The FREQUENCY of pulses in the analgesic stimulation.
The stimulation frequency would have an important role in the treatment efficiency - but there are many differences of opinion which exist even now; LOW frequencies (around 10Hz) should produce a delayed, and less intense analgesic action but longer lasting, whereas frequencies above 50Hz should determine a faster analgesic effect but of shorter duration.
Some Authors also suggest a selective stimulation in correspondence of Chinese acupuncture points, by using very low frequencies (1 to 3 Hz.), large pulse width (200 µsec.) and a stimulation level up to the motory stimulation threshold.
The variable currents exercise a strong stimulating action on the sensitive terminals at a coetaneous level, which the patient feels as a vibration or tingling. By increasing the intensity they rapidly transform into a painful burning or stinging sensation. The characteristic of the feeling in the skin depends not only on the current intensity but also on its frequency.
The maximum sensitivity is obtained with frequencies between 30 and 60 Hz, and it progressively decreases with higher frequencies, until it disappears completely with frequencies over 10Hz. For a correct use of electro stimulation it is advisable to remember that, the stimulation intensity must be set and maintained during the session, just under the pain threshold - regardless of the wave length characteristics of the current used.
It is advisable not to create unpleasant effects for the patient, as this would result in him not being motivated to continue successive treatment. It is equally important to make sure that the stimulation is optimum in every instance, that is the maximum level possible under the pain threshold.
Experience has shown that rectangular waveforms guarantee the most favorable results.