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Relationship between leaks and pressure?
#1
Because I am a very active sleeper I have struggled for a long time with unacceptable leak rates. Several months ago I started using a chin strap on top of the mask to help hold it in position.

I went through three different chin straps, the most recent being a custom make concoction. I am happy to say that this chin strap is finally doing the job. Here are data from the first five nights with it (the columns are average pressure, 95% pressure, maximum pressure, 95% leak rate, and maximum leak rate):

Mon 15.42 17.42 18.26 12.00 15.60
Tue 14.96 17.46 19.00 8.40 24.00
Wed 15.92 17.95 18.76 3.60 6.00
Thur 15.24 17.76 18.58 3.60 12.00
Fri 16.90 19.00 19.00 3.60 4.80

When looking at these data I am struck with how high my pressures have been since starting to use this chin strap. My machine is set for 14 to 19 cm. H2O and I have seen it get close to 19 once or twice in the past, but never hit it. It appears that I should probably increase the maximum all the way to 20.

Here are data for a week with the SP-CHADJ chin strap, which gave me pretty bad leak rates:

Mon 14.04 14.40 14.56 21.60 27.60
Tue 14.40 15.12 15.72 19.20 31.20
Wed 14.08 14.66 14.88 18.00 22.80
Thur 14.16 14.50 14.66 36.00 45.60
Fri 14.08 14.82 15.16 44.60 48.00

Note how my machine did not produce pressures nearly as high when the leak rates were higher. I looked at my daily data for the past couple of months and there is a loose but steady correlation between the leak rates and the pressures - the lower the leak rate the higher the pressure the machine will put out.

I find this very interesting.
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#2
It would be interesting to see if those are machine or mask pressures. Granted machine and mask pressures are related (in an ideal case, they should be equal, but there are losses pushing the air through the hose and with the venting at the mask). Regardless, though, it would make sense....bigger leaks mean more air escaping and a lower mask pressure...the air is escaping rather than being contained and generating pressure.
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