Smartphone-camera-acquired pulse photoplethysmographic signal for deriving respiratory rate

A method for deriving respiratory rate from smartphone-camera-acquired pulse photoplethysmographic (SCPPG) signal is presented. It combines information from three derived respiration signals based on pulse width, amplitude, and rate variability (PWV, PAV, and PRV). Evaluation is performed over a database containing SCPPG signals recorded from 10 healthy subjects during controlled respiration experiments at rates from 0.2 to 0.6 Hz with a step of 0.1 Hz, using iPhone 4S device. Results suggest that habitual spontaneous respiratory rates (0.2-0.4 Hz) can be estimated from SCPPG signals by PWV and by PRV with low relative error (median of order 0.5% and IQR of order 2%). PWV method maintained its performance at rates up to 0.5 Hz, and the accuracy can be improved by combining it with other methods such as PRV and PAV.