Note that the MATLAB ® code used to create this image is available here
Source: P. H. Charlton and T. Bonnici et al., An assessment of algorithms to estimate respiratory rate from the electrocardiogram and photoplethysmogram, Physiological Measurement, vol. 37(4), 2016. DOI: 10.1088/0967-3334/37/4/610 (CC BY 3.0)
Own work
Peterhcharlton