Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 145 records · Page 8Linked to original sources

PubMed1985

Detection and measurement of steady-state evoked potentials in real-time using a lock-in amplifier. Technical note.

A system for recording evoked potentials, in which a lock-in amplifier replaces the averaging computer, is described. With this system, the set-up is much the same as in the conventional apparatus, with the following exceptions: 1) the amplifier gain is set at only a few thousands; 2) analogue-to-digital conversion and computer averaging is replaced by a lock-in amplifier; and 3) the output of the system is an analogue signal representing the amplitude of the recorded steady-state evoked potentials and the phase of baseline crossings. This set-up is much less costly than the conventional apparatus, much easier to operate, and, with its real-time output, may provide an ideal technique for screening and monitoring purposes.

Electrophysiology↗

PubMed1985

Applications of auditory evoked potentials to evaluate hearing disorders: assets and limitations.

A variety of auditory evoked potentials for audiometric use are briefly reviewed and their assets and shortcomings discussed. Auditory brainstem evoked potentials provide the most audiometric parameters per patient evaluation time. Illustrative case reports are summarized to demonstrate the assets and pitfalls in evoked potential audiometric evaluations. Frequency contents of the stimulus used to evoke the potentials, the normative values for parameters evaluated, and the notion that the potentials reflect only the functioning of their generators must be constantly borne in mind. The primary concern must be the patient's welfare, and unnecessary procedures should be avoided.

Audiometry, Evoked Response↗

PubMed1984

Auditory brain-stem evoked potentials in Bell's palsy.

In an attempt to assess objectively the integrity of the auditory pathways in patients suffering from Bell's palsy, an audiometric evaluation was performed and auditory brain-stem evoked potentials (ABEP) were obtained from 24 patients within the first week from the onset of facial weakness. Despite negative audiometric findings, significant ABEP abnormalities (greater than 2.5 SDs) were observed for 25% of the sample. In each case the ABEP deviation suggested prolonged brain-stem conduction time; for some patients the aberration was only apparent with an increased stimulus repetition rate. The ABEP measures were found to be independent of the side or severity of the paralysis, the acoustic reflex, or reported dysacusis. The ABEP was of no value in predicting recovery of facial muscle function. It is suggested that the facial paralysis may be only the overt manifestation of a generalized pathologic condition.

Acoustic Impedance Tests↗

PubMed1984

Geometrical analysis of human three-channel Lissajous' trajectory of auditory brain-stem evoked potentials.

Three-channel Lissajous' trajectories (3CLTs) of auditory brain-stem evoked potentials (ABEPs) were obtained for a group of 15 normal humans. 3CLTs were studied using geometric spatial descriptors of rate of bending (curvature), local planarity (torsion), as well as the parameters of best fit planes along the trajectory. Point-by-point analysis enabled objective determination of apices (curvature maxima) which divided the trajectory to curvilinear segments. Consecutive apices defined planar segments (each consisting of two curvilinear segments) along the trajectory. Of the two possibilities of arranging apices in the middle of planar segments only one yielded consistently planar segments. The alternative set of apex triads represented transitions between truly planar segments. The variability of position and orientation measures of planar segments was greater than that of apex latencies and plane limits. The significance of planes, as well as their generation, in 3CLT of ABEP, remains to be studied.

Adult↗

PubMed1984

A pattern reversal stimulator using optical fibers.

A combination of light emitting diodes, as light sources, and optical fibers, as channels for the emitted light to form patterns, has resulted in a pattern reversal stimulator that is miniature in size, has pattern color options, is low in power requirements, and hence in possible stimulus artifacts. In addition, the use of optical fibers enables better separation of pattern elements and easier focusing on the pattern. The stimulator incorporates all the assets of previous versions of miniature pattern stimulators, is comparable or even less in price, and can interface with commercial averagers.

Electroencephalography↗

PubMed1984

Auditory brainstem evoked potential latency-intensity functions: a corrective algorithm.

The dynamic changes in the latency of the components of the auditory brainstem evoked potentials (ABEP) were analyzed and correlated with the psychophysical magnitude estimates of the stimuli evoking the potentials. This study included the reanalysis of the results originally reported by Pratt and Sohmer (1977, Electroencephalogr. Clin. Neurol., 43, 802-812), this time with correction for asymptote of the latency-intensity functions. The results of reanalyzing latency-intensity power functions have yielded exponents that were very similar across components, closer to the exponent of magnitude estimates and accounting for a higher amount of variance for all of the ABEP components. This procedure may also prove useful for clinical evaluation of auditory function.

Algorithms↗

PubMed1984

Localized pontine lesion: nearly total absence of REM sleep.

Eight whole-night polysomnographic recordings were conducted in a 33-year-old man with a localized pontine lesion inflicted by a shrapnel fragment. Sleep recordings revealed no rapid eye movement (REM) sleep in 3 nights, and markedly reduced REM sleep in 5 nights; non-rapid eye movement (NREM) sleep was normal. In spite of marked reduction of REM sleep, the patient conducted a normal life and had none of the typical symptoms of REM-sleep deprivation.

Adult↗

PubMed1984

Auditory evoked potentials and audiological follow-up of subjects developing noise-induced permanent threshold shift.

