Why more trouble equalizing on a CCR?

Michael Thornton

Michael Thornton

Rebreather Enthusiast
Fairly often while teaching CCR at the end of course one of my students will ask me why their ears are giving them more trouble after diving a CCR. They are confused as to why they have 0 problems on OC but their ears are still clogged up the day after diving a rebreather.
I don't have a good answer except for a few hearsay things but I don't like answering a question with answers that I am not confident in.
TDI has a little exam for doing rebreather discoveries (try dives or demos) and question 11 is a T/F "It is important to equalize every 15 minutes after surfacing for about 2 hours to prevent an ear squeeze after diving with a rebreather"

So maybe I should know this as an IT but can someone who knows more than me explain why it might be worse on a CCR besides their buoyancy not being great at the beginning?

Thank you in advance.


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Something to do with breathing richer mixes for a longer time I think...only read about myself the other day.

Was a thread on rebreather world about ear squeeze after diving an o2 rebreather
 
DeepUnderground said:
Something to do with breathing richer mixes for a longer time I think...only read about myself the other day.

Was a thread on rebreather world about ear squeeze after diving an o2 rebreather
Click to expand...

That's what I have always heard taught but I do not have anything to back it up so......


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Funnily enough, this same question was asked towards the end of my Meg CCR course in (which was in March) as well!

While I don't recall my instructor having a 100% solid answer, I believe it's because the oxygen you breathe travels up into the Eustachian tubes to the middle ear, which is more readily absorbed by the middle ear lining, thus creating a vacuum.

Since you have to "suck" on a rebreather more to get your gas, more oxygen travels in to the middle ear more readily, more so than on an open circuit regulator, since it "feeds" you air and therefore doesn't create as much of a negative pressure space.

I'm not claiming to be an expert but this is what was described to me. Kind of makes sense though. :)

[EDIT] Woohoo, first post here!
 
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Being fairly new to CCR, I've noticed a prolonged ear 'squeeze' while ascending and for quite a few hours afterwards. If I ascend slowly and sit at around 3m for a while I can actually feel my ears 'clearing'

I've never had this on OC and, while I don't know why, it's reassuring to read it's not just me.
 
As far as equalizing generally, I figure RayW is on to something. Since you have to actually inhale with the rebreather (as opposed to just tap a regulator on the shoulder and say, "would you force some air down my throat, please?") you're creating a little bit of negative pressure that confuses your muscle memory for whatever tiny muscles in your head control your eustachian tubes. Since it just feels wrong at first it feels like trouble.

For the following little while:
I figure the gas that's in your inner ear will have a bumped up PO2 of whatever your loop was when you hit the surface. Ever so slowly the soft, highly-vascular tissues of your inner ear will metabolize a couple of oxygen molecules here, a couple there, so that for a little while after the dive the volume of gas in your inner ear is minutely depleted into a slight vacuum which feels slightly strange until the gas is diluted to about ambient.
 
The high PO2 levels could have something to do with it, but i suspect that for beginning CCR students the ear equalization troubles have more to do with task loading and the fact that they are not equalizing as regularly and automatically as they would be doing on OC. They get distracted and don't equalize when they normally would have and are reminded when their ears start feeling the squeeze. After a few times of that squeeze, their ears get a little traumatized and angry!

Just my $.02
 
Having just spent a week in cave country for my Mod 1, I was wondering what's going on with my ears.
I did the circle of life constantly with each descent. Ears, loop, suit, ears, loop, suit.... Constantly on the ears and wondering why I had to equalize so much. Never had too that much on OC.

Now been out of the water 4 days and still having to equalize a few times a day... It's getting better each day though. I guess 14 dives, hour long minimum each, over 5 days is a bit much; loved it though.
 
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There are several articles about high PO2 breathing inducing a inner/middle ear pressure difference. Google "Middle Ear Oxygen Absorption Syndrome" and you'll find a lot of discussion. It does affect OC deco divers as well, I suspect that anyone who is "equalization-inefficient" for any reason may find it to be noticeable (i.e. sinus issues, low grade cold, inflamed ears from multi-day diving etc etc)
 
I think the high pO2 argument has to take into account the dive profile. On square profiles, the OC diver will typically experience 1.4 for the bulk of the dive while the CCR diver might be set at 1.2. So it could only be related to the ascent phase. And of course most OC divers would end up at 1.6 at 6m/20ft anyway. So I don't think that argument is really valid.
 
I think if you have to suck hard to get the loop volume around the pressure in your ears change at every breath you take.
OC it is easy , the regulator spits out air under pressure on a CCR your ears become a part of the loop.

R
 
Randy Thornton said:
The high PO2 levels could have something to do with it, but i suspect that for beginning CCR students the ear equalization troubles have more to do with task loading and the fact that they are not equalizing as regularly and automatically as they would be doing on OC. They get distracted and don't equalize when they normally would have and are reminded when their ears start feeling the squeeze. After a few times of that squeeze, their ears get a little traumatized and angry!

Just my $.02
Click to expand...

the o2 thing seems wrong to me , oc i used to run 1.45 bottom and hit 1.6 a few times at deco over all ppo2 is for me much the same diving ccr ,
unit is defalt 1.3 so i run with that but pump the ppo2 up as much as i can on the way back and on deco .

so id go with its a noddy thing . and should sort its self out over time ,
 
Remco said:
I think if you have to suck hard to get the loop volume around the pressure in your ears change at every breath you take.
OC it is easy , the regulator spits out air under pressure on a CCR your ears become a part of the loop.

R
Click to expand...

you may want to try sucking air at 70m on a oc reg ,
 
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I find CCR better. Long OC dives dry out my sinuses making it harder to equalise, especially over multiple days


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