Circadian rhythm is the biological process critical to the well-being of living organisms, from plants to insects and mammals. The circadian rhythms oscillate with a period of approximately 24 hours due to the 24-hour light-darkness pattern of the solar day. Some physiological processes, such as alertness regulation and hormone production, are related with circadian rhythm. Circadian disruption, as experienced by night shift workers, travelers across multiple time zones, submariners or miners, can lead to lower productivity, sleep disorder, and more serious health problems. Light pulses, applied at correct circadian argument, can be used for circadian re-entrainment by stimulating humans non-visual pathway. In cancer treatment, chronotherapy, in which the doctors time the delivery of chemotherapy drugs based on a patients individual circadian rhythm, helps to minimize the damage of chemotherapy to healthy tissues. By pinpointing the circadian argument that is best for treatment, higher doses can be delivered that do less harm to the rest of the body. In some chronobiology research, biological system needs to be stimulated at certain circadian phase to study how circadian rhythm influences the effect of the stimulus, e.g., Aschoff type I experiment protocol for phase response curve identification. To address the circadian rhythm monitoring process and other circadian entrainment needs, researchers at Rensselaer created a circadian monitoring system with a feedback controller using an adaptive rhythm augment estimator. The estimator is connected to biological signal sensors through the data acquisition port in the user interface. After initialization, the estimated circadian argument is displayed in real time to assist the time-dependent prescription for chronotherapy, circadian re-entrainment or biological research. The estimator is based on adaptive notch filter (or any frequency tracker) to extract the first order (and also higher order) harmonics of the noisy biological signal and adapt to the amplitude and phase parameters of these harmonics which may be time varying or imprecisely known. The system is recursive, making it efficient and suitable for continuous circadian rhythm monitoring in a wearable device.

Submission Date
Reference Number
R12-068
Contact
Natasha Sanford