1. Read out sensor data from Bluetooth respiratory sensor to PC:

https://www.eevblog.com/forum/testgear/read-out-sensor-data-from-sleep-tracker-with-bluetooth-sniffer-tools/msg3471796/#msg3471796

2. Vernier Go Direct Respiration Belt:

Vernier Go Direct Respiration Belt measures respiratory rate. Raw data are available from the software. It is also possible to get data from the Vernier Go Direct Respiration Belt via Python.

Personal, communicaton, John Melville, PhD.

an alternative is

3. Respiratory Rate estimation by Peter Charton, PhD:

http://peterhcharlton.github.io/RRest/

4. HealthyPi v3 by ProtoCentral

https://www.crowdsupply.com/protocentral/healthypi-v3