• The CPAP diaries (snooze-date 1 month)

    It’s been several weeks since an update, but there’s not much to tell. I’m just killing it on the CPAP machine.

    This isn’t just bragging. It’s objectively true. You see, my machine comes with an app that gamifies use. I automatically get scored every night on hours of use, mask seal, apnea/hypopnea events per hour, and mask removals.* I routinely get 98-100 points out of 100. The last time I scored below that was in the first week of use, when I got a shameful 96.

    Killing it. (I also feel a lot better, which matters too.)

    So, that’s not interesting. What is interesting is how variable the apnea/hypopnea index (AHI) is. Some nights I have literally zero events. Others, I have a few per night (or, like 0.3 per hour), with little discernible rhyme or reason. I don’t vary my diet (much), drinking (zero alcohol), other medication, bedtime, etc. Yet, my AHI varies. (I should point out that an AHI well below 1 per hour is off-the-charts awesome. Recall that 5 per hour is the threshold for mild sleep apnea. I suspect a lot of people I know without sleep apnea have higher AHIs than I do on the machine.)

    It’s not just me. I’ve watched instructional videos of people demonstrating how to interpret CPAP data. They show their own data and their AHI varies by night too. I am sure this is fairly common.

    Here’s my theory for the variation: our pathetic human airways are always very close to obstruction. The high prevalence of snoring is an indication of this. (Snoring is on the spectrum of sleep apnea.) Other evidence: It takes very little pressure to keep the airway open. I’m at about 6 cmH2O, which is like 0.09 PSI. It’s almost nothing. Even “high” CPAP pressures of 16 cmH2O isn’t much. Just imagine being half a foot under water and that’s the pressure. It hardly seems noticeable.

    But it’s enough to push collapsing airways open. Same goes for mandibular advancement devices. They thrust the lower jaw out by a whopping half a centimeter or so, typically. That changes the airway topology ever so slightly, but it’s enough to keep it open a lot more.

    With tolerance so tight, probably very slight changes in sleeping position or inflammation or breathing rate or whatever can tip one from zero AHI to a few points of AHI. That would explain the observed variability.

    Why humans evolved to be so close to not being able to breathe at night is a good question. Got answers? Send them my way.

    * Minor gripe: The mask removal scoring frustrates me, because it considers removing the mask at the end of the night a “removal.” You’re allowed only one more removal (like, to go to the bathroom) before your score gets lowered. It’s not enough! Sometimes one has to scratch one’s nose, chase a kid back to bed, or open a window. There are plenty of reasons to remove a mask more than once in a night. I would either allow three removals before point deductions or, better, not count the end-of-night removal as a removal. I mean, it’s not like you can avoid that removal.

    @afrakt

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