OxiMeter Latency

I am trying to sync my CMS50D+ data, which is recorded using the same computers clock I used to (manually) calculate the time offset of my system one (which is 3m23s fast)

There is some very neat correlation going on between the flow, spo2 & pulse waveforms graphs. Some instances are very subtle, others are cool to look at, but the oximeter has some latency due to it's internal algorithms, and I don't know how to set a time offset to counter this, because I don't fully understand whats going on physically.

When you have an apnea, at what point (during, after, etc) does your heart rate start to climb? During the heavy breathing afterwards?

At what point does your SpO2 supposed to start dropping? when your heartbeats gone up and oxygen is running out in bloodstream?

If I can get a clearer picture of the stages these things (generally) happen, I can analyze the graphs to calculate the algorithmic latency factor of the oximeter, which will be the same for everybody at least with the same model/group.

Wahoo. I think I figured out pictures.

I just noticed my CA/H/CSR events have gone down. Currently set on APAP 4.5-8.5. I also started using a 25 minute ramp instead of a 5 minute one.
Rejoicements! I still feel like crap though.

The doc had me start taking this Circadin 2mg stuff about a week ago, and I stopped using Temazepam or antihistamines.

Now I wake up every 2 stinking hours.. but the stats at least look better.

I can't answer your questions, JediMark. However, your handiwork is impressive. Congratulations and continued success!!

cpaptalk won't let me log in.

I can't answer specifically, but some of the pulse oxs that I have seen display a running average of the values from 8 to 16 measurements (heartbeats). Maybe your owners manual might tell you the specifics of your model.

Mike

Thanks Slinky!

Hmmm... thanks for that info Mike, makes a lot of sense.

The only time mentioned in the Engrish manual is how long it takes to ascertain the pulse rate. (5 seconds)

Which does give a clue into how is works. it implies up to 5 seconds of pulse data is needed to generate the average. So I'm betting on an average of 8 pulses.

The -5 offset figure alone will probably be enough accuracy for this anyway. It may be only one heartbeat if the dsp algorithm does a running average in a ring buffer.

Those screenshots are set at -20s offset on the Spo2/pulse

Whatever the case, the body takes longer than I thought to respond to apnea events with changes in oxigenation levels and pulse.

The pulse graph leads the SpO2 graph by the amount of time it takes the blood to travel from your heart to your fingertip. In general, that takes somewhere around 15 seconds, plus or minus a little depending upon the length of your arms.

To synchronize the pulse graph, you would need to listen to your heart with a stethoscope and see if there is any offset between the beat on the oximeter and what you are hearing.

You might be able to approximate the number of beats that your spo2 value lags behind, by observing the display and sticking your finger in and out of the sensor. See how long it takes to show a number after putting in your finger, or drop to 0 (on removing finger).

HoseCrusher, I was basically trying to figure a common ground to account for the oximeter hardware latency. I was hoping on the user being clever enough to do that other bit... however what you have told me is very useful to know.

If an average figure worked well enough for 99% people, then it perhaps might be a good idea. I only really need to get within 2 or 3 seconds anyway.

Stuff doing those measurements manually.. you'd have to compare the echo volumes and pulse variations for each beat.. Need some form of neck pulse signal/doppler/etc.. on about 10,000 people to get a good average.

I'll see what applying an offset does to the SPO2 graph using your guestimate..

Miketech...Hmmm. My CMS50D+ unfortunately shows both the first spo2 & pulse in the same raw data record after around 5 seconds of turning on. Both come on the screen at the same time. It drops the signal and clears the screen instantly when I pull out my finger.