Should EPAP=titrated pressure

SWS,

Good points - but I am really really curious about the impact of T mode.

I would like to be able to come up with a reproducable sequence that shows conclusively if T mode smothers either AI scores or HI scores when pressure is set too low or a bilevel gap is set that is to big a spread.

I can't get over that I ran the PB330 (in S/T) for over 8 months with generally good results (but no AHI data to verify them) using 8/15 then when I switched to the VPAP III (in S) so I could gather nightly data I see a mess of AHI scores (and on re examination, equally AI & HI based).

I really do want to know if T mode makes a difference. The more I think of it I am sure I can quickly (1 night) use the VPAP III S/T set up to match the PB330 (using the same CMS settings that caused such high AHI on the VPAP III S). If with T mode on, it shows modest AHI score which can be significally impacted by turning off the T mode, then I feel I will have learned a great deal.

DSM

(waiting for the week-nd to actually give this a go)

Well I got impatient to try this experiment so did it last night

Settings= VPAP III ST mode, 8/15, 6 BPM, 350 ms Risetime, 2.00 sec max insp.
Result - AHI 21, Leak 0.02, AI 3.6, HI 18.1 !!!

Not a nice nights result (but the leak rate was good )
Aerophagia returned but not what I would call severe.

The minute ventilation chart looks like a kid scribbling on a wall ! it varies constantly all night from 5 lpm to 20 lpm !

The AIs that were scored were up to 40 secs.
Tonight I will leave same settings but up the epap from 8 to 10.

DSM
(will post a chart + PO data tonight - I did see a few low SpO2 scores, under 88 - in fact the lowest SpO2 dips I have ever seen for myself. That is very interesting)

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CPAPopedia Keywords Contained In This Post (Click For Definition): AHI

rested gal wrote:Something that I didn't pay much attention to at the time because I had never tried at bipap machine back then was this quote from the guy who started the topic:

FL andy wrote:The RT from my DME said by raising the higher setting from 13 to about 17, it would actually help make my exhalation easier than it would be at a constant cpap of 13.

And because I had a bit of trouble exhaling at a cpap of 13, the RT said a BiPap setting of 17/13 would actually be easier for me to exhale than a setting of 13/10. Supposedly, a higher inhalation setting would help the exhalation.

This point intrigues me, I have no idea if the RT is right or not, and I would really appreciate you comments especially on this on this.

I've found what Andy's RT said to be true...for me, anyway. I can use straight cpap at 9 and it feels like work to exhale against the 9 coming in. Not objectionable and I get used to it after a few minutes, but...a bit of effort nonetheless. A feeling of breathing out against at least some resistance.

However, with bipap delivering 11 or 12 coming in and 9 for exhaling, the exhalation feels like nothing at all. I've often said, it feels like breathing out into an empty hose. Right from the very first breaths....no having to "get used to it." I think Andy's RT was exactly right about "higher inhalation pressure would help exhalation." It's apparently the relative difference between EPAP/IPAP that gives the extreme comfort of breathing out with a bi-level machine.

The above comments by Rested Gal, FL andy, and FL andy's RT are extremely interesting IMHO. It almost sounds as if for at least some BiLevel patients, the IPAP/EPAP cycling itself may yield some sort of comfort-related entrainment related to physiology. Perhaps for some patients that comfort is yielded by the rhythmic machine-sourced pressure differential provided to the stretch receptors. I know some patients are said to yield better respiratory drive synchronization from even spontaneous mode BiLevel therapy (not simply timed or backup modes). Yet, my impression is that sleep science does not have a consensus opinion of why or even if this is really happening. I am fairly convinced it is happening in at least some cases.

A very interesting topic in my opinion. Thanks so much to Rested Gal for bringing this highly thought-provoking subject up!

Last nights tests were very interesting in that before going to bed, I played with the VPAP III for a while trying various settings.

I varied BPM from 5 to 7 & settled on 6. I varied risetime from 200ms to 350ms & settled on 350ms. I varied max insp from 3.00 to 2.00s & settled on 2.00s. Mostly these settings were to try to duplicate the PB330 which has the best range of Bilevel adjustments I have ever come across (the VPAPs come 2nd).

What this playing around reminded me was that a timed Bilevel is really a 'Ventilator' (assuming a min epap/ipap gap of 4). A bilevel in spont mode is a 'ventilatory assist device'. This is why I believe the manufactures call them what they do. PB call the PB320 (the PB320 I have doesn't have timed mode) 'ventilatory assist' and the PB330 a 'ventilator' and last night while testing, that is exactly what it felt like - of course I had an 7cms gap (8 to 15) so I sure did notice the flip to ipap when it happened. If that ipap was set higher I am sure I would have great difficulty trying not to breathe.

So based on that I was sure I would get a low AHI but as it turned out it was over 20 but this is half what I was getting when using a VPAP III in S mode as show in the earlier linked charts. That week of use resulted in constant 40-50 AHI. I am sure that if I ran last nights test again but switched to S mode, the AHI would double back up to the 40-50 range as before. What I am deducing from this 1st S/T test last night is that Timed mode does smother some of the problems from a low epap & big gap spread.

Tonight I will be raising epap to 10 + I will up ipap to 16 to keep a good gap spread. If the results show a very big drop from the 20 AHI of last night, then I am satisfied it proves that the epap is the critical component. If there is little change then the deduction is still open & needs the ipap to be lowered to see that impact of that change.

