Just FYI as per request
Great perspectives. Reprinted from SOURCES.
Enjoy.
BW
SOME EARLY EVIDENCE FOR DUAL PHASE MODELS
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.
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, Steam Machines, 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.
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.
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 all. 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.
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
Great perspectives. Reprinted from SOURCES.
Enjoy.
BW
SOME EARLY EVIDENCE FOR DUAL PHASE MODELS
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.
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, Steam Machines, 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.
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.
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 all. 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.
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
