Article in IEEE Reviews in Biomedical Engineering · October 2017 https://www.researchgate.net/profile/Peter-Charlton-2/publication/320600049_Breathing_Rate_Estimation_From_the_Electrocardiogram_and_Photoplethysmogram_A_Review/links/5b742286299bf14c6da78d83/Breathing-Rate-Estimation-From-the-Electrocardiogram-and-Photoplethysmogram-A-Review.pdf Important review paper about Breathing Rate Estimation the Dalai Lama should read to start with.