Biomedical subjects

K J Gerhardt

Publications and source records attributed to K J Gerhardt.

At least 37 records · Page 2Linked to original sources

PubMed1996

Fetal hearing: characterization of the stimulus and response.

Before sounds originating outside the abdomen of pregnant women can reach the inner ear of the fetus, they must first pass through the tissues and fluids surrounding the fetal head. Low-frequency sound energy easily penetrates to the fetal head, less than 5 dB attenuation for frequencies below 500 Hz, whereas higher frequencies are attenuated by up to 20 to 30 dB. The sound energy in amniotic fluid stimulates fetal hearing through a bone conduction route rather than through the external and middle ear systems. During passage through the bones of the skull, sound energy is slightly diminished for frequencies less than 250 Hz (10 to 20 dB), yet significantly reduced for frequencies from 500 to 2,000 Hz (40 to 50 dB). Thus, the fetus in utero can easily detect low-frequency sound energy (< 500 Hz) produced at levels that are comfortably loud for its mother, but probably cannot detect acoustic energy at frequencies higher than 500 Hz.

Bone and Bones↗

PubMed1996

Vibration of the abdominal segment in pregnant sheep.

Mechanical vibration of the abdominal wall results in a frequency-related distribution of intra-abdominal sound pressure levels. A greater attenuation of applied signals of equal dynamic force occurs as frequency increases. A broad resonance peak exists between 6 and 18 Hz. Transducers fixed to the fetal head show clear increases in acceleration levels during stimulation of the abdominal surface with the artificial electronic larynx. Sine-wave stimulation results in a frequency-dependent increase in vibration levels of the abdominal wall of 4% to 140% of the input levels. At the fetal head, a broad peak in response was noted between 6 and 12 Hz, but the overall levels never exceeded 4% of the input level.

Abdominal Muscles↗

PubMed1996

Vibroacoustic stimulation with a complex signal: effect on behavioral state in fetal sheep.

An ideal vibroacoustic stimulus for testing fetal reactivity has yet to be developed. In the present study in fetal sheep we tested the effect on behavioral state of an amplitude and frequency-modulated signal produced at the abdominal surface of the ewe. The stimulus was presented during periods of fetal non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. Evaluation of behavioral state was accomplished by visual observation of strip-chart recordings. Assessed in this manner, vibroacoustic stimulation during NREM sleep consistently resulted in a change to an indeterminate state. However, stimulation during REM sleep failed to have an effect. Additional evaluation applying spectral analysis to the fetal electrocorticogram during stimulation in NREM sleep revealed a marked decrease in delta band power from 100 to 27 +/- 5% and in theta band power from 100 to 40 +/- 4% resulting in a decrease in total power from 100 to 35 +/- 4% (p < 0.05). Stimulation during REM sleep revealed a significant increase in beta band power from 100 to 123 +/- 14%. Vibroacoustic stimulation in both NREM and REM sleep led to an increase in spectral edge frequency, implying central arousal.

Acoustic Stimulation↗

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↗

PubMed1995

Fetal acoustic stimulation test: stimulus features of three artificial larynges recorded in sheep.

OBJECTIVE: The purpose of the current study was to evaluate the characteristics of vibroacoustic devices used for fetal stimulation. STUDY DESIGN: Intrauterine sound pressure levels over a frequency range of 40 to 5000 Hz were measured with hydrophones in anesthetized sheep. Stimulators included the AT&T (Martinsburg, W.V.) and Servox (Hearing Instruments, Piscataway, N.J.) artificial larynges, the Corometrics fetal acoustic stimulator (Wallingford, Conn.) and electric toothbrush. RESULTS: Intrauterine spectral patterns resulting from stimulation with the AT&T, Servox, and Corometrics devices were characterized by numerous high-level overtones above a fundamental frequency between 97 and 163 Hz. Fundamental frequencies recorded during toothbrush stimulation were 22 to 24 Hz with reduced but identifiable overtones up to 250 Hz. CONCLUSIONS: Fetal vibroacoustic stimulators that operate on the principle of the electronic artificial larynx produce very similar intrauterine sound pressure levels.

