Design and Intra-operative Studies of an Economic Versatile Portable Biopotential Recorder

Abstract

An economic, versatile, compact and portable biopotential amplifier [Electroneurograph] has been designed and implemented intra operatively. The most significant features of the instrument are variable cutoff for the low pass filter, variable gain, attenuation and optical isolation for the output. A fourth order low pass filter with bessel characteristic was designed using active filters. An attenuator is provided in between the gain stage and optical isolator such that the signals during supramaximal stimulations are attenuated. In this versatile bio-potential recorder, one of the outputs of the amplifier is isolated optically using IC MOC 3020 such that patient safely is ensured. The output portion of the instrumentation amplifier which is named head stage is designed separately and the inputs from the electrodes are given to the head stage by means of shielded coaxial cable. Also the whole bio-potential amplifier is properly shielded and grounded to minimize the noise effect. Offset control is provided for base line shift. The stimulating and recording electrodes were placed in appropriate positions and evoked responses were recorded. Conduction velocity was calculated by measuring the latency of waveform by stimulating at two different points along the nerve. Nerve conduction studies have been undertaken on leprosy patients who had undergone median and ulnar nerve corrective surgery and the result presented.