Consistency classification

There are rhythms that regard one concrete entity, i.e., «real rhythms». Other rhythms are instead the mere expression of a computational parameter, i.e., «virtual rhythms». The nychtohemeral profile of cortisol rhythm, when studied in blood, coincides with the within-day variations of its concentration in plasma or serum. By con­trast, the circadian rhythm of pH is caused by the interplay of numerous factors each one character­ized by its own rhythm.

Constitutive classification

There are biological rhythms which refer to a single variable (something that is definable by its characteristics), i.e., «elementary rhythms», and others which attain to complex functions, i.e., «com­posite or factorial rhythms». Examples may be the circadian rhythm of prolactin, on one side, and the circadian rhythm of mood, on the other.

If a rhythm is found to be complex, its eventual abolition could be dependent on an internal desyn­chronization among the constituent cyclic factors or mechanisms. Sometimes, the aperiodicity is mere­ly due to changes in phase resulting in an antiphasic oscillation of the cycles which contribute to the complex rhythm.

Hierarchical classification

In the magnificent organization of bioperiodic phenomena, it has been found that some rhythms play a prominent role in conditioning other biologi­cal cycles. These rhythms are called «guide or primary or independent rhythms» while the driven rhythms are called «guided or secondary or de­pendent rhythms». Guide rhythms have a strategic importance in the sense that their presence is essen­tial for the dependent periodicity. The lack of a guide rhythm usually produces desynchronizing ef­fects mostly due to the abrogation of the rhythmic interplay. The interruption of the relationship be­tween primary and secondary rhythms causes a phenomenon called «internal desynchronization». The guided rhythms will be absent due to an induced effect. Such a dramatic repercussion is called «endogenous masking effect». The en­dogenous masking may help us in understanding and interpretating the chronopathology of some biological rhythms.

Genesis of biological rhythms

The capacity to undergo rhythmic oscillations is a characteristic intrinsic to living matter. A funda­mental statement of chronobiology states «many rhythms persist even in complete isolation from the major known environmental cycles». This affirm­ation clarifies that the natural rhythms can be considered to lay outside of the period of the geophysical cycles. This means that living matter has its own time, i.e., the «biological time».

Assuming time as a fourth dimension of biology, one can conceptually and syllogistically argue that a chronome exists into the genome. Besides the physical (physemes) and chemical (chememes) sig­nals, one can assume that the genes provide infor­mation also in the form of «chronemes», i.e., signals of periodic type. In such a way the process of donation is timed by determined periods, and results in a combination of quantal and temporal messages which cause the biological functions to quantitat­ively change according to a programmed spectrum of periodicities. Speculatively, one could presume that the temporal signals find their periodic genesis within the helicoidal spirals of DNA where the chronome should reside. The DNA double helix could act as a metronome generating a vibration whose length is the period of donation.

It has been suggested that the gene inherits not only the capacity to clone (ergon) but also the capacity to endure (chronon). The concept of chronon refers to the expression of genes as a function of the chronological time which is linear, irreversible and progressive. The concept of cronome relates to the expression of genes accord­ing to the chronobiological time which is cyclical, irreversible but recursive. Accordingly, the chrono­logical time could be seen as the summation of the iterated periods which constitute the time base of biological rhythms.