Also one other observation is that Resmed appear to have made some software changes to their VPAPs - I have one that has the word 'enhanced' written on it & I wondered what that meant - well it came with a chart for setting it up in clinical menu - it seems they added two more adjustments that allow setting the sensitivity of the ipap/epep & epap/ipap switching. The settings are lo - med - hi (sensitivity). The PB330 allows these settings to be adjusted in ms (such a great machine - would be the absolute best if they had just added recording nightly data to it).

DSM

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CPAPopedia Keywords Contained In This Post (Click For Definition): resmed, AHI

Well, the results are not exactly matching my predictions

(see the very bottom items in this menu - show last 2 nights)
http://www.internetage.com/cpapdata/

The 1st charts for the 11th Jan (Ipap=15 Epap=8) show a wild night with regard to minute ventilation with airflow all over the place. The desats are very noticable. The AHI was 21.7 (AI=3.6 (low) & HI=18.1 (high))

The next night I upped Ipap to 16 & set Epap to 10. I was expecting the AHI to drop but no it went up. AHI was 25.7 (AI=3.0 (low) & HI=22.7 (high)).
BUT, the minute ventilation is settling down compared to the night before & the desats don't seem as bad Funny thing is I felt great this morning.

This VPAP S/T is a very quiet machine - quieter than any other I have tried & quieter than my BP330.

More later

DSM

Part 2.

Tonight I will drop Ipap to 14 so that the config is as follows.

Ipap=14 Epap=10 Risetime=350 MaxInsp=3.00 MinInsp=0.5 BPM=6

Some things worth adding are that I felt I was awake a lot of the night & was aware the machine seemed to be 'ventilating' me by this I mean, I wasn't in control of my breathing but was very much being driven by the machine. But, my wife commented that I seemed to go into bouts of fast breathing - panting - and if you look at the 'Resiratory Rate' for last night it hit 39.4 breaths per minute - now that is panting. The night before the rate hit 32 BPM. Both these rates seem very high to me (unbelievably high in fact).

The PO data is the worst I have ever recorded for myself (same for both nights) but last time I did the tests that had produced AHIs of 40-50, I did not have the PO set up so I suspect those nights may have been worse.

The conclusion I have draw thus far is that epap=8 was a problem but it appears the 6 CMS Ipap-Epap gap last night is still a problem. And, I also continue to think that being in Timed Mode prevented the AHI from being double what it was.

Another interesting addition. When I got up, (sat morning here) I went for a walk/jog. On Sat I usually go for a 6.5km walk/jog (jog up the hills & walk down them). This morning it felt so easy and in fact I added another 2.5 kms so did approx 9kms & felt very fit.

So the high AHIs don't seem to be doing any noticable harm to my wakefulness. I guess it is because there were so few AIs vs lots of HIs.

DSM

3rd Night results (graph posted later)

AHI 12 (AI 0.2 HI 11. This is roughly half the previous AHIs & in terms of AI events is negligable.

So the gap between Epap & Ipap is shaping up as a prime culprit. In light ofthese results there are two more tests I plan to carryout. These include

1) Dropping Ipap from 14 to 13 (leave Epap at 10) so that the gap is back to the optimal one I had been using before with such good results.

2) Drop Epap to 8 and set Ipap to 12 - this should give some indication as to if Epap plays that big a role in the blow-out AHI numbers.

3) A last test will be to revert to Ipap 13, Epap 10 and to switch off Timed mode (no BPM). This brings me full circle back to the earlier VPAP III S tests.

The above gap problems now raise in my mind the issue with any machine that varies the Ipap/Epap gap automatically. The evidence I am seeing is the smaller the gap the better the results (but bearing in mind also is the smaller the gap the less the relief), the wider the gap the worse the AHI.

DSM

Conclusion:

My conclusion from the past few days tests is that a gap wider than 3-4 between Ipap & Epap on a BiLevel machine (certainly for me & I believe thus probably for many others), is a problem.

The wider the gap, the greater the AHI. Both AI & HI will increase.

The SpO2 stats from the 3rd & 4th nights were very normal (median of 95-96) with only one minor desat on night 3 & none on night 4 (when Ipap=13 & Epap=10).

I haven't tried the test yet where I lower Epap to 8 & set Ipap to 12 - I will wait until next w/e.

All in all an interesting set of experiments - I am happy I learned from them.

DSM

PS - one thing that did intrigue me is this issue of fast breathing or panting (see 32 & 39 breaths per min in night 1 & 2 on the charts). I have interpreted this as my own respiratory system adjusting to the ventilatory impact of timed mode - 'T' mode seemed to me (nights 1 & 2), to be over ventilating my breathing (forcing a hyperventilation effect) & my theory is that by panting at such high rates was my respiratory system asserting its own control in opposition to the extra ventilation coming from the machine.

Put another way, on nights 1 & 2 the machine appeared to me to be pushing more air through my resipratory system that it needed or wanted so its' response was to go into very fast breathing which was a way of overcoming the higher than required airflow from the machine.

The night 1 & 2 SpO2 charts are also loaded with desats. These need more analysis but appear to reflect confused breathing in the face of the 'heavy' Ipap to Epap pressure difference combined with the ventilitory nature of this S/T machine.

I can see why some doctors regard straight cpap as 'safe'

DSM