Contactless Measurement of Heart Rate Variability from Pupillary Fluctuations

The ability to measure a person's physiological parameters in a contact less fashion (i.e., without attaching electrodes to the skin) has tremendous potential in a number of applications, from affective interfaces to healthcare delivery. In this paper, we present a proof-of-concept method for measuring one such vital parameter, heart rate variability (HRV), in a contact less fashion from spontaneous fluctuations in pupillary diameter. Our approach uses a remote eye tracker for imaging and an integro-differential algorithm for segmenting the pupil-iris boundary. We then estimate HRV from the relative distribution of energy in the low frequency (0.04 to 0.15 Hz) and high frequency (0.15 to 0.4 Hz) bands of the power spectrum of the time series of pupillary fluctuations. We validated the method under a range of breathing conditions and under different illumination levels. Our results show a high degree of agreement between our pupillary estimate of HRV and ground truth measurements from an ECG-grade heart rate monitor. These results support the feasibility of estimating HRV in a non-contact, non-invasive fashion.