Decompression theory: Difference between revisions

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===Efficiency and safety===

Two criteria that have been used in comparing decompression schedules: Safetyare efficiency and efficiencysafety, where [[decompression efficiency]] is defined as the ability of a schedule to provide acceptable safety from decompression sickness in the shortest time spent decompressing, and decompression safety, or converely, risk, is measured by the probability of decompression sickness incurred by following a given schedule for a given dive profile. Since it is impracticable to eliminate all risk using current knowledge of the effects of several variables, risk is estimated by statistical analysis of the recorded outcomes of exposure and decompression profiles, and an acceptable risk is stipulated, which may vary depending on the circumstances of the application.<ref name="Edel 1980" />

=== Tissue compartments ===

One attempt at a solution was the development of multi-tissue models, which assumed that different parts of the body absorbed and eliminated gas at different rates. These are hypothetical tissues which are designated as fast and slow to describe the rate of saturation. Each tissue, or compartment, has a different half-life. Real tissues will also take more or less time to saturate, but the models do not need to use actual tissue values to produce a useful result. Models with from one to 16 tissue compartments<ref name="Buhlmann 1984" /> have been used to generate decompression tables, and [[dive computer]]s have used up to 20 compartments.<ref name="Validation workshop" />

For example: Tissues with a high [[lipid]] content can take up a larger amount of nitrogen, but often have a poor blood supply. These will take longer to reach equilibrium, and are described as slow, compared to tissues with a good blood supply and less capacity for dissolved gas, which are described as fast.<ref name="DAN intro to DCS" />

Fast tissues absorb gas relatively quickly, but will generally release it quickly during ascent. A fast tissue may become saturated in the course of a normal recreational dive, while a slow tissue may have absorbed only a small part of its potential gas capacity. By calculating the levels in each compartment separately, researchers are able to construct more effective algorithms. In addition, each compartment may be able to tolerate more or less supersaturation than others. The final form is a complicated model, but one that allows for the construction of algorithms and tables suited to a wide variety of diving.<ref name="DAN intro to DCS" /> A typical dive computer has an 8–12 tissue model, with half times varying from 5 minutes to 400 minutes.<ref name="Validation workshop" /> The [[Bühlmann tables]] use an algorithm with 16 tissues, with half times varying from 4 minutes to 640 minutes.<ref name="Buhlmann 1984" />

Tissues may be assumed to be in series, where dissolved gas must diffuse through one tissue to reach the next, which has different solubility properties, in parallel, where diffusion into and out of each tissue is considered to be independent of the others, and as combinations of series and parallel tissues, which becomes computationally complex.<ref name="Goldman 2007" />

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===Ingassing model===

<!-- target for redirect [[Ingassing]] -->

The half time of a tissue is the time it takes for the tissue to take up or release 50% of the difference in dissolved gas capacity at a changed partial pressure. For each consecutive half time the tissue will take up or release half again of the cumulative difference in the sequence ½, ¾, 7/8, 15/16, 31/32, 63/64 etc.<ref name="Bookspan"/> Tissue compartment half times range from 1 minute to at least 720 minutes.{{sfn|Yount|1991|p=137}} A specific tissue compartment will have different half times for gases with different solubilities and diffusion rates. Ingassing is generally modeled as following a simple inverse exponential equation where saturation is assumed after approximately four (93.75%) to six (98.44%) half-times depending on the decompression model.<ref name="Huggins 1992 Chapter 2"/><ref name=logodiving /><ref name="Maiken" /> There is normally no phase change during ingassing after the gases are dissolved in the blood of the pulmonary circulation in the lungs. They remain in solution in whichever tissues they reach by perfusion and diffusion, so the model is fairly robust. The exception is for [[isobaric counterdiffusion]] which can induce bubble growth and posssibly bubble formation when a gas of different solubility is introduced to the breathing mixture.{{sfn|Hamilton|Thalmann|2003|pp=477–478}}<ref name="Lambertson 1989" />

This model may not adequately describe the dynamics of outgassing if gas phase bubbles are present.<ref name="Wienke 1990" /><ref name="Yount 1990" />

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<ref name="DAN data uploads">{{cite web |url=https://www.daneurope.org/send-your-dive-profile |title=Send your Dive Profile |last=<!-- not specified --> |website=daneurope.org |publisher=DAN Europe |access-date=13 February 2016 |archive-date=8 April 2016 |archive-url=https://web.archive.org/web/20160408170051/http://www.daneurope.org/send-your-dive-profile |url-status=live }}</ref>

<ref name="DAN intro to DCS" >{{cite web |url=https://dan.org/health-medicine/health-resource/dive-medical-reference-books/decompression-sickness/introduction/ |title=Chapter 1: Introduction to Decompression Sickness |website=dan.org |access-date=31 August 2025 }}</ref>

<ref name="DAN projects">{{cite web |url=https://www.daneurope.org/our-projects |title=Our Projects |last=<!-- not specified --> |work=DAN Europe website |access-date=13 February 2016 |archive-date=11 April 2016 |archive-url=https://web.archive.org/web/20160411164440/https://www.daneurope.org/our-projects |url-status=dead }}</ref>