Reversed ipsilateral acoustic reflex: a study on subjects treated with muscle relaxants.
OBJECTIVE
To rule out any possible involvement of the middle ear muscles in the genesis of the reversed ipsilateral acoustic reflex (RIAR).


METHODS
Prospective study to evaluate the effects of muscle relaxants on the RIAR of otosclerotic ears as well as on the acoustic reflex of individuals with normal middle ear function. Admittance recording during ipsilateral acoustic stimulation was performed in patients undergoing pharmacological treatment for surgical procedures. Fentanyl, propofol, and a muscle relaxant were sequentially administered intravenously. Ipsilateral acoustic reflexes were recorded before and after each drug injection. Three patients were affected from otosclerosis, whereas 14 individuals had normal middle ear function. Moreover, the ipsilateral acoustic reflex obtained in normal subjects after their treatment with muscle relaxants was compared with that of 10 otosclerotic patients who were not treated pharmacologically.


RESULTS
The RIAR of three otosclerotic ears was not inhibited by muscle relaxants as well as by fentanyl and propofol. Moreover, muscle relaxants, when administered in normal subjects, always induced the block of the stapedial reflex that was replaced by a reversed reflex strictly similar to the RIAR of the 10 otosclerotic patients not treated pharmacologically. Propofol could also induce, in most of the cases, the reduction and in some occasion even the reversal of the stapedial reflex, whereas fentanyl did not affect it significantly.


CONCLUSIONS
The RIAR does not appear to be related to the contraction of the middle ear muscles.
Ciardo
Alberto
A
Department of Otolaryngology, Ospedale Bassini, Cinisello Balsamo (MI), Italy.
Garavello
Werner
W
Leva
Marina
M
Graziano
Bruno
B
Gaini
Renato Maria
RM
D000161:Acoustic Stimulation; D000328:Adult; D016022:Case-Control Studies; D004432:Ear, Middle / Q000502:physiology*; D005260:Female; D005283:Fentanyl / Q000494:pharmacology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D009125:Muscle Relaxants, Central / Q000494:pharmacology*; D010040:Otosclerosis / Q000503:physiopathology*; D015742:Propofol / Q000494:pharmacology; D011446:Prospective Studies; D012022:Reflex, Acoustic / Q000187:drug effects*
D009125:Muscle Relaxants, Central; D005283:Fentanyl; D015742:Propofol