It would be very useful in the employment of nerve repair at the lesion of injured nerve in continuity if the nerve conductivity could be directly measured. The nerve conduction velocity has in general been calculated indirectly from the distance and latency of the evoked nerve action potentials through the terminal organs such as muscle or skin. However, the shortcoming of this measurement is that it is possible only under the condition where the terminal organ is not denervated. Therefore, in the case where the nerve regeneration does not reach to the terminal organ, the value of conduction velocity is calculated misguidedly as zero. In order to solve this problem, an electronic tester, where a stimulating electrode and a recording one were placed directly to the nerve trunk or the interneural funiculus separately at short distance, was developed for the diagnosis of functional continuity of the injured peripheral nerve.
The following three points were essential in the realization of this system. (1) To use an extremely low-noise differential amplifier with high CMRR, which was realized by a cascode differential stage employing high Gm JFETs. (2) To use a multi-strand low-noise stainless steel electrodes (large effective contact area) for the nerve impulse measurement. (3) To use a specially designed apparatus using a microprocessor and electronic circuits, with which the nerve action potentials evoked by repeated stimulations were processed (synchronous summation, moving average, latency measurement, velocity calculation, etc.), and then the results were displayed and recorded.
The electronic tester was applied clinically in a case suffered with traumatic brachial plexus palsy. Exact diagnosis concerning about functional continuity in each terminal branch of the plexus was obtained intraoperatively. Then neurolysis was performed at proper site of the plexus nerve.
