Oximeter Accuracy: Wellue vs. VirtuOx

[SunMesa]

I recently had occasion to do a side-by-side comparison of two pulse oximiters, specifically my Wellue O2Ring and a VirtuOx VPOD Ultra (the latter supplied by a local medical oxygen vendor).

The VirtuOx unit is a wristwatch-like affair with cabling to a fingertip clip-on oximiter, whereas the Wellue unit is worn like a ring. I had both on my left hand (I am right-handed), with the VirtuOx clipped to the end of my middle finger, and the Wellue on the index finger, slid down to the base of the finger.

I was able to get detailed data from both, and have attached a plot comparing their data output.The Wellue data (in red) is superimposed on the VirtuOx plot and data (in blue).

   

I was surprised at how different they were. Note that both are variously described as FDA 'listed', 'recognized', 'approved' (although to my knowledge neither claims to be a medical-grade device for use in clinical environments). Both also claim to be accurate to within 2% within the range of 70% to 100% SpO2. But the plot suggests that one (or both) of them is not, since at times they differ by as much as 7% SpO2.

They often track roughly together, but the Wellue tends to read lower overall, dropping and staying at lower SpO2 values (sometimes alarming ones), during which time the VirtuOx remains fairly steady (e.g., see ~4:15 AM). There is no point I can find where the Wellue reading exceeds that of the VirtuOx.

Can anyone here comment on which unit is considered more accurate? In this example it arguably makes the difference between an acceptable nighttime SpO2 report (at least at ~6000 ft elevation) and one that is alarmingly low. I frankly prefer the Wellue for comfort, convenience, and ease of data retrieval, but accuracy is a higher priority. Thanks for any feedback-

[Crimson Nape]

The O2 Ring has a stated accuracy of +/- 2% of the reading. What is the VirtuOx's accuracy? According to the NIH's document titled, "Comparison of SpO2 values from different fingers of the hands", you picked the 2 lowest ranked fingers. Here is the link if you're interested.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4627972/
- Red

[SunMesa]

@Crimson Nape,

Thanks for your reply and the excellent link.

While the results of the Basaranoglu et al study do suggest that the left index and middle fingers (on a right-handed person) produce slightly lower SpO2 values than the other fingers, it's by a very small amount (deviating from the mean of all fingers by less than 0.5%). They actually found no statistical difference between the readings on those two fingers, and the differences between any of the fingers was vastly less than the discrepancies appearing in the Wellue vs. VirtuOx plot, so that mystery remains. Nevertheless, it's good to know the best finger(s) to use, thanks again for the link.

VirtuOx makes the same claim as Wellue, accurate to 2% in the 70-100% SpO2 range. I gather that direct links to commercial sights are discouraged here, but you can replace the vertical slashes with forward slashes in the following to see their accuracy claims:

https://virtuox.net/DynDocs/Documents/VP...sFlyer.pdf
and
[DME Link Removed] See Supplier #40 - O2 Ring

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