Original Paper ORL 1992:54:285-294
Department of Otolaryngology. Cantonal University Hospital. Geneva. Switzerland
Electrically Evoked Auditory Brainstem Responses in Cochlear Implant Patients
Key Words
Abstract
Evoked potentials Auditory brainstem responses Electrical stimulation Cochlear implant Human
Electrically evoked auditory brainstem responses (EABR) were recorded in completely deaf patients implanted with Ineraid™ multichannel cochlear implants. Clear and reproducible EABR were obtained from all patients. Para metric differences with auditory brainstem responses (ABR) were demon strated and can be explained by the different natures of both types of stimula tions (electric versus acoustic). Evidence is given that other well-known prop erties of auditory evoked responses, like ‘binaural interaction' or suppression of responses in a forward masking paradigm, can be observed in EABR of implanted patients.
Introduction
Cochlear implants change sound into electrical signals to stimulate directly remaining auditory nerve fibers in profoundly deaf individuals. If one reasons that activa tion of the auditory system by electrical stimulation is a necessary, of course not sufficient, condition for success with a cochlear implant, then one needs means to evaluate the effects of electrical stimulation in deaf patients. Be havioral tests before and after implantation are used by most implant centers [ 1] as a help towards several impor tant decisions that need to be made in dealing with coch lear implant candidates or new cochlear implant users. Unfortunately, reliable behavioral responses are not available in many clinical situations, e.g. in case of con genital deafness, in deaf children or during general anes thesia. Therefore, we investigated the use of the electri cally evoked auditory brainstem response (EABR) as a possible complement to these procedures. In this paper we will summarize the results of a series of experiments we made in Geneva to characterize EABR in patients using the Ineraid™ multichannel cochlear implant system.
General Methods Subjects and Cochlear Implant
We report data from 12 patients, aged from 18 to 73 years. All patients had been completely deaf for periods ranging from 2 to 57 years. The patients' data arc summariz.ed in table 1. All patients were fitted with the Ineraid multichannel cochlear implant system (fig. 1). Recording Technique
Patients were lying comfortably on an hospital couch. Neither sedative nor anesthetic drugs were administered. Silver-silver chlo ride electrodes were attached on the forehead and to each mastoid. A self-adhesive ECG electrode on the arm served as ground. Elcctrophysiological responses were recorded simultaneously be tween the forehead and the mastoid electrodes, ipsi- and contralat eral to the simulated ear. Brain signals were amplified with a gain of 50,000 in a bandwidth from DC to 3.000 Hz and digitized (16 bits) at 20 kHz. At least 2.000 trials were averaged, and two separate record ings were made for each stimulus condition. Ground-isolated, lownoise amplifiers were specially constructed in the laboratory and designed to recover full sensitivity within a few hundred microse conds after stimulus end. Responses with voltages exceeding 65 pV after stimulus end were automatically rejected by the averaging pro gram.
Prof. Pierre Montandon Department of Otolaryngolog> Cantonal University Hospital 0 1 - 1 2 11 Geneva 4 (Switzerland)
1992 S. Karger AG. Basel 0301-1569/92/0546-0285 $2.75/0
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 10:19:48 PM
Andreas Kasper Marco Pelizzone Pierre Montandon
BR
Fig. 1. Electrode array of the Ineraid™ multichannel intracoch leär implant. The implanted part consists o f eight platinum elec trodes (spherical. 0.5 mm diameter) which arc directly connected to a percutaneous plug. Six electrodes, spaced at 3.6-mm intervals, are placed inside the cochlea. They are numbered from 1 to 6 from apex to base. Electrode 1 is usually located 18-25 mm from the round window into the scala tympani. Electrodes 7 and 8 are placed outside the cochlea and serve as far field ground.
TJ.
Table 1. Patient characteristics
Subject
Etiology
Duration
H .G . 1 (f. 1928)
Mondinia Mondini
57
Meningitis Unknown3
D. J. (m. 1921)
Otosclerosis
L. C.(f. 1919)
Ototoxic
L. A. (f. 1953) T. J. (f. 1938)
U nknown Otosclerosis
50 2 10 6 21
L. W. (f. 1959)
Meningitis
A.G. (m. 1952) C. M. (m. 1921)
Head trauma
10 7 14
Progressive
49
M. L. (m. 1941 )
Ototoxic
18
R. S. (f. 1948)
Meningitis
25
Patients are identified by their initials, sex and year of birth. The etiology as well as the duration (in years) of their total deafness is given. a Ears with presumed congenital deafness.
