Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 127 records · Page 7Linked to original sources

PubMed1986

Application of finite impulse response digital filters to auditory brain-stem evoked potentials.

Finite impulse response digital filtering is a linear non-distorting operation and hence can be used to differentiate ABEP components. Since the power spectrum of the ABEP indicates that it contains more than two frequency bands, they can be distinguished by applying digital filters with special characteristics: up to 200 Hz (slow components), 200-400 Hz (medium components) and above 500 Hz (fast components). The results, using these filters, indicate a different nature of components II and IV as compared to I, III and V. While II and IV are not detected under 500 Hz and thus are called 'fast components,' I, III and V are the 'middle components' and appear above 200 Hz. The slow filter results in a 'pedestal' whose peak coincides with peak V. The results of this study show that the ABEP wave form is obtained by the superposition of at least 3 major waves having distinct frequency bands.

Adult↗

PubMed1986

Geometrical principal component analysis of planar-segments of the three-channel Lissajous' trajectory of human auditory brain stem evoked potentials.

Three-Channel Lissajous' Trajectories (3CLTs) of Auditory Brain Stem Evoked Potentials (ABEP) were obtained from 15 normal humans. Planar-segments of 3CLT were identified and the orientations of the first two geometrical principal components, which interact to produce the planar-segments, were calculated. Each principal component's orientation in voltage space was quantified by its coefficients (A, B and C). Intersubject variability of these orientations was comparable to the variability of plane orientations. The principal components of planar-segments can indicate the type of generator activity that is involved in the formation of planar-segments. The results of this analysis indicate that planarity of each 3CLT component is produced by the interaction of simultaneous multiple generators, or by a single synchronous generator which changes its orientation. The coefficients of these principal components may complement plane coefficients as quantitative indices of 3CLT of ABEP.

Adult↗

PubMed1986

Three-channel Lissajous' trajectory of the human short latency visual evoked potentials.

Three orthogonally derived voltage-time records, when plotted simultaneously on three-dimensional voltage-voltage-voltage coordinates, produce a 3-Channel Lissajous' Trajectory (3CLT). 3CLTs of short latency visual evoked potentials (SVEP) were obtained for 8 adult humans (16 eyes) in response to monocular flash stimulation. Intersubject variability of 3CLT of SVEP was small enough to enable identification along the trajectory of comparable planar-segments of approx. 3-5 ms duration across subjects. In each planar-segment, the point at which the trajectory exhibited marked bending was noted. These points were called apices and they corresponded to maxima in the trajectory's distance from the origin (Trajectory Amplitude). Intersubject variability in apex latencies was comparable to, or smaller than, peak latency variability of single-channel records. 3CLT of SVEP consisted of 8 planar-segments in each of the latency ranges of 0-40, 40-70 and 70-100 ms. Analysis of 3CLT, combining the criteria of segment planarity, apices and trajectory amplitude peaks, enabled differentiation between components that had been considered the same in surface distribution studies. 3CLT of SVEP seemed to be influenced by the direction of propagation along the visual pathway.

Adult↗

PubMed1986

Auditory brainstem evoked potentials in evaluating the central effects of middle ear effusion.

Auditory brainstem evoked potentials (ABEP) were recorded to determine whether children who suffered in the past, or suffered at time of examination from Secretory otitis media (S.O.M.), exhibited slowed conduction along their auditory brainstem. Five groups of subjects were examined: children with active S.O.M. during the examination, children with S.O.M. in the past who were treated non-surgically and recovered, children with S.O.M. in the past who were treated surgically and recovered, children who were treated by insertion of ventilating tubes (V.T.), and had S.O.M. during the examination (recurrent S.O.M.), and a control group of neurologically and audiologically normal, age-matched children with no history of S.O.M. 205 ears were tested in all. Each of the groups was subdivided according to the severity of hearing loss, duration and type of treatment. These parameters were evaluated within and between groups, and in relation to the control group. Significant increases of interpeak latency differences (IPLD) between peaks V and III as well as V to I were found in the S.O.M. groups compared to the control group. The duration of the disease was found to be the dominant factor slowing central conduction. These findings confirm the suggestion that attenuation in auditory stimulation at an early age affects central conduction.

Audiometry, Evoked Response↗

PubMed1986

Auditory brainstem evoked potentials in evaluating the efficacy of surgical ventilation of the middle ear.

