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[Treatment] Acceptable AHI with worrying minute ventilation / tidal volume
#1
Acceptable AHI with worrying minute ventilation / tidal volume
Hi, new user of the forums, 3 months on CPAP.

Tested at 22 AHI when I was initially diagnosed, entirely obstructive. My obstructives completely disappeared with use of CPAP, but I did pick up about 2-3 central apneas per hour. I think my sleep quality is still lacking too - it's hard for me to judge, because it's better than it was previously, and I'm only 27 so I wouldn't be surprised if I've always had apnea, but I do find myself napping even after a solid nights sleep. Of course, that might just be because I need better sleep hygiene...

My doctor is not particularly attentive, so I did end up adjusting the clinical settings myself. I'm currently using EPR of 0, but have tried all levels of it, and have tried raising my pressure minimum a few times to 6/7/8, but have found that increasing my pressure only increases my centrals, not doing anything for the statistics I'm concerned about. We also did an overnight oximetry with CPAP a few weeks ago, but my doctor did not give me the detailed results for that, only that it was better than before I went on CPAP.

The statistics I'm concerned about are minute ventilation / tidal volume / respiratory rate. My respiratory rate concerned me prior to CPAP and actually was what drove me to initially ask my doctor about CPAP (along with both my parents having OSA and one of those cheap overnight pulse oximetry things measuring me with ). Basically, my smart watch was suggesting that when I went to sleep, my average respiratory rate jumped from around 12-13 brpm to ~16-17, though it doesn't have the resolution my data in Oscar does. This has not resolved with CPAP. My median respiratory rate while sleeping ranges from 17-19 brpm, where it's low when I'm awake, shoots up to a steady 18-ish when I'm asleep, and can hit 30 for extended periods of time at times when I'm sleeping and there are no flagged events. Meanwhile, my median tidal volume is 280-320, and during these hyperventilation periods can drop as low as 200. Starts high when I'm awake too then plummets for sleep. I did calculate what tidal volume I'm supposed to have based on height and ideal body weight and got 380. My minute ventilation is also a bit odd. I've read elsewhere on the forum that the expected range for sleep minute ventilation is 5-8 l/min. Mine is, by median, between 5-6, but again, there are a lot of times throughout the night where it dips down into the 3-4 l/min range, especially associated with the hyperventilation periods. Other than apnea, my only known conditions that could be influencing this are an anxiety disorder (though I don't ever hyperventilate from it when I'm awake), no lung disorders or anything.

Again, my doctor thinks this is all perfectly fine (Or, well, she's not interested in looking at the charts). Maybe it is? I've added a couple screenshots, one from a timepoint where I was breathing pretty steadily though still shallowly, and one from a timepoint where my breathing was a lot more erratic. Do you guys see breathing like this often?

Thinking about trying EERS - I've read the wiki entries on it, and it seems it does often have the effect of upping minute ventilation and tidal volume while dropping respiratory rate? Just nervous that it won't work and then I'll have ruined a mask elbow and bought the modification stuff for nothing.


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#2
RE: Acceptable AHI with worrying minute ventilation / tidal volume
What does your smartwatch say about SpO2 during sleep? 

Your tidal volume may be low depending on your physical characteristics, age, and medical history. Respiration rates vary as well, 12-20 is a normal range for most adults, but some healthy individuals will have their RR higher with no issues.

Are you taking any medications? Smoker or non-smoker? Is there anything in your medical history to share? 
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#3
RE: Acceptable AHI with worrying minute ventilation / tidal volume
The drops in respiratory rate align with your central apneas which signals a c02 imbalance causing you to pause your breath. It's also normal to pause breathing as you switch positions when sleeping as well. From the 2nd & 3rd screenshots it looks like you could use a little more pressure to help better round out those breaths. Have you considered switching to CPAP mode? What pressure was most effective during your 2nd sleep study @ controlling your obstructive events?

