Application of Spectral Methods of Analysis for Description of Ultradian Biorhythms at the Levels of Physiological Systems, Cells and Molecules (Review)

Abstract

The presence of biological rhythms is a characteristic of all living organisms. Over the past 60 years, scientists around the world have accumulated a huge amount of data on rhythmic processes in living systems at various levels. The acquired knowledge has found applications in human economic activity and medicine. The ultradian (less than a day) rhythms at the organismal, organ, and cellular levels are characterized by high diversity. Unfortunately, biorhythms in different systems are considered, most often, in isolation from each other. Much knowledge about biorhythms was obtained using expert evaluation methods, and later methods of spectral analysis were used to describe biorhythms. Ultradian rhythms have a relatively short duration; therefore, they can be characterized by spectral analysis methods. More and more researchers believe that in order to further expand the understanding of the nature and purpose of biorhythms, the use of more advanced methods of mathematical processing is required, and rhythms in different organs, tissues, and cells should be considered parts of a single system. This review is intended to provide the reader with the variety of ultradian rhythms in living systems (organismal, organ, cellular, molecular levels), the mechanisms of their generation, and their functions to give the reader a picture of the possible relationships between these rhythms. Further, the reader will be able to get acquainted with the variety of mathematical methods for analyzing biorhythms, including bispectral and cross-correlation analyses.