Ipsilateral Reflex Thresholds Research Articles

Acoustic Reflexes in Aural Atresia Patients: Evidence of an Intact Efferent System?

To record crossed acoustic reflex thresholds (xART's) postoperatively from patients after surgical repair of unilateral congenital aural atresia (CAA). To seek explanations for when xARTs can and cannot be recorded. We hope to understand the implications for this central auditory reflex despite early afferent deprivation. Patients who underwent surgery to correct unilateral CAA at a tertiary academic medical were prospectively enrolled to evaluate for the presence of xART. Preoperative ARTs in the normal (non-atretic) ear, and postoperative ipsilateral ARTs (stimulus in the normal ear) and contralateral ARTs (stimulus in the newly reconstructed atretic ear; record in the normal ear) were measured at 500, 1000, and 2000 Hz. Four of 11 patients with normal ipsilateral reflex thresholds preoperatively demonstrated crossed acoustic reflexes postoperatively (stimulus in reconstructed ear; record from normal ear). Four other patients demonstrated normal ipsilateral thresholds preoperatively but did not have crossed reflexes postoperatively. No reflexes (pre- or postoperatively) could be recorded in 3 patients. Crossed reflex threshold is significantly correlated with the postoperative audiometric threshold. There was no correlation between ipsilateral and contralateral reflex thresholds. Crossed acoustic reflexes can be recorded from some but not all postoperative atresia patients, and the thresholds for those reflexes correlate with the postoperative pure tone threshold. The presence of acoustic reflexes implies an intact CN VIII-to-opposite CN VII central reflex arc despite early unilateral sound deprivation.

Auditory Deficits and Hearing Loss Associated with Focal Brainstem Haemorrhage

Four cases of central pontine haemorrhage are described in which auditory dysfunction was documented. Two cases had a hearing loss, in one of which there was recovery of the low frequencies. This case provides support for the tonotopic organization of the auditory pathways in the caudal pontine area, with the lowest frequencies being encoded medially. In all cases, there were abnormalities of the auditory brainstem responses, wave V being consistently involved, while wave III was abnormal in only one patient. In three cases, the masking level differences and crossed acoustic reflex thresholds were abnormal. The ipsilateral reflex thresholds were normal at least on one side in all cases. In the patient with the most significant hearing loss, loudness recruitment, assessed both psychophysically and with the acoustic reflex thresholds, was evident. These data are interpreted in terms of there being damage to the medial superior olivary nuclei and trapezoid body involving both afferent and efferent fibres.

Tympanometric and acoustic-reflex studies in neonates.

Tympanograms and acoustic reflexes for a broadband noise and for a 1000-Hz tone were measured in normal neonates. Notched tympanograms were typical of neonatal ears for a 220-Hz probe tone. A single-peaked tympanogram was most characteristic for a probe frequency of 660 Hz. Ipsilateral and contralateral acoustic reflexes were present more frequently for a 660-Hz probe tone compared to a 220-Hz probe tone, but acoustic-reflex thresholds were not significantly different between probe tones. As with adults, acoustic-reflex thresholds for the noise were significantly lower than for the tone, and ipsilateral reflex thresholds were lower than contralateral reflex thresholds. Reliability of acoustic-reflex and tympanometric measures was high. Age change from 2 to 4 days had no significant effect on tympanometric or acoustic-reflex characteristics. There was no apparent relation between tympanometric pattern and acoustic-reflex characteristics.