Conductive hearing loss in children is most commonly associated with Secretory otitis media (S.O.M.). Since auditory brainstem evoked potentials (ABEP) reflect conductive damage in prolonged peak latencies, the present study evaluated the efficacy of surgery for ventilating the middle ear, by comparing changes in peak latencies. These changes were compared in 4 groups of children (4-12 years old): children with S.O.M. in the past, who recovered as a result of conservative treatment; children with S.O.M. in the past, who had been operated on with insertion of ventilation tubes (V.T.); children with S.O.M. in the past, who had been operated on and who still had V.T. at the time of study, and a control group with healthy ears. In all, 183 ears were tested. The results indicate that there is no significant audiometric and electrophysiological difference between the groups who recovered with or without V.T.

Audiometry, Evoked Response↗

PubMed1986

Auditory brain stem evoked potentials in patients suffering from peripheral facial nerve palsy and diabetes mellitus.

Forty-two patients affected by acute idiopathic peripheral facial palsy (AIPFP) underwent auditory brainstem evoked potential (ABEP) investigation in order to further our understanding of the nature of facial palsy. Twenty-two of these patients suffered from diabetes mellitus. Our results indicate that the AIPFP of the diabetic person may be considered as a preliminary sign of diabetic peripheral neuropathy.

Adult↗

PubMed1986

Auditory brainstem evoked potentials in asymptomatic lead-exposed subjects.

Auditory Brainstem Evoked Potentials (ABEP) were recorded from 29 adults and children, accidentally exposed to lead through food until approximately a year prior to this study. ABEP were recorded in response to 75 dBHL clicks presented at rates of 10/sec. and 55/sec. Average values were calculated for peak latency and for interpeak latency differences. Average values of the effect of increasing stimulus rate were calculated as well. Similar values were calculated for normative child and adult control groups. IPLD(I-III) showed the most significant and recurring results, with longer intervals in lead-exposed children compared with their control group. Increasing stimulus rate, on the other hand, affected the adult lead-exposed subjects more than the children. These results may imply an impairment of the peripheral portion of the auditory system with axonal and myelin involvement. ABEP is suggested as a sensitive detector of subclinical lead exposure effects on the nervous system.

Adolescent↗

PubMed1986

A comparison of auditory brain stem evoked potentials in hyperlipidemics and normolipemic subjects.

Twenty-five hyperlipidemic, neurologically and audiologically asymptomatic patients were compared to 20 normolipemic control subjects regarding different interpeak latency differences (IPLD) of auditory brain stem evoked potentials (ABEP). ABEP were recorded in response to click stimuli presented at a rate of 10/sec and 55/sec. The net effect of increasing stimulus rate (ISR) on IPLD of ABEP was significantly greater in the hyperlipidemic patients for IPLD (V-I) and IPLD (III-I). ISR of ABEP indicates a trend of subclinical impairments of brain stem function in hyperlipidemic patients, probably due to ischemia accelerated by their condition.

Acoustic Stimulation↗

PubMed1986

Alcoholism and prevalence of medical and psychiatric disorders.

Prevalence of medical disorders was determined for 10,758 consecutive admissions for inpatient alcoholism treatment to 13 hospitals located in eight states of the United States. The majority of patients (approximately 70% of the men and 73% of the women) had a significant medical problem other than alcoholism. The most prevalent disorders were diseases of the liver, gallbladder and pancreas; bronchitis; emphysema; and asthma. Hypertensive disease was found in 15% of the men and 7% of the women. Psychiatric disorders associated with alcoholism were neuroses, personality disorders and other nonpsychotic states. Less than 10% of all patients were referred by physicians; more than 90% had not been previously diagnosed or treated for medical or psychiatric disorders associated with alcoholism. The high prevalence of medical disorders indicates that inpatient treatment of alcoholism should be undertaken in facilities that have expertise and resources for concurrent treatment of serious medical illness.

Adolescent↗

PubMed1986

Follow-up of auditory-evoked potentials and temporary threshold shift in subjects developing noise-induced permanent hearing loss.

The effects of auditory fatigue, using a temporary threshold shift (TTS) paradigm, on cochlear microphonics (CM) and on auditory brainstem-evoked potentials (ABEP), were studied in normal-hearing subjects during the development of permanent threshold shift (PTS). Behavioral threshold shifts were accompanied by different effects on CM and on ABEP, as PTS was gradually induced by occupational noise. Measures of the effect of increasing stimulus rate (ISR) on ABEP revealed decreased latency shifts during auditory fatigue. ABEP proved useful in early detection of changes in the auditory system, resulting from exposure to noise. In addition, this study further supports the suggestion that TTS acts as a peripheral attenuator of the effect of ISR on the central auditory pathway.

Adolescent↗

PubMed1986

Time domain analysis of VEPs. Detection of waveform abnormalities in multiple sclerosis.

Visual evoked potentials (VEPs) are a useful tool in the diagnosis of multiple sclerosis. To improve their diagnostic power in the early stages of the disease, the VEP shape, as well as its latency, were considered. The Karhunen-Loeve expansion (KLE) was used because it affords an unique advantage in classifying the VEPs by their shape, and gives a well-defined criterion based on similarity to the normative prototype. Using this criterion, it was possible to quantitatively define normative limits of waveform. We were also able to detect early changes in VEPs recorded from suspected multiple sclerosis patients. KLE promises to enable classification of waveforms in early stages of the pathology, when peak-latency comparisons are the least effective.

Adult↗

PubMed1986

Somatosensory evoked potentials to muscle percussion in humans: upper extremity.

Cortical as well as presumably subcortical potentials were recorded from 20 normal subjects in response to mechanical percussion of the thenar eminence. Nuchal-to-frontal recordings detected an initial negative component at 21 msec, followed by positivities at 29 and 36 msec. C-prime to frontal recordings produced prominent positivities at 29 and 44 msec. Recordings over the peripheral nerve did not reveal consistent potentials. Control experiments indicate that potentials are initiated by fast-adapting muscle receptors. If additional control experiments continue to support these findings, yet another constituent of electrically evoked somatosensory potentials--which may prove useful in the definition of muscle innervation disorders--will have been identified.

Adolescent↗

PubMed1985

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. I. Normative measures.

Three-channel Lissajous' trajectories (3-CLTs) of auditory brainstem evoked potentials (ABEPs) were obtained from 14 humans (28 ears) in response to 75 dB nHL, 10/sec alternating polarity clicks. A normative set of 3-CLT quantitative measures was calculated and compared with amplitudes and latencies of the simultaneously recorded, single-channel, vertex-mastoid ABEP. The comparison included average values as well as intersubject variability. The 3-CLT measures included: apex latencies; planar segment durations, orientation, size and shape; trajectory-amplitude peaks and their latencies. Apex latencies of 3-CLT were comparable to peak latencies of the vertex-mastoid records, both in absolute values and in intersubject variability. Durations of planar segments were approximately 0.7 msec and their standard deviations were about a half of their average. Individual planar segment orientations were typically within 50 degrees of the normative average. Trajectory amplitudes were, in general, somewhat larger than peak amplitudes of the vertex-mastoid records, while their intersubject variabilities were comparable. Size and shape measures of planar segments were variable across subjects, making their clinical use, in their present form, questionable. The quantitative study of the 3-CLT of auditory brain-stem evoked potentials will enable evaluation of normal, as well as pathological, evoked potentials, to further the understanding and utility of this comprehensive representation of brain-stem function.

Adult↗

PubMed1985

Discordance of plasma DHEA-S, DHEA, and cortisol responses with various ACTH regimens.

The origin and time course of ACTH-stimulated adrenal androgens are controversial. Since previous protocols have used differing ACTH preparations and routes of administration, we sought to compare plasma DHEA and DHEA-S responses to four ACTH regimens. Fourteen young men underwent the following five three-day study periods: (1) placebo, (2) alpha 1-24 ACTH, 400 micrograms intravenously (IV); (3) alpha 1-39 ACTH, 400 micrograms intramuscularly (IM); (4) alpha 1-18 (D-Ser1, Lys17, Lys18) ACTH, 400 micrograms IM; and (5) alpha 1-18 ACTH, 400 micrograms IV. alpha 1-18 ACTH IV had the most potent and prolonged corticotropic effect, listing more than 24 hours, as measured by plasma cortisol, 17-OHCS, and cortisol secretion rates. alpha 1-39 ACTH and alpha 1-18 ACTH IM were corticotropic up to 12 hours, and alpha 1-24 ACTH IV was corticotropic only up to one hour. Plasma DHEA rose acutely at one hour with all of the ACTH regimens (P less than 0.05). This response was correlated with cortisol (r = 0.62, P less than 0.01) and reflected the relative corticotropic potency of each of the ACTH regimens. Plasma DHEA-S, on the other hand, did not rise acutely at one hour with any of the regimens. DHEA-S did rise at 12 hours with three of the ACTH regimens (alpha-1-24, alpha 1-39, alpha 1-18 IM), but this response was not synchronous with cortisol (r = 0.14, P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1985

Cerebral somatosensory potentials evoked by muscle stretch, cutaneous taps and electrical stimulation of peripheral nerves in the lower limbs in man.

