CO2 Monitor (End-tidal) - good news

[Dave Sutton]

But I'm sure you can see how an accurate estimation of the true arterial CO2 (such as a correctly measured end tidal CO2 value) would be a MUCH more useful piece of data.

So.... using technology that is present today and perhaps looking ahead, oh... 12 months to the future, how exactly would you propose that this be done?

Start with a clean slate and imagine what you would do. Not in theory, but using real world hardware that is either mature now, or clearly emergent and will be "ready for prime time" in 2013. Not in theory, but something that I can be confident can be built and installed for the season beginning 12 months from now. How would you implement it, and what parameters would you monitor, and how?

I would love to have a reason to fire up the Bridgeport and Lathe, make some housings, do some system integration to an existing platform (I'd likely use a Meg), and do it rather than talk about it. There's plenty of capable expertise here... let's get on with it and make it.


Dave


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[tecdiverdude]

Maybe a bit of collaboration from all interested parties here is in order...what we really need is an electronics engineer to spend the time designing it.. with input from all of the above,once we have decided on a workeable unit, we impliment it into a housing. I think for simplicity an under -drysuit unit would be fine for now,as most CCR divers dive Dry dont they?

 

[Dave Sutton]

Personally... I'd like to built in into the loop, using whatever method seems possible. I'm tired of talk and scientific papers and PDF files and am ready to make chips fly on the milling machine.

Dave

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[tecdiverdude]

Whaoo there Pronto...
First someone needs to volunteer to play with the electronics....

 

[GLOC]

Dave,

Having only come into the world of academia fairly recently, one of the things I have noticed is that unless you do something correctly from the start and collect evidence as you go, when you come up with the results at the end, unless you have repeatable systems, then people have a hard time believing you. Look at the APOC for a classic example.

There were a couple of 'experiments' presented at the weekend which looked promising (one of which looked at the veracity of the 5min pre-breathe and did it do any good) but because the methods were questionable, then the results are not that credible. However, it did promote some discussion about how to improve the experiment to make it more rigourous.

Homebuilds are great and there is no doubt, this is where the innovation starts. But with any project, there needs to be a requirement and from that requirement you can generate test criteria/test processes. In this case what is it you are trying to do? By defining your requirements clearly, you can focus on what needs to be done and also importantly, how you are going to test it; this includes the resolution of the testing. If you need to measure to 0.1kPa every XX secs, then you need to sample at a higher resolution (so you can monitor trends/peaks/troughs) so likely 10 times as fast and that pressure. Do you have the ability to measure that? Can you test in the environment you want to simulate? Baby steps are the way to go, but if you don't have the technology to repeatably conduct the experiment at the resolution required, you are in the potential situation of the APOC ALBOV, a great tool that can't be used because of limitations of the human physiology and the sensor technology that is out there.

Not trying to put you off Dave (or others), far from it, but bear in mind that one of the reasons that this hasn't been done yet is likely due to cost for the components for such a capability (to be repeatable and in the environment required) and there chance that the NRE will be recouped. For a 'fun' project this isn't a problem, but for a company trying to make money (or stay alive in the current economic climate), this is a major issue.

Regards

 

[Dave Sutton]

In my day job I work as a test pilot.. I know all about doing things from the ground up so they work correctly the first time (or ought to.... Which is why we still pay test pilots).

From what I see, my challenge to quit talking and citing scientific papers and looking at PDF files of designs and getting down to actually doing something is proving the point that all we have now is a lot of talk. There isn't a good CO2 sensing technology yet available that will reliably work in a rebreather at present.

Dave

 

[matt]

In my day job I work as a test pilot.. I know all about doing things from the ground up so they work correctly the first time (or ought to.... Which is why we still pay test pilots).

From what I see, my challenge to quit talking and citing scientific papers and looking at PDF files of designs and getting down to actually doing something is proving the point that all we have now is a lot of talk. There isn't a good CO2 sensing technology yet available that will reliably work in a rebreather at present.

