Registering the response of tissues exposed to an interferential electric current stimulation

Electrotherapy is a treatment method in which an electric stimulus is used to achieve physiological changes in the body. When increasing the level of the electric stimulus, three sensory, three motor and a pain response can be found. In this paper the three sensory threshold levels (1st just noticeable weak tingling sensation, 2nd a very fine but definite tingling and 3rd moderate strong tingling) were studied with an interferential electric current stimulus. The interferential electric current can be achieved by summing two alternating currents with little different frequencies with each other. As a current source, the study used a value intended for interferential electric current therapy. The threshold value measurements were performed on 5 days to 6 volunteers. The method of limits is a frequently used technique for determining sensory thresholds where ascending or descending stimuli is used and the observer reports of the appearance or disappearance of the sensation, respectively. A Bekesy's algorithm is a threshold tracking method with a variable stimulus. They were used for controlling the interferential electric current stimulus, and hence, for studying the,thresholds. By using the method of limits, the measurements were done at three sensory threshold levels at interferential frequencies deltaf of 10 Hz, 30 Hz, 50 Hz, and 100 Hz caused by two sine waves, one with a frequency between 2490 Hz and 2400 Hz, and the other constant 2500 Hz. In the method based on Bekésy's algorithm the interferential frequency deltaf was increased from 1 Hz to 100 Hz by changing the first frequency from 2499 Hz to 2400 Hz and the measurement was repeated for all three sensory thresholds. The sensory thresholds for interferential current stimuli seem to be quite unaffected by the interferential electric current frequency among the healthy test persons, and no distinct interferential electric current frequencies at which the threshold values should be measured were found in this study.