Any ideas on what's going on

Good point. Will do.

I'm a little late to the party, but here are my thoughts/observations.

I think what we're seeing here are cardiac artifacts. As mentioned above, cardiac artifacts result from pressure waves produced as the heart beats.
These are relatively normal, but not usually seen as pronounced as in Dave's chart. Typically, since a normal heart beat is around 60 BPM or 1 every second and typical respiration is around 15 or so with an inspiration time of 1.5 seconds and an expiration time of 2.5 seconds, we might see 1 beat during inspiration and 2 during exhalation.

In the example posted above by PR, the Respiration Rate can be determined by measuring the length of one complete cycle of the Flow Rate. By eyeball, the period of each appears to be about 5 seconds which corresponds to a rate of about 12 breaths per minute. At the same time, we can count about 6 beats in 5 seconds for a heart rate of about 72. Both would seem to be normal.

We measured the Respiration Rate and got 12, but SleepyHead is reporting a much higher rate at times, because, I believe, it is falsely counting the cardiac artifacts as breaths. In the above discussion, there was some talk of filters to rid the results of these artifacts and I think that might be the case with certain machines, but not necessarily for non-ventilator types of machines. I think it is worth mentioning that ResScan does not report Respiration Rate, or inspiration and expiration times for non-ventilators, i.e, S9 and S9 auto and Airsense 10 and Airsense 10 auto, but SleepyHead does, and I believe, often in error when cardiac artifacts are present.

Finally, why are Dave's so pronounced? I don't know, but I do think as mentioned earlier, position might have an effect. Also whether or not the subject is mouth breathing or not, with the effect seemingly more prevalent with mouth breathing. Further, if we look at the example posted by PR, it can be seen that during the time the artifacts are pronounced, Dave's breathing is relatively shallow with breaths only about 1/2 the amplitude of when the artifacts are not being seen. So maybe it's not the artifacts that are pronounced, but the breathing that is diminished.

Bottom line: I'm guessing Dave's abnormal looking results are normal, brought about by stomach sleeping and mouth breathing. The operative word here is guessing.

Jay,

Thanks for the observations and opinions. I've been playing around and have noted the following:

1) PAP mode doesn't make any difference. Tried APAP at 14-17, CPAP at 14, CPAP at 16 - no difference I can see or feel.
2) breathing rate is 12 - 14 since I've been paying attention
3) without rope and a vice, I can't seem to alter my sleep position
4) you are correct on the heart rate. I have a pacemaker and believe it is set to a minimum of 72 bpm.

Thanks again

For those interested, I finally had my appt with the cardiologist today. I asked him how his thoracic physics was, and he said "moderate".
He gave a great explanation of how he thought the saw tooth pattern is created - the heart twists when it beats causing it to make contact with various structures in the area (lungs, pericardial sac, blood vessels, etc.). Since everybody is a little unique as to the size and even orientation of these structures, it did not surprise him. He did confirm sleep posture would play a role, along with the strength of the heartbeat. He was kind of surprised when I told him about this being seen in only about 12% of the population. He said that if you could "turn up the gain" on the pressure sensor, everybody would show the pressure wave artifact.

As far as what it means, he didn't know and it's nothing he's seen or heard of in a disease or pathology.

Take home message: I'm more concerned about my head spontaneously falling off than this artifact.

I have an appointment with my general cardiologist on 8/3. If he has anything to add, I will report back.

RiverDave

Thanks for the update...

It's the flow sensor that's picking it up... I know that doesn't really matter, but you know how I like to be accurate

As always, you are correct. Dr was emphasizing pressure changes vs flow rate. I honed in on pressure in his response. You tha man
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