Dave

Two points - firstly let me get some sarcasm out of the way. Forums are only talk. Now I'm feeling better...

You're right, I don't see any workable solution just yet and I doubt very much that it will be originated in this field. If we're lucky something will come from the military or from medicine, but from diving, nah - waste of time even thinking that will happen.

Matt.

 

[matt]

...In this case what is it you are trying to do? By defining your requirements clearly, you can focus on what needs to be done and also importantly, how you are going to test it; ...

I'm still not clear what, in practice, a diver is going to do about it? Once retained CO2 is retained then what...

Having the limits defined and the appropriate diver responses enumerated seems something a forum can do if the guru's are about.

Matt.

 

[matt]

Too save me having to read thu all these posts that simply fry my brain :amstupid: what's wrong with the CO2 probe that VR use on the Sentinel? I realize it's on the inhale side so guess it doesn't qualify as end-tidal.

It's not end-tidal. The "debate" isn't about CO2 sensing it's about end-tidal monitoring without having a car battery floating behind you...

 

[Ben Field]

IMVHO if there are divers willing to look at reducing the potential ills of CO2 then their efforts would be best spent on the causes of its increase and rise.

We don't have the technology to detect it in the right place in a diving enviroment but we can work on reducing WOB (and lay off the cr*ppy food & drinks and hit the treadmill :bounce

Sadly it looks like we're a technological step away from what you all want and its a step that needs to be taken in a mature industry (which is not SCUBA diving equipment)


Lastly- how big an issue is this really? I've only had one encounter with CO2 in my CCR diving experience and a couple of retained issues on OC, nothing to write home about... would I spend $thousands$ to guard against it? Probably not.

 

[matt]

IMVHO if there are divers willing to look at reducing the potential ills of CO2 then their efforts would be best spent on the causes of its increase and rise.

We don't have the technology to detect it in the right place in a diving enviroment but we can work on reducing WOB (and lay off the cr*ppy food & drinks and hit the treadmill :bounce

I agree with the sentiment, although I'd like to know what effect crappy food and drinks have - if any. I'm not even clear on the effect fitness actually has on CO2 production.

Lastly- how big an issue is this really? I've only had one encounter with CO2 in my CCR diving experience and a couple of retained issues on OC, nothing to write home about... would I spend $thousands$ to guard against it? Probably not.

I've never had a CO2 issue, so for me I'm just not interested other than the academic debate that irritated Dave for a few minutes back there!

Unless someone can categorically say what the real-life action is to reduce the affect of CO2 then I don't think we're heading in the right direction. GLOC is right - what's the requirement here?

Matt.

 

[Ben Field]

I agree with the sentiment, although I'd like to know what effect crappy food and drinks have - if any. I'm not even clear on the effect fitness actually has on CO2 production.

Sorry that was a slightly throw-away comment, many divers are beer-swilling gut buckets (I include myself in that as am overweight IMO) :lol: and could do with loosing a few lb's. Being fit and healthy has got to be a benefit when it comes to breathing through a small tube for hours?

I seem to recall that extreme fitness can actually make you more likely to suffer from CO2 effects should the level rise? (Dr Simon prob best placed to correct me here?)

Anyway- I was trying to suggest that a healthy diver might have to work less therefore produce less CO2 therefore the crappy design of rebreather will cope longer before being a contributory factor in retaining CO2, breakthrough or any of the other issues that may or may not need a magical sensor to monitor. :dunce:

 

[Dave Sutton]

Too save me having to read thu all these posts that simply fry my brain :amstupid: what's wrong with the CO2 probe that VR use on the Sentinel? I realize it's on the inhale side so guess it doesn't qualify as end-tidal.

It doesn't work (very well).

Because....

