Underventilated?

Hello All, I really appreciate and value some experienced opinion on this.

How does one determine adequate ventilation / tidal volume?

Background:
I failed APAP, then BiPAP, and have improved on ASV, but still feel low-grade headache, light-headed, and rather exhausted every day. Some days are better than others, but when I have a bad day, it doesn't seem to improve as the day goes on. ASV has been a definite improvement over APAP/BiPAP, but I'm nowhere near feeling normal as a few years ago. I have a history of asthma and difficulty exhaling against higher EPAP pressures. If I set EPAP higher than around 10.4, 10.6 cm, it seems I wake up very dizzy and feeling awful the entire next day - it would never subside. Looking at Sleepyhead, it seems the ASV machine rarely 'maxes out' above 10 cm anyway. This is perhaps why I felt dizzy and awful on APAP every single day, when EPAP was typically near or over 10 cm? Breath-stacking / CO2 build-up, perhaps?

ASV has improved overnight spO2 readings, but it can still go to 88-90% for a couple of minutes a night. On APAP, it frequently reached 10-15 minutes a night below 88% (82% lowest). I improved slightly on BiPAP, but abandoned it after 2 months as I did not feel appreciably better and the AHI went from 3-5 to around 6-10/hour, the majority being Centrals.

My current sleep doc recently gave me a 4-night test using a higher quality Nonin 3150 pulse-ox unit and the results were 3 nights approx 3-10 sec. at 88%, and one night at 67 sec. at 88%, nothing lower. He thinks this is fine, no improvement needed. My CMS50F unit seems to be reading intermittently lately (it looks like the sensor cord is failing), but that unit consistently has shown my spO2 on ASV cycling to lows around 88% to 90%. Not a lot of time spent at the lows, just frequently cycling to that level and then back up to the mid-90% again, 20 minute or so cycles.

The sleep doc thinks ASV is the right machine and that I am adequately ventilated. He believes a VAPS machine would only improve someone with severe hypoventilation syndrome or COPD patients. I have a reduced lung function of around 7% as tested in the chamber around 10 years ago. I'm guessing it's time to visit a pulmonary sleep specialist, but it's difficult not to waste money on medical incompetency in my experience.

Question:
I spend 2-3.5 hours a night at a tidal volume of 350-390 mL; my median values are typically 400-420 mL. For a 60" tall male, is this 'normal'? I sometimes review my friends Sleepyhead data with him (we are getting to be old farts with no lives); he is 10 years older than me, the same height, and his tidal volumes are consistently 1.5X greater than mine, and his therapy is not even optimized yet. He rarely goes below 91% spO2, either.

In my case, would it be worth it to trial a VAPS unit? And what's the most adjustable for someone with complex apnea and assuming hypoventilation? The Resmed iVAPS S/T A, or other?

I've read a lot of differing data on tidal volume. Is this reasonable?
https://www.mdcalc.com/endotracheal-tub ... calculator
300 mL
Tidal volume if target is 6 mL/kg, IBW 50 kg
400 mL
Tidal volume if target is 8 mL/kg, IBW 50 kg

Supporting Info:
Some recent Sleepyhead screenshots are here:
http://imgur.com/a/yfj8C

Here are some others showing close-ups of flow pattern from a period where I had a very bad night/following day. The very flattened portion of flow highlighted continues uninterrupted for nearly 90 minutes. I seem to exhibit this similar flow pattern and duration when I wake up feeling very poor.

http://imgur.com/a/Blpe8

My AHI is less than 1/hour, zero centrals. I take 5 mg Zolpidem (Ambien) a night for the past 18 months. I had tapered it to 2.5 mg, but had to increase again due to difficulty falling alseep.

Everything else I can think of's been tested: full metabolic panel, blood sugar, ABG, Thyroid, Vit B / D all normal. D is 65 ng/mL. Have not had a brain MRI; Sleep Doc is a neurologist and says low probability of issue given no symptoms, it's up to me to have it done.

Opinions are very much appreciated! And Happy 4th of July!

xxyzx wrote: ============

adequate ventilation would keep you spo2 closer to 95++
adequate Vt would depend on your lungs and the RR
The ASV shoudl do all this automatically

PERFECTION IS NOT POSSIBLE

if you have central apnea you may not be able to fix taht and the OSA too
some compromise may be needed

you may need to have o2 added via the machine

ASV is the right machine
88-90% is marginal but not death threateningly low
ask your doctor about addign O2 if you dont feel good though

your tidal volume depends on you
what is a population average 'normal' is not necessarily your normal
if your body needs more oxygen your RR goes up
the lung volume is fixed
you cant change that so dont worry about tidal volume unless your doctor says it is a problem

i think you can chase perfection but are likely to waste money and cause more problems
if anything i would push for some added o2 to help the headaches

you can add oxygen side load to the resmed ASV
you should have AN ASV IF YOU HAVE CENTRALS
they breathe for you when the central stops your effort so as to keep the o2 adequate

Thank you very much for responding. I am not chasing perfection, either in AHI or spO2 levels. I have been on PAP therapy for nearly two years and was hoping to be feeling better than I am by now, is all. I'm not complaining, others have lost their jobs, or worse, their lives, due to OSA. My case is nowhere near as severe, however, I am trying to avoid losing my job as some days are a struggle, Friday's in particular.

