Biomedical subjects

Fuh-Cherng Jeng

Publications and source records attributed to Fuh-Cherng Jeng.

6 recordsLinked to original sources

PubMed2006

Electrical excitation of the acoustically sensitive auditory nerve: single-fiber responses to electric pulse trains.

Nearly all studies on auditory-nerve responses to electric stimuli have been conducted using chemically deafened animals so as to more realistically model the implanted human ear that has typically been profoundly deaf. However, clinical criteria for implantation have recently been relaxed. Ears with "residual" acoustic sensitivity are now being implanted, calling for the systematic evaluation of auditory-nerve responses to electric stimuli as well as combined electric and acoustic stimuli in acoustically sensitive ears. This article presents a systematic investigation of single-fiber responses to electric stimuli in acoustically sensitive ears. Responses to 250 pulse/s electric pulse trains were collected from 18 cats. Properties such as threshold, dynamic range, and jitter were found to differ from those of deaf ears. Other types of fiber activity observed in acoustically sensitive ears (i.e., spontaneous activity and electrophonic responses) were found to alter the temporal coding of electric stimuli. The electrophonic response, which was shown to greatly change the information encoded by spike intervals, also exhibited fast adaptation relative to that observed in the "direct" response to electric stimuli. More complex responses, such as "buildup" (increased responsiveness to successive pulses) and "bursting" (alternating periods of responsiveness and unresponsiveness) were observed. Our findings suggest that bursting is a response unique to sustained electric stimulation in ears with functional hair cells.

Animals↗

PubMed2005

Effects of acoustic noise on the auditory nerve compound action potentials evoked by electric pulse trains.

This study investigated the effects of acoustic noise on the auditory nerve compound action potentials in response to electric pulse trains. Subjects were adult guinea pigs, implanted with a minimally invasive electrode to preserve acoustic sensitivity. Electrically evoked compound action potentials (ECAP) were recorded from the auditory nerve trunk in response to electric pulse trains both during and after the presentation of acoustic white noise. Simultaneously presented acoustic noise produced a decrease in ECAP amplitude. The effect of the acoustic masker on the electric probe was greatest at the onset of the acoustic stimulus and it was followed by a partial recovery of the ECAP amplitude. Following cessation of the acoustic noise, ECAP amplitude recovered over a period of approximately 100-200 ms. The effects of the acoustic noise were more prominent at lower electric pulse rates (interpulse intervals of 3 ms and higher). At higher pulse rates, the ECAP adaptation to the electric pulse train alone was larger and the acoustic noise, when presented, produced little additional effect. The observed effects of noise on ECAP were the greatest at high electric stimulus levels and, for a particular electric stimulus level, at high acoustic noise levels.

Action Potentials↗

PubMed2004

Intracochlear and extracochlear ECAPs suggest antidromic action potentials.

With experimental animals, the electrically evoked compound action potential (ECAP) can be recorded from multiple sites (e.g., round window, intracranial and intracochlear sites). However, human ECAPs are typically recorded from intracochlear electrodes of the implanted array. To bridge this difference, we obtained ECAPs from cats using both intracochlear and nerve-trunk recording sites. We also sought to determine how recording the site influences the acquired evoked potential and how those differences may provide insight into basic excitation properties. In the main experiment, ECAPs were recorded from four acutely deafened cats after implanting a Nucleus-style banded electrode array. Potentials were recorded from an electrode positioned on the nerve trunk and an intracochlear electrode. We manipulated stimulus level, electrode configuration (monopolar vs bipolar) and stimulus polarity, variables that influence the site of excitation. Intracochlear ECAPs were found to be an order of magnitude greater than those obtained with the nerve-trunk electrode. Also, compared with the nerve-trunk potentials, the intracochlear ECAPs more closely resembled those obtained from humans in that latencies were shorter and the waveform morphology was typically biphasic (a negative peak followed by a positive peak). With anodic monophasic stimuli, the ECAP had a unique positive-to-negative morphology which we attributed to antidromic action potentials resulting from a relatively central site of excitation. We also collected intracochlear ECAPs from twenty Nucleus 24 implant users. Compared with the feline ECAPs, the human potentials had smaller amplitudes and longer latencies. It is not clear what underlies these differences, although several factors are considered.

Action Potentials↗

PubMed2004

Estimating air-bone gaps using auditory steady-state responses.

