Biomedical subjects

R M Abrams

Publications and source records attributed to R M Abrams.

At least 37 records · Page 2Linked to original sources

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

Fetal behavioral state patterns during and after prolonged exposure to cocaine in sheep.

OBJECTIVE: Studies on the effects of cocaine in fetal animals have been limited to acute exposures to the drug. We hypothesized that a prolonged infusion of cocaine to the fetal sheep would initially interrupt normal behavioral state cycling but the effects would be short lived as the fetus gained tolerance to the drug. STUDY DESIGN: The study was performed in a university laboratory on six time-dated pregnant ewes at 125 days' gestation. Fetal sheep, surgically instrumented 3 days before study, were given cocaine hydrochloride 0.6 mg/min for 6 hours. Fetal behavioral state before, during, and after the infusion was compared by repeated-measures analysis of variance. RESULTS: Infusion of cocaine caused a drop in the percentage time that the fetuses spent in both rapid-eye-movement (p < 0.03) and non-rapid-eye movement (p < 0.001) sleep, which was sustained throughout the 6-hour infusion. This was related to a decrease in the number of rapid-eye-movement and non-rapid-eye-movement episodes as opposed to a decrease in the lengths of these behavioral states. With cessation of cocaine infusion, the fetal sheep showed an increase in rapid-eye-movement sleep, with a higher percentage than during control periods (p < 0.02). CONCLUSIONS: Cocaine disrupts fetal rapid-eye-movement sleep without evidence for tolerance to the drug over a 6-hour period. "Catch-up" rapid-eye-movement sleep occurs with cessation of cocaine infusion. Neurobehavioral abnormalities associated with in utero cocaine exposure may be caused by chronic disruption of rapid-eye-movement sleep.

Analysis of Variance↗

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

Respiratory muscle activities after birth in asphyxiated preterm lambs.

Laryngeal and pump muscle activities are important in the establishment and maintenance of functional residual capacity (FRC) after birth. The aim of this study was to determine the expiratory mechanisms by which laryngeal and diaphragmatic activities achieve the increments in FRC postnatally. Wire electrodes were placed in: the laryngeal abductor, a major laryngeal adductor, the inferior pharyngeal constrictor and the diaphragm of six fetal sheep. The lambs were delivered prematurely by cesarean section and a face mask with a pneumotachograph applied. A grunting respiratory pattern was characterized by severe expiratory airflow retardation, associated with laryngeal adductor activity. In grunting breaths, minimal volume loss at end-expiration and incremental increases in FRC occurred when the onset of diaphragmatic activity preceded the onset of laryngeal muscle activities associated with laryngeal opening. Thus the timing order of laryngeal and diaphragmatic muscle activities near end-expiration is a determinant of increments in FRC.

Animals↗

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

Cocaine depresses cerebral glucose utilization in fetal sheep.

To assess if cocaine alters cerebral glucose metabolism in the fetus, we infused cocaine 0.6 mg/min intravenously to 6 of 13 fetal sheep for the 55 min prior to measurement of glucose utilization by an autoradiographic method. Overall, local cerebral glucose utilization (LCGU) was lower in cocaine-exposed fetuses than in 7 controls (P = 0.058). In the cocaine-exposed fetuses, 33 of 34 structures had lower mean LCGU than in the comparable structures of control fetuses. In addition, the autoradiographs in 4 of 6 cocaine-exposed fetuses revealed thin, dark lines of increased glucose utilization within the central white matter of some frontal gyri which were not seen in any of the 7 control fetuses. These lines were distributed similarly to ones seen earlier in severely hypoxic newborn lambs. In fetal lambs, cocaine resulted in a generalized decrease in LCGU and a specific increase in glucose utilization in parts of cortical white matter of the frontal gyri, possibly secondary to local ischemia.

Animals↗

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

Laryngeal and diaphragmatic muscle activities and airflow patterns after birth in premature lambs.

The nature and control of early neonatal respiratory patterns were determined in 10 premature, asphyxiated lambs. Severe retardation of early expiratory airflow (braking) characterized an initial pattern (A), but was absent in a final one (B). During a transition pattern (pattern T), pattern A and B airflow types occurred. Close temporal relationships between the airflow patterns and posterior cricoarytenoid (PCA), thyroarytenoid (TA), and diaphragm (D) integrated muscle activities were demonstrated quantitatively. Specifically, in pattern A, the duration of braked expiratory airflow was related to the durations of TA burst activity and the absence of PCA burst activity (r2 = 0.99). In pattern A, pH, but not arterial PCO2 or arterial PO2, differed from that in patterns T and B [7.01 +/- 0.14 (A), 7.11 +/- 0.12 (T), 7.19 +/- 0.08 (B) (P < 0.03)]. Within-breath airflow and respiratory muscle activity relationships and differences in neural and mechanical respiratory timing intervals between patterns suggested that neural feedback was important in the control of central pattern generation. Thus activities of PCA, TA, and D shape the early neonatal airflow patterns and are influenced mainly by neuromechanical, and not chemical, feedback.

Animals↗

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↗

PubMed1993

Fetal vibroacoustic stimulation test: vibrator response characteristics in pregnant sheep postmortem.

OBJECTIVE: To determine the effect of small decreases in battery voltage on the sound pressure level and spectral features of sound within the uterus during vibroacoustic stimulation with a battery-powered electronic artificial larynx. METHODS: In eight pregnant, recently sacrificed sheep, the fluid-borne, intra-amniotic sound pressures resulting from vibration of the abdominal wall with an electronic artificial larynx were compared with airborne sound pressures produced by an artificial larynx and measured at 50 cm. RESULTS: At all frequencies, the intrauterine sound pressure was higher than the sound pressure in air. Decreasing battery voltage from 9 to 7 V resulted in a 5-18-dB decrease in intrauterine sound pressure at the electronic artificial larynx fundamental frequency and most overtones, but only a 4-8-dB decrease in the airborne signal. The results indicate that for frequencies relevant to fetal hearing, the reduction of sound pressure level caused by inadequate battery voltage may result in a difference in fetal response. CONCLUSION: Routine verification of the function of a vibroacoustic device by means of a battery voltage check is recommended.

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

Disposition and pharmacodynamics of methamphetamine in pregnant sheep.

To determine the placental transfer of methamphetamine, its subsequent fetal disposition, and its hemodynamic effects, we administered methamphetamine intravenously to 15 pregnant ewes 3 days after placement of maternal and fetal vascular catheters. Methamphetamine crossed the placenta within 30 seconds of its administration. Although the ewes had higher peak concentrations, the fetuses' longer elimination half-life ultimately led to higher fetal than maternal methamphetamine concentrations. The ratio of fetal tissue to plasma drug concentration 2 hours after administration was highest in the lung, followed by the placenta, kidney, intestine, liver, brain, and heart. Methamphetamine caused a 54% to 63% rise in maternal blood pressure, a 20% to 37% increase in fetal blood pressure, and a drop in fetal oxyhemoglobin saturation and arterial pH. We conclude that methamphetamine, in doses at or below what is commonly abused, has effects that could be detrimental to the health of the mother and her fetus.

Animals↗

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↗