Design And Analysis Of Somatosensory Evoked Potentials Measuring Apparatus

Surgery with instrumentation is associated with the risk of iatrogenic injuries to the nerve. Somatosensory evoked potential (SSEP) monitoring has resulted in a high degree of sensitivity in predicting postoperative neurologic outcomes. By detecting intraoperative neurologic compromise early, SSEP monitoring can allow surgical interventions to decrease the incidence of new-onset postoperative neurologic deficits. Thus it is potentially one of the most widely applicable monitoring techniques in intraoperative neurologic monitoring.In this article, a system for extracting SSEP was designed. First, the system produced adjustable pulse voltage for stimulation which was isolated power supplied for the safety of object. Second, the corresponding electroencephalogram (EEG) response was acquired, amplified and A/D converted by the system. The most important thing was that SSEP was extracted from the signal by independent component analysis (ICA) in our system, instead of common coherent average. The results from animal experiments revealed that ICA required less times of stimulation and less details of the EEG response were lost than coherent average. It can extract and display SSEP more quickly and exactly.For the purpose to differentiate neurologic injury by SSEP change effectively, SSEP change in different anesthesia states such as normal and lesion state were studied. Besides latency and amplitude of the SSEP waveform, new indices such as mean amplitude, entropy and mean residence time (MRT) were evaluated to show the SSEP difference. Results revealed that MRT maximally represented the difference and it should be the best index to the SSEP change in a neurologic injury.Meanwhile, when the lesion state of the rat was to an extreme that the nerve was transected and reached the devastation state, the change in SSEP became large and abnormal. We thus analyzed SSEP in another extreme state– the death state and compared it with the devastation state. Contrary to the concept that neurologic injury causes retardation in latency and reduction in amplitude in SSEP, both the latency and amplitude shrank in the devastation and death state of the rat.