Any cpap machines better for RDI with low AHI ?

[feeling_better]

Hi, I have been away for some time. I was busy with a number of projects...I have a question; but may get a chance to read/respond this forum only sporadically at best for the next 3 weeks or so, since we are on vacation, and about to go on a long cruise from Seattle to Florida. but I thought I would start the thread

A couple of weeks ago I had a follow up overnight study, this time with just exactly my machine/mask everything, except they can add monitoring. I wont see the doc until I get back, but I did get a call from the doc before she went on vacation on Sunday! The AHI was almost nil (as I have been seeing) but I had high RDI -- cant recall the number -- and I am going in for another sleep study. The doc wants to try(?) a BiLevel or some other types --- currently using M1 auto in 5.5cm fixed node to get the very low <3 AHI.

So my question: Are machines like BiLev known to be better for this high RDI, already low AHI condition? Or this just going to be trial and see method? Sorry, I dont have net connection long enough to do any research until we get back...

[ozij]

I assume the point of a Bi-Level is the attempt to give you enough inhale pressure to avoid RD's cause by mild obstuctions, and yet lower exhale pressure to avoid central apneas. And if you need low rather low inhale pressure (and even lower exhale), you will need a Bi-level, since simple exhale relief may not kick in, when your inhale pressure is very low.

Do whatever you can to get a trial machine before you buy. Rent if necessary. Response to different algorithms can be very different -- more so I believe when the problem is more complicated.

O.

[-SWS]

Are machines like BiLev known to be better for this high RDI, already low AHI condition? Or this just going to be trial and see method?

The short answer: trial-and-see, for the reasons ozij nicely summarized above.

Now for a looooong technical excursion:

Are machines like BiLev known to be better for this high RDI, already low AHI condition? Or this just going to be trial and see method?

I don't think sleep science has empirically examined whether BiLevel tends to yield better results across the SDB patient population presenting with a high-RDI/low-AHI ratio. However, a comparatively high-RDI/low-AHI combination hints at possible UARS. Barry Krakow MD has some interesting posts on this message board in which he discusses experimentally treating UARS with BiLevel (see both links).

I found Dr. Krakow's experimental work in treating UARS with BiLevel to be interesting and potentially promising. If I understand Dr. Krakow's treatment premise correctly, the essence of his titration protocol is to gradually increase IPAP until there are absolutely no signs of Flow Limitation (FL) or wave flattening on the inspiratory half of the sinusoidal flow curve. However, achieving that perfectly rounded inspiratory patient flow curve can quite often entail a higher IPAP value than most labs titrate.

Additionally, Dr. Krakow's BiLevel titration protocol pays very close attention to the expiratory flow curve---that bottom half of the patient flow trace. Dr. Krakow tries to attain a perfectly rounded expiratory flow curve by maintaining a sufficiently low EPAP value. Thus Dr. Krakow's BiLevel titration protocol strives to not only eliminate all wave shape traces of flow limitation on the upper half of the flow trace---but his titration protocol also strives to normalize or round the expiratory or lower half of the patient's flow trace. In essence, Dr. Krakow's titration protocol strives to achieve a perfectly rounded sinusoidal flow curve throughout both respiratory phases.

So in summary, Dr. Krakow's experimental BiLevel titration protocol attempts to achieve a perfectly rounded sinusoidal wave trace, by raising IPAP high enough and dropping EPAP low enough. The difference between IPAP and EPAP is also termed Pressure Support (or PS). And the end result is that Dr. Krakow's experimental BiLevel titration protocol seems to rely on much higher PS values, than conventionally employed, toward eliminating all traces of FL during inspiration and all traces of expiratory resistance.

What's so interesting about Dr. Krakow's method of achieving that perfect sinusoid during both top and bottom halves of that respiratory flow trace? Any perfect sinusoid contains a single energy-related frequency harmonic. The most energy-efficient neuromuscular kinetic transfer that Mother Nature has to offer would be those perfectly sinusoidal breathing patterns or oscillations. So when Dr. Krakow chases both IPAP and EPAP to achieve his perfect sinusoidal flow trace (top and bottom) he is pursuing the smoothest and most energy-efficient use of respiratory muscles. He is thus methodically minimizing the neuromuscular effort or energy the patient must exert in order to breathe during sleep.

And excessive RDI that is unaccompanied by apnea/hypopnea is believed by some researchers to be all about patients having to make excessive neuromuscular respiratory effort---such that the patient's sleep is disturbed by that excessive required neuromuscular effort. At least in theory, Dr. Krakow's unusually high BiLevel PS mechanically offloads much of that breathing-related neuromuscular effort---thereby eliminating those RDI sleep disturbances formerly associated with that excessive neuromuscular respiratory effort.

Possible Caveats: I kind of suspect such high IPAP and PS values may prove more suitable for addressing high fixed upper airway resistance problems rather than efficiently addressing highly variable resistance problems. If an etiology hypothetically entails variable resistance, Dr. Krakow's unusually high IPAP and PS may theoretically become excessive and possibly counterproductive during recurrent low-resistance moments or periods during sleep. I suspect those recurring moments of excessive relative pressure may, in turn, yield higher side-effect rates such as aerophagia and/or erratic chemoreceptor/stretch issues across the SDB patient population. In other words, I suspect Dr. Krakow's experimental BiLevel treatment protocol may very nicely solve breathing problems for some patients, while creating a unique set of pressure-related treatment side-effects for yet other patients. I could be very wrong about that.

Interesting and promising work by Dr. Krakow IMHO.

the next 3 weeks or so, since we are on vacation, and about to go on a long cruise from Seattle to Florida.

Your vacation sounds nice! Let us know how your cruise went when you get back.