An Adaptive Single Frequency Phase Vocoder for Low-power Heart Rate Detection - Development of a Fast and Low-power Heart Rate Estimation Algorithm for Mobile Phone Applications.

Mobile phones can be used as a platform for clinical decision making in resource-poor and remote areas. Their limited battery and computational resources, however, demand efficient and low-power algorithms. We present a new algorithm for the fast and economical estimation of heart rate (HR) from the photoplethysmogram (PPG) recorded with a pulse oximeter connected to a mobile phone. The new method estimates the HR frequency by adaptively modeling the PPG wave with a sine function using a modified phase vocoder. The obtained wave is also used as an envelope for the detection of peaks in the PPG signal. HR is either computed using the vocoder center frequency or the peak intervals in a histogram. Experiments on a mobile device show comparable speed performance with other time domain algorithms. Preliminary tests show that the HR computed from the vocoder center frequency is robust to Noise in the PPG. The instantaneous HR calculated with the vocoder peak detection method was more sensitive to short-term HR variations than the vocoder center frequency method. These results point to further developments using a combination of both HR estimation methods that will enable the robust implementation of adaptive phase vocoders into mobile phone applications.