I have pasted the following report on a recent study on the differences in Auto Adjusting machines.
Once again it highlights the differences in the algorithims used, something I have always suspected. After all any machine will only do what it is instructed to do and as the cpap manufacturers are still undecided on which route to go either individually or as a group it is the poor OSA sufferer who must put up with the problems.

I am aware that many of the 'old school' of sleep specialists are not in favour of prescribing these machines despite the ongoing sales pressure from the cpap companies.

Only last Friday I called to my DME supplier for some pads for the forehead and on making general enquiries was told that 'a lot of our older customers/patients were still on the standard machines (as distinct from the auto paps), but that they hoped to switch them over gradually'. Here's one who won't be switching until such time as they come up with a standard algorithim.

I'd love to hear some comments, particularly from those of you who use these machines.

Daniel.




CPAP devices for sleep apnea ‘both have limitations’
Aug 03, 2005 - Results from a study comparing two different devices for automatic continuous positive airway pressure (auto-CPAP) to treat obstructive sleep apnea syndrome (OSAS) show that both have clinical limitations, and further research into this area is needed.

“Auto-CPAP machines differ mainly in algorithms used for respiratory event detection and pressure control,� explain Hai-Bo Shi (Kyushu University, Fukuoka) and colleagues.

“The auto-CPAP machines operated by novel algorithms are expected to have better performance than the earlier ones in the treatment of OSAS.�

For their study, the researchers compared the therapeutic characteristics of two different auto-CPAP devices – the third generation flow-based (f-APAP) and the second-generation vibration-based (v-APAP) – during an initial night of treatment for OSAS.

They retrospectively reviewed the records of 43 OSAS patients who underwent overnight polysomnography diagnosis to confirm the disease followed by auto-CPAP treatment with either the f-APAP or v-APAP device under a second polysomnography evaluation.

The results, published in the journal Auris Nasus Larynx, showed that 13.6% of patients retained a residual apnea/hypopnea index of more than 5 during f-APAP therapy, compared with 61.9% of those who underwent v-APAP.

Furthermore, the researchers found that the f-APAP was more effective than the v-APAP at reducing the patients’ apnea/hypopnea index, hypopnea index, and apnea index, as well as at improving the lowest oxygen saturation index and shortening stage 1 sleep.

In contrast, however, the v-APAP was more effective at reducing the patients’ arousal/awakening index.

“In conclusion, flow-based auto-CPAP works better than vibration-based one in abolishing nocturnal respiratory events and improving the lowest SaO2. However, the latter is more effective than the former in reducing sleep fragmentation,� summarize Shi et al.

“Therefore, even in devices that generally work well, they still have some principal limitations. “

They add that “further studies are needed, importantly, to evaluate the efficacy of long-term use of auto-CPAP therapy for OSAS.�

Auris Nasus Larynx 2005; 32: 237–241
Journal

My understanding of how any machine works is extremely limited.  How radio or a simple Brownie box camera works are beyond me!  

I'd be interested in knowing what pressure range was used with autopaps in the study.  Perhaps wide open at 4 - 20 cm H2O?  Assuming that was the case, I'd say this:   Just because an autopap is capable of using a 4 - 20 range, doesn't mean that's the best way to use one.  Sleep disruptions that might occur running a wide open range might disappear if the range were tightened up considerably.   It would also be interesting to see exactly which brand of the more modern flow-based machines the researchers used.  One brand? Or more than one brand of modern machines?

From what I've read, and from my own experience using 4 autopaps (PB 420E, ResMed AutoSet Spirit, and two Respironics REMstar Autos - one before they added C-Flex to their auto, one with C-Flex; and with the software for each machine) I believe many people get their best results on autopap if the lower pressure is set up fairly close to their titrated pressure.

Example, if a person's titrated pressure from a sleep study is 10,  they might do well to set their autopap's range at 8 or 9 for the low, and "whatever" (perhaps 14) for the upper pressure.

In that case, what would be the use of having an autopap if one is going to set the lower pressure almost on the prescribed "single" pressure?   I think doing it that way could give a smoother treatment for some.  Smoother, yet still getting benefit from using a lower pressure much of the night.   All bets are off, of course, if a person truly needs their full titrated pressure almost all the time all night.    

To my way of thinking, if a person gets good treatment most of the night by using even a one or two cm reduction in pressure from the "worst case scenario" single pressure prescribed from a PSG sleep study, the one or two cm's less could make a difference - perhaps less mask leaks, perhaps less chance of aerophagia, perhaps less chance of difficulty breathing against pressure.  Sometimes one cm makes all the difference in any of those situations.

Also, setting the lower pressure to fairly close to "prescribed" pressure would not negate the other (perhaps even more important)  benefit of using an autopap, as far as I'm concerned.  The benefit of having an upper ceiling set three or four points above what the machine normally has to use for me during most nights.   Having that extra unused margin up there gives me the reassurance that the pressures the machine is using are getting the job done.  Also gives some space up there for the possibility of a need for more pressure if there are changing circumstances in the future that would suggest a single prescribed pressure might not be right.  No wondering, "Is this pressure still right for me?",  or having to go back to the sleep lab for a new titration simply to find out that a single pressure needs to be raised a notch or two.

I agree Daniel, that with each manufacturer using their own algorithms, there can be differences in whether one autopap or another works best for each individual.  That can be looked at as a negative (and sometimes expensive experimentation) - "Which autopap should I get?"   Or as a positive... if one maker's autopap doesn't suit, another's might.

Personally, I get more comfortable treatment and better sleep using any of the autopaps I've tried than by with any single fixed pressures I've tried.   The only machines that have done as well regarding comfortable sleep have been two bi-level machines I've tried.  My equally good experience with the bi-levels probably had a lot to do with having many months of data to look at from the autopaps I've used...to determine how I wanted to set the bi-level IPAP and EPAP.  

Regarding autopaps (the modern flow-based autopaps...not the vibration based ones which were compared with modern machines in the study) the bottom line for me regarding the value of getting an autopap vs a straight cpap:

The autopap can always be set to use in straight single pressure "cpap" mode.  Can use it either way.   With a straight cpap machine, that's all you have.   Of course, what matters is what gives good treatment.

I'd like to see a study someday comparing results using a narrow range of pressure with autopap - specifically, comparing "wide open" vs setting the lower pressure no more than a couple of points below a PSG "titrated" pressure and upper pressure no more than 3 points above the titrated pressure.   I think that could be more useful than studies comparing flow-based vs vibration-based autopaps.

Thanks for posting information from that study, Daniel!  Non-techie though I am, I do find studies, as well as opinions, about all these machines very interesting.

I've only used the Auto-Set Spirit and had not much luck.  My settings were 7-20.  My previous cpap was set to 12.  I now use a VPAP III and I have an inspiration of 11 and an expiration of 7.  This seems to be working fine.  We are still fine-tuning the time for inspiration and expiration, however, I am sleeping all night now.

Just my experience...


_________________
Joe Camel

OSA Feb '04
S-7 EliteCPAP Feb '04
AutoSet Spirit July '04
VPAPIII August '05 (CHF & MCTD)
Heated Humification
Mirage Activa Nasal Mask(previous Mirage Ultra Nasal Mask, Breese Nasal Pillows, Breese Nasal Mask)

Which APAPs are considered flow-based and which are vibration-based?