The sensors don't work (very well)

When I dove the apoc with the CO2 measuring system installed, it worked.... Just not (very well). Sensing technology is just not there (yet). When I famously said as a *very casual and very off the cuff* remark that it all worked, it seemed to work, was responsive to CO2 increases, was an active instrument, and from a casual observation point "worked" but.... In the end (not very well).

I guess my point is that I'm sort of bored with scientific papers and PDF files. it's like asking for a rocket belt (for now).


Let's see what happens in sending technology over the next 5 years. For now it's a low WOB rig using a proven and fully tested scrubber, with helium diluents, and the gym. Prevent rather than measure.



Dave

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And therein lays the problem. No measurement = no instrument.

All of the rest of two years of talk is just that: pie in the sky talk.

 

[matt]

Sorry that was a slightly throw-away comment, many divers are beer-swilling gut buckets (I include myself in that as am overweight IMO) :lol: and could do with loosing a few lb's. Being fit and healthy has got to be a benefit when it comes to breathing through a small tube for hours?

I hear the argument but I don't know the facts. Don't be sorry - I think it a valid comment.

I seem to recall that extreme fitness can actually make you more likely to suffer from CO2 effects should the level rise? (Dr Simon prob best placed to correct me here?)

I'm pretty sure I saw an experiment for that too where a super fit chap has problems on a bicycle test due to excess CO2 cause by being over-fit?? If I knew where I saw it I would did it out :-(

Anyway- I was trying to suggest that a healthy diver might have to work less therefore produce less CO2 therefore the crappy design of rebreather will cope longer before being a contributory factor in retaining CO2, breakthrough or any of the other issues that may or may not need a magical sensor to monitor. :dunce:

Agreed. Perhaps deriving a test to detect CO2 retainers would be more fruitful...

Cheers
Matt.

 

[GLOC]

Sorry Dave, didn't know your background, you may not know that mine is a Requirements Manager for Defensive Aids System so writing unique, measurable and testable requirements is my job, especially when contractors aren't necessarily fully open with their declarations of performance in a representative environment! The way the UK does T&E is very different to the US when it comes to DAS.

You are right, that in effect we can do as much as possible to sort out the equipment and 'operational' issues (e.g. scrubber, gas, WOB etc) but that the physiological requirements are going to be a much harder nut to crack! To determine the need for a new capability, there is a need to define the gap in capability and the measure of risk you are taking by having that gap. The problem is two-fold, we don't know the scale of the problem (how many people are really suffering) and as a consequence the community don't know how much to spend on solving the problem.

In the military they are likely to accept a greater level of risk to conduct the mission, but mitigate this by making sure their combat swimmers are as fit as possible. That doesn't help the retainers which is why some Forces have put screening processes in place. If the risk was really big, lots of guys would be dying from CO2 related issues which couldn't be solved by system design, and the military would spend the money to solve the problem; we are broke and need to spend wisely making a balance of risk/benefit. As it is, the number of military rebreather fatalities is relatively small compared to the amount of R&D plus qualification that would be required to solve the problem.

This leaves the 'home builders' to solve the problem, but the technology required to build such a system is likely to be beyond the capability of most 'home builders'.

Regards

 

[GLOC]

Matt, regarding CO2 retainers, the military have tried this AIUI and there are ways of fooling the system if you know that is what is being done...because if you are retainer, then you are out of a job.

Might help the sport CCR divers out there, but seeing as a very large percentage won't pay for a basic medical, what chance do we have of the majority of the population paying for a CO2 retaining test?

Regards

 

[matt]

Matt, regarding CO2 retainers, the military have tried this AIUI and there are ways of fooling the system if you know that is what is being done...because if you are retainer, then you are out of a job.

Interesting, what's the test?

Might help the sport CCR divers out there, but seeing as a very large percentage won't pay for a basic medical, what chance do we have of the majority of the population paying for a CO2 retaining test?

Regards

Test needs to included with the monitoring kit - there's always a queue of people waiting to fix non-existent problems with technology/cash.

