From Big Medical Encyclopedia

DECREMENT (Latin decrementum reduction, a decrease) — the physical quantity characterizing decay rate of fluctuations in mechanical, electric, molecular and other oscillatory systems. The pendulum of hours, a metronome, the sounding string, a tympanic membrane, cardiovascular system, an oscillatory contour of the generator of electromagnetic or acoustic radiation, oscillatory cycles of a metabolism in live organisms, etc. can be examples of such systems. In the equipment D. is of great importance during the calculations of various electrotechnical and acoustic devices, in physiology — during the studying of spread of activation on nerve and muscle fibers.

In the simplest case of. (A) it is equal to a natural logarithm of the relation of two consecutive maximum deviations (x 1 and x 2 ) the fluctuating size [Δ = ln(x1/x2)] also characterizes reduction of amplitude of fluctuation during this fluctuation. For mechanical oscillations of D. depends on the mass (density) and elastic properties of oscillatory system, and also power losss in it on all types of friction; for electromagnetic oscillations — from a ratio of reactive elements (inductance and capacity) and the active resistance of an oscillatory contour. If these parameters cannot be measured directly, then D. can determine by relative reduction of energy (dw) during fluctuation, i.e. Δ = dw/w where w — the energy reserved in an oscillatory contour or the fluctuating system. Size, the return Δ, i.e. = 1/Δ shows to n number of the periods during which maximum deviation of the fluctuating size decreases in e time (e — natural logarithm in number equal 2,72). E.g., for a tympanic membrane Δ = 0,5 — 0,3 therefore its own mechanical oscillations completely fade already through 2 — 3 periods of fluctuation, for a tuning fork Δ = 0,001, i.e. the tuning fork does apprx. 1000 fluctuations before amplitude of fluctuations decreases approximately three times, etc.

In physiology Is a weakening of excitement in process of its distribution along nerve or muscle fiber. Carrying out excitement, as a rule, happens without attenuation («bezdekrementny carrying out). However if intensity of an irritant is insufficiently big, then the arising electric answer quickly fades — decremental conductibility takes place. This phenomenon has big biol, value since protects an organism from constant response to the external influences which do not have at present the vital value (e.g., insignificant force noise indoors «does not sink» in the person and does not distract from work). Only influence of sufficient force provides signal transmission to executive bodies. At some animals, in particular at clams, carrying out excitement has only decrement character.

Bibliography: The buyer V. Biofizika, the lane with it., M., 1962; Pasynsky A. G. Biophysical chemistry, M., 1968.

Yu. M. Petrusevich.