Respiratory rate influence in the resulting magnitude of pulse photoplethysmogram derived respiration signals

Parameters derived from the pulse photoplethysmographic (PPG) signal, such as pulse rate, amplitude, and width variability (PRV, PAV and PWV) have been previously proposed for deriving respiratory rate, obtaining less accurate estimates for higher respiratory rates (0.5-0.6 Hz). In this work we analyze the power of respiration related oscillations in PRV, PAV and PWV as a function of respiratory rate in controlled respiration experiments. PPG signals from 14 subjects breathing at constant rates from 0.2 to 0.6 Hz (with an increment of 0.1 Hz) during 2 minutes were analyzed. In addition, smartphone-camera-acquired-PPG signals from 10 subjects using three different devices (iPhone 4S, iPod 5 and Samsung Galaxy S3), during the same kind of experiments were also analyzed. Powers of PRV, PAV and PWV respiration-related oscillations were estimated by integrating their Welch periodograms at the respiratory band. When analyzing PRV and PWV, clear tendencies of power decrease as respiratory rate increases were observed, while less evident tendencies were observed when analyzing PAV.