Paper published by Swiss researchers about respiratory rate estimation during running using the Polar H10 heart rate monitoring system
You can use the Polar H10 when an accuracy of more than 5.5% is not required:
https://mdpi-res.com/d_attachment/sensors/sensors-21-05651/article_deploy/sensors-21-05651-v2.pdf
You don t have to read all the papers of Peter H. Charlton and his PhD thesis, if you are interested in Respiratory Rate Estimation, maybe it is sufficient to read this paper, or this paper is at least a good starting point.
21.3.22 15:26
There is currently no consumer grade respiratory monitor which for me personally is satisfying:
The above paper demonstrates, that Respiratory Rate Estimation from Polar H10 has an inaccuracy of about 5 percent, which is acceptable for many applications. A Polar H10 is more comfortable to wear than an ECG device. Unfortunately, there is no product available which uses the Polar H10 as a (real-time) Respiration Monitor. It would be highly desirable that Garmin updates their watches with more accurate respiration algorithms:
This will take time. There is a Polar SDK available. A real-time respiratory rate app using the Polar H10 as an application of the above paper would be highly desirable.