Acoustic Stimulation↗

PubMed1995

Effect of stress on cochlear glucocorticoid protein: acoustic stress.

Levels of glucocorticoid (GR) receptor protein were determined by a quantitative enzyme-linked immunosorbent assay (ELISA) technique in inner ear tissue of rats exposed daily to 85 dB SPL white noise for 4 hours on 3 consecutive days. GR levels in spiral ligament and organ of Corti tissues were detected using a monoclonal antibody to the GR receptor, BuGR2. A non-significant 13% decrease in GR levels of spiral ligament tissues was observed in the noise exposed animals relative to untreated animals. A statistically significant decrease of 27% in GR protein levels was seen in the organ of Corti region (P < 0.03), however. There was a concomitant increase of serum corticosterone levels (P < 0.03) in noise exposed animals as opposed to those of controls. These results indicate a tissue specific response of GR receptor to acoustic stress. Inner ear GR protein therefore may be a useful marker in determining the effect of stress on the inner ear. Finally, such data may be applicable to support the hypothesis that stress is an etiological agent in Ménière's disease.

Acoustic Stimulation↗

PubMed1995

Combined effects of adrenalectomy and noise exposure on compound action potentials, endocochlear potentials and endolymphatic potassium concentrations.

The effects of removal of endogenous corticosteroids via bilateral adrenalectomy in combination with noise exposure (30 min at 100 dB) were determined by recording compound action potential (CAP) and endocochlear potentials (EP), and by measuring potassium concentrations (K+e) within the endolymph. Thirty-eight Long-Evans rats were divided into groups according to experimental treatments: adrenalectomy (ADX) or non-ADX and noise exposure or non-noise exposure. CAP thresholds, EP and K+e values were subjected to repeated-measures analysis of variance with group and time as factors classifying the measurements. Noise exposure resulted in significant elevations of CAP thresholds in both the ADX and non-ADX animals, but had no effect on either EP or endolymphatic K+e. Recovery was noted during all post-exposure measurement periods and was significantly faster for ADX animals. EP and K+e did not change during or after noise exposure. ADX animals showed a non-significant reduction of EP and a statistically significant increase of K+e during all measurement periods as compared to non-ADX animals.

Acoustic Stimulation↗

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

The perception of speech sounds recorded within the uterus of a pregnant sheep.

The intelligibility of speech stimuli recorded within the uterus of a pregnant sheep was determined perceptually using a group of untrained judges. The intrauterine sound environment of the ewe was intended to simulate that of a pregnant woman. Two separate lists, one of meaningful and one of nonmeaningful speech stimuli, were delivered through a loudspeaker to the side of the ewe and were simultaneously recorded with an air microphone located 15 cm from the flank and with a hydrophone previously sutured to the neck of the fetus. Perceptual test tapes generated from these recordings were played to 102 judges. The intelligibility of the phonemes recorded in the air was significantly greater than the intelligibility of phonemes recorded from the uterus. A male talker's voice was more intelligible than a female talker's voice when recorded from within the uterus, but not so when recorded in the air. An analysis of the feature information transmission from recordings inside and outside the uterus revealed that voicing information is better transmitted in utero than place or manner information.

Animals↗

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↗

PubMed1993

Three-dimensional intraabdominal sound pressures in sheep produced by airborne stimuli.

OBJECTIVE: Our aims were to investigate how airborne sound was distributed within the abdominal cavity of sheep as function of frequency. STUDY DESIGN: Airborne broad-band noise was measured with a hydrophone at 45 locations within the abdomen of five nonpregnant sheep post mortem and with a microphone extraabdominally. Sound pressure attenuation provided by the abdomen and its contents was determined for frequencies between 50 and 5000 Hz. An analysis of variance was applied to assess the effects of frequency, hydrophone location, and animal on intraabdominal distribution of sound pressures. RESULTS: Below 250 Hz sound pressure was higher inside the animal than outside. Little attenuation (< 10 dB) was found for sounds > 3000 Hz. Attenuation was greatest in the center of the abdomen and least along the inner margin of the abdomen. Intraabdominal sound pressure level varied with frequency (p < 0.0001) and with position of the hydrophone in the cross-sectional plane (p < 0.005) but not in the sagittal plane (p = 0.51). There was no animal effect (p = 0.18). CONCLUSION: During maternal exposure to airborne, broadband noise the fetus could be subjected to intense sound pressures at low frequencies regardless of position within the uterus and at high frequencies when positioned near the abdominal surface.

