The aim of this research project is to investigate the feasibility of surreptitiously detecting elevated stress levels in a subject during questioning by remote, non-contact measurement of changes in heart rate, heart rate variability and respiration using small, concealable, microwave-Doppler-based sensors. The use of covert sensing of physiological indices could minimize or even eliminate the use of countermeasures by the subject, while providing the ability to measure the dynamical changes of heart rate ("heart rate variability" or HRV) that reflect the activity of the autonomic nervous system (ANS), which is measurably altered during mental provocation. Miniaturized microwave-based systems also have potential medical applications, such as non-contact monitoring of vital signs at a bedside, for burn victims and for research, where the discomfort associated with electrocardiographic (ECG) leads may interfere with a study, as might occur in sleep apnea research when a subject's discomfort alters normal sleep habits. Previous work, has demonstrated the efficacy of microwave-Doppler sensing to measure respiration, pulse rate and eye blinks. The case of "uncooperative" subjects has received little attention. In order for a microwave-based system to be useful in realistic settings, several issues related to uncooperative subjects must be addressed concerning signal and noise variability arising from: (1) sudden, unpredictable subject movements, (2) variation of signal with location on the thorax and the angle of incidence, and (3) fluctuation of the distance between the sensor and the subject with time. Remote detection serves a number of medical purposes, including in burn patients which standard sensors of heart variability are in themselves stressful.