286
M.L.
30 CM. I--------- 1--------- 1---------1--------- 1--------- 1 0
2
4
6
8
10m s
Fig. 2. EABR from 12 implanted patients. Only ipsilateral re sponses are shown. Stimuli were biphasic (100 ps/phase) current pulses presented every 91 ms. Current levels were chosen to be in the upper part of the patients' dynamic ranges. In most cases. 2,048 trials were averaged for each trace. Vertex-positive deflections are plotted upwards. The patients’ initials are given on the right.
Kasper/Pelizzone/Montandon
EABR in Cochlear Implant Patients
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 10:19:48 PM
H .G . 2(f. 1928) B. R. (m. 1969) H. F. (f, 1958)
Fig. 3. Electrical versus acoustic activa tion o f the autory system, a-c Brain re sponse evoked by electrical stimulation of the auditory nerve in an implanted deaf patient (B. R.). d-f Brain responses evoked by acoustic stimulation in a normal-hear ing subject (A. K.). a, d Short latency or brainstem responses, b, e Middle latency responses, c, f Long latency or cortical re sponses. For short and middle latency re sponses. stimuli were biphasic (100 ps/ phase) pulses repeated every 100 ms. at least 2.048 trials were averaged for each trace, and vertex-positive deflections are plotted up wards. For long latency responses, stimuli were tone bursts ( 1.000 Hz. duration 20 ms) repeated every 2 s. at least 256 trials were averaged for each trace, and vertex-negative deflections are plotted upwards.
Stimuli were biphasic current pulses with sinusoidal shape pre sented at a rate of 11/s and with alternating polarity of the initial phase. Pulse duration was usually 100 ps/phase and. in a few cases. 200 ps/phase. The stimulus current was measured in pA peak-topeak (pApp). The stimuli were delivered directly to the implanted electrodes via the percutaneous plug. The current generator was sepa rated from the common ground by optoisolated amplifiers, and all electronic equipment connected to the patients was battery powered. Details of the stimulation and recording equipment are described elsewhere [2], At the beginning o f each recording session, the behavioral thresh old and the uncomfortable loudness level were measured for each stimulus condition. These values served to define the range of accept able stimulation levels in the subsequent recording sessions.
Results
Experiment I: EABR in Implanted Patients The goal of this first experiment was to evaluate the reproducibility of EABR from different patients. The waveforms recorded from all patients are shown in fig ure 2. Clear and reproducible responses were observed. The morphology and latency of the most prominent peaks was consistent across patients. Two vertex-positive peaks were systematically observed in all recordings, one at a latency of about 3.9 ms and a second at about 2.2 ms. In
some recordings, a third peak was found at about 1.4 ms as well as a small indentation, at about 3.4 ms, on the ascending limb of the biggest peak. Experiment 2: Electrical versus Acoustic Activation o f the Auditory System This experiment was designed to compare auditory evoked responses elicited by electric stimulation of the cochlea in a totally deaf patient (B. R.) to those obtained by acoustic stimulation in a normal hearing subject (A. K.). Recordings were obtained on the same equip ment. The stimulus waveform was the same in both cases, except that the acoustic stimuli were generated by passing the electric stimulus through TDH-39 earphones (96 dB SPL). Responses were recorded in three different time windows (0-10 ms, 0-50 ms and 0-500 ms) that are typi cal of short, middle and long latency auditory evoked responses [3]. Results are presented in figure 3. Vertex-positive peaks of the electrically evoked brainstem responses were la beled with roman numerals according to Jewett and Williston [4], Peaks of the electrically middle latency re sponses were labeled according to Goldstein and Rodman [5]. Peaks of the electrically evoked long latency responses were labeled according to Davis and Zerlin [6].
287
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 10:19:48 PM
Stimuli
Table 2. EABR versus ABR latencies
Peaks
EABR
ABR
latency 1 II III IV V VI II-V III-V IV-V
_
n
_
1.38 + 0.09 2.16 + 0.18 3.43 ±0.24 3.94 ±0.22 2.54 ±0.13 1.79 ±0.17 0.44 ±0.2
7 16 7 16 7 16 7
latency
n
1.7 ± 0 .15 2.8 ±0.17 3.9 ±0.19 5.1 ±0.24 5.7 + 0.25 7.3 ±0.29 2.9 ± 0.17 1.9 ± 0.18 0 .7 ± 0 .19
50 50 50 50 50 50 50 50 50
Difference“ t test P
_ 1.42 1.74 1.67 1.76 0.36 0.11 0.26
_ 2 X 1 0 -7
Department of Otolaryngology. Cantonal University Hospital. Geneva. Switzerland
Electrically Evoked Auditory Brainstem Responses in Cochlear Implant Patients
Key Words
Abstract
Evoked potentials Auditory brainstem responses Electrical stimulation Cochlear implant Human
Electrically evoked auditory brainstem responses (EABR) were recorded in completely deaf patients implanted with Ineraid™ multichannel cochlear implants. Clear and reproducible EABR were obtained from all patients. Para metric differences with auditory brainstem responses (ABR) were demon strated and can be explained by the different natures of both types of stimula tions (electric versus acoustic). Evidence is given that other well-known prop erties of auditory evoked responses, like ‘binaural interaction' or suppression of responses in a forward masking paradigm, can be observed in EABR of implanted patients.