Personally I didn't have any formal-tests but am happy to say I've made some home-built tests of my own and I'm testing false for CO2-retainer and PFO!

To this end I shall spend my cash on the aforementioned crappy-food and, most importantly, the drink.

Cheers
Matt.

 

[GLOC]

Links I could find in my library and Google Scholar...

Effects of respiratory muscle training on respiratory CO2 sensitivity in SCUBA divers.
Undersea Hyperb Med 33:6, 447-53 (2006)
Pendergast, DR, Lindholm, P, Wylegala, J, Warkander, D, and Lundgren, CE
Center for Research and Education in Special Environments, School of Medicine and Biomedical Sciences, University at Buffalo, USA.
Typically, ventilation is tightly matched to CO2 production. However, in some cases CO2 is retained (SCUBA diving). One factor behind hypoventilation in divers may be low respiratory CO2 sensitivity. If this is due to inadequate respiratory muscle performance it might be remedied by respiratory muscle training (RMT). We retrospectively investigated respiratory CO2 sensitivity prior to and after RMT in several groups of SCUBA divers. CO2 sensitivity (slope of expired ventilation as a function of inspired PCO2) was measured with a rebreathing technique in 35 subjects with diving experience. RMT consisted of either isocapnic hyperventilation or intermittent vital capacity breaths (twice/minute) against spring loaded breathing valves imposing static and resistive loads generating average inspiratory pressures of approximately 40 cmH2O and expiratory pressures of approximately 47 cmH2O; RMT was performed 30 min/day, 3 or 5 days/week for 4 weeks. Based on pre-RMT CO2 sensitivity the subjects were divided into three groups: low sensitivity: < 2 l/min/mmHg PCO2, normal: 2-4 l/min/mmHg, and high sensitivity: > 4 l/min/mmHg of inspired PCO2. The normal group had a Pre-RMT CO2 sensitivity of 2.88 +/- 0.60 and a post RMT sensitivity of 2.51 +/- 0.88 l/min/mmHg (Mean +/- SD, n = 19, p = n.s). Response in low sensitivity subjects increased from 1.41 +/- 0.32 to 2.27 +/- 0.53 (n = 10, p = 0.002,) while in the high sensitivity group it decreased from 5.41 +/- 1.25 to 2.90 +/- 0.32 l/min/mmHg (n = 6, p = 0.003). These preliminary findings showed that 46% of the subjects had abnormal sensitivity, and suggest that RMT may normalize it in hypo- and hyper-ventilating divers. If the present results are verified, RMT may be an effective means of enhancing safety in CO2 retaining divers

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Response to CO2 in novice closed-circuit apparatus divers and after 1 year of active oxygen diving at shallow depths
Mirit Eynan, Ran Arieli, and Yochai Adir

Israel Naval Medical Institute, Israel Defense Forces Medical Corps, Haifa, Israel
Address for reprint requests and other correspondence: M. Eynan, Israel Naval Medical Institute, POB 8040, Haifa 31080, Israel (E-mail: emirit@netvision.net.il)
Submitted 25 June 2004. Accepted 10 December 2004.
Abstract

Elevated arterial PCO2 (hypercapnia) has a major effect on central nervous system oxygen toxicity in diving with a closed-circuit breathing apparatus. The purpose of the present study was to follow up the ability of divers to detect CO2 and to determine the CO2 retention trait after 1 year of active oxygen diving with closed-circuit apparatus. Ventilatory and perceptual responses to variations in inspired CO2 (range: 0***8211;5.6 kPa, 0***8211;42 Torr) during moderate exercise were assessed in Israeli Navy combat divers on active duty. Tests were carried out on 40 divers during the novice oxygen diving phase (ND) and the experienced oxygen diving phase. No significant changes were found between the two phases for the minimal mean inspired PCO2 that could be detected. The mean (with SD in parentheses) end-tidal PCO2 during exposure to an inspired PCO2 of 5.6 kPa (42 Torr) was significantly higher in the novice diving phase than in the experienced diving phase [8.1 kPa (SD 0.7), 62 Torr (SD 5) and 7.8 kPa (SD 0.6), 59 Torr (SD 4), respectively; P ***8804; 0.001]. One year of shallow oxygen diving activity with a closed-circuit apparatus does not affect the ability to detect CO2 nor does it lead to increased CO2 retention; rather, it may even bring about a decrease in this trait. This finding suggests that acquiring experience in oxygen diving with a closed-circuit apparatus at shallow depths does not place the diver at a greater risk of central nervous system oxygen toxicity due to CO2 retention.