Auditory steady-state responses (ASSR) were recorded using stimuli presented both via air conduction (AC ASSR) and bone conduction (BC ASSR) in 10 normal-hearing subjects with different degrees of simulated conductive hearing losses. The ASSR-estimated ABG (air-bone gap) was compared with the ABG measured using traditional pure-tone audiometric procedures. Reproducibility of the BC ASSR electrophysiological thresholds was also assessed. Additionally, a group of five subjects with profound sensorineural hearing loss was used to establish stimulation levels in which the BC ASSR was contaminated by stimulus artifact. Results of this investigation showed that the ASSR and behavioral ABGs were strongly correlated with each other (r = .81). However, ASSR-estimated ABGs slightly overestimated the magnitude of the behavioral. Reproducibility of the BC ASSR electrophysiological thresholds was good. Data from the five subjects with profound hearing loss, however, demonstrated that the levels where stimulus artifact became problematic were relatively low. This means BC stimulation may be appropriate only for subjects with normal or mildly impaired cochlear sensitivity.

Adult↗

PubMed2003

Auditory response to intracochlear electric stimuli following furosemide treatment.

The influence of functional hair cells on electrical stimulation of the auditory nerve is an important issue as individuals with significant residual hearing are now cochlear implant candidates. Previous work has shown that chemical deafening during the course of acute experiments changes the auditory nerve's responses to electrical stimulation [Third Quarterly Progress Report, NIH contract N01-DC-9-2106 (2000), Final Report, NIH Contract N01-DC-9-2106 (2002)]. This study extended that work by investigating the changes and subsequent recovery following furosemide injections which reversibly impair hair-cell function [Hear. Res. (1980) 79-89; Hear. Res. 14 (1984) 305-314, J. Physiol. 347 (1984) 685-696; Hear. Res. 71 (1993) 202-207]. Acoustic sensitivity of guinea pig subjects was repeatedly monitored with the click-evoked compound action potential. Responses to single biphasic electric pulses and biphasic electric pulse trains delivered by a monopolar intracochlear electrode were also repeatedly assessed using the electrically evoked compound action potential (ECAP). Our measures demonstrated a clear relationship between the state of hair-cell function and ECAP responses, as changes in the latter coincided with the loss or recovery of acoustic sensitivity. ECAP growth functions demonstrated increased slope and increased maximum (saturation) amplitude. Both trends were reversible and followed approximately the time course of post-furosemide hearing recovery. Additional changes were observed using electric pulse-train stimulation: (1) the magnitude of ECAP amplitude alternation (observed in response to successive stimulus pulses) increased, (2) the degree of ECAP adaptation (measured 80-100 ms after pulse-train onset) increased, and (3) the degree of refractoriness (measured by the ratio of ECAP amplitudes to the second and first pulses) tended to increase. All these trends are consistent with the hypothesis that functional hair cells desynchronize the population of auditory nerve fibers, thereby changing the electrically evoked responses. Viable hair cells may therefore provide positive effects on auditory response to electric stimuli delivered to implant patients with residual hearing, as they may enhance the random activity of the stimulated nerve.

Animals↗

PubMed2003

Relationship of preoperative findings and ossicular discontinuity in chronic otitis media.

BACKGROUND: Ossicular discontinuity may result from chronic otitis media, with or without cholesteatoma, and usually cannot be determined unless an operation is performed. If preoperative information can be used to determine whether or not the ossicular chain is intact, the patient can be better informed and the surgeon can be better prepared before surgery. OBJECTIVE: To examine the correlation between preoperative findings and the status of the ossicular chain at surgery. STUDY DESIGN: Retrospective. SETTING: A tertiary referral center. PATIENTS: Data from 190 patients (212 ears) who were undergoing their first operations for chronic otitis media were reviewed. INTERVENTION: The operations for the cholesteatoma or noncholesteatoma ears were classified into different groups and analyzed separately. Ossicular discontinuity was identified only if the discontinuity of the ossicular chain was confirmed at the time of operation. RESULTS: The cholesteatoma group consisted of 59 ears, and the noncholesteatoma group contained 153 ears. In the cholesteatoma group, two statistically significant preoperative parameters were observed to be significantly correlated with ossicular discontinuity: persistently draining ears (p = 0.026) and a cholesteatoma that extended to the tympanic sinus (p = 0.006). In the noncholesteatoma group, only one parameter was observed to be predictive of ossicular discontinuity. In this group of patients, perforation of the tympanic membrane with an edge adherent to the promontory occurred significantly more frequently in patients with ossicular discontinuity (p = 0.004) than in those with intact ossicular chains. Surprisingly, an air-bone gap was not significantly correlated with ossicular discontinuity. The cholesteatoma and granulation tissue in the middle ear cavity may serve as transmission bridges of acoustic energy, resulting in narrowed air-bone gaps. CONCLUSIONS: In the cholesteatoma group, both cholesteatoma extension into the tympanic sinus and persistently draining ears were predictive of ossicular discontinuity. In the noncholesteatoma group, perforation edges adhering to the promontory also revealed a higher incidence of ossicular discontinuity. Therefore, all these findings can be considered as potential preoperative predictors of ossicular discontinuity in chronic otitis media.

Adolescent↗