SAUL decompression model
- Thread starter scubadada
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
OP
- Messages
- 19,794
- Reaction score
- 18,661
- Location
- Philadelphia and Boynton Beach
- # of dives
- 1000 - 2499
There may be significant differences between the four compartment serial model used in the DCIEM algorithm vs. the interconnected model in SAUL decompression algorithm. Perhaps all the innovative decompression data comes from Canada? I may be wrong but doesn't Citizen watches use the DCIEM algorithm? The NDLs in the DCIEM table for 1st dive are not much different than Oceanic PZ+/BUHLMAN ZHL-16C and are considerably more conservative than the Pelagic DSAT algorithm.
I took the liberty of submitting this queston to the blog on Modern Decompression and look forward to a response from Dr Goldman. Dave Sawatzky is a contributing editor to Diver, where I first read about the SAUL algorithm. Doppler, do you read Diver "the longest established scuba diving magazine in North America"?
Good diving, Craig
Last edited:
No, but I know David and a couple of the folks who worked on the DCIEM testing.
The old NAUI tables were DCIEM... very good tables.
OP
- Messages
- 19,794
- Reaction score
- 18,661
- Location
- Philadelphia and Boynton Beach
- # of dives
- 1000 - 2499
Perhaps you could ask your friend, Dr Sawatzky, if he might want to comment on the topic, published in his magazine.
Sometimes, us older folks, have more difficulty evaluating new concepts.
I really enjoyed your book, The Six Skills and Other Discussions. I've read through my signed copy several times.
Best, Craig
OP
- Messages
- 19,794
- Reaction score
- 18,661
- Location
- Philadelphia and Boynton Beach
- # of dives
- 1000 - 2499
Dr Goldman wrote a very detailed response to my question on his Modern Decompression Blog. For those of you still following the discussion, here is the reply:
Q: This question was posted by Craig in comments to The Doctor is In part II
An interesting discussion has come up on ScubaBoard. What are the major differences between your model and the 4 compartment serial model used by DCIEM?
A:
The answer to this question may be of interest to readers in general, but not always to the same degree. So, what I’ve done is printed both a reasonably complete answer (in black type), with each paragraph preceded by a quick-and-easy overview (in red type).
There are three main differences between the DCIEM interconnected model and SAUL. (1) the way the compartments are connected, (2) the calculation of how the inert gases move between compartments, and (3) which compartment(s) are risk-bearing.
Here is the more detailed description of the main differences between the DCIEM interconnected model and mine. There are three major differences : (1) the geometric arrangement of the tissues and circulating blood, (2) the “order” of the diffusion kinetics that is presumed, and (3) whether one or more than one compartment carries explicit risk. Let’s consider these one at a time.
(1) The DCIEM model has 4 compartments connected in series – i.e., almost like a train or subway – you (or the gas) can move from the first to the second to the third, and so on, but not directly from the first to the third. In SAUL, the arrangement of compartments is more like a wheel, with the risk bearing compartment as the hub and gas moving between the hub and the spokes in either direction. This type of model was first described 70 years ago by Morales and Smith who concluded that it was better than other arrangements of compartments in illustrating how gases or other substances moved in tissues.
(1) The compartmental geometry I chose to use – wherein the compartments are interconnected in parallel – originated almost 70 years with the work of Morales and Smith, two US Navy modellers. The work is cited in refs 25-27, 31, 32 in my J APPL PHYSIOL paper, with ref 26 being most relevant. These modellers examined a number of different compartmental arrangements, and concluded that on balance, their so-called “competitive parallel arrangement” (not to be confused with parallel models, like Haldane, which are not competitive) best captured tissue perfusion. Their competitive parallel arrangement is the geometry illustrated in Fig 1B of my J APPL PHYSIOL paper. They did not consider DCS active/DCS – inactive issues. They used the term “competitive” to reflect the fact that all the tissues “compete” for the circulating dissolved gases. The DCIEM model involves 4 compartments that are connected in series, which is clearly a different arrangement from what Morales and Smith, and I used.
(2) SAUL uses the same method of calculating the rate at which dissolved gas can flow between compartments as is used by essentially all decompression work I know of, other than the DCIEM model. The DCIEM model adds in an additional term which I would only expect to see in circumstances where the dissolved concentration of gas was at least 10 times greater than would ever occur in diving. I have never seen a satisfactory explanation of their use of this term.
