Ultradian rhythmometry by adaptive line enhancer.

Widrow's adaptive line enhancer (ALE) was applied to human rectal temperatures at 12-min intervals for 9 days. Changes along the scale of 9 days in circadian pattern suggested the occurrence of infradian variation, resolved by analyses of the entire series by linear-nonlinear rhythmometry. Once the original signal is filtered to extract the circadian component, ultradian components appear. A wide peak with a period of about 100 min, seen each day, may reflect a consistent ultradian component. Other peaks at lower ultradian frequencies (around a period of approximately 8 hr) are unsteady and may correspond to harmonics of the partially extracted circadian oscillation. Ultradian components with periods of approximately 131 and approximately 68 min were also suggested independently by population-mean cosinor summarizing data collected over a total of 158 days. Results show the ability of ALE to detect and reconstruct periodic components in noise and to track their changes in frequency, notably when other methods are also used to assess separately the components and the corresponding uncertainties involved.