End tidal CO2 Monitoring

[gianaameri]

Brad,

thank-you for posting this. It is really interesting.

I had a quick read through and it seems to me "umbrella" valves are acceptable, although not the "ideal" solution.

Do you read it the same way?

Anyone knows if Draeger one-way valves are umbrella or flat (will check tomorrow on my BOV and kind of picture it as flat... having said that I cannot believe Draeger had not already thought of any such potential problems with their valves... they have much better knowledge and resources than Deep Life or anybody else in the industry)?

 

[Brad_Horn]

I had a quick read through and it seems to me "umbrella" valves are acceptable, although not the "ideal" solution.

Do you read it the same way?

Acceptable based on the results of the testing in the ALVBOV, yes. Though the ALVBOV has flow diverters and based on the FMECA, had a lot of engineering work done on the spiders, retaining the valves. So those same acceptable umbrella valves in the ALVBOV may not be acceptable in a different BOV, without what seems like a lot of expensive testing done, verifying that they are fit for purpose.

having said that I cannot believe Draeger had not already thought of any such potential problems with their valves...

I wasn't aware Drager made a BOV? Have you asked them directly, for a copy of the CO2 flow based testing they did with those valves in that BOV before they sold it to you?

they have much better knowledge and resources than Deep Life or anybody else in the industry)?

Do they?
Seems there is a lot of information flow out of DL based on the testing they have been required to do to meet CE minimums that doesn't seem to appear elsewhere...

Regards
Brad

 

[gianaameri]

duplicate/deleted

 

[gianaameri]

duplicate/deleted

 

[gianaameri]

Briefly,

Draeger makes one-way valves (flat type, I checked, and not umbrella type) and DSV (not BOV, but close enough for the purpose of this discussion).

My BOV uses Draeger one-way valves and has a spider different from that of the ones shown on the Deep Life research/advertisement.

My BOV WOB is declared by the manufacturer to be lower than the WOB of Deep Life's ALVBOV.

Those are the ony facts I have to go by... the rest I have to second-guess.

I cannot see how a reflux can occurr in my BOV and tried to provoke it many ways (rudimentary test, but better than none).

Also, although a reflux may affect the EN14143 testing (causing a trigger of the pCO2 upper limit), I do not think it can change my life if it is minimal... it would simply have the effect to add 1 square millimiter or so of dead-space in my mouth (surely we all come with different sized mouths and passageways).

However, indeed all EN14143 CO2 tests should be done equally "at the mouth" and published, for all the good reasons you say (but we are very far from that as some manufacturers are lying to us in respect of the CE certifcation of their products... that is they do no hold the Certifcate of Conformity to attest their product meets the "standard" which they say they meet).

 

[Brad_Horn]

Draeger makes one-way valves (flat type, I checked, and not umbrella type) and DSV (not BOV, but close enough for the purpose of this discussion).

Based on the report about the CO2 bypass fault that design appears to be easily compared with the published results. IIRC the report also talks about the testing of other types of BOV and DSV.

My BOV WOB is declared by the manufacturer to be lower than the WOB of Deep Life's ALVBOV.

Really!
Published OC WOB at 50m for the ALVBOV 0.89 J/L, similar to an Apeks Tx100.
Published WOB in CC mode 0.56J/L for the ALVBOV at 75Lpm at 40m on Air.

Those are the ony facts I have to go by... the rest I have to second-guess.

Seems you need to check one of your facts.
Pity that you have to guess about the performance of life support equipment isn't it!

I cannot see how a reflux can occurr in my BOV and tried to provoke it many ways (rudimentary test, but better than none).

Add depth, helium, gas flow and turbulence to the equation!
Looking at the report there doesn't seem to be any way to duplicate the fault on the surface. One would appear to need to rely on the manufacturer actually testing their BOV in a lab capable of measuring end tidal CO2 at the mouth at 100m.

Also, although a reflux may affect the EN14143 testing (causing a trigger of the pCO2 upper limit), I do not think it can change my life if it is minimal...

