ric and duodenum ulcers, etc.), arterial hypertension, etc.
Cyclic recurrence is a property of systems not of a living organism only. Any system operates in cycles. If external influence is retained at a stable level, the system would operate based on this minimal steady-state cycle. But external influence may change cyclically as well, for example, from a sleep to sleep, from dinner to dinner, etc. These are in fact secondary, tertiary, etc., Cycles. Provided constructing the graphs of functions of a system, we get wavy curves characterizing recurrence. Examples include pneumotachogram, electrocardiogram curves, curves of variability of gastric juice acidity, sphygmogram curves, curves of electric activity of neurons, periodicity of the EEG alpha rhythm, etc. Sea waves, changes of seasons, movements of planets, movements of trains, etc., - these are all the examples of cyclic recurrence of various systems. The forms of cyclic recurrence curves may be of all sorts. The electrocardiogram curve differs from the arterial pressure curve, and the arterial pressure curve differs from the pressure curve in the aortic ventricle. Variety of cyclic recurrence curves is infinite. Two key parameters characterize recurrence: the period (or its reciprocal variable - frequency) and nonuniformity of the period, which concept includes the notion of frequency harmonics. Nonuniformity of the cycle period should not be resident in SFU (the elementary system) as its performance cycles are always identical. However, the systems have transition periods which may have various cycle periods. Besides, various systems have their own cyclic periods and in process of interaction of systems interference (overlap) of periods may occur. Therefore, additional shifting of own systems 'periods takes place and harmonics of cycles emerge. The number of such wave overlaps can be arbitrary large. That is why in reality we observe a very wide variety of curves: regular sinusoids, irregular curves, etc. However, any curves can be disintegrated into constituent waves thereof, ie disintegration of interference into its components using special analytical methods, e.g. Fourier transformations. Resulting may be a spectrum of simpler waves of a sinusoid type. The more detailed (and more labour-consuming, though) the analysis, the nearer is the form of each component to a sinusoid and the larger is the number of sinusoidal waves with different periods.
The period of system cycle is a very important parameter for understanding the processes occurring in any system, including in living organisms. Its duration depends on time constant of the system's reaction to external impact/influence. Once the system starts recurrent performance cycle, it would not stop until it has not finished it. One may try to affect the system when it has not yet finished the cycle of actions, but the system's reaction to such interference would be inadequate. The speed...
