CCR and laryngospasm

[rjack321]

Sometimes well into a dive (2 hours+) I find my soft palate getting tired and start unintentionally exhaling through nose. I have been told that this is not uncommon with rebreathers which always have some exhale WOB. Flexing neck , trimming head down and increasing loop volume helps without need to bail out.
Could it be the same phenomenon (palate fatigue due to increased wob and mouth breathing) instead of a real laryngospasm?
@doctormike probably knows this stuff.

On my Meg I have a BOV with a drager gag strap. That mouthpiece makes my gag something fierce out of the water. Its a huge challenge to make it through a pre-breath without gagging. Shockingly, in water its super comfy, have you tried one? I typically run a little higher than min loop for the same reason, I notice the accumulation of minor low volume insults (ADV off) over multi hour dives.

 

[doctormike]

Sometimes well into a dive (2 hours+) I find my soft palate getting tired and start unintentionally exhaling through nose. I have been told that this is not uncommon with rebreathers which always have some exhale WOB. Flexing neck , trimming head down and increasing loop volume helps without need to bail out.
Could it be the same phenomenon (palate fatigue due to increased wob and mouth breathing) instead of a real laryngospasm?
@doctormike probably knows this stuff.

I don't know about this as an ENT doc, but I did have something very similar happen to me in MOD 1 training. The best that I could figure out was that I wasn't use to the airway pressures on CCR as compared to OC, and that it was triggering some sort of laryngospasm. I bailed out, calmed down, and got back on the loop. Hasn't happened since then.

I would think that the sorb dust would be less likely, assuming that you have a well packed and well designed scrubber.

 

[wedivebc]

what you are describing is exactly what hapened to me when I first started diving a rebreather. A Draeger Dolphin placed high on your back with a drysuit equals a negative static pressure which caused a little gag in the back of my throat. Usually toward the end of the dive as I was getting tired.

 

[michael-fisch]

Back last year, I unfortunatly inhaled a caustic cocktail. Spent a week in the hospital, had 2-3 months of rehab and my voice started coming back after about 6 weeks. After my doctors had given me their oks to dive again 3.5 months later, my voice was again very hoarse after the first RB Dive.
Solution was putting JJ Scrim Filters on both ends of my axial scrubbers and wrapping the inner tube of my radial scrubbers with 1 layer of the material used for industrial vaccum cleaner bags held in place with a few rubberbands.
What a difference! If you are not yet using a Scrim Filter, give it a try, I think you'll like it.
Since I had to buy a package of industrial vaccum cleaner bags, I've got a supply of the material that should last me untill I'm at least 150 years old.

Michael

 

[kensuf]

Are you using Intersorb or Sofnolime? Just curious..I've always found dust varies between kegs but in my observation Intersorb tends to be more dusty than Sofnolime. I've had some really dusty kegs of Sofnolime too so it's not always the case.

When I fill I decant sorb into a smaller 4.5kg container first.. I use a fan that blows sorb dust away and a put funnel into the smaller container. I find that this cuts down on sorb dust considerably. It could help if you think dust is causing the issue.

Also as others suggested, you may want to use an additional filter in your scrubber.

I was going to ask this same question. I switched to Sofnolime about a year ago. It's substantially less dusty. It's also more expensive, but I get it through Subgravity and can pick it up in Ft. White.

Also try using a box fan when you're packing the scrubber to blow the dust away. Set the fan up about 5-6' away from the scrubber can and when you fill, make sure to hold the keg about 8-12" above the scrubber can to allow enough of a gap for the dust to get picked up by the wind from the fan. This will help blow a lot of the dust away.

BTW -- I've had a real laryngospasm underwater, so have two of my friends (Bob and Forrest). All three of us got it from a bit of water. It's not an experience you can easily forget and is quite distinctive. Based on your description, my thought is Mrs. rddvet's issue has more to do with sorb dust causing a slight reaction rather than a real laryngospasm.

