Has anyone had a “free flowing” nose on a rebreather?

[PEDiver]

To preface, I am a relatively new rebreather diver (only ~20 hours on the unit). On three distinct dives, with all three being more strenuous or task-intensive, I’ve had an issue where my nose will begin to “free flow” or “vent” on inhalation. My first reaction was to reduce loop volume. Unfortunately, that did not solve the problem (even after sitting in position for 20 mins miserably). The only way to “solve” the issue is to hold my nose when I breathe. I’ve never experienced this same issue on OC under similar (or any) circumstances. Has anyone else experienced this? If so, how did you solve it? What is causing it?

 

[MinimalMayhem]

I had a period of a few weeks when my nose would 'vent' while hanging on deco, typically on a trapeze or shot line...but this was on exhaling, not inhaling. In the end I was gently pressing on the glass of my mask to maintain the seal.

I'm not entirely sure what solved it but I think it might have been to do with changing positioning of mouthpiece retaining strap, how bov was oriented on the loop hose, hood, mask age etc. all leading to a less than ideal seal - it seems to have fixed itself now.

 

[kierentec]

It’s usually a result of CO2 loading and increased work of breathing. What unit are you diving, what gas, and at what depth?

 

[Rollin Bonz]

I've had this happen a couple of times. Also new (35ish hours) RB diver. Felt more like the muscles responsible for holding the nasal airway closed were fatigued. Always near the end of the dive.

 

[PEDiver]

It’s usually a result of CO2 loading and increased work of breathing. What unit are you diving, what gas, and at what depth?

I'm diving the O2ptima CM. The last dive was on nitrox dil at ~60 feet. It was a very high-flow environment and I was definitely working harder than normal (also trying to keep conscious of over-breathing the unit). Happened on a slow descent fighting flow. The time prior to that was at ~155 feet on 21/20 (no flow, but was playing around with a new scooter). The only other time was during training (~50 feet, air dil).

 

[PEDiver]

I've had this happen a couple of times. Also new (35ish hours) RB diver. Felt more like the muscles responsible for holding the nasal airway closed were fatigued. Always near the end of the dive.

Unfortunately, it seems to strike at random times during a dive for me. I originally thought it was an issue with loop volume and over-pressurizing my nasal cavities, but I always run at a min loop volume so that doesn't seem to be the issue. I definitely think muscle fatigue is possible and makes sense based on how my nose seems to "spasm" slightly when it happens.

 

[kierentec]

I'm diving the O2ptima CM. The last dive was on nitrox dil at ~60 feet. It was a very high-flow environment and I was definitely working harder than normal (also trying to keep conscious of over-breathing the unit). Happened on a slow descent fighting flow. The time prior to that was at ~155 feet on 21/20 (no flow, but was playing around with a new scooter). The only other time was during training (~50 feet, air dil).

High workload, increased gas density, and likely a bit of stress managing new equipment (playing with the DPV and in your course) can all attribute to CO2 buildup.

I’ve found this issue to be more common on FMCLs (increased hydrostatic WOB on the exhale) and especially units with smaller loop volumes (much easier to over breathe).

Keep work loads extremely low in the future and if you feel yourself starting to breathe hard, stop all activity and rest until it is under control, and use adequate He for deeper dives (18/45 would be a more appropriate mix for dives in the 150ft range).

 

[Rollin Bonz]

Unfortunately, it seems to strike at random times during a dive for me. I originally thought it was an issue with loop volume and over-pressurizing my nasal cavities, but I always run at a min loop volume so that doesn't seem to be the issue. I definitely think muscle fatigue is possible and makes sense based on how my nose seems to "spasm" slightly when it happens.

I'm also diving a Choptima. Not sure if the Dil during those specific dives. I normall vent through my nose on ascent rather than the OPV on the CL, I find that kind of natural. Not sure if that is the norm. Being newish, I may have not been venting quickly enough during my ascent, causing a higher CL volume. Holding my nasal passage closed against a higher pressure may have lead to early fatigue of the muscles. I also had to physically close my nose with my fingers a couple of times during my 20 ft stop to stop the flow.

 

[Heat Miser]

I had it when I did a Helitrox Cross-over on the choptima. I think it was because I had stuck a wrist slate in the front pocket (backwards, i.e. round part pointing inwards) and the counterlung was constricted.

I have never had it on the revo.

Certainly felt difficult breathing out, and thus felt like I wasn't getting enough air breathing in.

 

[broncobowsher]

I have had some "snorting" and you could feel the mask cycling in and out as I breathed. Happened a fair bit when I first started on the rebreather. No so much anymore. I recall there was good info on it on rebreatherworld.com, back when it still existed.