Adaptive Algorithms

In the 1990s, Professor Albert Bühlmann (1923 – 1994) wanted to reflect the change in blood perfusion to various body organs when the diver is subjected to temperature and/or workload variations, as changes in blood perfusion would alter the inert gas saturation tolerance. In other words, he wanted to develop an algorithm to deal with all the real time variables throughout the dive, not just the depth and time. The result was ZH-L8 ADT, a model using 8 evenly-distributed tissue compartments halftimes ranging from 5 to 640 minutes (for nitrogen). Some of the ‘initial’ halftimes (particularly those of the mid compartments) get altered during the dive to reflect what’s going on with the diver’s body. The idea is that coldness causes vaso-constriction (mainly at the skin and the muscles), thus reduces perfusion. To mathematically simulate this change in perfusion level, the ‘corresponding’ halftimes should be altered.

As you might have guessed, this model is useful for dive computers only. It is implemented in some of Uwatec models. The dive computer has a sensor to monitor the water temperature throughout the dive. The feedback is then sent to the algorithm. One drawback of this approach is that the water temperature is not always a measure of what the diver is feeling. The diver might be wearing a swimsuit and a T-shirt, or a dry suit with a heavy undergarment, so skin temperature would have been a more appropriate indicator. The workload is calculated by monitoring the reduction in tank pressure (gas consumption rate). This is considered by some divers as another drawback, as increased consumption rate is not always an indication of elevated workload. The newer, top line models include an optional ‘integrated heart rate monitor’. This is a ‘belt’ that allows the workload calculation to take into account actual blood circulation. In some models, the workload is an adjustable setting, which is good for unfit divers or, for instance, when the diver knows beforehand that there’d be a demanding situation (swimming against current, long surface swim before the descent, etc…).

Based on his personal communication with Professor Albert Bühlmann and Dr. Max Hahn, my friend Dr. Albrecht Salm provided me with some details on which ZH-L16 halftimes would need getting altered to reflect cold and/or increased workload. This enabled me to introduce ZH-L16D in Ultimate Planner. ZH-L16D is a more conservative model than both ZH-L16B and ZH-L16C, and it would generate more suitable schedules for unfit divers or for anticipated colder and/or more demanding dives. For instance, assuming the last stop depth is at 6 meters (20 feet), the total run time of a 30 minute dive on air to 45 meter (150 foot) depth would be 73 minutes (ZH-L16B), 84 minutes (ZH-L16C) or 87 minutes (ZH-L16D).

P.S.: This article was first published in the fourteenth issue of Tech Diving Mag.

