Brian Hills Letter To Wienke

[BRW]

Listees,

Have been asked to pass this onto SB -- great
historical perspectives from the Father Of Modern
Decompression Theory. Is part of article from
SOURCES.

BW



Some Early Evidence for Models Dual-Phase

By Brian A. Hills
Editor’s note: Brian Hills was one of the early advocates of deep stops and dual-phase modeling. His work was long disregarded if not denigrated because Haldanian models held the bastions. More recently with the introduction of the Reduced Gradient Bubble Model and a general dual-phase awareness, Hills’ work is being re-evaluated and is gaining the recognition it deserves. Recently, when we received a copy of an email that Brian Hills sent to Dr. Bruce Wienke, we asked Bruce if we could reprint it. Bruce said "by all means " and provided a brief introduction. Our growing knowledge of decompression and diving has been, if anything, less than linear, as the following brief history more than amply demonstrates.
We begin with Wienke’s introductory comments:

Like all progress in science, advances in decompression theory and application in the real world of diving have been slow, like a century's worth since the time of Haldane. Though it has long been known that bubbles cause decompression sickness (DCS) and that Haldane’s original medical approach to staging divers only focused on dissolved gases (not bubbles), it has just been in the last ten years or so that realistic dual-phase models (like RGBM), treating dissolved gases and bubbles in a coupled framework, have been successfully employed, tested, and accepted across the wide spectrum of diving. A central feature of dual-phase dynamics are deep stops and shorter overall decompression times (hang time on a line or lift bag) for technical diving. For recreational diving, surface intervals, repetitive and multi-day diving frequency, reverse profiles, and altitude are also impacted.
The new NAUI recreational and technical RGBM Tables bear witness to all this. The growing number of dive computers with RGBM algorithms safely deployed by technical and recreational divers underscores both popular acceptance and a fine safety record. To date; Suunto, Mares, Dacor, Plexus, HydroSpace, and Zeagle dive computers embody the dual-phase RGBM for all diving, nonstop to deco, air to mixed gases, sea level to high altitude, sport to technical, bounce to saturation diving. Both ABYSS and GAP market diver software with the RGBM model. Expect others shortly to add to the above list.
Much of RGBM success is due to you out there, the "living laboratory" of divers, testers, analyzers, students, instructors, scientists, operation teams, doctors, and intelligent software users.
And RGBM has been incorporated into NAUI diver training courses, even at the entry level. NAUI was first on the street with important changes in diving technology and training.
The spectacular success of dual-phase models today, however, mask the path to success, and the faces of early players. In that regard, the following letter to me from Brian Hills is poignant, highly illuminating, and I would like to share it with NAUI Worldwide. Brian Hills, in collective estimation, is truly the prime mover for modern dual phase models-the "Father Of Deep Stops." His contributions are monumental.
Read on and enjoy. Bruce R. Wienke

Dear Bruce,

Quite recently I received an email from a Dean Laffan in Melbourne who was researching the archives for early models of programming decompression profiles for deep-sea divers. After 20 years of advocating two-phase models, I finally gave up because, at the time (1980), Haldanian methods were simply too deeply ingrained in the psyche of diving medical officers for any alternative to be considered. A two-phase system for gas (dissolved versus separated from solution) also involved mathematics that were too complex to program into the laptop computer, which had just become so popular.
It was therefore with much interest that I read Dean Laffan's comment about the current acceptance of two-phase models and of your dual-phase model in particular. I would be most interested to hear more about the current status and level of acceptance of these models. I first challenged the Haldane single-phase concept back in 1968 with a paper in J.A.P. entitled "Relevant Phase Conditions for Predicting the Occurrence of Decompression Sickness," but it never attracted any attention despite our success in interpreting the experience of Australian pearl divers.
I gave up calculating decompression tables the day I observed two bubbles in living tendon; one shrinking while, simultaneously, the other was growing. We later discovered "intermittent perfusion," but that made mathematical modeling a real nightmare.
Taking a very wide view, you could say that one can approach decompression formulation in two ways, the most civilized employing mathematical modeling.
The other and most extreme approach is purely empirical, modifying the dive profile every time there is a death or serious neurological case. This is effectively what happened in Australia with the pearl divers between 1850 and 1950 when there were about 4,000 deaths and many more cases of residual decompression injury. We were just in time (in 1960) to put this vast distillate of human experience on record before the pearling industry went out of business. This amounts to over 100 million air dives. The other day I came across these records, all showing deep initial stops derived purely empirically with no input from science, medicine, or mathematics. We published a summary back in the 1960s, but the data would seem good for testing new models because they range from 100 feet to 300 feet depth and up to two hours bottom time and even include some repetitive air dives.
It was our conclusion at the time that the data can only be explained on a two-phase model. Hence, I should be most interested to hear how two-phase models have developed.

Brian k Hills, Professor and Laboratory Head
Golden Casket Pediatric Research Laboratory
Mater Medical Research Institute Aubigny Place
Raymond Terrace
South Brisbane, QLD
Australia

 

[The Iceni]

. . . was also considered a heretic!

Fascinating stuff!

(I wish I had studied advanced maths!)

 

[BRW]

Right On, ICENI.

Columbus sailed the wrong way too.

 

[DepartureDiver]

Does anyone have an email address for Dr. Hills? I'd like to contact him and let him know that his work was not totally ignored. I had the pleasure of doing my college biophysics project on deep stops and Dr. Hills thermodynamic approach back in 1986 and was also fortunate enough to get a copy of the book he wrote entitled "Decompression Sickness Volume 1 The Biophysical Basis of Prevention and Treatment" that John Wiley & Sons published in 1977.