Not sure what the specific tests are though!

Regards

 

[Gary K]

When I dove the apoc with the CO2 measuring system installed, it worked.... Just not (very well). Sensing technology is just not there (yet). When I famously said as a *very casual and very off the cuff* remark that it all worked, it seemed to work, was responsive to CO2 increases, was an active instrument, and from a casual observation point "worked" but.... In the end (not very well).

Well thats how you remember it anyway, most of us saw it as a "boo hoo, yahoo, sucks to you" comment that now looks very stupid :doh:

 

[Dave Sutton]

Well thats how you remember it anyway, most of us saw it as a "boo hoo, yahoo, sucks to you" comment that now looks very stupid :doh:

Well then... the message received was far from the message I was trying to send.

I think that the agendas being played out at the time precluded "some" from understanding that I was making friendly and enthusiastic comments regarding my (now obviously premature) but very honest excitement that it looked like we *finally* had C02 measurement "close at hand". I had rather a lot of time to evaluate the system as it was at that time, and there were (are) a lot of VERY interesting things in the "intelligent" pods. The "Voice of God" audible warnings and PP02 readings broadcast into your mouth thru the DSV was VERY interesting, and the audibility of the warnings was VERY good. Really earth shatteringly good actually. The C02 measurment system "seemed to work fine" from the users viewpoint, bearing in mind that I am not a physiologist, and that Simon will tell everyone (probably correctly) that it's all being done wrong... But with that said, it seemed to work, it showed clear responses to C02 increases and decreases using both calibration gas and my respiration, when we installed a "known to be at end of life" scrubber it clearly indicated scrubber breakthru, and, that was all that my comments were ever meant to say. When the hate mail started, I realized that there was no point in dealing with angry people, so I just quit talking and went diving. Lesson learned: No good deed goes unpunished.

So, whatever other "value" (or lack thereof) attached to a very casual comment were values assigned by others, not by me. In the end the weak link was (is?) the actual C02 sensor, or so it appeared (appears) to me now. When that's solved I think we will see systems working made by a number of manufacturers that follow on the prior art laid down by this design.

Frankly, even if imperfect, I was *really* sorry to need to send the pods back. They were cool toys then, and they would be cool toys now. I never got wrapped up into whatever other peripheral business issues are plaguing the apoc: Frankly I did not care then and I care far less now. I just like technology and wanted to share my access with others. All I am is a dumb diver who had the opportunity to play with a pretty cool, if imperfect, toy. If my sharing in innocent enthusiasm stepped on other toes, it was certainly not intended and what I wrote was written in the spirit of friendly sharing.


Oh well.. on to the next chapter of life. If we can't live, learn, and laugh then what's the point? Wag more and bark less I always say. Lead, follow, or get outta the way...



So, rather than dwell in the past, what can we do to lead? I'm all for building on prior experience and trying to get something that works, which is based on best knowlage, using the physiological advice of Simon, whatever electronic advice we can get from anyone who wants to assist, and my capability to rapidly prototype and manufacture in the Little Diveshop of Horrors. If we can... great. If "the state of desire" is premature compared to "the state of the art" as regards sensors, then perhaps we are screwed (for now).

Dunno.... <sigh>, which is why I mooted the question "How can we do this within the year?". So far no answers.


Smile,


Dave

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