Biomedical subjects

L L Pierson

Publications and source records attributed to L L Pierson.

7 recordsLinked to original sources

PubMed1999

Effects of intense noise exposure on fetal sheep auditory brain stem response and inner ear histology.

OBJECTIVE: To evaluate, in two separate experiments, the effects of intense noise exposures delivered to fetal sheep in utero during a time of rapid auditory development. DESIGN: In the first experiment, auditory brain stem response (ABR) thresholds to clicks and tone bursts were recorded from chronically instrumented fetal sheep in utero before and after exposure of pregnant ewes to intense broadband noise. A single 16 hr exposure was delivered at 113 days gestational age, a time when the ABR is just emerging. Thresholds were compared with an age-matched, nonexposed control group. In the second experiment, fetal sheep at the same gestational age were exposed four times to broadband noise and their cochleae were harvested 20 days later for histological analysis by the use of scanning electron microscopy. Comparisons were made with an age-matched, nonexposed control group. RESULTS: Experiment One: ABR thresholds recorded between 10 to 20 days after the exposure were not as sensitive as thresholds obtained from control fetuses. There was a tendency for thresholds to 0.5 kHz tone bursts to be more affected than thresholds to clicks. Experiment Two: Scanning electron microscopy of the organ of Corti from fetuses exposed to noise from 111 to 114 days gestational age revealed significant damage to inner and outer hair cells in the middle and apical turns of cochleae. Similar hair cell damage was not present in control fetuses. CONCLUSIONS: Intense exogenous noise penetrated the uterus of pregnant sheep and resulted in elevations in ABR thresholds 2 to 3 wk after exposure. In fetuses repeatedly exposed to noise, the middle and apical turns of the cochlea showed greater hair cell damage than found at the same locations in control cochlea. The basal turn of the cochlea was not damaged.

Animals↗

PubMed1996

Auditory brainstem response in sheep. Part II: Postnatal development.

The auditory brainstem response (ABR) was recorded from 15 chronically instrumented lambs between birth and 7 weeks of age as well as from four adult ewes. Latency changes observed within two days of birth may be related to the dissipation of fluid from the lamb external auditory canal and middle ear cavity. Developmental changes observed in the lambs included an early period of wave latency decrements from 1 to 4 weeks followed by a subsequent increase in wave latencies from 4 to 7 weeks. These changes were significant for the I-IV interwave interval, possibly reflecting the combined effects of increased myelinization and increased neural track length. Responses from 7 week-old lambs were not significantly different from those obtained from the ewes.

Aging↗

PubMed1996

Hazards of noise exposure on fetal hearing.

Many women of childbearing age are occupationally or recreationally exposed to hazardous levels of noise. Questions regarding the possibility of noise-induced hearing loss during fetal life have been posed. Advice to pregnant women regarding the safe limits of noise exposure has been lacking, because the evidence concerning the existence of fetal noise-induced hearing loss is sparse and the effects of intense noise exposures on the fetuses of pregnant women are largely unknown. Because of the nature of the fetal sound environment and the development of the ear, it is possible that fetal noise-induced hearing loss presents itself very differently than adult noise-induced hearing loss. Previous research in small mammals has suggested a critical period in development when susceptibility to noise exposure may be greater. Several investigations, using sheep as a model for in utero hearing loss, have provided evidence of fetal hearing changes after noise exposure. Although the reported epidemiological studies concerned with the possibility of fetal hearing loss had limitations, there were some suggestions of noise-induced hearing loss in children whose mothers experienced noise exposure. This article provides some background information concerning the possibility of fetal noise-induced hearing less.

Animals↗

PubMed1995

Auditory brainstem response in sheep. Part I: Fetal development.

The Auditory Brainstem Response (ABR) was recorded from fetal sheep in utero between gestational ages of 111 days and 136 days (Normal gestation is 145 days). The ABR was detected at 111 days gestation (dGA) and morphology of the waveform improved rapidly from 116 to 123 dGA. At 123 dGA, the four vertex-positive peaks were similar to those observed in adult ewes. Thresholds of the ABR to clicks and tone bursts improved rapidly between 111 and 123 dGA. From 123 to 136 dGA, ABR thresholds continued to improve, but at a much slower rate. Latencies for the peaks also decreased during development from 111 to 136 days, with latencies for Waves III and IV showing a greater decrease than latencies for Waves I and II.

Animals↗

PubMed1994

Noise induced hearing loss in fetal sheep.

The auditory brainstem response (ABR) was recorded in utero from chronically instrumented fetal sheep prior to and following exposure of pregnant ewes to intense broadband noise (120 dB SPL for 16 h). ABRs were elicited by clicks and tone bursts (0.5, 1, 2, and 4 kHz) delivered through a bone oscillator secured to the fetal skull. Latency-intensity functions for most of the four vertex-positive waves (labelled I-IV) were prolonged and ABR thresholds were temporarily elevated by an average of 8 dB following the noise exposure. Results show that exogenous sounds can penetrate the uterus and result in alterations of the fetal ABR.

Acoustic Stimulation↗

PubMed1994

Effect of impulse noise on the auditory brainstem response of the fetal sheep and the adult ewe: case study.

Auditory brainstem responses (ABR) were obtained from a sheep fetus in utero and from a nonpregnant ewe before and after a noise exposure generated by 10 105-mm howitzer impulses (160-166 dB peak pressure). Fetal ABR thresholds shifted by less than 15 dB, whereas the adult thresholds shifted more than 50 dB. Comparison of exposed and nonexposed fetal cytocochleograms revealed minimal sensory cell loss in two age-matched animals. Although fetal ABR threshold shifts were noted in this study, the magnitude of shift was modest when compared to the significant elevation of the adult ABR thresholds.

Acoustic Stimulation↗

PubMedDate not supplied

Relationship between outer ear resonance and permanent noise-induced hearing loss.

INTRODUCTION: Prolonged exposure to noise produces permanent hearing loss in the frequency region centered around 4,000 Hz despite differences in the spectral and temporal characteristics of the noise. It is unclear to what extent properties of the auditory system contribute to the development of permanent hearing loss in this frequency region. This study was designed to evaluate the relationship between the frequency of peak outer ear resonance and the frequency of maximum hearing loss in a population of patients with a history of noise exposure. MATERIALS AND METHODS: Analysis of the frequency of maximum hearing loss was completed with sweep frequency Bekesy audiometry with resolution of 100 Hz. Peak outer ear resonant frequency was determined with a resolution of 175 Hz. RESULTS: The mean frequency of maximum hearing loss was 4,481 Hz whereas the mean peak outer ear resonant frequency was 2814 Hz for 43 ears. Pearson product correlation coefficient equaled .64 (P < .0001). CONCLUSIONS: Despite differences in the type and duration of noise exposure reported by the patients, the positive correlation between outer ear resonant frequency and frequency of maximum hearing loss emphasizes the role that external ear properties play in the development of the 4,000 Hz audiometric notch.

Audiometry, Pure-Tone↗