Introduction
Cochlear implants change sound into electrical signals to stimulate directly remaining auditory nerve fibers in profoundly deaf individuals. If one reasons that activa tion of the auditory system by electrical stimulation is a necessary, of course not sufficient, condition for success with a cochlear implant, then one needs means to evaluate the effects of electrical stimulation in deaf patients. Be havioral tests before and after implantation are used by most implant centers [ 1] as a help towards several impor tant decisions that need to be made in dealing with coch lear implant candidates or new cochlear implant users. Unfortunately, reliable behavioral responses are not available in many clinical situations, e.g. in case of con genital deafness, in deaf children or during general anes thesia. Therefore, we investigated the use of the electri cally evoked auditory brainstem response (EABR) as a possible complement to these procedures. In this paper we will summarize the results of a series of experiments we made in Geneva to characterize EABR in patients using the Ineraid™ multichannel cochlear implant system.
General Methods Subjects and Cochlear Implant
We report data from 12 patients, aged from 18 to 73 years. All patients had been completely deaf for periods ranging from 2 to 57 years. The patients' data arc summariz.ed in table 1. All patients were fitted with the Ineraid multichannel cochlear implant system (fig. 1). Recording Technique
Patients were lying comfortably on an hospital couch. Neither sedative nor anesthetic drugs were administered. Silver-silver chlo ride electrodes were attached on the forehead and to each mastoid. A self-adhesive ECG electrode on the arm served as ground. Elcctrophysiological responses were recorded simultaneously be tween the forehead and the mastoid electrodes, ipsi- and contralat eral to the simulated ear. Brain signals were amplified with a gain of 50,000 in a bandwidth from DC to 3.000 Hz and digitized (16 bits) at 20 kHz. At least 2.000 trials were averaged, and two separate record ings were made for each stimulus condition. Ground-isolated, lownoise amplifiers were specially constructed in the laboratory and designed to recover full sensitivity within a few hundred microse conds after stimulus end. Responses with voltages exceeding 65 pV after stimulus end were automatically rejected by the averaging pro gram.
Prof. Pierre Montandon Department of Otolaryngolog> Cantonal University Hospital 0 1 - 1 2 11 Geneva 4 (Switzerland)
1992 S. Karger AG. Basel 0301-1569/92/0546-0285 $2.75/0
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 10:19:48 PM
Andreas Kasper Marco Pelizzone Pierre Montandon
BR
Fig. 1. Electrode array of the Ineraid™ multichannel intracoch leär implant. The implanted part consists o f eight platinum elec trodes (spherical. 0.5 mm diameter) which arc directly connected to a percutaneous plug. Six electrodes, spaced at 3.6-mm intervals, are placed inside the cochlea. They are numbered from 1 to 6 from apex to base. Electrode 1 is usually located 18-25 mm from the round window into the scala tympani. Electrodes 7 and 8 are placed outside the cochlea and serve as far field ground.
TJ.
Table 1. Patient characteristics
Subject
Etiology
Duration
H .G . 1 (f. 1928)
Mondinia Mondini
57
Meningitis Unknown3
D. J. (m. 1921)
Otosclerosis
L. C.(f. 1919)
Ototoxic
L. A. (f. 1953) T. J. (f. 1938)
U nknown Otosclerosis
50 2 10 6 21
L. W. (f. 1959)
Meningitis
A.G. (m. 1952) C. M. (m. 1921)
Head trauma
10 7 14
Progressive
49
M. L. (m. 1941 )
Ototoxic
18
R. S. (f. 1948)
Meningitis
25
Patients are identified by their initials, sex and year of birth. The etiology as well as the duration (in years) of their total deafness is given. a Ears with presumed congenital deafness.
286
M.L.