Abdomen↗

PubMed1993

Abdominal vibration alters sleep state in fetal sheep.

Many pregnant women are exposed to low frequency sounds and vibrations while at work or play. How the fetus is affected by these physical stimuli is not clearly documented. We recorded behavioral state and intrauterine sound pressure levels in eight fetal sheep previously instrumented with electrocortical, electroocular and neck electromyographic leads, and with a miniature hydrophone. Data were collected before, during and after 30 min of abdominal vibration using a belt vibrator commonly used by humans in weight reduction programs. A sudden shift in behavioral state occurred at the onset of vibration. There was a decrease in non-rapid eye movement sleep (P < 0.02) and an increase in time during which the sleep state could not be determined (P < 0.03). A 63% increase in number of epochs spent in this indeterminate period was evident during vibration. During the post-stimulus period, percentage of time spent in rapid eye movement sleep decreased as compared to the pre-stimulus period (P < 0.04), and non-rapid eye movement sleep increased as compared to the stimulus period (P < 0.01). Vibration-induced intrauterine sound pressures ranged from 131-142 dB at the fundamental frequency of 19 Hz and were 20-40 dB lower at the overtones which appeared in the spectrum between 35-200 Hz. Results indicated that environmental vibration can disrupt fetal behavioral state, induce abnormal state changes, and alter distribution of sleep states.

Acoustic Stimulation↗

PubMed1993

Vibroacoustic stimulation in fetal sheep: effect on cerebral glucose utilization and behavioral state.

Behavioral state and cerebral glucose utilization were measured in six fetal sheep subjected to high intrauterine sound pressures created with a vibroacoustic stimulator pressed against the maternal abdomen. The signal consisted of a complex waveform that varied over time with a 50% duty cycle. An implanted hydrophone showed highest spectral levels between 3,000-16,000 Hz. The pulsed sound resulted in a significant loss of fetal rapid eye movement and non-rapid eye movement sleep. The stimulus also resulted in a disruption in the normally close relationship between these sleep states and cerebral glucose utilization rates in the brain as a whole and in its component parts.

Acoustic Stimulation↗

PubMed1992

Effect of cocaine on electrocortical activity in fetal sheep.

The effect of cocaine on the behavioral state of six fetal sheep was studied during gestational ages between 128-135 days. Two to eight days after surgery, fetuses received either a continuous 60 min intravenous infusion of cocaine HCl (33.4 mg) or saline. The infusions were preceded and followed by control periods of 102 min. Cocaine induced a disruption in fetal behavioral state cyclicity and a decrease in the amount of time spent in rapid eye movement sleep (P < 0.01) and non-rapid eye movement sleep (P < 0.05) during the infusion, but not during the recovery period. Spectral amplitude of the electrocortical activity at all three cortical locations increased within most one-third octave bands between 0.8-4 Hz and decreased within most bands between 16-25 Hz (P < 0.05) compared to controls. There were no differences in spectral amplitude between pre- and post-cocaine periods at any location over the 25 frequency bands studied (P > 0.6) except for one frequency band centered at 12.5 Hz. The effects of a one hour cocaine infusion on fetal cortical electrical activity are diffuse, but short-lived, and occur independently of changes in fetal oxygenation.

Animals↗

PubMed1992

Sound levels in the human uterus.

