Posted by Charlie Smith on May 05, 1998 at 20:54:17:

In Reply to: CO2 rebreathing with BiPAP masks posted by Barbara Metzler on May 04, 1998 at 19:18:46:

Barbara -
If you don't already, check out the alt.support.sleep-disorder newsgroup. Doug Ruth (a little fanatic, but does follow this subject with detail) has been recently describing exactly the problem you describe. According to him, it is a problem specific to all of the Respironics masks. Paraphrasing his remarks, Respironics is unable to locate the air exit holes in the mask close enough to the nose to prevent CO2 buildup, due to a patent restraint. Imagine breathing through a bag, but the only hole is at the far end. You can't clear the exhaled air from the middle of the bag and constantly rebreath your own CO2. Some new air mixes in, but not enough to prevent a higher concentration than normal of CO2. Respironics has redesigned the "swivel port" several times to address studies showing this effect, according to Doug, so that they can invalidate the studies saying they were performed with the "old" version. Nonetheless, without relocating the port closer to the nose, it makes no difference.

According to Doug, this is a significant problem. The solution is simple. Switch to a mask like the mirage or the nasal pillows which have the exhaust ports close to the nose.

Good Luck
Charlie

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