PP502 - Comparison of Auditory Brainstem Responses Recorded from Three Different Clinical Systems

Abstract:
The Auditory brainstem response (ABR) is the primary procedure to estimate hearing thresholds in infants.Chirp is the newly recommended stimulus used to estimate hearing thresholds in infants, it elicits ABRs with large amplitudes at threshold levels which reduces overall test time. Currently, studies are scarce comparing FDA-approved clinical ABR systems. In this study we analyzed the InteracousticsEP-25, Intelligent Hearing System, and Vivosonic Integrity V500, with click and tone bursts and broadband and narrowbandchirp stimuli, on eleven normal hearing adults. Within and between clinical system differences were observed for different test stimuli.

Summary:
Rationale:
Auditory brainstem response (ABR) testing is the gold standard procedure to estimate hearing thresholds in infants, young children, or difficult-to-test populations The ABR can be recorded by presenting short-duration stimuli that are broadband (broadband Click and Chirp) or frequency tone bursts (TB) or narrowband chirps (NBC) Click stimulus dominantly activates the base of the cochlea and not the apex of the cochlea.

Chirp is a new stimulus that is mathematically designed such that it simultaneously excites a wide range of the cochlea from base to apex resulting in a large response amplitude. Hence, researchers recommend using a chirp stimulus for ABR threshold estimation. A variety of FDA approved ABR recording systems are available.

These ABR systems use of chirp stimuli to record ABR. In theory, these ABR systems should yield similar results for all test stimuli. However, we are not aware of any studies that have compared ABR results between commercially available ABR systems. In this research, we examined whether there are any significant differences in ABR thresholds for different stimuli between the three FDA-approved systems. 

Design:
Eleven normal-hearing adults (22-37 years) were included in this study. ABRs were recorded using the following systems from one ear only Interacoustics EP-25, Intelligent Hearing System and Vivosonic Integrity V500. ABR systems were either factory-calibrated Vivosonic] or calibrated by a certified technician Interacoustics EP-25 ABRs were recorded for traditional stimuli [click, TBs (0.5,1, 2, and 4 kHz)] and chirp stimuli broadband chirp (CE-LS-Chirp,iChirp, and vChirp), and NBCs (>0.5, 1, 2, and 4 kHz)]. The ABRs were averaged over a 25 ms window, amplified, and filtered (30-3000Hz). All stimuli were presented at a rate of 39.1/sec. ABR thresholds for all test stimuli were obtained. 

Results: ,
Within System comparison: The EP25 system showed similar ABR thresholds for 0.5 kHz TB and 0.5 kHz NBC. ABR thresholds were lower (p < 0.05) for remaining chirp stimuli compared to traditional stimuli. The IHS system showed similar ABR thresholds for chirp and traditional stimuli. The Vivosonic system showed elevated ABR thresholds 0.5 kHz NBC when compared to thresholds for 0.5 kHz TB. ABR thresholds for remaining chirp and traditional stimuli were similar. 

Between system comparison: ABR thresholds of the Vivosonic system for 0.5 kHz NBC were significantly higher compared to the EP25 system. No other significant differences in ABR thresholds for other stimuli were observed between systems.

Estimated hearing levels (eHL) for tone bursts were similar between systems and closely matched with published literature. However, for narrowband chirps were different between systems ( > 5-10 dB).

Conclusions:
Within the manufacturer, differences were between traditional and chirp stimuli. However, all three FDA-approved ABR systems showed similar thresholds for traditional stimuli and chirp stimuli except for 0.5 kHz NBC. Based on these findings we recommend that system-specific eHL should be collected for chirp stimuli.