(2) I used 1st order kinetics to describe the rate of dissolved inert gas flow between compartments, while the DCIEM model included a quadratic contribution to the kinetics. All decompression work that I am aware of (Haldane, US Navy probabilistic models, etc.) other than the DCIEM model, presumes 1st order kinetics for dissolved inert gas exchange. From the perspective of basic physical chemistry, 1st order kinetics, whereby the rate of dissolved gas diffusion out of a compartment is proportional to the 1st power of the dissolved inert gas concentration in that compartment (e.g. see Eq. A2 in my Appendix A), is essentially always sufficient to capture the underlying kinetics, except for concentrations that are extremely large. I wouldn’t expect a quadratic contribution to kick in until the dissolved concentration became at least an order-of magnitude greater than is encountered in decompression problems. I never understood the DCIEM inclusion of a quadratic contribution to the kinetics, and I have never seen it satisfactorily explained.
(3) In SAUL the risk is carried entirely by the “hub” or central compartment. The other compartments do not carry risk but they affect the risk in the “hub” by receiving dissolved gas from the “hub” (which lessens the risk there) or sending dissolved gas to the “hub” (which increases the risk there). In the main DCIEM model all the compartments carry risk. I have found that, by keeping the risk only in one compartment SAUL is better able to predict decompression stress than other models. In comparing different models’ ability to predict DCS on direct ascents from saturation, SAUL was the only one that correctly reproduced the shape that best fits the data.
(3) In my models the risk is carried entirely by the relatively well-perfused central compartment, while the peripheral compartments are not themselves explicitly risk-bearing. They influence risk indirectly by acting as sources or sinks (depending on conditions) of dissolved inert gas, relative to the central risk-bearing compartment. In the main DCIEM model, i.e. the one developed later into a probabilistic model [as described in P. Tikuisis, R.Y. Nishi, and P.K. Weathersby, Undersea Biomedical Research, 15(4), 301-313 (1988)] all the compartments bear risk. I have found that if more than one compartment in a parallel interconnected model is allowed to be explicitly risk-bearing, the predictive capability of the model deteriorates. Specifically have a look at FIG 2 in my J APPL PHYSIOL paper. This illustrates the P(DCS) predictions of a number of different models for the simplest profile that exists – i.e. a direct ascent from saturation. While the parallel interconnected models shown both have a sigmoidal shape that fits the data, the other models uniformly fail to properly predict the observed results. They do not swing up fast enough with increasing saturation depth. Model failure here is serious, because, as previously indicated, this is the simplest possible profile that can exist. I have found that if an explicit risk is put into more than one compartment, the interconnected models deteriorate, i.e. they lose their sigmoidal shape, reduce to a quasi-linear form, and fail to reproduce the observed data.
I find the Saul decompression model compelling, I'd wager we'll all see it more in times to come.
Best, Craig
Q: This question was posted by Craig in comments to The Doctor is In part II
An interesting discussion has come up on ScubaBoard. What are the major differences between your model and the 4 compartment serial model used by DCIEM?
A:
The answer to this question may be of interest to readers in general, but not always to the same degree. So, what I’ve done is printed both a reasonably complete answer (in black type), with each paragraph preceded by a quick-and-easy overview (in red type).
There are three main differences between the DCIEM interconnected model and SAUL. (1) the way the compartments are connected, (2) the calculation of how the inert gases move between compartments, and (3) which compartment(s) are risk-bearing.
Here is the more detailed description of the main differences between the DCIEM interconnected model and mine. There are three major differences : (1) the geometric arrangement of the tissues and circulating blood, (2) the “order” of the diffusion kinetics that is presumed, and (3) whether one or more than one compartment carries explicit risk. Let’s consider these one at a time.
(1) The DCIEM model has 4 compartments connected in series – i.e., almost like a train or subway – you (or the gas) can move from the first to the second to the third, and so on, but not directly from the first to the third. In SAUL, the arrangement of compartments is more like a wheel, with the risk bearing compartment as the hub and gas moving between the hub and the spokes in either direction. This type of model was first described 70 years ago by Morales and Smith who concluded that it was better than other arrangements of compartments in illustrating how gases or other substances moved in tissues.
