Fisher & Paykel algorithm woes

[wallsocket]

My Fisher & Paykel SleepStyle HC254 AUTO CPAP has an algorithm for adjusting air pressure that isn't working for me because it falsely detects apneas/hypopneas (or their precursors). When I sleep on my back, I have horrible numbers (AHI anywhere from 20 to 40 according to my machine) and I wake up a lot in the middle of the night with the machine at maximum air pressure. Not only that, but the pressure won't drop within a reasonable period of time once I'm wide-awake and breathing normally. It's a shame that I have less daytime sleepiness when I don't use CPAP at all!

Has anyone ever solved their problem with an overly-aggressive auto-CPAP? I don't have a solution, but I do have some observations that I wanted to share with the community:

Tilting the head down (even very slightly) from a neutral position causes a flow limitation that these machines can detect. I believe that a good algorithm should ignore it, but my machine responds to it by increasing the pressure. I believe this is the cause of many (though not all) of my machine's inappropriate responses, based on experiments I've done using the machine while laying down awake and obviously breathing normally. The problem is compounded by the fact that when using a full-face mask, the headgear tends to tilt the head down because of the strap that goes from the bottom of the mask, underneath the ears, and around the back of the neck (in most designs there is a network of straps that connect behind the head; it is the part that touches the neck that is problematic). When I tighten my mask enough to prevent leaks (I don't believe my mask is overly tightened) my head tilts down sightly, and I'm sure it tilts even further once I'm asleep and my muscle tone decreases.

About full-face mask headgear: every design I've seen works the same way, with the strap on the neck. The problem could be avoided with a completely different headgear design that involves straps going from the bottom of the mask *over* the ear, or *above* the ear, not touching the back of the neck at all. I experimented with such a design using shoelaces and found that it worked for lower pressure settings, but for the higher pressures it couldn't prevent leaks from occurring on the lower part of the mask, which wasn't being pulled straight into the face hard enough. That's probably why the mask designers don't use the design. (It might be worth offering for people whose apnea can be treated at very low pressure settings.)

Because of a completely different headgear design, using a nasal mask avoids this problem. (I can't use a nasal interface however because of mouth breathing.)

Sleeping on my side substantially avoids this problem because there are other mechanical forces that prevent my head from tilting down when I relax.

[When mask type makes a big difference]

Generally, for a given air pressure, different mask types (full-face, nasal, etc.) are considered to be equally effective at preventing breathing events. That is why doctors are not concerned about what mask type a patient selects after a titration study; a prescription for CPAP is written and the patient selects a mask from a vendor.

I wrote this six months ago:

My Fisher & Paykel SleepStyle HC254 AUTO CPAP has an algorithm for adjusting air pressure that isn't working for me because it falsely detects apneas/hypopneas (or their precursors).

I wrote that because when using a full-face mask, my machine reports long strings of breathing events (they blur together in my PeformanceMaximizer charts) yet when I use a nasal mask these strings are rare and shorter. Six months back I had hypothesized that with the full-face mask, my headgear was causing my head to tilt down, slightly reducing my airway cross section, resulting in false detections. I'm here to retract part of my statement: I can no longer say with any confidence that the Fisher & Paykel algorithm is falsely detecting breathing events. What I can say is that there is something about my physiology that causes my breathing to be much different when using a full-face versus nasal mask. It's impossible to say whether the breathing events with the full-face are real or false detections. A few ideas:

1) The breathing events are real, and there is something about my physiology and mode of airway collapse that makes collapse more likely while mouth breathing. A full-face mask lets me mouth breath, ergo I have more breathing events with a full-face.
2) The breathing events are false but there is something about my pattern of breathing (when mouth-breathing) which fools the machine.

Breathing through a semi-congested nose (as mine always is) increases inhalation and exhalation time so that breathing is more continuous, with little or no pause in between breaths. In contrast, mouth breathing allows one to get air in and out faster, with pauses in between breaths. In these two situations the airway physics is different, and I can see either hypothesis above being true. Unfortunately, I'll never be able to resolve the question myself.

By the way, I had ruled out my head-tilt hypothesis by using my full-face mask with my mouth taped shut. The long strings of breathing events went away.

It's interesting that in my case, mask type makes a huge difference in what the machine is reporting despite conventional wisdom saying it shouldn't matter. Has anyone else noticed this, and also, is anyone aware of research showing that different mask types at the same air pressure should *not* be considered equivalent?

[DoriC]

You say nothing about your pressure setting? Did you have a sleep study? What was your titration? What type of bed pillow do you use? How many masks have you tried? More info would be helpful. Keep us posted.

[Stormynights]

I don't have any problems with my machine. I wish it had EPR but other than that I have no complaints.