OBJECTIVE: We sought to determine the degree to which noises and voices are attenuated or enhanced as they pass into the uterus. METHODS: In eight parturients, a hydrophone in the uterus was used to measure sound pressure levels for externally generated one-third-octave band noises, male and female voices, and the subject's voice. RESULTS: Low-frequency sounds (0.125 kHz) generated outside the mother were enhanced by an average of 3.7 dB. There was a gradual increase in attenuation for increasing frequencies, with a maximum attenuation of 10.0 dB at 4.0 kHz. Sound attenuation was slightly less if the insonation was from in front of the woman rather than behind. Intrauterine sound levels of the mother's voice were enhanced by an average of 5.2 dB, whereas external male and female voices were attenuated by 2.1 and 3.2 dB, respectively. The effect of frequency on attenuation, the differences between front and back insonation, and the differences between speakers in attenuation were all statistically significant. CONCLUSIONS: The intrauterine environment is rich with externally generated sounds. This may imply fetal risk from maternal noise exposure and may aid in understanding fetal imprinting from prenatal exposure to voices.

Acoustics↗

PubMed1991

Effects of vibration frequency and tissue thickness on intrauterine sound levels in sheep.

Pure-tone sinusoidal mechanical vibratory stimuli ranging in frequency from 4 to 4000 Hz were applied to the ventral abdominal wall of pregnant ewes, and intrauterine sound pressure levels were recorded with a hydrophone 5, 10, 15, and 20 cm from the surface. There were significant decreases in sound pressure levels with increasing frequencies (p less than 0.0001) and increasing depth (p = 0.01). There was no significant interaction between these two variables. An electronic artificial larynx was also activated on the abdominal wall, resulting in quite high sound pressure levels (mean, 119 dB) measured 5 cm from the surface, with a significant decrease in sound pressure levels as the thickness of the intervening maternal tissues increased (p = 0.005). These results suggest that the frequency of vibratory stimulus used and the thickness of the maternal abdominal wall could influence fetal response to the vibroacoustic stimulation test by affecting intrauterine sound pressure levels.

Acoustic Stimulation↗

PubMed1991

Intraabdominal sound levels during vibroacoustic stimulation.

Vibroacoustic stimulation is widely used in the United States as a test for fetal well-being, yet little information is available on the adequacy of the electronic artificial larynx that is commonly used as the stimulator. To determine whether the intraabdominal sound pressure level was dependent on the static force applied to the electronic artificial larynx, we measured the sound pressure level at a position 20 cm from the surface of the anterior abdominal wall in nonpregnant ewes. The electronic artificial larynx was pressed against the surface with three levels of static force: mild, moderate, and strong. Between mild and strong static forces there was a trend toward a reduction in sound pressure level at the fundamental frequency (85 Hz) and the overtones (170 to 1600 Hz) (p less than 0.08). To further examine the relationship between the static force of sound source against the abdomen and the intraabdominal sound pressure level, sine wave oscillations between 20 Hz and 4.0 kHz were produced with an industrial shaker. With a constant dynamic force (0.16 N) applied to the shaker across frequencies, the sound pressure level was greatest at lower frequencies (100 to 110 dB) and less at higher frequencies, above 1.0 kHz (60 to 80 dB). Consistent with the electronic artificial larynx experiments, strong application of the shaker resulted in greater transmission of sound than did mild application (p less than 0.02).

Abdomen↗

PubMed1991

Influence of outer ear resonant frequency on patterns of temporary threshold shift.

Noise-induced hearing loss following a broadband noise exposure has been characterized by a notch in the audiogram in the 3.0 to 6.0 kHz range. It has been postulated that loss of sensitivity in this frequency range is related to the primary resonant frequency of the external auditory meatus. In order to further explore this hypothesis, 31 normal-hearing subjects provided measurements of acoustic gain of the external ear and temporary threshold shift (TTS). Subjects completed sweep frequency Bekesy tracking procedures prior to and immediately following a 30-minute broadband noise exposure (95 dBA). The frequency maximally affected by the noise exposure (Max TTS) was correlated to primary resonant frequency of the outer ear (Max RF). A significant positive correlation between these two measures was identified. A 100 Hz difference in Max RF resulted in approximately a 140 Hz change in Max TTS. Thus, the external ear plays a significant role in the frequencies affected by a broadband noise exposure.

Acoustics↗