(1) The compartmental geometry I chose to use – wherein the compartments are interconnected in parallel – originated almost 70 years with the work of Morales and Smith, two US Navy modellers. The work is cited in refs 25-27, 31, 32 in my J APPL PHYSIOL paper, with ref 26 being most relevant. These modellers examined a number of different compartmental arrangements, and concluded that on balance, their so-called “competitive parallel arrangement” (not to be confused with parallel models, like Haldane, which are not competitive) best captured tissue perfusion. Their competitive parallel arrangement is the geometry illustrated in Fig 1B of my J APPL PHYSIOL paper. They did not consider DCS active/DCS – inactive issues. They used the term “competitive” to reflect the fact that all the tissues “compete” for the circulating dissolved gases. The DCIEM model involves 4 compartments that are connected in series, which is clearly a different arrangement from what Morales and Smith, and I used.
(2) SAUL uses the same method of calculating the rate at which dissolved gas can flow between compartments as is used by essentially all decompression work I know of, other than the DCIEM model. The DCIEM model adds in an additional term which I would only expect to see in circumstances where the dissolved concentration of gas was at least 10 times greater than would ever occur in diving. I have never seen a satisfactory explanation of their use of this term.
(2) I used 1st order kinetics to describe the rate of dissolved inert gas flow between compartments, while the DCIEM model included a quadratic contribution to the kinetics. All decompression work that I am aware of (Haldane, US Navy probabilistic models, etc.) other than the DCIEM model, presumes 1st order kinetics for dissolved inert gas exchange. From the perspective of basic physical chemistry, 1st order kinetics, whereby the rate of dissolved gas diffusion out of a compartment is proportional to the 1st power of the dissolved inert gas concentration in that compartment (e.g. see Eq. A2 in my Appendix A), is essentially always sufficient to capture the underlying kinetics, except for concentrations that are extremely large. I wouldn’t expect a quadratic contribution to kick in until the dissolved concentration became at least an order-of magnitude greater than is encountered in decompression problems. I never understood the DCIEM inclusion of a quadratic contribution to the kinetics, and I have never seen it satisfactorily explained.
(3) In SAUL the risk is carried entirely by the “hub” or central compartment. The other compartments do not carry risk but they affect the risk in the “hub” by receiving dissolved gas from the “hub” (which lessens the risk there) or sending dissolved gas to the “hub” (which increases the risk there). In the main DCIEM model all the compartments carry risk. I have found that, by keeping the risk only in one compartment SAUL is better able to predict decompression stress than other models. In comparing different models’ ability to predict DCS on direct ascents from saturation, SAUL was the only one that correctly reproduced the shape that best fits the data.
(3) In my models the risk is carried entirely by the relatively well-perfused central compartment, while the peripheral compartments are not themselves explicitly risk-bearing. They influence risk indirectly by acting as sources or sinks (depending on conditions) of dissolved inert gas, relative to the central risk-bearing compartment. In the main DCIEM model, i.e. the one developed later into a probabilistic model [as described in P. Tikuisis, R.Y. Nishi, and P.K. Weathersby, Undersea Biomedical Research, 15(4), 301-313 (1988)] all the compartments bear risk. I have found that if more than one compartment in a parallel interconnected model is allowed to be explicitly risk-bearing, the predictive capability of the model deteriorates. Specifically have a look at FIG 2 in my J APPL PHYSIOL paper. This illustrates the P(DCS) predictions of a number of different models for the simplest profile that exists – i.e. a direct ascent from saturation. While the parallel interconnected models shown both have a sigmoidal shape that fits the data, the other models uniformly fail to properly predict the observed results. They do not swing up fast enough with increasing saturation depth. Model failure here is serious, because, as previously indicated, this is the simplest possible profile that can exist. I have found that if an explicit risk is put into more than one compartment, the interconnected models deteriorate, i.e. they lose their sigmoidal shape, reduce to a quasi-linear form, and fail to reproduce the observed data.
I find the Saul decompression model compelling, I'd wager we'll all see it more in times to come.
Best, Craig
A couple of questions come to mind. How is a compartment risk ascertained? Has there been any empirical testing on this model or is it all theoretical?
OP
- Messages
- 19,794
- Reaction score
- 18,661
- Location
- Philadelphia and Boynton Beach
- # of dives
- 1000 - 2499
Similar threads
