Equipment IPE and Regulator Adjustments

[SubSoul]

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.

EDIT: Some additional information that may be relevant:
- The incident occurred 4 minutes into the dive and started when we reached the maximum depth of 115 ft
- I was using EAN28
- The water temperature at depth was 45-degrees
- I was wearing a drysuit with thermal layers appropriate for the conditions and I dive this location frequently
- My equipment or set up has not changed (MTX-RC long hose set up) and was just serviced in March 2024
- I was diving with a group of 4 divers
- Once I reached 115 ft, I felt like I swallowed a bit of water. After a few more breathes, I felt like some more water had entered my mouth and lungs and I began choking. I alerted my dive buddies, then went unconscious. After they got me to the surface and gave me some rescue breaths, I began breathing on my own and quickly regained consciousness.

 

[grf88]

I would think that anything that increased the pressure differential could contribute to IPE. I am surprised that those settings could make the regulator that hard to breath but maybe that depends on the regulator and it's base setting.

 

[grf88]

I have talked to some people who think a hard breathing regulator is good as it helps them reduce their air consumption. The above is one very good reason to have an easy breathing regulator.

 

[rsingler]

115ft on some sort of EAN is not too far distant from @Dr Simon Mitchell 's knee in the curve of critical gas density for CO2 retention due to difficulty in moving gas.
With a reg on max cracking effort and min Venturi and high gas density, the extra inspiratory effort could have contributed.
It's not totally unlike flash pulmonary edema in the operating room, where an awakening patient has laryngospasm, tries very hard to inhale, and has a fluffy chest xray two hours later in the Recovery Room.

I have talked to some people who think a hard breathing regulator is good as it helps them reduce their air consumption.

And this just makes me crazy.

 

[lexvil]

115ft on some sort of EAN is not too far distant from @Dr Simon Mitchell 's knee in the curve of critical gas density for CO2 retention due to difficulty in moving gas.
With a reg on max cracking effort and min Venturi and high gas density, the extra inspiratory effort indeed could have contributed!
It's not totally unlike flash pulmonary edema in the operating room, where an awakening patient has laryngospasm, tries very hard to inhale, and has a fluffy chest xray two hours later in the Recovery Room.



And this just makes me crazy.

I wish I could give you triple bullseye for this one!

 

[SubSoul]

115ft on some sort of EAN is not too far distant from @Dr Simon Mitchell 's knee in the curve of critical gas density for CO2 retention due to difficulty in moving gas.
With a reg on max cracking effort and min Venturi and high gas density, the extra inspiratory effort indeed could have contributed!
It's not totally unlike flash pulmonary edema in the operating room, where an awakening patient has laryngospasm, tries very hard to inhale, and has a fluffy chest xray two hours later in the Recovery Room.



And this just makes me crazy.

Thanks for the response. Leaving the Venturi on - and the cracking pressure at maximum was an oversight made by me. I could definitely feel a difference in the breathing effort. The doctor did also discuss what you mentioned above about a laryngospasm (mammalian dive reflex) as being a possibility.

 

[Kendall Raine]

For those interested in the topic (esp. Rob's "knee in the curve") see attached.

 

[Kendall Raine]

115ft on some sort of EAN is not too far distant from @Dr Simon Mitchell 's knee in the curve of critical gas density for CO2 retention due to difficulty in moving gas.
With a reg on max cracking effort and min Venturi and high gas density, the extra inspiratory effort indeed could have contributed!
It's not totally unlike flash pulmonary edema in the operating room, where an awakening patient has laryngospasm, tries very hard to inhale, and has a fluffy chest xray two hours later in the Recovery Room.



And this just makes me crazy.

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? I'm sure it's not as simple as that, but wondering whether you know a way to impute the impact on Mitchell's 6g/l threshold gas density for differences in cracking pressure (holding all other factors like static lung load, etc., constant)?

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?

 

[inquis]

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?

No, the IPs would be about 1% different on identical first stages. Negligible impact on an unbalanced 2nd and even less on a balanced 2nd.

 

[BoltSnap]

I have talked to some people who think a hard breathing regulator is good as it helps them reduce their air consumption.

Total BS!!!