Dr Deco
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Dear Readers:
Haldane Theory
When discussing current and old tables it is necessary to understand what are the basics behind the Haldane Model. These could be listed as:
Metastable Limit
These ideas begin to be questioned in the early 1940s by Edmond Newton Harvey (a physicist). Substituted was instead (1) the idea that microbubbles were formed by muscular (= kinetic) activity of the tissues producing low-pressure regions (if only for a moment), and (2) the Young-Laplace equation linking microbubble radius and degree of supersaturation for bubble growth.
How the microbubbles actually form has remained a question, but many have believed it for decades; I begin to use the concept in 1971 when I entered this research field. Research then shattered the Haldane paradigm that bubbles were not present in DCS-free animals {MR Powell. Detection of gas-liquid phase separation in tissues by through-transmission ultrasound. 15th Annual Meeting, Biophysical Society, New Orleans, (1971); MR Powell. Leg pain and gas bubbles in the rat following decompression from pressure: monitoring by ultrasound. Aerospace Med., 43, 168-172 (1972); MR Powell. Gas phase separation following decompression in asymptomatic rats: visual and ultrasound monitoring. Aerospace Med., 43, 1240-1244 (1972)}.
NDLs
The No-decompression limits are the starting points for all decompression models, including the RGBM. There do not exist any ab nihilo (= from nothing) models. All are based on this experimentally derived data. From there, it depends on how you wish to extrapolate the limits to deeper depths. The M-value approach is on and it based on limited supersaturation. It could also be expressed as the Young-Laplace limiting criterion linking critical radius to bubble growth. We have discussed this idea on numerous occasions in this FORUM.
Bubble Growth versus Bubble Volume
It this point, the RGBM or VPM (Hills or Yount, Gernhardt, or Weinke , or Gerth, or Vann, or Srinivasan/Gerth/Powell) models depart. The idea now becomes that a bubble (Gernhardt) or a group of bubbles (the others) expands to a point where injury occurs. These are the so-called two-phase models , and they have currently supplanted the Haldane concept. They will automatically produce slower ascents (or deep stops) than the ad hoc Haldane ascent rate.
Assumptions in the Models
The assumptions inherent in the models are important. The devil is in the details . An understanding of the mathematics is of little value, since the models are mathematically correct and self-consistent. Where the discussion lies is in the application of research findings. Because something is mathematically elegant does not mean that it is physically or physiologically correct. There must be some assumptions because the mechanism of DCS is, overall, very complex. I for one would leave out the idea of lipid tissues and unchanging half times.
Your Part
It is demonstrable from experiments that activity levels will play a big role in DCS. This you must control. As with driving a car, maps (or GPS) is good, but nothing replaces the skill of the driver. In a day and age where personal responsibility is often minimized, you are really the one most responsible for your welfare.
Dr Deco :doctor:
Haldane Theory
When discussing current and old tables it is necessary to understand what are the basics behind the Haldane Model. These could be listed as:
- the concept of a metastable limit below which tissue gas phase (= bubble) formation will not occur;
- multiple tissues that are loaded in a certain, unchangable fashion (= exponential rise and decay);
- lipids are responsible for the longer halftime tissues.
Metastable Limit
These ideas begin to be questioned in the early 1940s by Edmond Newton Harvey (a physicist). Substituted was instead (1) the idea that microbubbles were formed by muscular (= kinetic) activity of the tissues producing low-pressure regions (if only for a moment), and (2) the Young-Laplace equation linking microbubble radius and degree of supersaturation for bubble growth.
How the microbubbles actually form has remained a question, but many have believed it for decades; I begin to use the concept in 1971 when I entered this research field. Research then shattered the Haldane paradigm that bubbles were not present in DCS-free animals {MR Powell. Detection of gas-liquid phase separation in tissues by through-transmission ultrasound. 15th Annual Meeting, Biophysical Society, New Orleans, (1971); MR Powell. Leg pain and gas bubbles in the rat following decompression from pressure: monitoring by ultrasound. Aerospace Med., 43, 168-172 (1972); MR Powell. Gas phase separation following decompression in asymptomatic rats: visual and ultrasound monitoring. Aerospace Med., 43, 1240-1244 (1972)}.
NDLs
The No-decompression limits are the starting points for all decompression models, including the RGBM. There do not exist any ab nihilo (= from nothing) models. All are based on this experimentally derived data. From there, it depends on how you wish to extrapolate the limits to deeper depths. The M-value approach is on and it based on limited supersaturation. It could also be expressed as the Young-Laplace limiting criterion linking critical radius to bubble growth. We have discussed this idea on numerous occasions in this FORUM.
Bubble Growth versus Bubble Volume
It this point, the RGBM or VPM (Hills or Yount, Gernhardt, or Weinke , or Gerth, or Vann, or Srinivasan/Gerth/Powell) models depart. The idea now becomes that a bubble (Gernhardt) or a group of bubbles (the others) expands to a point where injury occurs. These are the so-called two-phase models , and they have currently supplanted the Haldane concept. They will automatically produce slower ascents (or deep stops) than the ad hoc Haldane ascent rate.
Assumptions in the Models
The assumptions inherent in the models are important. The devil is in the details . An understanding of the mathematics is of little value, since the models are mathematically correct and self-consistent. Where the discussion lies is in the application of research findings. Because something is mathematically elegant does not mean that it is physically or physiologically correct. There must be some assumptions because the mechanism of DCS is, overall, very complex. I for one would leave out the idea of lipid tissues and unchanging half times.
Your Part
It is demonstrable from experiments that activity levels will play a big role in DCS. This you must control. As with driving a car, maps (or GPS) is good, but nothing replaces the skill of the driver. In a day and age where personal responsibility is often minimized, you are really the one most responsible for your welfare.
Dr Deco :doctor:
