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Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 109 records · Page 6Linked to original sources
PubMed1989

Auditory brainstem evoked potentials peak identification by finite impulse response digital filters.

Linear phase finite impulse response (FIR) filtering can be used to differentiate auditory brainstem evoked potentials (ABEP) components. The power spectrum of ABEP at high intensities indicates that they contain 3 frequency bands that can be distinguished by applying appropriate digital filters with the following characteristics: up to 240 Hz (revealing slow components), 240-483 Hz (resulting in medium components) and above 500 Hz (leaving only fast components). The results using these filters, indicate that the medium components coincide with peaks I, III and V and that the slow filter results in a 'pedestal' whose peak coincides with peak V. These findings were used for automatic identification of ABEP peaks. A coincidence of the 'pedestal' peak with a medium component was sought and labelled peak V. The preceding medium peaks were labelled, in order of decreasing latency, III and I. Validation of this procedure was conducted on ABEP from normal subjects, using different stimulus rates and intensities, as well as from selected neurological patients with lesions affecting the brainstem. Provided the waveform included a 'pedestal', the results proved this procedure to be reliable and in very good agreement with manual identification and measurement of ABEP peaks.

Adult↗
PubMed1988

Brainstem auditory evoked potentials to different stimulus rates in parkinsonian patients.

Twenty-five Parkinson's disease (PD) patients were studied by brainstem auditory evoked potentials (BAEP) with increased stimulus rate (ISR) and compared to a control age and hearing matched group. A second comparison was made between L-dopa-treated and untreated PD patients. The results of the study suggest that there is subclinical involvement of the auditory brainstem in PD patients, possibly due to the dopamine influence upon the blood vessels. Our results also indicate that dopamine is probably not involved in the synaptic transmission along the auditory pathway of the brainstem.

Aged↗
PubMed1988

Cisplatin ototoxicity in guinea pigs with special reference to toxic effects in the stria vascularis.

The toxic effects of cisplatin (cis-diamminedichloroplatinum [II]) on the organ of Corti are well established. Few and conflicting data on this drug's effects on the stria vascularis exist. The present study presents animal experiments on the toxic effects of cisplatin in the stria vascularis and in the organ of Corti. Cisplatin-induced toxicity in albino and pigmented guinea pigs was evaluated morphologically and functionally, using light and transmission electron microscopy as well as auditory brainstem-evoked potentials on the organ of Corti and the stria vascularis. The results showed variability in hearing thresholds, ranging from no change to hearing loss of 30 dB, and prominent damage in the organ of Corti and in the stria vascularis. The toxic effects to both the organ of Corti and the stria vascularis should be considered when cisplatin is used in chemotherapy.

Animals↗
PubMed1987

Three-channel Lissajous' trajectory of auditory brain-stem potentials evoked by specific frequency bands (derived responses).

Three-channel Lissajous' trajectories (3-CLT) of the auditory brain-stem evoked potentials were recorded from 14 adult subjects in response to different frequency bands as well as to unmasked clicks. The frequency bands (8 kHz and above, 4-8 kHz, 2-4 kHz, 1-2 kHz and 1 kHz and under) were obtained by subtraction of wave forms to clicks with high-pass masking at these frequencies (derived responses). The 3-CLTs were analysed and described in terms of their geometrical measures. All 3-CLTs included 5 planar segments whose latencies progressively increased with decreasing stimulus frequency, and whose durations and orientations did not change across frequencies. Apex trajectory amplitudes as well as planar segment sizes decreased between unmasked clicks and specific frequency bands, and with decreasing frequency. The changes noted for apex latency and trajectory amplitude were paralleled with corresponding changes in amplitude and latency of single-channel records. The changes in 3-CLT measures with changes in stimulus frequency reflect the contribution of different parts of the cochlea. The unchanged measures may be attributed to the unchanged anatomy of the generators under the different stimulus conditions. The results of this study do not support the wide band of stimuli as responsible for the planarity of 3-CLT segments. In addition, these results indicate that different cochlear processes are responsible for the latency changes observed across stimulus intensities and for those associated with stimulus frequency.

Adolescent↗
PubMed1987

Auditory brain-stem evoked potentials to clicks at different presentation rates: estimating maturation of pre-term and full-term neonates.

Auditory brain-stem evoked potentials ABEPs were recorded from 57 neonates ranging in gestational age between 27 and 43 weeks. Averages and standard deviations of I, III and V peak latencies, I-V, I-III and III-V inter-peak latency differences (IPLDs), for 10/sec and 55/sec clicks were calculated for each age group. An additional measure, the net effect of increasing stimulus rate (ISR), was calculated by subtracting 10/sec measures from their 55/sec counterparts. Correlations between ABEP measures and subject age were determined. The results of this study demonstrate a significant correlation between gestational age and electrophysiological measures of peripheral, as well as central, conduction: an inverse correlation between age and peak latencies as well as IPLDs. The slope of this correlation was steeper for the higher stimulus rate. The slope of 55/sec measures vs. age was the sum of the respective slopes of 10/sec measures and of ISR. The maturation of 10/sec measures may reflect white matter development, while ISR changes with gestational age represent maturation of synaptic efficacy. Thus, the maturation of 55/sec measures reflect the combined maturation of nerve conduction velocity and synaptic efficacy along the neonatal auditory nerve and brain-stem. This differential evaluation may enable more accurate determination of developmental age of neonates, with respect to total maturation as well as its constituents.

Brain Stem↗
PubMed1987

Auditory brainstem evoked potentials in sudden deafness.

Auditory Brainstem Evoked Potentials (ABEP) were recorded from 53 adult subjects suffering from sudden deafness at the time of examination. The onset of sudden deafness was up to three years prior to the study. ABEP were recorded in response to 75 dBHL clicks presented at rates of 10/sec and 40/sec. ABEP peak latencies as well as interpeak latency differences, and also the effect of increasing stimulus rate, were determined for each patient and compared with the clinical symptoms. The psychoacoustic and ABEP detection thresholds were also compared. A highly significant correlation was observed between ABEP detection threshold and the psychoacoustically determined hearing threshold, and the differences between them were found to be insignificant. The results of this study indicate a central component in sudden deafness. This impairment manifests itself in abnormal effects of increasing stimulus rate on ABEP, and may be related to reduced central synaptic efficacy.

Adult↗
PubMed1987

Brainstem auditory evoked potentials with and without increased stimulus rate as diagnostic tool in brainstem minor transient changes.

Two clinical groups of patients - 25 with Parkinson's disease and 17 with migraine - were evaluated using brainstem auditory evoked potentials (BAEP) to regular (10/s) and increased (55/s) stimulus rates. Each group of patients had an age-matched control group. The BAEP data were statistically evaluated, comparing the data of migraine patients during and between migraine spells, and the parkinsonian patients before and after L-dopa treatment. We believe that when group data are compared BAEP to an increased stimulus rate is an efficient tool for detecting even minor transient reversible physiologic changes of the brainstem.

Adolescent↗
PubMed1987

Three-channel Lissajous trajectories of auditory brainstem-evoked potentials in patients with neurological lesions affecting the brainstem: preliminary impressions.

Three-channel Lissajous trajectories (3CLT), as well as vertex-mastoid records of auditory brainstem-evoked potentials (ABEP) were obtained from 12 patients with neurological lesions localized to the auditory nerve, the medulla, the pons, the pons and midbrain and the midbrain. Patients selected had well-localized lesions at the levels of the presumed generators of ABEP (10 patients), as well as below (1 patient) and above (1 patient) those levels. The 3CLT measures used were trajectory amplitude, peak latency and amplitude, planar segment number, apex latency, duration, orientation in voltage space, as well as size and shape. Latencies and amplitudes of vertex-positive peaks I-V, as well as interpeak latency differences, were determined. Vertex-mastoid ABEP and 3CLT were compared in terms of their sensitivity to the existence of a lesion, the accuracy of lesion localization as well as their specificity to the lesion. 3CLT had an advantage in all three comparisons, with the most prominent advantage in specificity, which was over twice as high as that of single-channel ABEP. The results of this preliminary study indicate that 3CLT affords a sensitive analysis of ABEP, which is superior to single-channel analysis in sensitivity, accuracy and specificity. These results also indicate that the 'contralateral effect' of peak V latency prolongation in cerebellopontine angle tumors may be related to anatomical changes of its generators' orientation, rather than slowed conduction along the upper brainstem.

Brain Diseases↗
PubMed1987

Application of the three-channel lissajous trajectory of auditory brainstem-evoked potentials to the question of generators.

In studies of generators of auditory brainstem-evoked potentials (ABEP), depth recordings and clinical correlates may not reflect all the activity involved. Although the 'inverse problem' is mathematically ill-posed, a synthesis of physico-anatomical data with a three-channel Lissajous trajectory (3CLT) may indicate the actual number and identity of generators. A 3CLT of ABEP in three-dimensional voltage space, is isomorphic with the vector tip representing the momentary centrally located dipole in a uniform, spherical volume conductor. This isomorphism enables approximations of ABEP dipole equivalents to be made. 3CLT summarizes the surface activity in a single plot. It accentuates correlations within the orthogonal records, such as planarity of segments, allowing segmentation of the analysis epoch into components. These properties of 3CLT simplify the analysis of parametric effects on the surface distribution of ABEP components. The results of applying this technique indicate the experimental conditions under which the assumptions for the approximation of generators are closest to being fulfilled. Of all the points along the trajectory, apices (points with maximum absolute amplitude and curvature) have the most unique generators. The 3CLT to low-intensity and high-rate clicks, indicate more unique generators than the customarily used high-intensity slow-rate clicks, in which considerable temporal overlap of generator activity exists.

Brain Stem↗
PubMed1986

Noninvasive recordings of cochlear evoked potentials in Meniere's disease.

Noninvasive meatal electrocochleography simultaneously recorded with brain stem auditory evoked potentials were performed on 24 adult patients with unilateral Meniere's disease. Data from the affected ear were compared with those of the nonaffected ear and with those of ten healthy normally hearing adults. The most striking finding was the significant deviation from the norm of the nonaffected ears' action potential duration. The combination of simultaneously recorded surface meatal electrocochleography and brain stem auditory evoked potentials complement the diagnostic battery of Meniere's disease in ruling out retrocochlear involvement, indicating cochlear involvement of the affected ear, and revealing subclinical changes in the contralateral ears.

Adult↗
PubMed1986

Auditory brain-stem evoked potentials in patients undergoing dialysis.

Auditory brain-stem evoked potentials (ABEPs) and pure-tone audiograms were obtained for 38 patients with renal failure, undergoing dialysis, before and after a dialysis session, and for 40 healthy normal subjects. Blood chemistry was also evaluated for each patient before and after dialysis. ABEP abnormality (using 10/sec click rate) was observed for 24% of the patients, rising to 44% when 55/sec measures were included. Abnormalities included prolongations of peak latencies for both click rates, and prolongation of interpeak latency differences. Pre-dialysis calcium was significantly different between patients with or without ABEP abnormality. In addition to this chronic effect on ABEPs, an acute effect of the dialysis session was found. Blood chemistry data, ABEP latencies and I-III interpeak latency differences were significantly different before, as compared to after dialysis. The acute effect of dialysis on blood calcium levels correlated with its effect on latencies of peaks III and V at 10/sec click rate, and on peaks I and V latency at 55/sec. These results may indicate the types of dysfunction revealed by increased stimulus rate measures.

Auditory Perception↗
PubMed1986

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. II. Effects of click intensity.

Three-channel Lissajous' trajectories (3-CLT) of the human auditory brain-stem evoked potentials (ABEP) were recorded from 14 adult subjects at 15, 45, and 75 dB (nHL). The 3-CLTs were analysed and described in terms of their constituent planar segments and their trajectory amplitudes at each stimulus level. At 75 dB, 9 planar segments were observed, each having unique apex latency, boundaries, duration, shape, size and orientation in voltage space. As stimulus levels were lowered, changes were noted in apex latency and trajectory amplitude which parallelled changes seen under similar experimental conditions using single-channel ABEP. In addition, changes were seen in planar segment number, boundaries, duration, shape, size and orientation, all of which could be related to decreased generator activity. It is proposed that at high stimulus levels, there is significant temporal overlap of generator activity which results in a larger number of planar segments and single-channel peaks than at low stimulus levels. This may be important to the identification of the specific generators of the ABEP and their appropriate clinical usage.

Brain Stem↗
PubMed1986

Comparison of fiber optical and video monitor stimulators in normals and multiple sclerosis patients.

A comparison of VEP findings using a fiber optical stimulator with three color combinations (black/red, black/green and red/green) and a conventional video monitor stimulator in black/white was performed in 3 groups of subjects: a group with definite lesions in the visual pathway, a group with suspected lesions and a control group. No significant correlations of P100 latency were found in the normative group, probably because of the small range of their values. All correlations were significant in the two patient groups, except for the red/green stimuli in the definite group. In general, the red/green combination was inferior to other color combinations in eliciting VEPs. The patient groups with definite, as well as suspected, lesions indicated no benefit from the color stimuli, as compared with black/white. The major advantage of the fiber optical stimulator is its simplicity, the lack of stimulus artifacts and the accessibility to the patient's bed side, thanks to its small size. Stimulators with higher illuminance and improved pattern element shape should narrow the still unacceptable normative variability of the wave forms recorded.

Adolescent↗
PubMed1986

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. III. Effects of click rate.

Three-channel Lissajous' trajectories (3-CLT) of the human auditory brain-stem evoked potentials (ABEPs) were recorded from 14 adult subjects using click rates of 10, 55 and 80/sec. The 3-CLTs were analysed and described in terms of their constituent planar segments and their trajectory amplitudes at each stimulus rate. Increasing stimulus rate resulted in an increase of planar segment duration which was more pronounced for segments 'a' and 'e', an increase in apex latency which was more pronounced the later the component and a decrease in planar segment size and peak trajectory amplitude which was more pronounced the earlier the component. These findings support the involvement of synaptic efficacy changes in the effects of stimulus rate on ABEP. The results are explained by overlapping convergence and divergence in the ascending auditory pathway. These results support the notion that the principal generator of each component is activated by the principal generator of the previous component, with some temporal overlap of their activities. Such temporal overlap may be minimized by using low intensity high rate stimuli.

Brain Stem↗