 

[Dr Deco]

Hello Readers:

Decompression Models

1. Models come and go. The concepts of Dr Brian Hills have a rather long history. Basically when the “thermodynamic model” started, the dive industry was performing “bounce dives” to several hundred feet and the divers were decompressed in a chamber. This allowed the divers to walk around and nucleate their legs, although this concept was not known at the time. (It developed from my NASA research.)

2. To increase the efficiency of the dive procedure, the US navy and some commercial groups turned to “saturation diving” and simply passed up any questions of decompression schedules.

3. Recreational divers were not making dives to any depths exceeding 150 fsw and decompression was rare in the SCUBA world.

4. Money to test dive procedures was either from commercial companies (and not given to outside scientists) or from the US navy. The sums were small and would rarely have permitted the testing of any decompression schedule in a realistic manner. That is simply a problem with scientific research and is not recognized by the general public. (This is true of any profession. Seldom is it what we really imagine it to be – or what Hollywood portrays it as.)

5. The model of Dr Hills was based on gas pressures remaining within the Oxygen Window and not allowing the inert gas tension to ever arise above supersaturation; phase separation [bubble formation] was thus avoided. There were not two phases in the “critical tissues” in the schedules proposed by Hills using his Thermodynamic Method.

6. The idea of short lifetime nuclei generated by stress-assisted nucleation did not exist; it came from my NASA research. Many of these new decompression schedules work, in part I believe, because the decompression is performed in the water and new nuclei are not generated. Whether they would work as well in a dry chamber (with the divers able to move around) is a very different case, I maintain.

7. Dr Hills was a new driving force in a field where physical scientists are rare. His doctorate was in chemical engineering with a specialization in thermodynamics. The world of diving was simply not ready for him yet.

Dr Deco :doctor:

 

[Saturation]

Hello Readers:

6. The idea of short lifetime nuclei generated by stress-assisted nucleation did not exist; it came from my NASA research. Many of these new decompression schedules work, in part I believe, because the decompression is performed in the water and new nuclei are not generated. Whether they would work as well in a dry chamber (with the divers able to move around) is a very different case, I maintain.

7. Dr Hills was a new driving force in a field where physical scientists are rare. His doctorate was in chemical engineering with a specialization in thermodynamics. The world of diving was simply not ready for him yet.

Dr Deco :doctor:

Thanks Dr. D. Your abstract published in the Summer 2003 UHMS about lower extremity adynamia and its effects on bubbles adds more fuel to fire up the value of nucleation. As you and co-workers continue to clarify the physiology, I believe the benefit/risk is sufficiently great that implementing these preliminary findings into diving practice can be advised.

 

[BRW]

Hello Readers:

Decompression Models

1. Models come and go. The concepts of Dr Brian Hills have a rather long history. Basically when the “thermodynamic model” started, the dive industry was performing “bounce dives” to several hundred feet and the divers were decompressed in a chamber. This allowed the divers to walk around and nucleate their legs, although this concept was not known at the time. (It developed from my NASA research.)

2. To increase the efficiency of the dive procedure, the US navy and some commercial groups turned to “saturation diving” and simply passed up any questions of decompression schedules.

3. Recreational divers were not making dives to any depths exceeding 150 fsw and decompression was rare in the SCUBA world.

5. The model of Dr Hills was based on gas pressures remaining within the Oxygen Window and not allowing the inert gas tension to ever arise above supersaturation; phase separation [bubble formation] was thus avoided. There were not two phases in the “critical tissues” in the schedules proposed by Hills using his Thermodynamic Method.

67. Dr Hills was a new driving force in a field where physical scientists are rare. His doctorate was in chemical engineering with a specialization in thermodynamics. The world of diving was simply not ready for him yet.

Dr Deco :doctor:

All,

There are a couple of addenda to the above
and a few corrections need be made -- coming
from both (my) USN/LANL diving experiences of the time
and model diving correlations over many years and venues:

1) the oxygen window was not the criteria for staging
in the thermodynamics model (TM), rather a
mechanical "pain" point based on bulk modulus,
and/or estimates based on separated phase volume
once separation took place. The window appears
in the TM and the inactive component takes up
inert gas;

2) the "separated phase" was bubbles, and once
established, had characteristic 1/r properties
assigned to it (thus giving deep stops to
control separated phase);

3) using the oxygen window ("zero supersaturation"
approach proposed by Behnke) would not give the
TM staging profiles, and would take very long, as
tested by Behnke/USN back in 50s;

4) "before phase separation" mechanics were not
spelled out in the TM, nor linked to seeds/bubbles;

5) Hills, Hempleman, and the Royal Navy found
that the deep stops induced by the TM were
very beneficial and incorporated them in
Royal Navy in 1975, but these incorporations
were not one-to-one with the TM;

6) the USN did a bunch of testing of TM (Sas, 1976)
with 20 fsw dropout producing bubbles, and scaring
all for the wrong reasons:

7) Starck and Krasberg did extensive testing of TM via
tests in the open ocean, results were favorable
with some modifications , but all that vanished
behind a proprietary shield;

8) C & C Dive Team (me and others) adopted TM,
used it extensively in 80s, modified it in the
field using bubble precursor dynamics, and also
eliminated bulk modulus criteria -- one day,
data and risk analysis will be published in the
open. Some resides now in RGBM Data Bank;

9) looking back on TM, and contrasting with modern
dual phase staging models, it did a very creditable
job, with the main problem one of not staying deep
enough long enough at times, plus a bigger problem
with dropout at 20 fsw if invoked (better to switch
to pure O2 and stay awhile);

Regards,

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr
NAUI BOD Vice Chairman