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CPAP vs Oximetry Device Time Discrepancy Test
#1
CPAP vs Oximetry Device Time Discrepancy Test
I have been noticing that I could never totally synchronize the times of my CPAP and the oximeter.   The following represents my best effort in trying to create an objective analysis.  I hope this may reduce any frustrations anyone else has been having with this.

Initial parameters:
For this analysis, I am using a Resmed AirCurve, a Wellue SleepU oximeter, and the Atomic Clock app for my Android phone. Immediately prior to testing, all devices were updated to the most current time using the clock app's time as the standard. The CPAP's time was set manually and the SleepU's time was set using the ViHealth app.  

Test:
To commence this test, the target time was the start of a minute, to the second. The first to be started was the CPAP, followed exactly one minute latter was the oximeter.   All times were recorded on paper because previous attempts were met with a vague memory.  When starting the SleepU, I recorded the atomic time and the time displayed on the SleepU's display, they both matched.  

Analysis:
After downloading all the data and importing it into OSCAR, the starting times were compared.   The CPAP start time was exactly as the logged time.  However, the start time of the SleepU was 1 minute latter than its logged initial time.  Also, its end time was 1 minute latter than the actual stop time.

I would be interested in the results from the CMS-50 E, F, or I, (the models with a built-in clock) would have with this test.

- Red
Crimson Nape
Apnea Board Moderator
www.ApneaBoard.com
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Useful Links -or- When All Else Fails:
The Guide to Understanding OSCAR
OSCAR Chart Organization
Attaching Images and Files on Apnea Board
Apnea Helpful Tips

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#2
RE: CPAP vs Oximetry Device Time Discrepancy Test
I intend to check this matter for my CMS-50I tonight. 

For analytical purposes I have long turned all my devices on and off during the final second before my record of the minute as shown by my old Blackberry's analog clock with a second hand. 

Along the line of what you are doing, I'd appreciate any tips regarding the following.

I finally gave up on anything but making adjustments for recent fast-slow determinations for VAuto, 50I and the X2 accelerometer which, for the past week and latter two devices, I began omitting as the results are just ho-hum. The Dreem 2 with RTC on UTC has always agreed with that Z10 phone time. I usually start simultaneously the Dreem 2's initial pre-sleep-onset start time with the VAuto Auto-on start. For the X2 at 16 Hz its RTC drifts so I have to do two imports of it into OSCAR, one to measure the time offset delta between sharp tips of peak out flow daggers of sigh exhalations, which the X2 senses sharply, and one after adjusting all times by formula--just one of the pains of sometimes being OCD. 

I once hoped to find a way to make good judgments of what  I thought were arousals as indicated by X2 and by the FR pattern up to the first burst of high amplitude  FRs. I got the Dreem 2 to help, but it clearly does a poor job of distinguishing WAKE in Light and REM sleep. I have lain awake for up to an hour after a late  bladder drain and had it all characterized as sleep in either stage.

I had some weird results for the CMS-50I when starting it for a time just to bench test the fast-slow. But now it seems to show good agreement with paced (rate adjusted) PR rise corresponding mostly to motion. But I doubt there is close agreement to the second. I start it at a known offset time and make the adjustment OSCAR affords.

Also, I have about a 6 second starting lag for the X2 vs the curve from the VAuto. 

I'd always wanted to pin down the lag of the CMS-50I response to large FL and to large arousal burst start and end marks. At the middle finger tip it seemed there was close to a 30 second lag behind the FR change that showed up later in many roughly corresponding  SpO2 drops and rises.
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#3
RE: CPAP vs Oximetry Device Time Discrepancy Test
My Dreamstation and CMS-50F looked pretty well matched, but when I reverted back to my System-One (with foam removed) I discovered that the CPAP machine's clock had drifted by 50 minutes!! I can't fix the clock in the CPAP but I can compensate for the drift in the CPAP preferences in OSCAR. I worked out the amount of drift by hitting the Ramp button at a known time then looked at the time where OSCAR graphed the step change in pressure.
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#4
RE: CPAP vs Oximetry Device Time Discrepancy Test
I have a thread where I describe how to get both the Contec and the ResMed blower to have the same internal clock down to a second or too. I wear the contec on my left wrist, and I always start both devices simultaneously by pushing the machine start with my left hand and pulse-ox button with my right hand.

When I go to load the data in the morning, the pulse-ox start time is always about 6-8 seconds behind the machine start time.

I'm thinking that the right process for my particular device is to push the pulse-ox button first, and then when it boots into the main screen THEN start the blower.

I'm going to try that tonight...
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#5
RE: CPAP vs Oximetry Device Time Discrepancy Test
It would seem that the oximeter recorded start time is not until it senses vital signals and not the physical start.
Crimson Nape
Apnea Board Moderator
www.ApneaBoard.com
___________________________________
Useful Links -or- When All Else Fails:
The Guide to Understanding OSCAR
OSCAR Chart Organization
Attaching Images and Files on Apnea Board
Apnea Helpful Tips

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#6
RE: CPAP vs Oximetry Device Time Discrepancy Test
Right -- but I have the probe on my finger when I push the button on the wrist part, so as soon as it finishes booting it starts recording. (Imagine my left arm: contec strapped to wrist above fitbit, probe on 4th finger, index finger poised on the button to start the cpap.) I think I need to start the contec device and then wait until the red light on the probe lights up to hit the power button on the cpap.
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