Best of luck, let us know if changing your filling practices helps.

 

[rddvet]

Sometimes well into a dive (2 hours+) I find my soft palate getting tired and start unintentionally exhaling through nose. I have been told that this is not uncommon with rebreathers which always have some exhale WOB. Flexing neck , trimming head down and increasing loop volume helps without need to bail out.
Could it be the same phenomenon (palate fatigue due to increased wob and mouth breathing) instead of a real laryngospasm?
@doctormike probably knows this stuff.

Thanks all for the replies. There's been a lot more helpful information than expected. Hopefully I remember to respond to the most of the remarks.
When she read taimen's explanation, she immediately said that it sounds exactly like what she's feeling except its on inhaling that she feels like she's uncontrollably inhaling through her nose and not her mouth eventhough she's orally inhaling like normal. She also said that when it occurs, it depletes the volume in her mask quickly which then leaks slighlty and she inhales a little water making it worse.

On the fathom there is a baffle on the inhale side. Our first tub of sorb was sofnolime and it was extremely powdery. I then got a deal on intersorb and bought a bunch of them. The first couple had less dust than the sofnolime, but the current one is worse. All of the filling tips are very helpful. We always pack the scrubbers outdoors, but not usually in an area where a breeze can get to us. We actually fill the canister with the sorb tub very close to canister in order to minimize spillage. I never really thought about filling from high to let the dust blow off. We are going to start by cleaning the dust from our sorb canisters really well and then start filling the sorb from a height with a box fan blowing across it. We may also fill another dust free container with some sorb poured in the same way to see if that's better.

All of our dives have been in the 60-90 range since we're still getting used to the units. On the most recent dive, she said it happened about 25 minutes in. She also said that she bailed out relaxed and it seemed to go away, but then started recurring as she went back on the loop so she bailed out again and all was fine. She says it's a pretty strong reaction and is pretty uncomfortable/stressful, but easy to deal with. This last one was annoying enough to almost have her end the dive.

 

[rddvet]

Back last year, I unfortunatly inhaled a caustic cocktail. Spent a week in the hospital, had 2-3 months of rehab and my voice started coming back after about 6 weeks. After my doctors had given me their oks to dive again 3.5 months later, my voice was again very hoarse after the first RB Dive.
Solution was putting JJ Scrim Filters on both ends of my axial scrubbers and wrapping the inner tube of my radial scrubbers with 1 layer of the material used for industrial vaccum cleaner bags held in place with a few rubberbands.
What a difference! If you are not yet using a Scrim Filter, give it a try, I think you'll like it.
Since I had to buy a package of industrial vaccum cleaner bags, I've got a supply of the material that should last me untill I'm at least 150 years old.

Michael

I looked up the scrim filters. Is it just a thin reusable material that sits on either end of the canister. Looks like I would have to cut a center hole in the filter to get it around the inner tube of the canister

 

[victorzamora]

I looked up the scrim filters. Is it just a thin reusable material that sits on either end of the canister. Looks like I would have to cut a center hole in the filter to get it around the inner tube of the canister

Scrim filters are for axial scrubbers. Are y'all using radials or axials?

 

[rddvet]

Radial. I thought he was modifying them somehow, but now I re-read that he's only using them for axial

 

[michael-fisch]

I use one layer of an industrial vaccum cleaner bag for my radial scrubbers.
How to:
Measure the height of the inner tube and then measure around the inner tube with a piece of string adding 1" to the string.
This gives you the height and width that you need to cut to.
Now cut a piece of one layer of the industrial vaccum cleaner bag to match the height of the inner tube and the circumferance of the inner tube + 1 inch.
Wrap the piece around the inner tube and affix with 4 rubber bands spaced 1.5-2.5 inches apart. If you did it right the piece covers the grating on the inner tube completely and lays nice and flat. If not try again, it took me several tries before I got it right.
Now fill the cannester with sorb as usual, put the lid on it and enjoy your now dustfree sorb cannester.

Michael