I have zero centrals as I've mentioned. And I've brought up adding O2 to my sleep doc twice previously, and both times he said my levels are adequate, and that it could induce unwanted centrals. I don't know if I'm in agreement based on how I feel, my spO2 levels, and the fact I register no centrals per night, so perhaps it's time to push this again. However, I tried the Respironics 960 ASV unit as well for a couple of months and some nights my patient triggered breathing was as low as 25%, and averaged only 75%. But what could a trial hurt, I'm thinking, the O2 port's already built into my ClimateMax hose. The only other choice seems to be a VAPS machine anyway, if that is even a viable option.

Over-thinking anything will only make it worse.
You expect results faster than they can happen.
For your own sake, please be patient.

your charts look good, the zoomed in shows a very good breath, the asv is working well for your breaths,, you are overthinking it, but I can see why. I would think it doesn't matter if o2 increases centrals, that's what the asv is for. that's its job to fix them. 88% minimum is considered ok and not needing o2 supplement. They will try to titrate you to be above 90%

I would raise the min PS to 8 or10 and raise the max ps to 15 which is the default setting. Try that, it should ventilate you more. You really need to be sleep study titrated, most doctors can't do it as well. The study have the different machines, to see what works and any supplemental o2 needed.
As you know, the ASV doesn't react to low o2 by increasing ps for more ventilation, so you have to manually adjust for this. as said you may need to supplement with O2. I would certainly see a pulmonary sleep doctor.

I can't see a st doing a better job if you have severe PB/cheyne stokes. The st-a ivaps has the assured volume, that may be worth a sleep trial on. The asv can be set up to give a better volume than generic settings, ASV doesn't have a set target volume.

these are the targets for weight and height for reference.



https://www.resmed.com/us/dam/documents ... lo_eng.pdf
• VPAP (Bilevel) – Delivers two treatment pressures — one for inspiration (IPAP) and one
for expiration (EPAP) — and provides control over the following bilevel therapy modes:
»» S (Spontaneous) – Follows the natural breathing pattern, allowing patients to breathe
at their regular respiratory rate and rhythm
»» S/T (Spontaneous/Timed) – Augments any breaths initiated by the patient,
but will also supply additional breaths if the breath rate falls below the clinician’s
set “backup” respiratory rate
»» PAC (Pressure Assist Control) – The inspiration time is preset in the PAC mode.
There is no spontaneous/flow cycling. The inspiration can be triggered by the patient
when respiratory rate is above a preset value, or time-triggered breath will be delivered
at the backup breath rate.
»» T (Timed) – The fixed respiratory rate and the fixed inspiration/expiration time set by
the clinician are supplied regardless of patient effort
»» VAuto – Automatically adjusts pressure in response to flow limitation, snore and apneas;
pressure support (PS) is fixed throughout the night and can be set by the clinician
»» Adaptive Servo-Ventilation (ASV and ASVAuto) – Treats the spectrum of central
breathing disorders, including mixed sleep apnea, complex sleep apnea (CompSA) and
periodic breathing such as Cheyne–Stokes respiration (CSR)
»» iVAPS – Treats hypercapnic respiratory insufficiency, including obesity hypoventilation,
chronic obstructive pulmonary disease, neuromuscular disease and restrictive conditions

you can't set a Vt on a resmed asv, a vaps function does that. The philips ASV is not as automated and may have a Vt setting, but I haven't looked that hard. I've read Vt is adjusted by PS. with NIV PS of 40 are heard of. niv ps is about two thirds of a ventilated ps ..niv ps15 = ps 10 ventilated

Vt is one part of an equation, the ability to transfer gas in the lung sack to and from capillary, is another

Be aware that end-of-alphabet boy has never had a good night on CPAP. So, he has no qualifications to help you.

What is the cause of your reduced lung function? Is asthma your only documented medical illness?

I believe ASV machines target the proper minute ventilation breath by breath, to prevent over/under shoots; it is a very different algorithm than VAPS which in general has a slower response (AVAPS at least; I believe iVAPS is a hybrid mode of servo-ventilation). Phillips Respironics has a sleep titration guide which gives you recommended initial settings for ASV.

