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76 Chapter Five
FIGURE 5.5 Refractory periods.
5.3 Influence of Frequency on the Effects of Current
A sine wave of frequency f can be thought as a collection of impulses,
regardless of the sign, constituting electrical stimuli of duration T/2
(Fig. 5.6).
An equal intensity current, of frequency f 1 > f, applies equal
strength stimuli, but of a shorter duration T 1 /2 < T/2. In this case,
the stimuli may not excite the cell, because of their lower application
time, which put them below the excitability curve of Fig. 5.4. High-
frequency (>100 Hz) currents are, therefore, less dangerous than low-
frequency ones of same intensity, and their threshold of perception is
higher than those at low frequency.
FIGURE 5.6 Sine waves as collection of stimuli.
