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The intensity of the steady current just sufficient to excite a tissue when suddenly applied.



the minimum potential of direct electric current necessary to produce excitation in living tissues. The concept was introduced into physiology in 1909 by L. Lapicque, who in studies on the minimum threshold of excitable tissues determined the dependence between the intensity of a current and the duration of the action of a current.

The rheobase, like the chronaxy, gives an idea of tissue and organ excitability from the threshold of the intensity and duration of stimulation. It corresponds to the stimulation threshold and is expressed in volts or milliamperes. Its value can be computed from the formula i = a/t + b, where i is the current potential, t is the duration of the action of a current, and a and b are constants determined by the properties of a tissue. The constant b is the rheobase because with prolonged stimulation by a current, the a/t ratio will be very low and i will be virtually equal to b. The rheobase often refers to the threshold values of other stimuli besides those that are electric.