Chronological changes in the eighth cranial nerve compound action potential (CAP) in experimental endolymphatic hydrops: the effects of altering the polarity of click sounds.
CONCLUSIONS
Using a guinea pig model of experimental endolymphatic hydrops, click sounds of altered polarity showed different latencies and amplitudes in hydropic compared with normal cochleae. Latency changes appeared as early as 1 week after endolymphatic obstruction. This method can help diagnose endolymphatic hydrops.


OBJECTIVE
The goal of the study was to develop an objective electrophysiological diagnosis of endolymphatic hydrops.


METHODS
Endolymphatic hydrops were created surgically in guinea pigs. The latency and the amplitude of the eighth cranial nerve compound action potential (CAP) for click sounds of altered polarity were measured up to 8 weeks after the surgery.


RESULTS
At early stages after surgery, the latency for condensation clicks became longer, and at later stages the latencies for both condensation and rarefaction became longer. The discrepancy in the latencies for rarefaction and condensation click sounds (rarefaction minus condensation) became larger by the first week after surgery, but no further discrepancy occurred thereafter. Compared with latency changes, amplitude changes in the CAP were rapid and progressive following surgery, suggesting ongoing damage to hair cells.
Morizono
Tetsuo
T
Department of Otolaryngology, Nishi Fukuoka Hospital, Fukuoka, Japan. morizono2004@yahoo.co.jp
Kondo
Tsuyoshi
T
Yamano
Takafumi
T
Miyagi
Morimichi
M
Shiraishi
Kimio
K
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001300:Audiometry, Evoked Response / Q000379:methods*; D004195:Disease Models, Animal; D018159:Endolymphatic Hydrops / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D008297:Male; D011237:Predictive Value of Tests; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D000159:Vestibulocochlear Nerve / Q000503:physiopathology*