As a six (6) foot tall man, you can calculate your target Tidal Volume (Vt) according to height/Ideal Body Weight (IBW) here: https://www.mdcalc.com/ideal-body-weight. Your actual body weight isn't used to calculate it.

Phillips Respironics AVAPS protocol is to set a target Vt of 8 mL/kg which would be 620mL Vt...so your exhaled tidal volumes seem rather low. Even a target Vt of 6mL/kg, which is generally a lung-protective strategy/for those with bulbar a dysfunction/stiff chest wall, is calculated to target a Vt of 465mL. Your Dr. is correct though in that for serious hypoventilation/respiratory insufficiency you would be using a VAPS machine not ASV.

When you trialed bi-level did they give you a unit with a backup rate? On bi-level spontaneous I get central apneas due to muscle weakness...I am not able to keep an adequate respiratory rate during REM sleep and sometimes can't trigger the ventilator on my own. A bi-level s/t unit eliminates all my centrals.

Using a high EPAP can have cardiac consequences such as hypotension, reduced cardiac output and an increase in dead space (more volume of air that does not participate in gas exchange).

Chevie wrote:Be aware that end-of-alphabet boy has never had a good night on CPAP. So, he has no qualifications to help you.

Great name for him

AFAIK, asv targets 90% of the last 3-4 minutes, if it was 300, the 90% target would be 270 if it was 600 the target would be 540. I don't know if philips asv has a min Vt setting but resmed doesn't seem to.

At 67 inches, I rarely reach the recommended tidal volume on the chart above. Clogged nasal passages can really lower my tidal volume. The extra 60 pounds above IBW probably negatively affects my tidal volume, too.

I average 400 to 440 in tidal volume, sometimes higher. Pretty sure I wake up if it gets below 250. I spend a lot of time in the mid 300s, too.

I would guess that something else besides tidal volume /02 is disturbing your sleep.

I suspect the Resmed ASV targets 90% of last 3 minutes of Minute Ventilation as best in can under the circumstances, and continues the most recent breaths per minute rate based on a few breaths before the event (decrease in Minute Ventilation below Target Minute Ventilation?) is detected.

For example, when I have my sleep transition problem episodes, my breathing rate drops, the ASV kicks up the pressure, holds BPM constant and Tidal Volume increases dramatically. However, Minute Ventilation, Target Minute Ventilation and max IPAP slope downwards left to right almost parallel until I pick up the breaths per minute rate. I suppose the low BPM, despite the increased Tidal Volume, is not enough to maintain a constant Minute Ventilation, so Target Minute Ventilation drops for me.

http://imgur.com/3JlO9zN




Cpapped-Adapts charts seem to indicate that Cpapped-Adapted's events (decrease in Minute Ventilation below Target Minute Ventilation?) occur at a higher BPM rate and occur quite often, and Resmed ASV applies pressure support quite often. The combination of higher BPM rate and modest Tidal Volume is enough to maintain Minute Ventilation and Target Minute Ventilation for Cpapped-Adapt. However, something is disturbing Cpapped-Adapt's quality of sleep.

Thanks for that, the algorithm target is the minute vent, not the tidal vol.

Thank you so much for responding everyone. It will take me more time than I have right now to respond to everyone, so my apologies.

Over-thinking anything will only make it worse.
You expect results faster than they can happen.
For your own sake, please be patient.

Got it, Chunkyfrog, the first year and a half was a complete bust, and the ASV still may not be set properly (I've been on it since Dec. 2016), perhaps an overnight titration and time will fix this. Doc kinda discouraged me from the overnight, saying my AHI was so low and spO2 not so bad, so little to be gained. I'm going to push this again with him.

these are the targets for weight and height for reference.

Thank you, Ajack, I'd seen that chart before but lost it! Thanks for linking it again. I do not have any C-S/PB, just high number of centrals while on BiPAP, once the pressure was raised to the point it did any good. Forget APAP, I went back to it twice after the initial 9-month failure and it was the same result every time. A horrible, horrible following day. Never again! So I raised PS Min and PS Max each 1.6 cm last night. I don't do things in big step changes, ever. I feel better today, coincidence perhaps, or not. Unfortunately Mr. PulseOx has been acting up so I don't have spO2 results to show. There are only a few instances in the past where I've flatlined at max PS, so not sure raising that much more is going to do anything. And then I don't want to induce high leak rate, either. Minimum PS, I don't know. I want to let the ASV algorithm do it's thing, raising PS to high could get in the way of that, would it not?