Overall your data looks ok but I'd be more inclined to swap over to an Aircurve 10 to eliminate central apnea before I considered EERS. Are you around 5ft tall and relatively slender? That may explain the tidal volume.
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#4
RE: Acceptable AHI with worrying minute ventilation / tidal volume
Add in some EPR using settings of minimum pressure 6.0, maximum pressure 10.0, EPR 2. If centrals increase or decrease we will learn something about how to proceed. You don't have flow limitation, so I suspect you don't have a significant obstructive apnea problem. It would be interesting to see your sleep study results.
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#5
RE: Acceptable AHI with worrying minute ventilation / tidal volume
I'm not talking about the drops in respiratory rate - I expect respiratory rate to drop when I'm not breathing, that makes sense. What concerns me is the rapid shallow breathing when my body compensates.

I have not tried swapping to CPAP mode. There was no second sleep study, I was just given APAP and sent off. I do have flow limitations, but when I've tried upping my pressure the centrals get worse.

I am 5'3" and obese (BMI ~33, working on it). But when I calculated based on my ideal body weight (not current weight, the fomula of 49 kg + 1.7 kg for every inch over 5 feet) on the 7 mL per kg formula which seems to be the recommended one on these forums, the recommendation was 380 tidal volume. Additionally, you can see in one of the screenshots I'm breathing so shallowly I go below 200.

Thing about the aircurve 10 (that's bilevel, right?) is that to get the insurance to cover it I need to get my doctor to approve, whereas EERS is something I can do myself.
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#6
RE: Acceptable AHI with worrying minute ventilation / tidal volume
(Yesterday, 06:39 PM)Sleeprider Wrote: Add in some EPR using settings of minimum pressure 6.0, maximum pressure 10.0, EPR 2.  If centrals increase or decrease we will learn something about how to proceed.  You don't have flow limitation, so I suspect you don't have a significant obstructive apnea problem.  It would be interesting to see your sleep study results.

Will try that. Home sleep test, so the data is unfortunately limited, but I've attached what I do have with identifying info blacked out?


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#7
RE: Acceptable AHI with worrying minute ventilation / tidal volume
To go to the ResMed AirCurve VAuto bilevel, it can be as simple as a complaint your CPAP isn't comfortable. At least it's good enough for some doctors. If they do a script change as a follow-up to bilevel, insurance covers it, minus your copay.

Your tidal volume, minute vent aspect requires more ventilation, attained by more pressure and adding pressure support for leverage (EPR on the AutoSet).
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEBSITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#8
RE: Acceptable AHI with worrying minute ventilation / tidal volume
(Yesterday, 06:23 PM)PeaceLoveAndPizza Wrote: What does your smartwatch say about SpO2 during sleep? 

Your tidal volume may be low depending on your physical characteristics, age, and medical history. Respiration rates vary as well, 12-20 is a normal range for most adults, but some healthy individuals will have their RR higher with no issues.

Are you taking any medications? Smoker or non-smoker? Is there anything in your medical history to share? 

Unfortunately it's out for warranty repair right now Sad  But I did have it concurrently with CPAP for a while, and saw drops in O2. Not the greatest data quality which is what prompted the O2 test, but my doc didn't give me the actual results for that, just 'it's better than before you went on CPAP so don't worry about it.'

Non-smoker, am on a SSRI for the anxiety though. Nothing else relevant under medical history.
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#9
RE: Acceptable AHI with worrying minute ventilation / tidal volume
Made Sleeprider's suggested adjustments.

Still tired, might nap after work, but then, I probably also need more hours of sleep.

CAs are up - not sure I trust that they're real centrals, since I often have that big breath right in front of them, but even if they're not real centrals, they're measuring some form of sleep disturbance. This matches with my experience when I previously tried higher pressures / EPR. I also got some of the periodic breathing I tend to slip into in one of the screenshots, though it tends not to be flagged as anything.


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#10
RE: Acceptable AHI with worrying minute ventilation / tidal volume
I also had low tidal volume and I'm experimenting with EERS right now. The first thing would be to increase your pressure and maybe try EPR. You don't need to do EERS unless that causes centrals to increase. EERS helped my Tidal volume, but it seems the biggest increase so far is because it allows me to increase the pressure and add EPR of 1 which I couldn't tolerate before.  The main point of EERS is to stabilize and reduce problems from sensitivity to slight changes in pressure.
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