10 Responses

  1. The assertion that <em>this model is useful for dive computers only</em>, is untrue. It can also be used to determine maximum safe altitudes that one may go to after a dive. I have been interested in this concept for quite some time because I am a pilot. The general rule (from DAN) is that you wait 24 hours. That is extreme overkill, but it is predicated on the fact that one assumes that the safest course is to just make sure all gas perfusion effects have dissipated. If you know, however, that after a specific dive you could safely fly at 5000', then if you are flying your own plane you can just stay under 5000. Commercial aircraft are pressurized to 8,000' and so that could be calculated for using the Bühlmann model.
  2. Cochran is the exclusive provider to the U.S. Navy and its dive computers are Approved for Military Use (“AMU”) listed and its dive computers are being used by other international Navies and have NATO part numbers. With that said please click on the following link "Enviromental Compensation"<br /> <br /> <br /> <a href="http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf">http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf</a><br /> <br /> <br /> <a href="http://www.DiveCochran.com">www.DiveCochran.com</a><br /> [email]sales@DiveCochran.com[/email]<br /> [email]salesmanager@DiveCochran.com[/email]<br /> <br /> Come visit Cochran Undersea Technology at the DEMA SHOW 2014 in the Las Vegas Convention Center, Las Vegas, NV November 19-22, Booth 1351.
  3. <blockquote><strong>WetCell;7154929 wrote:</strong> The assertion that <em>this model is useful for dive computers only</em>, is untrue. It can also be used to determine maximum safe altitudes that one may go to after a dive. I have been interested in this concept for quite some time because I am a pilot. The general rule (from DAN) is that you wait 24 hours. That is extreme overkill, but it is predicated on the fact that one assumes that the safest course is to just make sure all gas perfusion effects have dissipated. If you know, however, that after a specific dive you could safely fly at 5000', then if you are flying your own plane you can just stay under 5000. Commercial aircraft are pressurized to 8,000' and so that could be calculated for using the Bühlmann model.</blockquote> <br /> The assertion that <em>this model is useful for dive computers only</em>, is <strong>true</strong>. It has nothing to do with flying after diving. Actually researchers assert that diving decompression is different from altitude decompression. Bühlmann model could be used to create profiles for diving at altitude, which is totally different from flying after diving.<br /> <br /> For more info on flying after diving (and accelerating the pre-flight surface interval), take a look at the fifteenth issue of <a href="http://www.techdivingmag.com">Tech Diving Mag</a>.<span style="color: Silver;"><br /> </span>
  4. Cochran Undersea Technology designs, manufactures, and markets state-of-the-art diving computers for recreational, technical, CCR and commercial divers from our facility located in Richardson, TX. Cochran has been designing dive computers for itself and others for over twenty years. Cochran is the exclusive provider to the U.S. Navy and its dive computers are Approved for Military Use (“AMU”) listed and its dive computers are being used by other international Navies and have NATO part numbers. With that said please click on the link below "Enviromental Compensation"<br /> <br /> <br /> <a href="http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf">http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf</a><br /> <br /> <br /> <a href="http://www.DiveCochran.com">Cochran Undersea Technology</a><br /> [email]sales@DiveCochran.com[/email]<br /> [email]salesmanager@DiveCochran.com[/email]<br /> <br /> <br /> Come visit Cochran Undersea Technology at the DEMA SHOW 2014 in the Las Vegas Convention Center, Las Vegas, NV November 19-22, Booth 1351.
  5. Cochran Undersea Technology designs, manufactures, and markets state-of-the-art diving computers for recreational, technical, CCR and commercial divers from our facility located in Richardson, TX. Cochran has been designing dive computers for itself and others for over twenty years. Cochran is the exclusive provider to the U.S. Navy and its dive computers are Approved for Military Use (“AMU”) listed and its dive computers are being used by other international Navies and have NATO part numbers. With that said please click on the link below "Enviromental Compensation"<br /> <br /> <br /> <a href="http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf">http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf</a><br /> <br /> <br /> <a href="http://www.DiveCochran.com">Cochran Undersea Technology</a><br /> [email]sales@DiveCochran.com[/email]<br /> [email]salesmanager@DiveCochran.com[/email]<br /> <br /> <br /> Come visit Cochran Undersea Technology at the DEMA SHOW 2014 in the Las Vegas Convention Center, Las Vegas, NV November 19-22, Booth 1351.
  6. Cochran Undersea Technology designs, manufactures, and markets state-of-the-art diving computers for recreational, technical, CCR and commercial divers from our facility located in Richardson, TX. Cochran has been designing dive computers for itself and others for over twenty years. Cochran is the exclusive provider to the U.S. Navy and its dive computers are Approved for Military Use (“AMU”) listed and its dive computers are being used by other international Navies and have NATO part numbers. With that said please click on the link below "Enviromental Compensation"<br /> <br /> <br /> <a href="http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf">http://www.divecochran.com/techpubs/Docs/EnvironmentalCompensation.pdf</a><br /> <br /> <br /> <a href="http://www.DiveCochran.com">Cochran Undersea Technology</a><br /> [email]sales@DiveCochran.com[/email]<br /> [email]salesmanager@DiveCochran.com[/email]<br /> <br /> <br /> Come visit Cochran Undersea Technology at the DEMA SHOW 2014 in the Las Vegas Convention Center, Las Vegas, NV November 19-22, Booth 1351.
