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I don't think you'll ever be able to get away from some sort of algorithm, since even if the devices precisely measure bubbles and declare a perfect ascent rate, you still need something to breathe...

One possibility is the computer could develop gas consumption estimates as actual decompression data for the individual is accumulated. Gas planning could begin with tables but be replaced as the system learns more about your physiology. Gas planning probably won’t be such a problem by then anyway if predictions about rebreathers prove true… which is more a sensor and CO2 absorbent problem than any other.
 
Get him busy on CO2 and CO blood sensors. The market would be relatively huge in general and emergency medicine plus divers could use it too.

Already in production. We carry them on our fire trucks. Made by Mosimo, they measure heart rate, oxygen sat and CO sat. Can't remember is CO2 is one also, but I think they can be programmed differently depending on the need.
 
To predict, maybe — but probably not to measure the actual decompression required. It really doesn’t matter which tissues are outgassing, only that the diluent is accumulating faster than the body can clear it. The sensor research I am aware of is targeting blood clots and air emboli in the medical setting, not DCS. However it “should” work for DCS too.

You still need a decompression model running in a computer, that computer still being external to the body. The sensor would not compute a decompression schedule but would measure N2 and prepare the data to be transmitted to the DC in a form that could be the same that DC's already work with. That is, a ppN2 in atm's. You may be asking, what do we gain by puttings sensors in the body? Well, preventing DCS is about managing the rate of offgassing. To do that you need to measure the amount of N2 leaving the tissues. A sensor gives you accuracy.

Of course that is assuming that dominant decompression theory is correct. I have read that there is some debate among physiologists that actual bubble formation may not be the root cause of DCS. Apparently some believe it is possible to get bent without bubbles in the blood stream. The logic presented was way over my head.

I've read some of that too. My understanding is that clinical DCS may be caused by inflamation (damage) in the blood vessels. Bubbles are know to cause this. If bubbles are not the sole cause then this suggests sensing something else such as a particular enzyme. However, regardless of the root cause of the symptoms it begins with N2 offgassing and sensing the amount of N2 is probably where we should start.

According to him, the real show stopper was hypo and hyperthermia. Somewhere around 50% of our normal heat loss is through respiration and plays a key role in controlling our core temperature. Thermal conductivity of a suitable liquid like perfluorocarbon is around 25x higher than air so the physical mechanics of circulating/ventilating the fluid and controlling the temperature that precisely is a huge practical barrier. They calculated that shock would set in within a minute or two if heating were lost or wondered too far. We can’t reliably keep hot water flowing to tethered saturation divers within that window. The heat loss requirements, like today, make an untethered deep working dive impractical.

One problem with maintaining heat (or cooling) in tethered divers is the losses in the tether itself. For an untethered diver a controller using well understood control principles can regulate the heat. The liquid path is shorter and therefore you don't need complicated feed-forward control techniques. The return liquid temp can be used in the feedback of the controller.

The next problem he brought up was how would the diver communicate? Vocal cords won’t work immersed in fluid. It sounds like a small thing until you start analyzing the work you want to diver to accomplish.

The answer? Texting.

---------- Post added September 10th, 2014 at 10:40 AM ----------

More than 10 years ago, I had a neighbor who was an engineer whose work dealt in some way (beyond my understanding) with detecting gas levels in the body. He was not a diver. We had a conversation in which he talked about those simple little clips you place on your finger that can detect the current O2 levels in a couple of seconds. I bought one for home use a while ago--it was dirt cheap. He wondered if there was any market for a similar detector for nitrogen levels in diving. He was wondering about the feasibility of inventing such a device and making some money. He indicated that even back then it would not be that hard to do. I think such ability would have a number of uses.

Indirectly measuring gas levels, particularly N2 if that can be done, is a cheap solution but it won't work. The problem is that DCS is often localized and to prevent it you need to measure the N2 flow at that site. Another cheap solution would be to measure the amount of N2 in exhaled breath. But, again we have the same problem. There could be a tissue exceeding the safe rate while another tissue has a very low rate. This could result in no change of exhaled N2 and no warning or calculated deco stop.

