club a few months ago. One of the most fascinating things he presented was some work he did, studying bubble formation in divers under certain conditions. What was most amazing to me was that there were some people who NEVER bubbled, no matter what they did . . . this may account for why some buddy pairs can do an identical dive, and one will have symptoms and the other will not. One of them may be one of those bubble-resistant people!
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