30 CM. I--------- 1--------- 1---------1--------- 1--------- 1 0
2
4
6
8
10m s
Fig. 2. EABR from 12 implanted patients. Only ipsilateral re sponses are shown. Stimuli were biphasic (100 ps/phase) current pulses presented every 91 ms. Current levels were chosen to be in the upper part of the patients' dynamic ranges. In most cases. 2,048 trials were averaged for each trace. Vertex-positive deflections are plotted upwards. The patients’ initials are given on the right.
Kasper/Pelizzone/Montandon
EABR in Cochlear Implant Patients
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 10:19:48 PM
H .G . 2(f. 1928) B. R. (m. 1969) H. F. (f, 1958)
Fig. 3. Electrical versus acoustic activa tion o f the autory system, a-c Brain re sponse evoked by electrical stimulation of the auditory nerve in an implanted deaf patient (B. R.). d-f Brain responses evoked by acoustic stimulation in a normal-hear ing subject (A. K.). a, d Short latency or brainstem responses, b, e Middle latency responses, c, f Long latency or cortical re sponses. For short and middle latency re sponses. stimuli were biphasic (100 ps/ phase) pulses repeated every 100 ms. at least 2.048 trials were averaged for each trace, and vertex-positive deflections are plotted up wards. For long latency responses, stimuli were tone bursts ( 1.000 Hz. duration 20 ms) repeated every 2 s. at least 256 trials were averaged for each trace, and vertex-negative deflections are plotted upwards.
Stimuli were biphasic current pulses with sinusoidal shape pre sented at a rate of 11/s and with alternating polarity of the initial phase. Pulse duration was usually 100 ps/phase and. in a few cases. 200 ps/phase. The stimulus current was measured in pA peak-topeak (pApp). The stimuli were delivered directly to the implanted electrodes via the percutaneous plug. The current generator was sepa rated from the common ground by optoisolated amplifiers, and all electronic equipment connected to the patients was battery powered. Details of the stimulation and recording equipment are described elsewhere [2], At the beginning o f each recording session, the behavioral thresh old and the uncomfortable loudness level were measured for each stimulus condition. These values served to define the range of accept able stimulation levels in the subsequent recording sessions.
Results
Experiment I: EABR in Implanted Patients The goal of this first experiment was to evaluate the reproducibility of EABR from different patients. The waveforms recorded from all patients are shown in fig ure 2. Clear and reproducible responses were observed. The morphology and latency of the most prominent peaks was consistent across patients. Two vertex-positive peaks were systematically observed in all recordings, one at a latency of about 3.9 ms and a second at about 2.2 ms. In
some recordings, a third peak was found at about 1.4 ms as well as a small indentation, at about 3.4 ms, on the ascending limb of the biggest peak. Experiment 2: Electrical versus Acoustic Activation o f the Auditory System This experiment was designed to compare auditory evoked responses elicited by electric stimulation of the cochlea in a totally deaf patient (B. R.) to those obtained by acoustic stimulation in a normal hearing subject (A. K.). Recordings were obtained on the same equip ment. The stimulus waveform was the same in both cases, except that the acoustic stimuli were generated by passing the electric stimulus through TDH-39 earphones (96 dB SPL). Responses were recorded in three different time windows (0-10 ms, 0-50 ms and 0-500 ms) that are typi cal of short, middle and long latency auditory evoked responses [3]. Results are presented in figure 3. Vertex-positive peaks of the electrically evoked brainstem responses were la beled with roman numerals according to Jewett and Williston [4], Peaks of the electrically middle latency re sponses were labeled according to Goldstein and Rodman [5]. Peaks of the electrically evoked long latency responses were labeled according to Davis and Zerlin [6].
287
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 10:19:48 PM
Stimuli
Table 2. EABR versus ABR latencies
Peaks
EABR
ABR
latency 1 II III IV V VI II-V III-V IV-V
_
n
_
1.38 + 0.09 2.16 + 0.18 3.43 ±0.24 3.94 ±0.22 2.54 ±0.13 1.79 ±0.17 0.44 ±0.2
7 16 7 16 7 16 7
latency
n
1.7 ± 0 .15 2.8 ±0.17 3.9 ±0.19 5.1 ±0.24 5.7 + 0.25 7.3 ±0.29 2.9 ± 0.17 1.9 ± 0.18 0 .7 ± 0 .19
50 50 50 50 50 50 50 50 50
Difference“ t test P
_ 1.42 1.74 1.67 1.76 0.36 0.11 0.26
_ 2 X 1 0 -7
