Posted by Sleepyhead on February 13, 2003 at 07:14:55:

Sleepy Coote and SGS,

I must say that was a very interesting discussion below. It raised several questions from me.

1. SGS, You measured you O2 levels during a very long breath holding period with minimal desaturation. Being a diver too I wondered if you hyperventilated before holding you breath as you would do when free diving. I’m not “throwing stones” at your experiment, just thinking about the variables. I know I would take at least 3 beep breaths with long exhalations to increase blood O2 and purge CO2 before a free dive to maximize the length of the dive.

I had desaturations my first sleep study in the 78% range with apneas lasting less than one minute. But my average saturation levels during the entire length of the study (without CPAP) were in the high 90% (normal) range. I do not believe we hyperventilate before onset of an apnea event. Your experiment makes me wonder about the extreme desaturation in such a short period of time.

2. Would it be true that an apnea event (obstructive or central) occurs after exhaling? Do they occur at all while breath holding during sleep?
3. During the pressures experienced during diving the SCUBA self-demand regulator matches (slightly above) the pressure of water on the body at depth. This also prevents over pressuring the lungs and causing an embolism. I know little about the HR reflex but it seems that during a dive the internal / external pressures are matched so, during a breath, the diaphragm can expand against the water ppressure and we can take a breath more or less normally. Maybe this prevents the HR reflex.

BTW, I do not experience the over pressure feeling at all with CPAP pressure fixed at 13cmH2O. Been on the hose since April 2002. I did seem to give me the pressure feeling at first but now it seems to be quite normal breathing on the inhale and exhale.

4. Is the pressure indication on a xPAP machine simply an indication from an internal pressure calibration curve developed by the manufacturer that adjusts the motor speed to the set point? Or is it an actual indication by a pressure sensor? It seems to me that it works on a curve because my machine pressure indication does not change when I block the hose. Maybe an indication of both should go on the CPAP wish list.

Follow Ups:

• Re: Optimum pressure caveats II SGS 11:55 2/13/03 (2)
  • Re: Optimum pressure caveats II - Sleepy Coote 19:43 2/13/03 (0)
  • Re: Optimum pressure caveats II Sleepyhead 15:47 2/13/03 (0)

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