Physiological parameter monitoring from optical recordings with a mobile phone

Abstract

We show that a mobile phone can serve as an accurate monitor for several physiological variables, based on its ability to record and analyze the varying color signals of a fingertip placed in contact with its optical sensor. We confirm the accuracy of measurements of breathing rate, cardiac R-R intervals, and blood oxygen saturation, by comparisons to standard methods for making such measurements (respiration belts, ECGs, and pulse-oximeters, respectively). Measurement of respiratory rate uses a previously reported algorithm developed for use with a pulse-oximeter, based on amplitude and frequency modulation sequences within the light signal. We note that this technology can also be used with recently developed algorithms for detection of atrial fibrillation or blood loss.

Fig. 1

(a) Example green band PPG signal obtained after averaging a 50×50 pixel region. (b) Example HR_ECG (thin black line) and HR_GREEN (thick blue line) during spontaneous breathing. (c) Example HRV plots from ECG (thin black line) and GREEN (thick blue line). Additional high-frequency noise (>0.4 Hz) is present in the GREEN signal.

Fig. 2

(a) AM and (b) FM sequences obtained from time-frequency analysis of the GREEN cardiac signal. (c) PSD of FM sequence (thick lines) and respiration trace signal (thin dashed lines) during metronome breathing at 0.2 (black), 0.3 (red), and 0.4 (blue) Hz.

Fig. 3

Oxygen saturation measured by a commercial pulse-oximeter (thin black line) and computed using the model shown in eq. (1) from RED and BLUE band signals obtained from a mobile phone camera (thick black line) for two subjects.