Preliminary investigation of pupil size variability: toward non-contact assessment of cardiovascular variability

World´s aging population and prevalence of chronic diseases have led to growing interest in the development of home-based wearable biomedical sensors for patient-monitoring. Monitoring of the pupil´s properties is a feasible alternative application, as it has the advantages of non-invasive and non-contact measurement, as well as feasible implementation using wearable image sensors. Recent researches have discovered the presence of heart rate variability (HRV) and blood pressure variability (BPV) frequency components in pupil size variability (PSV). Aims of this study are to investigate effect of physical exercise on PSV spectrum, and to address the feasibility of PSV monitoring. Electrocardiogram, respiration effort, finger arterial pressure, and pupil images were recorded from ten subjects before and after exercise. Normalized high frequency (0.15-0.5 Hz) power of PSV in seven subjects and total (0.04-0.5 Hz) power of PSV in nine subjects decreased after exercise, followed by an increase during recovery. The patterns of changes are generally paralleled by corresponding indexes from spectra of HRV and BPV. Preliminary results suggest that PSV has the potential to be a novel physiological indicator used in patient-monitoring.