Some algorithms for circadian rhythm identification

We present two approaches to the detrending of physiological data derived from brain-injured human patients. This is important in circadian rhythym characterization. The proper identification of a patient's rhythm is known to be important in clinical treatment. One detrending approach is an ad hoc polynomial fitting strategy, while the other is a modification of the so-called cosinor model where subharmonic terms are added. The latter method is based on the fact that many nonlinear dynamic systems when driven with a sinusoidal input produce an output containing subharmonics of the input. The latter method seems to provide consistently superior performance to the polynomial method.