Rarely Getting Sleep Stages

[Bill_209]

I purchased my wife and I an Inspire 3 device in March of this year and despite all the device FW or App SW update induced issues that have been reported on this forum since then, I have almost always gotten Sleep Stages and all 5 Heart Metrics returned every morning, but my wife very rarely got them returned several months ago and then never got them since then.

We have tried everything suggested on this forum to resolve this issue but nothing worked and then we eventually confirmed that an Inspire 3 device that worked reliably for me to provide Sleep Stages and Heart Metrics did not work for her, no matter what we tried.

My wife's Inspire 3 device was reporting HR readings in the low 40s at times and a Doctor's evaluation determined that she has a heart arrhythmia as well, so changes to her blood pressure  medication were made to normalize the HR for the most part, but the arrhythmia was unaffected by the change.

My wife's HR is typically within the normal 60 - 100 bpm range now, but she still never gets Sleep Stages and BR/HRV Heart Metrics.  I was hoping that the new Google ML Heart rate measurement algorithm used in the 210.26 FW would resolve the issue but, unfortunately, it did not.  

I read that Google-Fitbit uses HRV measurements as one of the metrics to determine Sleep Stages, so can someone from Google-Fitbit tell me if having a heart arrhythmia makes it difficult to measure HRV, even though the HR curve is always continuous and normally within the 60 - 100 bpm range?

[JohnnyRow]

I don't remember if I have told you this, specifically, before, but, wearing a monitor for 2 weeks found I was having heart blocks at night, without any symptoms I was aware of, but the danger was that if I had there during waking hours, they could cause me to faint.
On the scale visible on Fitbit charts, my HR chart looked completely continuous to me but I very rarely got sleep stages or a score.  I assume this was because my heart blocks were so short, at most a second or 2, that they wouldn't show up on the scale I could show but frequent enough to upset sleep stages measurement.  Anyhow,  I got a pacemaker inserted, and started getting sleep stages and scores right away and have continued to do so.  Incidentally, my heart rate was dropping into the 40s overnight.  The pacemaker min was set at 60 and now it looks like I flatline at 60 overnight except when I get up for the toilet.  I don't know if the 40s before was realistic or included the blocks.

Bottom line: pacemaker got me sleep stages and scores right away with no change in Fitbit.

[LZeeW]

@Bill_209  All Fitbit algorithms are proprietary (secret), so you won't get an answer from Google.  They don't share.  My background id physiology, so I hope these two explanations will help.

First, Fitbits collect data on a beat to beat basis.  With we breathe, there is a subtle, periodic change in our heart rates when we inhale and exhale.  Our heart rate very slightly increases when we inhale and very slightly decreases when we exhale.  This happens over the few seconds it takes to inhale and exhale.  Yes, your heart rhythm needs to be predominantly normal to calculate breathing rate.

With respect to HRV, it's best to use ECG for precise measurement.  Fitbit does this with the optical heart rate monitor, the green LEDs.  This works best when someone is in a normal rhythm most of the time, but describing how it works is more complicated.

Your daily heart rate graph show an average heart rate over five minutes and can't capture the subtle changes in beat to beat data.  Premium users get a sleeping heart rate graph that shows data every minute.  Even that is too long to pick up the beat to beat data.  Fitbit heart rate data is very reliable at rest.  This is why certain data is collected while sleeping.  The release notes for the firmware update say that the new algorithm should help during exercise.  I don't if it changed heart rate at rest much.

So yes, a significant arrhythmia will keep you from getting BR, HRV, and sleep stages.

[Bill_209 · Accepted solution]

Thank you for your detailed response to my question, @JohnnyRow and @LZeeW.

My wife has premature ventricular contractions (PVCs), which is a spurious extra beat between regular heartbeats.  The Google-Fitbit heart rate algorithm is doing a good job filtering out those spurious extra heartbeats to measure her HR, but it is apparently not good enough to measure HRV under those same conditions, which is unfortunate.

That being said, it would have been great if Google-Fitbit simply documented that limitation instead of being secretive about it, because my wife has been wasting her time for the last 7 months trying all the things recommended by the Google-Fitbit CS team to resolve the issue of not getting sleep stages and heart metrics, when there was never any chance of that ever happening.

[JohnnyRow]

@Bill_209  Recently, since my pacemaker, a cardiac nurse mentioned in passing that she saw a few PVCs, that apparently are not interfering with my Fitbit sleep stage detection.  She just happened to mention them in passing as if they were barely worth mentioning.  I assume they had superseded my pacemaker and still remain.

[Bill_209]

Thanks for the additional information @JohnnyRow.

I went back and looked at my wife's 2-week heart monitor results and she actually has premature atrial contractions (PACs), not PVCs, with a 30% burden, but the spurious heart beat issue is basically the same as with PVCs, as I understand it.

Fitbit-Google has AFib detection, which is great, but I don't know if people having AFib arrhythmias get sleep stages or not.  It's too bad that Google-Fitbit doesn't have PAC and PVC arrhythmia detection as well, because that would have alerted my wife to this issue 7 months ago.  In any case, my wife is working with her primary care physician to see if she can get a consultation with a Cardiologist regarding the PAC issue, which is good.