SP Amplitudes Research Articles

Clinical Significance of Positive Summating Potential in Menière’s Disease

The positive summating potential (+SP) in Menière's disease was compared with that in normal ears and in cochlear deafness of other origin than endolymphatic hydrops in order to assess a specificity of the +SP in Menière's disease. The +SP was recorded in 21 of 47 Menière ears (45%) on stimulation with 8-kHz tone bursts, whereas the +SP was recorded in none of 10 normal-hearing ears and in 1 of 28 ears with cochlear deafness of other origin than endolymphatic hydrops (4%). The incidence of the +SP in Meniére's disease was higher on stimulation with 8-kHz tone bursts than with 4-, 2- and 1-kHz tone bursts and clicks. No correlation between SP amplitudes recorded with 2- and 8-kHz tone bursts was found. The results suggest that Menière's disease may involve a pathophysiological condition which allows the +SP to be frequently recorded.

An intermediate depth earthquake beneath Tibet: Source characteristics of the event of September 14, 1976

This paper presents the results of a detailed study of an intermediate depth earthquake beneath southern Tibet (September 14, 1976; 0643:51.6 UT; 29.8l°N, 89.57°E; focal depth 90±10 km; mb = 5.4). From the differences in arrival times of P, pP, and sP and from Rayleigh wave spectral densities the focus is estimated to be at depth of 90±10 km and therefore in the uppermost mantle. From the polarities of the first motions of P waves, inversion of the relative amplitudes of P, pP, and sP, and synthesis of their waveforms, the source mechanism is constrained to be predominantly normal faulting with the T axis approximately horizontal and trending east‐west. This mechanism is similar to those of shallow earthquakes in Tibet. The occurrence of an earthquake at depth of 90 km is consistent with rapid, deformation at a temperature of about 700° to 800°C in the mantle beneath the Tibetan crust. The seismic moment of an equivalent double couple point source is estimated to be about 9 × 1024 dyne*cm (with an uncertainty factor of 1.3) from the sP amplitudes in the period range near 10 s, and 5 × 1024 dyne*cm (also with an uncertainty factor of 1.3) from the spectral density of Rayleigh waves with periods of 50 s.

か電図におけるＮｅｇａｔｉｖｅ ｓｕｍｍａｔｉｎｇ ｐｏｔｅｎｔｉａｌｓ（−ＳＰ電位）の異常増大現象の発生機構について

With the view of clarifying the mechanism of occurence of abnormally large amplitude of negative summating potentials (-SP) in clinical electrocochleography, electric responses of the cochlea were recorded from guinea pigs whose endolymphatic sac and duct were oblitered.In reference to the waveform of AP, SP complex obtained by AVE recording using click stimuli, the animals were devided into three groups, i.e., (I) cases showing broadened waveform of AP, SP complex due to enhanced of the -SP, (II) cases showing -SP and normal waveform of AP, SP complex, and (III) cases showing +SP as in normal cases.The waveform of AP, SP complex in Group I was very similar to that of clinical electrocochleographic findings in certain cases of pathological ears such as Meniere's disease and sudden sensorineural hearing loss. In all tested stimulus frequency functions the SP polarity recorded in scala vestibuli(SV), scala tympani(ST), and AVE SP and DIF SP proved to be predominantly negative in its trend. Histological investigation indicated the distension of endolymphatic compartment of the cochlea with displacement of Reissner's membarne, but -SP amplitudes were not always proportional to the degree of distension in these cases.In this study it was postulated that the large amplitude of -SP would reveal the pathophysiological conditions in the cochlea, three of the scalae, i.e., SV, ST and scala media, all showed negative polarity in SP, leading to a negative SP of increased amplitude as a total sum or synthetic vector of SP components with the dominating negative polarity.

Electrocochleographic Changes Accompanying Fluctuations in Hearing Loss in Ménière's Disease

Electrocochleographic changes accompanying fluctuations in hearing loss on 4 patients with Meniere's disease were reported. Extratympanic electrocochleography (ECochG) was performed again after the audiogram had changed at one or more frequencies. The intervals between these ECochGs ranged from 1 month to 2 years. In two patients whose audiogram had changed only at one frequency, no significant change in ECochG was found. In two patients whose audiogram had changed at three frequencies, changes in action potential (AP) thresholds corresponded to changes in the audiograms. Negative summating potential (-SP) detection thresholds and -SP amplitudes remained unchanged, but -SP/AP ratios were significantly changed. In one of two patients with significant changes in ECochG N1 latency was prolonged accompanying progression of the hearing loss. The mechanism causing changes in ECochG accompanying fluctuations in hearing loss was discussed.

Long and Short Period P-wave amplitudes from Earthquakes in the Range 0 -114

Summary Long period (16 s) and short period (1 s) P-wave amplitudes from shallow earthquakes recorded in the distance range are analysed to separate the effects of earthquake size, epicentral distance and station structure. The LP and SP vertical component amplitudes are analysed separately so that any period dependent effects can be determined. The results show that distance effects on both LP and SP amplitudes are significant when the whole range 0-114 is considered but between about 30 and 90 the distance effects are not significant. Further the distance effects do depend on period in the range 0-114 but again between 30 and 90 the distance effects are independent of period. In determining magnitude then a single constant correction for distance can be applied to both LP and SP recordings in the range 30-90. Outside this range the correction depends on both distance and period. Station effects are significant for both the LP and SP analyses with little correlation between the LP and SP effects for individual stations. The SP effects can be attributed to variations in Q in the upper mantle; stations recording below average amplitude being underlain by lower Q than those recording amplitudes above average. The SP effects for a particular station will thus also be source effects for shallow events with epicentres near the station. The value of applying corrections for such source effects to magnitude estimates is demonstrated using data from two explosions of the same yield fired at two widely different test sites. Without corrections for source effects the magnitudes differ by 0.6 units, with source effects the difference is 0.02 units. The LP station effects are more difficult to interpret, but for one group of stations on the coastal plains of the Gulf of Mexico and Eastern USA which show large positive effects (above average amplitudes) it is demonstrated by modelling that these effects could be explained by the amplification effects of the large thicknesses of sediment underlying the stations. Comparing the estimates of magnitude (earthquake size) obtained from the LP and SP analyses shows that on average the LP and SP magnitudes are equal but correlation of LP and SP magnitudes for individual earthquakes is poor. This lack of correlation may simply be due to lack of data since only a small number of readings (1-4) contribute to each magnitude estimate, but this needs further study.