Depends I guess on the link that DL mention with regards the fault possibly being associated with hypercapnia related fatalities from their accident studies. The CE standard hasn't changed for 7 years so I am sure plenty of other manufacturers have also done the testing so it should be pretty easy to verify.

The comment about large differences in scrubber endurance when mouth measurements were made compared to measurements where the inhaled CO2 was sampled upstream of the inhale one-way valve could be interesting....

Regards
Brad

 

[gianaameri]

...the fault possibly being associated with hypercapnia related fatalities from their accident studies.

The "CE" system and testing is not where it should be, so we have to do with what we have/can (like it or not, and I don't like it).

What I do not understand is how a small reflux can generate hypercapia. As I see it, if it is just a reflux as described in the Deep Life research, it will have a minimal increase in dead-space (and we have plenty already).

If you do test Medisorb though, or any other sorb, and you get a sudden pCO2 breakthrough on a new scrubber, than before you conclude that Medisorb is no good, you better check the spike was not your bad DSV/BOV design in the first place.

The WOB on my BOV is quoted as 0.4077 (but then again who knows if we are comparing apples with apples).

 

[Brad_Horn]

What I do not understand is how a small reflux can generate hypercapia. As I see it, if it is just a reflux as described in the Deep Life research, it will have a minimal increase in dead-space (and we have plenty already).

Diver exhales.
Diver inhales, due to the valve fault some (25%?) exhaled gas is sucked back past the exhale valve and re-breathed.

Diver then as I understand the report gets CO2 at roughly the CE level of 0.5% SEV plus whatever CO2 gets through the scrubber. Fresh scrubber, diver only breathes 0.5% SEV which from the documentation available isn't a major drama. As breakthrough starts to occur you appear at risk of breathing a higher % CO2 that is ~0.5% more then planned based on the rebreather in questions published scrubber duration.

Not sure why your focusing on the deadspace aspect. The deadspace in the ALVBOV would only appear to be a factor when looking at the end-tidal CO2 monitoring aspect as its internal volume is different compared with the swept volume, which is contrary to other makes of BOV. See the previously posted link to the Eurotek pesentation....

If you do test Medisorb though, or any other sorb, and you get a sudden pCO2 breakthrough on a new scrubber, than before you conclude that Medisorb is no good, you better check the spike was not your bad DSV/BOV design in the first place.

If the valve fault is present and if the test for CO2 is done at the mouth rather then the inhale hose. The sorb used appears to not matter as the fault would appear to be present at the start of the dive as well as all the way through it.

The testing by DL would have been done using only EACs with known performance characteristics.

The WOB on my BOV is quoted as 0.4077 (but then again who knows if we are comparing apples with apples).

Only BOV I am aware of with that specific WOB figure published is as per the graph at The Deco Stop where the graph indicates 40lpm RMV.

Hard to therefore compare directly, but based on what is available DL's single scrubber rebreather has a WOB of:
- 40m 40RMV = 0.41J/L
- 40m 75RMV = 1.44J/L
I am sure you can then form your own conclusion, based on the ALVBOV having a WOB of 0.57J/L at 40m at 75lpm RMV in air....

Regards
Brad

 

[gianaameri]

Hey, I just heard the good news... I hope to try an APOC soon!

I do not understand why SGS is asking Alex to do the tests in a more strict way that they asked everybody else, and why everybody else can get away with not testing this potential reflux problem properly such that it is taken into account.

I still have difficulty envisaging how a tiny amount of reflux can kill someone when in my mouth and airway there is anyway between 4% and 8% of CO2 (the latter if I half empty my lungs, hold my breathm and run on the spot before testing).

 

[jar546]

Although I started this thread based on my experiences with monitoring etCO2 in intubated patients, my intention was the use of the CO2 detection technology can be helpful. I can clearly see how detection on the inspiration end of breathing would be much more effective and useful than etCO2.

If some form of CO2 detection were not important, there would probably not be any activity in exploring the options that there clearly are. It is the CO2 issue that still keeps me off a CCR as I am uneasy with only knowing my O2.