Impedance changes elicited by tactile and electrocutaneous stimulation.

In each of 24 randomly selected outpatient the size of the impedance changes elicited by touching the skin in the ipsilateral cavum conchae with cotton wool were compared with those elicited by electrical stimulation of the same skin area. Pulse trains of 0.5 s duration, consisting of individual squarewave constant current pulses of frequency 200 Hz and duration 1 ms, were used. In all ears a current of 0.5-1 mA produced impedance change of about the same size as the tactile stimulus. Therefore, in testing the middle ear function observation of impedance changes elicited by tactile as well as electrical stimulation can be used. Electrical stimulation, however, has the following advantages: 1) Artifacts produced by accidently touching the probe tip are avoided. 2) The electrical stimulus is well defined and reproducible.