---------- Post added September 10th, 2014 at 01:01 PM ----------

More than 10 years ago, I had a neighbor who was an engineer whose work dealt in some way (beyond my understanding) with detecting gas levels in the body. He was not a diver. We had a conversation in which he talked about those simple little clips you place on your finger that can detect the current O2 levels in a couple of seconds. I bought one for home use a while ago--it was dirt cheap. He wondered if there was any market for a similar detector for nitrogen levels in diving. He was wondering about the feasibility of inventing such a device and making some money. He indicated that even back then it would not be that hard to do. I think such ability would have a number of uses.

Your neighbor might be thinking of using the light absorbtion properties of N2. N2 will absorb light at a certain wavelength and reflect other wavelengths. In the case of absorbtion it's a matter of measuring the amount of reflected light given off by N2 and collected by a sensor. The difference being what is absorbed. Here is a link to the molecular absorption spectra. As you can see N2 absorbs light at two peak wavelengths on either side of 4.3 um. The complication is that other substances in the blood may be absorbing or reflecting light at those same wavelengths.
 
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…One problem with maintaining heat (or cooling) in tethered divers is the losses in the tether itself...

The loss of an umbilical is an extraordinarily rare occurrence, in saturation or surface supplied diving. Problems with interruption of flow, excessive, or insufficient heat from the system happens all the time. There is a rapid acting alarm system though… the diver lets everyone know immediately in the most unambiguous terms imaginable. :wink:

The problem is working divers operate 24/7 in a very hostile environment. Hot salt water supplied as a utility on most DSV (Diving Support Vessels) has become pretty reliable but managing the temperature reaching the diver +/- about one degree F. is a constant battle. There are a lot of variables and moving parts. It’s not laboratory or even factory floor conditions out there. It is very difficult for recreational divers to imagine how brutally rugged offshore oil and salvage work is.

… For an untethered diver a controller using well understood control principles can regulate the heat. The liquid path is shorter and therefore you don't need complicated feed-forward control techniques. The return liquid temp can be used in the feedback of the controller...

Where are you going to get the 100,000 BTU/hour plus required to heat the diver untethered? NASA, the world’s navies, and inventors trying to cash in on the offshore oil fields have tried to replace hot water suits for decades. Drysuits might be adequate for recreation and some science divers but are far too delicate for working divers, especially when hypothermia becomes a super time-sensitive life support problem.

The thermal conductivity of Helium is bad enough at about 6x higher than air. Controlling the comfort level with the lungs full of a media that transfers heat about 25x faster would be very difficult in real-world working conditions. DSVs that cost $100,000 to $500,000/day to charter can afford the most advanced thermal control technology available.

… The answer? Texting...

I’ll try that the next time I’m hanging off a hog line with a spud wrench in one hand, steadying myself with the other, and directing the crane to lower 5 millimeters. Should be interesting wearing heavy work gloves. Unless divers are doing complex and often very heavy work, it is safer and cheaper to send a ROV (Remote Operated Vehicle).

I forgot to mention these in my earlier post but there are a lot of other concerns with liquid breathing. Imagine 6-8 liters of fluid weighing around 17 Lbs in the delicate lung tissues. Falling out of bed or stepping off a curb would be enough to cause considerable damage. Will divers have to stay submerged 24/7 until they are “dried out”? It doesn’t sound like the physics of emptying and drying lungs quickly on a daily basis will be practical.

Then there’s the problem of eating and waste removal. It is difficult to feed people in hospitals intravenously without infections. It’s hard to imagine how you could pull it off in the ocean. It is also questionable if skin could handle continuous immersion is salt water that is close to body temperature. Six to eight hours a day in hot water suits makes skin easily abraded and susceptible to infection. Oh well, at least the divers should sleep well.

… Indirectly measuring gas levels, particularly N2 if that can be done, is a cheap solution but it won't work. The problem is that DCS is often localized and to prevent it you need to measure the N2 flow at that site...

