Little is known about clinical significance of summating potential (SP) recorded from human subjects with normal hearing and with inner ear diseases. An extensive study was performed to elucidate the pathophysiology and clinical usefulness of SP, in association with AP, recorded by the transtympanic technique of electrocochleography. Both SP and AP were recorded from 21 normal hearing subjects, 20 patients with sensorineural hearing loss, and 12 patints with Meniere's disease. Measurements were made on the input-output relation of AP, the amplitude and polarity versus frequency relation of SP, and the amplitude and polarity versus intensity relation of SP, in addition to informations of the waveforms and thresholds of AP and SP.
The conclusions were as follows:
It was clear that both SP amplitude and polarity in man, just as reported in the animal experiments, were highly and systematically dependent upon stimulus intensity and frequency. There was a strong tendency to the negative SP in decreasing the stimulus frequency. The polarity of SP was completely negative (-SP) for the lower frequency than 6 KHz, and it showed a general tendency towards the positive SP to the very high frequencies of 8 KHz or 10 KHz. The most striking phenomenon was a significant enhancement of negative SP amplitude which could be expressed as an increase in negative SP amplitude to AP amplitude ratio. Our suggestion was that the significant enhancement of negative SP might be valuable in diagnosis and elucidation of Meniere's disease, and it might reflect the sense-organ malfunction due to endolymphatic hydrops in the cochlea. On the contrary, the amplitude of SP decreased clearly in sensorineural hearing loss. This might be related to presynaptic subtractive loss of sensory units in the cochlea. The significant changes in AP were the H-curve pattern configuration of the input-output relation in sensorineural hearing loss. This also might indicate the presense of subtractive loss of sensory units in the cochlea.