Somatosensory cerebral evoked potentials were recorded in man to natural forms of somatosensory stimulation of the lower extremity including stretching of the muscle tendons, tapping on muscle bellies and tapping on cutaneous surfaces. These potentials were compared with those evoked by electrical stimulation of peripheral nerves measuring the amplitudes and latencies of the evoked potential components and defining the effects of stimulus variables on these parameters. Spinal cord potentials could only be detected to electrical stimuli. Mechanical stimulation of tendons and muscle bellies evoked scalp potentials at latencies earlier than those evoked by electrical stimulation of the peripheral nerve and by cutaneous stimulation at the same level of the leg. Muscle receptors, most probably muscle spindles, are the source of the short latency components obtained by the stretching of tendons and tapping on muscle bellies. The proximal location of these receptors as well as very rapid spinal conduction account for the latency difference. The potentials were larger to electrical stimulation of nerve trunks than to mechanical stimulation of tendons or skin, suggesting the asynchronous activation of a smaller number of fibres by the latter. Individuals with the largest potentials to one form of stimulation usually had the largest potentials to the other modes of stimulation. The use of physiological stimuli such as muscle stretch to test the transmission in specific neural pathways might be useful in investigating the processing of relatively selective afferent volleys using noninvasive evoked potential recordings.

Adult↗

PubMed1985

Subclinical effects of exposure to inorganic mercury revealed by somatosensory-evoked potentials.

This study examined the validity of evoked somatosensory potentials as a measure of subclinical neurological damage to workers chronically exposed to nonorganic mercury. In this study potentials were recorded along the somatosensory pathway from the periphery to the primary cortex in response to electrical and mechanical stimuli. The findings of this study indicate that such workers exhibit subclinical damage which manifested in a delay in nerve ending conduction times at the periphery, and an acceleration of the conduction from brain stem to cortex. These findings support the suggestion that evoked potentials may be a sensitive and reliable measure in the detection of subclinical neuropathic phenomena. They may consequently be utilized as an efficient early warning system in the prevention of clinical symptoms.

Adolescent↗

PubMed1985

Auditory brainstem evoked potentials in blast injury.

Blast injury typically consists of a mixed conductive and sensorineural hearing loss. The sensorineural component includes temporary as well as permanent threshold elevations. Auditory brainstem evoked potentials (ABEP) are sensitive to functional changes in various levels along the auditory pathway. ABEP were recorded from 37 survivors of blasts and latency measures were correlated with clinical findings. Prolongation of peak latencies was correlated with the conductive component of blast-induced hearing loss, as well as with the TTS component of the sensorineural impairment. No central effects of blast on the auditory system were detected. In addition to their objectivity, ABEP hold the promise of differentiating between the permanent and temporary effects of blast on hearing.

Adult↗

PubMed1985

Auditory-evoked potential correlates of susceptibility to noise-induced hearing loss.

Correlations between changes in cochlear microphonics (CM) and auditory brainstem-evoked potentials (ABEP) resulting from transitory-threshold-shift (TTS)-inducing noise, in normally hearing subjects, and the eventual permanent threshold shift (PTS) which the same subjects developed after 9-14 months of well-quantified occupational noise were evaluated. In addition, the predictive value of pigmentation, as an indicator of eventual PTS, was assessed. Eleven CM and ABEP indices which showed significant correlation with the eventual hearing loss were identified. Eight of these indices reflect the effect of increased stimulus rate and experimental TTS-inducing noise. These results show that the difference in ABEP latencies as a result of increased stimulus rate is smaller in persons with large eventual PTS (high susceptibility to noise-induced hearing loss). The effect is larger in persons that eventually developed a small PTS (low susceptibility). Pigmentation, as reflected by iris and skin color, was found to have a negative correlation with susceptibility to noise, i.e. the more pigment the less PTS developed. The above indices may be useful to determine personal susceptibility to noise in normally hearing subjects.

Adolescent↗