Chevie, I like your avatar, I can't comment on the rest yet. Not to worry, I'm a fairly careful study.

What is the cause of your reduced lung function? Is asthma your only documented medical illness?

I believe ASV machines target the proper minute ventilation breath by breath, to prevent over/under shoots; it is a very different algorithm than VAPS which in general has a slower response (AVAPS at least; I believe iVAPS is a hybrid mode of servo-ventilation). Phillips Respironics has a sleep titration guide which gives you recommended initial settings for ASV.

As a six (6) foot tall man, you can calculate your target Tidal Volume (Vt) according to height/Ideal Body Weight (IBW) here: https://www.mdcalc.com/ideal-body-weight. Your actual body weight isn't used to calculate it.

Phillips Respironics AVAPS protocol is to set a target Vt of 8 mL/kg which would be 620mL Vt...so your exhaled tidal volumes seem rather low. Even a target Vt of 6mL/kg, which is generally a lung-protective strategy/for those with bulbar a dysfunction/stiff chest wall, is calculated to target a Vt of 465mL. Your Dr. is correct though in that for serious hypoventilation/respiratory insufficiency you would be using a VAPS machine not ASV.

When you trialed bi-level did they give you a unit with a backup rate? On bi-level spontaneous I get central apneas due to muscle weakness...I am not able to keep an adequate respiratory rate during REM sleep and sometimes can't trigger the ventilator on my own. A bi-level s/t unit eliminates all my centrals.

Raisedfist, Athsma is the only doumented lung condition, aside from GERD - which is on the mend since going on CPAP. I'm not certain the level of knowledge my doctor has regarding VAPS algorithms, but perhaps given what klv329 wrote it would respond too slowly. Proper tidal volume really confounds me. Look at klv329's response; he seems to get by find with much lower (based on height) than what you suggest. However, my friend, who is the same height, puts out 1.5X greater than mine: he's even higher than your 8 mL/kg value. He is in great physical shape for his age though. So perhaps it's more about baselining ones 'normal', then going from there. But then, the algorithms are targeting minute ventilation so as klv329 mentions, my BPM is higher, the pressure support is kicking in more often, and the minute vent is being maintained. Or not. I'm confused. Regardless, I'm not going to go flinging more hard-earned cash at an iVAPS machine unless I have some good professional advice that argues it being a reasonable option; perhaps it is. I've had to buy the last 3 machines out-of-pocket, and 2 of them were ASV's. Ouch!

why raise the pressure ?
he does not hit max pressure
and his AHI is good

the ASV is supposed to AUTOMATICALLY ventilate him at his normal Vt and either his RR or his average that they slowly move to 15 for resmed.
it knows the proper volume so setting it differently would not be helpful
nor would downgrading to an s/t a ivaps or other device that wuold let the centrals go untreated and possibly cause even more of them

the question is how to improve the o2 level and stop the headaches
it may not be possible without making the central apnea worse

perfection is not possible
this may be as good as it gets for the OPer

it would be nice to have the oximeter data plotted here too
to show when the low o2 problem is happening and see what might be causing it

i see it says the o2 went to 79 which should be of concern to the doctor
did i misread his sleepyhead summary ?


XXYZX, you point is well taken regarding raising max. PS. If it's not maxing out, no point in raising it, I get it. Only a few times a night it does, and some nights it doesn't. I raised it as I said earlier, 1.6 cm to eliminate those flat-line events. Let's see what happens. I wish I had more synchronized spO2 data, but as I said, the sensor cables starting to give me intermittent signal dropping. Anyway, one of the pictures I posted shows the spO2 cycling in a sine wave pattern. It's done this virtually every night since I started ASV. And I don't really trust the CMS unit all that much. When I compared it the Nonin unit the doctor gave me overnight, the CMS read 1-2% lower consistently, and I showed some weird very low readings on the CMS when the Nonin showed none. The Nonin's a $900 unit, there's no comparison. I've also never been able to synch my CMS unit with Sleepyhead, although I can synch my friend's identical CMS unit. Go figure.

At 67 inches, I rarely reach the recommended tidal volume on the chart above. Clogged nasal passages can really lower my tidal volume. The extra 60 pounds above IBW probably negatively affects my tidal volume, too.

I average 400 to 440 in tidal volume, sometimes higher. Pretty sure I wake up if it gets below 250. I spend a lot of time in the mid 300s, too.

I would guess that something else besides tidal volume /02 is disturbing your sleep.


Thank you for the perspective, klv329. I'm not sure what to mention that I haven't already previously. Probably time to take this up with a Pulmonary Sleep specialist.

At this point I gotta run. Thank you everyone for your concern and caring to take the time to respond and share your knowledge, I really appreciate it. Catch you later.