The same is true for clots and emboli in medical settings. The objective is to look for markers. My understanding is dissolved diluent gas (Nitrogen and/or Helium) in the blood elevates before bubbles form that cause perceptible tissue damage or blood flow restriction. The idea is to monitor dissolved gas in the blood, not bubbles. Granted, tiny localized bubbles could form in very small areas but they will dissipate if the gas tension in the blood is low enough.
 
Another benefit would be much higher ascent rates or possibly no maximum rate.

Try it. Then let me know how your ear drums feel after they've exploded. :D
 
Where are you going to get the 100,000 BTU/hour plus required to heat the diver untethered?

I wasn't thinking of heating the entire diver or of commercial extended dive operations. I agree that extending LTV to the commercial diver presents formidable problems. A dry suit with thermal underwear and maintaining the breathing medium at some comfortable temperature should be OK for extreme depths. The diver that went to 900 ft. at Bushman's hole spent over 10 hours in the water on a rebreather supplying gas heated by the body alone. I was thinking of only relatively short dives of one to two hours.

Non-commercial divers won't have their hands full all the time. A lot of dives can be carried out without communications to the surface. If it's necessary a pencil from a slate can be used to poke the keys for texting.

---------- Post added September 11th, 2014 at 12:38 PM ----------

Try it. Then let me know how your ear drums feel after they've exploded. :D

For divers on TLV there are two ways to equalize the sinus and ears: with gas or liquid. An inert gas and oxygen will be needed. The O2 to replenish the breathing medium and the other gas to be used for clearing the mask, to fill the BCD/dry suit, and equalizing ears and sinuses. I would choose to use liquid for the ears/sinuses because equalization wouldn't be necessary and therefore ascent rates can be high. On gas the ascent rate would need to be limited which IMO makes gas unsuitabe for equalization.
 
Already in production. We carry them on our fire trucks. Made by Mosimo, they measure heart rate, oxygen sat and CO sat. Can't remember is CO2 is one also ...

Cool! I had never heard of that company.

Looks like Masimo of Stockholm makes a small end-tidal carbon dioxide monitor that might be easy to connect to a regulator second stage.

They also make a range of other gas monitoring products, from cheap, disposable, stick-on acoustic respirometers up to some very complicated looking tricorder type devices for use by anesthesiologists during surgery.
 
Algorithms for inert gas uptake / discharge will be needed but the accuracy can be improved immensely by any actual, real time measurements. This is exactly like navigating when flying to the moon. You make predictions based on known physics and make adjustments on the way based on real time navigational fixes. Albeit the physics of space flight is more predictable than the physiology of inert gases at pressure in the body.
 
It's very curious the way that technology is used by society. A small segment maximizes the potential while the majority draw the advances back down to mundane levels.
Cell/smart phones being a good example. Some of the most powerful handheld technology available yet most people use it to view cat videos or tweet where they are eating french fries.
I could easily see real time monitoring of a divers blood gasses but wonder if more information is really the solution. It sometimes seems passive dependence creates an unintended dumbing down effect. Part of my understanding of gas physiology came from the process of having to work through decompression models and manipulate variables.

I also wonder, other than dives on the fringe of capacity, how this advanced technology would change the way most people dive. It strikes me that the problem is not that people don't have data available, it's that they don't know/care how to respond to it. A dive algorithm/computer/table, followed properly, will keep most people from getting bent. People who do get bent are either anomalies or violate procedure. Real time monitoring could help the anomalies but not necessarily the violators (as they would tend to violate real time procedures as well).

With liquid ventilation. What dives would one do with this that can't be done now? It seems divers are limited to depth by extreme pressure effects and duration by exposure/fatigue degradation.
 
…With liquid ventilation. What dives would one do with this that can't be done now?...

In theory a diver could descend as fast as a jettisonable weight will take them, reach any depth in the ocean, spend as much time on the bottom as they are physically able, and ascend equally fast. In practice, there are a lot of functional barriers already discussed. Drying people out so they can breathe gas again is pretty daunting given an adult male has about 750 Ft² of lung surface area and the smallest cavities do most of the work.

This is an interesting intellectual exercise considering the poor reliability of dive computers and lights today.
 

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