Effect of intravenous lidocaine hydrochloride on electrocochleographs.
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Lidocaine HCl is used in the treatment of tinnitus, but its site of action is still unknown. We report our findings on the sequential monitoring of electrocochleographs during administration of lidocaine HCl in 129 patients.<BR>Measurements were recorded on a PDP-11 microcomputer. By 1024 samplings at 5 microsecond intervals, we were able to obtain sufficient resolution on the time axis. The average electrocochleograph, following either 300or 600 sweeps, was recorded on floppy diskettes. The time required to process this information was approximately 30 seconds for an average of 300 measurements. We were therefore able to record data at exactly one minute interval by the real time clock.<BR>Following attachment of the electrodes, measurements were recorded for ten minutes. 60 to 100mg of lidocaine HCl was then given intravenously within 30 seconds. Electrocochleographs were recorded for 20to 30 minutes following drug administration. The 129 patients studied were made up of 73 males and 56 females with an average age of 45 years (range: 16 to 72 years). Changes in AP latency were studied from the electrocochleographs. In 48 cases (37%), there was no change, however, in 36 patients (28%), there was a prolongation of AP latency. A shortening is observed in 9 cases (7%). Other 36 cases (28%) were unknown, because accurate measurement of AP latency failed due to the included noise.<BR>Our conclusions are as follows:<BR>(1) There was a wide variation in the effect of lidocaine on AP latency, showing a prolongation in some, a shortening in others and no effect on the others.<BR>(2) It was not possible to clarify the relationship between the effect upon latency time, efficacy in treating tinnitus and clinical diagnosis of this disease state.<BR>(3) In the cases where a shortening of latency occurred, the change was slight and it was not clear from the time course whether this effect was truly due to administration of lidocaine HCl.<BR>(4) In the cases where a shortening of latency occurred, however, the effect was rapid and evident showing a correlation with the tissue concentration. This effect appeared two to five minutes following administration of lidocaine HCl and correlated almost exactly with the symptomatic relief of tinnitus and its effect upon hearing.<BR>(5) At the same time, SP latency was also prolongated and the peak values of SP and AP were decreased.<BR>(6) From the effect on SP, it is evident that lidocaine affects the organ of Corti directly. However, regarding the effect on AP, since it follows the effect on SP, it is not possible to determine whether or not this is a direct effect of lidocaine on the cochlear nerve. It is believed that the effect on N<SUB>2</SUB> is not a direct effect of lidocaine HCl.<BR>From the above findings, we can conclude that lidocaine HC1 has a direct electrophysiological effect upon the cochlea. The time course of this effect correlates directly with the disappearance of tinnitus and it is believed that the inhibition of tinnitus is cochlear-mediated.
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