Hello scubadada :
SAUL Decompression Model
I must apologizefor my very slow response to this question. My area of specialization is the cause of decompression sickness and notmathematical models. It therefore tookme a while to read and [try to] understand what was involved. Even in the development of the PADI tables, Iwas in charge of the test program and not the development of the model perse. The bigger delay has been that Ihave been ill – enough to be in the hospital. It is nothing particularly life threatening but certainly more than an uncomfortableannoyance.
The material Iwas able to read spoke only about gas exchange and little aboutmicronuclei. There is no question the authorknows about these, but they were not particularly included in the initial papers. The SAUL model is thus primarily about gas exchange. [Dr. Goldman states that adding microbubbles to themodels produces minor improvements while going to the interconnected modelmakes a very large improvement.]
Haldane’s Model
The modeldeveloped a century ago by J. S. Haldane saw the body as a large collection oftissues perfused by the blood at differing rates. These tissues, today referred to as“compartments,” were seen by Haldane as being in parallel with respect to theblood. This meant that blood came fromthe heart and was divided by the arteries, passed through the tissue compartments,and finally entered into veins to return to the heart. There was no passage ofnitrogen from one tissue to another; the local blood supply to that specifictissue was the only way in and out. Thisis referred to as “independent parallel compartments.” That is, thecompartments were completely isolated from one another.
The tissueshad differing amounts of blood flow [perfusion] and this accounted for the rateof dissolved nitrogen rise and fall and thus the “halftime.” As Haldane saw it, all compartments played arole in decompression sickness. If theinert partial pressure rose too high in one compartment, bubbles would form andDCS result.
Saul “Interconnected Model”
It has been long considered [more than 50 years] thatdissolved nitrogen could diffuse from one tissue into another. This is true notonly for gases in diving but also drugs administered for medical purposes.
Thus, nerve tissue lying next to fatty[adipose] tissue could be supplied with nitrogen by diffusion from fat tonerve. This concept is not entirely new,but no one has made a decompression model [algorithm] utilizing the concept. Anolder version of the concept was termed the “competitive parallel arrangement” firstpresented in 1944.
Dr Saul Goldman’smodel has one compartment that is considered important for DCS and is termedthe “central risk-bearing compartment.” Itis associated with other peripheral compartments that do not provoke DCS butcan load the central [“risk-bearing”] compartment by diffusion with dissolvednitrogen.
What thepaper demonstrates is that it is possible to take known decompression data anduse this data to test various models. Commonly,data is broken into at least two sets. Oneset is used to develop the parameters [calibration regime] of the different modelsand other data to test the models and see how they perform with respect toaccurately predicting DCS incidence.
Some modelstested had compartments in parallel [Haldane model] and other models hadcompartments fed by nitrogen diffusing from, e.g., adipose tissue, into the centralcompartment.
In this Saul“interconnected model” model, only one compartment [termed the centralcompartment] will contribute to DCS. [This might be DCS-prone connective and associated nerve tissue.] Nitrogen is absorbed by all tissues of thebody, and some of these might be reservoirs for considerable amounts ofnitrogen. Fatty tissue is a good exampleof a “feeder” tissue. The result is thatthe “interconnected model” had the best fit to predicting DCS.
As far as I cantell, this is a demonstration that the concept is a valid one. It does not appear that he would develop tablesat the current time. He does demonstratethe effect of different “stop times” with the various models. We will watch how all of this plays out.
Dr Deco :doctor:
