Equipment IPE and Regulator Adjustments

[Duke Dive Medicine]

I was involved in a diving accident early this year where immersion pulmonary edema is suspected. It was verified through xray that I had “fluffy lungs” but they cannot determine whether I aspirated on water or ipe is the cause. I did take in a little water as I was struggling to get air from my reg. I can provide more details if needed, but my question relates to my regulator.

The regulator I was using has both a Venturi switch and a knob to adjust the cracking pressure (MTX-RC). After the accident, my dive buddy noticed that the Venturi was set to - and the cracking pressure knob was turned all the way in. Our depth was 115 ft when I started to experience difficulties. ****This was an oversight by me - I always turn the Venturi to + once my reg is in and I adjust the cracking pressure to where it feels smooth as I descend****

If the culprit was IPE, I’m just trying to understand if my regulator setting was partially to blame as this has never happened before on similar dives. Could the negative pressure breathing have triggered IPE?

I got the approval to dive again (with restrictions) but would like to better understand potential reasons for this accident.

Note: Not looking for medical advise. Reg has been tested and is working fine. Evaluated by 2 independent Dive Doctor’s.

@rsingler alluded to negative pressure pulmonary edema (NPPE) earlier in the thread. High inspiratory effort could have been a factor but going only by what you've posted it would be hard to determine the degree to which it contributed.

Best regards,
DDM

 

[SubSoul]

@rsingler alluded to negative pressure pulmonary edema (NPPE) earlier in the thread. High inspiratory effort could have been a factor but going only by what you've posted it would be hard to determine the degree to which it contributed.

Best regards,
DDM

Thanks for the insight. I’d be glad to share more details but I was not sure what would be pertinent and I didn’t want to over share info that may be irrelevant. If you don’t mind, what other factors should be considered? Or what questions should be asked. Thank you in advance for any information or guidance you can give me.

 

[DiveLikeAMuppet]

Thanks for the insight. I’d be glad to share more details but I was not sure what would be pertinent and I didn’t want to over share info that may be irrelevant. If you don’t mind, what other factors should be considered? Or what questions should be asked. Thank you in advance for any information or guidance you can give me.

My understanding of IPO/IPE was that you were more likely to notice symptoms as you get shallower - due to dropping PPO2, pressure difference between lungs and mouth - so describing more might help.

If you were at depth, with high gas density and a bit of CO2 retention that can lead to pretty nasty narcosis, you might have aspirated some water?

 

[lexvil]

Since the header for this is equipment, let’s just say regardless of any equipment cause, these were both (pre-dive and cracking effort) easily correctable by you during the dive, yes you admitted that so I’m not doing a told you so thing but please in the future, anyone reading this, check the things you can during the dive if not before.

 

[rsingler]

Do you know how to determine the relative impact on WoB from different cracking pressures? For example, if WoB of a regulator is 1.2" does tuning it to, say .8" reduce WoB by a 1/3?

As you suggested later, it's indeed quite complex. The change in WOB is more related to the total joules in the ANSTI loop, of which cracking effort is only the bottom right corner.
BUT... hot tuning a reg can have knock-on effects that shift a reg into either less negative inhalation resistance, or even positive assistance during mid-breath that would decrease WOB. Alas, it's not linear.

Also, in OC, does the depth of the first stage relative to second stage (e.g. side mount v back mount) affect WoB to any material degree?

Though @Luis H would be the double-hose expert here, I don't believe second stage relative position matters for common hose lengths. For a hookah with a ridiculously long hose length, the absolute IP of a first stage higher in the water column (i.e., at the surface) could theoretically be less than the relative IP required for a second stage at depth to breathe easily.
For example, with a first stage with an IP of 145psi/10bar at 1 ft depth, an unbalanced second stage would be tuned to function well with that. However, at 264 ft/80m the extra 7 atm wouldn't be available to the first stage to raise absolute IP to 261psi/18 bar, since it's still at 1ft. Meanwhile the second stage on its long, long hose has 145 psi/10 bar IP, MINUS 101 psi/7 bar of ambient.
The only second stages that can function at 44 psi/3 bar relative IP are the TFX and the D400, due to their exquisite center balanced valves.

 

[SubSoul]

My understanding of IPO/IPE was that you were more likely to notice symptoms as you get shallower - due to dropping PPO2, pressure difference between lungs and mouth - so describing more might help.

If you were at depth, with high gas density and a bit of CO2 retention that can lead to pretty nasty narcosis, you might have aspired some water?

Ah, interesting. This happened a few minutes into the dive just after we descended to our maximum depth. I did add some details to the bottom of my original post for clarification. I actually toyed with the idea of narcosis but the doctor seemed quick to rule that out.

 

[SubSoul]

Since the header for this is equipment, let’s just say regardless of any equipment cause, these were both (pre-dive and cracking effort) easily correctable by you during the dive, yes you admitted that so I’m not doing a told you so thing but please in the future, anyone reading this, check the things you can during the dive if not before.

100% agree with you. I normally do this ans soon as I put the reg in my mouth but apparently did not on this dive. I have no clue why I overlooked this step…

 

[CG43]

Hello GingerDives

If the culprit was IPE, I’m just trying to understand if my regulator setting was partially to blame as this has never happened before on similar dives. Could the negative pressure breathing have triggered IPE?

I got the approval to dive again (with restrictions) but would like to better understand potential reasons for this accident.

Note: Not looking for medical advise. Reg has been tested and is working fine. Evaluated by 2 independent Dive Doctor’s.

In order to estimate what proportion the setting of this special reg. could have had, one must first know what pressure difference it is.
You can easily determine this by a small experiment.

!.) set the reg. so that it works just before the freeflow.
2.) Dip the reg. mouthpiece upwards in water until the reg. responds. Mark this position.
3.) Now the same attempt with the reg. in the setting you had with your problem dive.
4.) Mark the position and measure the difference.

During the tests, there should be no air in front of the inhaled membrane. For this it may be necessary to hold the mouthpiece closed and tilt the reg. in the water so that the air can escape. Before the test itself, the reg. must be lifted out of the water so far that it does not respond and only then is the mouthpiece to be opened. If the mouthpiece with nozzle is too short in length, it can be replaced by a longer hose for the test

 

[grf88]

Ah, interesting. This happened a few minutes into the dive just after we descended to our maximum depth. I did add some details to the bottom of my original post for clarification. I actually toyed with the idea of narcosis but the doctor seemed quick to rule that out.

Just after you reached depth could also indicate an only partially opened cylinder valve restricting flow.

 

[SubSoul]

Just after you reached depth could also indicate an only partially opened cylinder valve restricting flow.

This happened while I was working abroad so the incident report had to be interpreted, but it looks like my cylinder was checked immediately and the valve was opened fully.