  7. <strong>"Enviromental Compensation"</strong><br /> <br /> <br /> Cochran Dive Computers are a new breed of dive computers that adapts its algorithm to the users diving environment and style as originally pioneered by Cochran. All of Cochran’s current dive computers incorporate this capability<br /> <br /> <br /> Water Temperature<br /> <br /> <br /> Diving in cold water can lead to a lower diver core and skin temperature which can affect the gas exchange rate of the body’s tissues. All Cochran dive computers feature two modes of Temperature Compensation, Normal or Reduced. The dive computer progressively makes its algorithms more conservative as the water temperature declines below 75 degrees F. Above this water temperature, there is no temperature compensation. In the Reduced Mode, the temperature compensation is made less conservative by approximately one-half the amount of the Normal Mode. If the diver is wearing an insulated dry suit and is relatively warm even in cold water, this temperature compensation factor may be set to Reduced Mode at the divers discretion using the Analyst® PC software.<br /> <br /> <br /> Altitude<br /> <br /> <br /> While many dive computers require the diver to manually set the altitude, Cochran products are fully automatic. Driving or flying to a dive site significantly higher in altitude requires special modifications to the "sea level" algorithm. All Cochran dive computers regularly sample the ambient barometric pressure to determine these changes in altitude whether the unit is On or Off. Accordingly, the algorithm is changed to reflect these barometric pressure changes. Note that temperature and weather systems also affect barometric pressure and hence, apparent altitude. Using the Time-To- Fly digits, the number of hours required to “adapt” to the new altitude is immediately known to the diver. If a significant altitude change occurs, a minimum of one hour should pass before diving to allow both the diver and the unit to adapt to this new altitude.<span style="color: Silver;"><br /> <br /> <span style="font-size: 11px;">---------- Post added June 27th, 2014 at 02:45 AM ----------</span><br /> <br /> </span><strong>"Enviromental Compensation"</strong><br /> <br /> Microbubbles<br /> <br /> <br /> There are several theories regarding the exact method by which an inert gas bubble forms from a microbubble which was formed from micronuclei. Currently the predominant theory states that in addition to other factors, more rapid ascents accelerate bubble formation. All Cochran dive computers comprehend and adjust for this phenomenon.<br /> <br /> <br /> User Added Conservatism<br /> <br /> <br /> Current dive computers cannot tell if the diver is dehydrated, tired, smokes, overweight, or has some other physical issue that may require additional conservatism in the algorithm. All Cochran dive computers allow the diver to input an added degree of conservatism to the algorithm from 0 to 50 percent in one-percent increments. This can be done via the Touch Contact Programming Mode or with the Analyst® Personal Computer Interface.<br /> <br /> <br /> Previous Dive Profiles<br /> <br /> <br /> One theory states that under some circumstances, recent dive activity can have an effect on inert gas loading, particularly if the diver engages in inverted profile diving. This occurs when a deep dive is followed by an even deeper dive. This recent dive history is used to compensate the inert gas loading for the current dive. This can be enabled or disabled with the Analyst® Personal Computer Interface. Current theories indicate that diving Inverted Profiles has no appreciable effect on Nitrogen loading. This compensation is turned off when the dive computer is shipped and must be turned on by the user.<span style="color: Silver;"><br /> <br /> <span style="font-size: 11px;">---------- Post added June 27th, 2014 at 02:48 AM ----------</span><br /> <br /> </span><strong>"Enviromental Compensation"</strong><br /> <br /> Salt Water / Fresh Water<br /> <br /> <br /> There is approximately a three percent difference in depth readings taken in salt water versus fresh water. Some dive computers are calibrated in feet of fresh water and some are calibrated in feet of seawater. Diving in a medium different from what the dive computer is calibrated will cause apparent depth errors. Only Cochran dive computers actually determine the type of diving medium and compensate the depth reading accordingly. This is accomplished by measuring the conductivity and capacitance of the water during a dive. Caution must be taken in interpreting this reading since some apparent fresh water is actually high in minerals or contaminants and is correctly compensated as salt water (High Conductivity, higher density). This commonly occurs in some caves, springs, and lakes.<br /> <br /> <br /> Workload Compensation<br /> <br /> <br /> This feature is available only on the Cochran Gemini dive computer which is Air Integrated. When a diver’s work rate or exertion level increases, he consumes more breathing gas and his Breathing Mix Gas Consumption (GC)/Surface Air Consumption (SAC) increases. The diver exchanges and retains higher levels of nitrogen in his tissues at a high work rate as compared to a low work rate. As work load increases, Cochran dive computers compensate by progressively increasing the conservatism of its algorithms. The Workload Compensation starts when the diver’s GC exceeds 35 psi per minute and reaches maximum compensation at 98 psi per minute. For accurate Workload Compensation the cylinder size, in liters, must be set correctly. This can be done via the Touch Contact Programming Mode or with the Analyst® Personal Computer Interface<span style="color: Silver;"><br /> <br /> <span style="font-size: 11px;">---------- Post added June 27th, 2014 at 02:55 AM ----------</span><br /> <br /> </span><strong>"Enviromental Compensation"</strong><br /> <br /> <br /> Cochran Dive Computers are a new breed of dive computers that adapts its algorithm to the users diving environment and style as originally pioneered by Cochran. All of Cochran’s current dive computers incorporate this capability<span style="color: Silver;"><br /> <br /> <span style="font-size: 11px;">---------- Post added June 27th, 2014 at 02:56 AM ----------</span><br /> <br /> </span>"Enviromental Compensation"<br /> <br /> <br /> Cochran Dive Computers are a new breed of dive computers that adapts its algorithm to the users diving environment and style as originally pioneered by Cochran. All of Cochran’s current dive computers incorporate this capability<span style="color: Silver;"><br /> <br /> <span style="font-size: 11px;">---------- Post added June 27th, 2014 at 02:56 AM ----------</span><br /> <br /> </span>"Enviromental Compensation"<br /> <br /> <br /> Cochran Dive Computers are a new breed of dive computers that adapts its algorithm to the users diving environment and style as originally pioneered by Cochran. All of Cochran’s current dive computers incorporate this capability
  8. Why is<strong> "Enviromental Compensation"</strong>deleted again?
  9. I am interested in this concept because i am a Pilot.The assumption that this model is useful for dive computers only is false.It can also be used to determine maximum safe altitudes that one may go to after a dive.
  10. Just curious... is there some formal study of the usefulness of this algorithm, and what is the metric of usefulness that it improves on when compared to ZH-L16C?

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