AHI correlated to length of therapy?

[RiverDave]

I was running my end of year data review and noticed a strong correlation (I'm a nerd, so I ran statistics on it) between the number of hours of therapy and my AHI. It is a positive correlation (the longer I slept the higher my AHI, on average).

Has anyone else noticed this? Any explanations? I turn the machine on right before falling asleep (there may be 10 minutes of wakefulness between lights out and sleep) and I turn it off within about 30 seconds of waking up, so I don't think there are any false events included. My leak rate is good (average 95%tile leak rate is < 5 l/m above the mask's intentional rate).

Just curious.

[ozij]

One possible modrator may be depth of sleep. A short night, correlated to light sleep may cause lower AHI.

O.

[Wulfman]

I was running my end of year data review and noticed a strong correlation (I'm a nerd, so I ran statistics on it) between the number of hours of therapy and my AHI. It is a positive correlation (the longer I slept the higher my AHI, on average).

Has anyone else noticed this? Any explanations? I turn the machine on right before falling asleep (there may be 10 minutes of wakefulness between lights out and sleep) and I turn it off within about 30 seconds of waking up, so I don't think there are any false events included. My leak rate is good (average 95%tile leak rate is < 5 l/m above the mask's intentional rate).

Just curious.

I had noticed similar correlations the first year or so of my therapy. According to what I've read here, we spend more time in REM sleep as the night goes on......about every 90 min. or so we cycle through our sleep stages.

It used to really frustrate me that after about six hours of sleep, after I'd gotten up and went to the bathroom and then went back to sleep (for a few more hours), I'd have many, many more events in those subsequent (fewer) hours than in the more hours previously.

That situation has pretty much gone away in the last couple of years.

Den

[RiverDave]

Ozij and Den,

Thanks for the explanations. Both sound good to me.

[Cajunman]

Wulfman, I've noticed the same thing. My pressures are very high ... 24 IPAP ... and I suspect some of my readings of events are caused by ... well, self inflicted. I think that when I even change my breath rate, or cough into my full face mask, I set off the machine to record an AHI. I don't know .. I'm a newbie .. but my numbers AHI are going down as I notice that I'm getting used to not panicking in the mask and gasping and such. I think my machine is picking up a large number of false events while I was getting used to XPAP.

[ozij]

Wulfman, I've noticed the same thing. My pressures are very high ... 24 IPAP ... and I suspect some of my readings of events are caused by ... well, self inflicted. I think that when I even change my breath rate, or cough into my full face mask, I set off the machine to record an AHI. I don't know .. I'm a newbie .. but my numbers AHI are going down as I notice that I'm getting used to not panicking in the mask and gasping and such. I think my machine is picking up a large number of false events while I was getting used to XPAP.

Somewhat off RiverDave's question:
My first weeks on cpap included many sleepless toss and turn sessions in which apneas, especially "open airway" apneas were recorded by my PB 420E APAP. They were skewing my data. Since the PB can export session data to a csv file, I created a fomula that excluded all session that were less that X minutes long. X being 90 minutes when I started therapy - I really did have sleepless sessions that long. When I finally started sleeping normally, I lowered X to 60 minutes. For me, anything less than 60 minutes long is either a nap, or a bout of insomnia.

O.