Three examinations, including cochlear microphonics (CM) to 99/s 1-kHz tones and auditory brainstem evoked potentials (ABEP) to 10/s and 55/s clicks, as well as psychoacoustical tests, were performed on 31 normally hearing subjects, exposed to occupational noise for over a year. The results showed prolongation of the absolute latency of peaks I, III and V, without significant changes in interpeak latency differences (IPLD) or CM latency. The site affected by increasing stimulus rate, giving rise to increased IPLD, appears to be central rather than cochlear. The efficacy of increased stimulus rate in detecting noise-induced auditory changes was higher than achieved applying the 10/s click rate.

Adolescent↗

PubMed1984

Auditory brain stem potentials evoked by clicks in notch-filtered masking noise: audiological relevance.

Auditory brainstem-evoked potentials (ABEP) to clicks in notch-filtered masking noise were recorded from 10 adults with normal audiograms and from 10 adults with hearing losses. Masking noise had 0.5-octave-wide notches with central frequencies of 8 000, 2 000, 1 000, 500 and 250 Hz. For each notch frequency, decreasing-intensity series in 10-dB steps (for both the click and the noise) were derived until the detection threshold of ABEP was reached. From the detection thresholds of normal subjects, the normative detection threshold for each frequency was calculated. Deviations from the normative detection thresholds were considered ABEP estimates of hearing loss. The results of this study showed that while ABEP to clicks in notched noise were sensitive to hearing losses, correlations between audiometric hearing loss and ABEP estimates of hearing losses at specific frequencies were nonsignificant. At the present stage of the procedure, ABEP to clicks in notched noise cannot estimate hearing thresholds at specific frequencies.

Adult↗

PubMed1984

Auditory middle latency-evoked potentials during sleep apnea.

Auditory middle-latency evoked potentials (AMEP) were recorded in 10 subjects with predominantly central sleep apnea. AMEP were recorded during: waking; non-rapid eye movement (non-REM) sleep between apneic episodes; first half of apneas; and second half of apneas. Latencies of vertex positive peaks Po and Pa were determined, and the effect of the apnea phase on these latencies was evaluated. The latencies measured did not reveal chronic or acute functional abnormality of central auditory structures, which may result from or cause apneic episodes during non-REM sleep. The normalcy and stability of AMEP during apneic sleep may indicate effective compensatory mechanisms in central auditory structures. Alternatively, the lack of changes may result from the variability of AMEP, which may obscure small functional changes.

Adult↗

PubMed1983

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

By simultaneously recording from 3 orthogonal electrode montages, and plotting the 3 voltage-time records on three-dimensional voltage-voltage-voltage coordinates, a spatial Lissajous' trajectory is obtained. This 3-Channel Lissajous' Trajectory (3CLT) represents the simultaneous voltage values from 3 independent montages and, assuming a uniform volume conductor, it includes all the information required for calculation of the dipole equivalent of surface-recorded activity. In 3CLT time is not explicitly graphed, but is implied as motion along the trajectory. Thanks to the small distribution of the generators of BAEPs, relative to their distance from the recording electrodes, 3CLT of BAEPs holds the promise of summarizing all activity from the surface. Comparing 3CLT of BAEPs to left vs. right ear stimulation has confirmed the lateralization of components I and III, but has also shown lateralization for the other components, which detailed surface mapping studies had overlooked. 3CLT may offer a more sensitive, yet less cumbersome, alternative to detailed surface mapping of BAEPs. The full promise of 3CLT can only be evaluated after quantitative indices of the trajectory are developed.

Adult↗

PubMed1983

Auditory brainstem evoked potentials during sleep apnea.

Auditory brainstem evoked potentials (ABEPs) were recorded from seven subjects with predominantly central sleep apnea. ABEPs were recorded during: (1) waking, (2) non-REM sleep between apneic episodes, (3) first half of apneas, and (4) second half of apneas. Latencies of vertex positive peaks III, V, and VI as well as the V-III interpeak latency difference were determined, and the effect of apnea phase on these measures were evaluated. The measures studied did not reveal chronic or acute functional abnormality of auditory brainstem, which may result from or cause apneic episodes during non-REM sleep. The normality and stability of ABEPs during apneic sleep indicate effective compensatory mechanisms in auditory brainstem. Brainstem functional changes associated with central apneas may not be reflected in the ABEP measures studied, unless they are part of a more extensive dysfunction.

Adult↗

PubMed1983

Photoperiodic effects on thermoregulation in a 'blind' subterranean mammal.

Thermoregulatory responses to changes in photoperiod were studied in the 'blind' mole rat Spalax ehrenbergi (Nehring). Acclimation of cold-sensitive individuals to short photoperiod (8L:16D) at an ambient temperature (Ta) of 22 degrees C increased their thermoregulatory capacity in cold conditions, when compared to individuals which were acclimated to a photoperiod of 12L:12D at the same Ta. Acclimation of cold-resistant individuals to Ta = 17 degrees C but with a photoperiod of 16L:8D caused a decrease in thermoregulatory capacity. Evaluation of the visual pathway through the visual-evoked potentials showed that the mole rat does not respond to flash stimuli and can thus be considered to be effectively blind.

Animals↗

PubMed1982

Replicable abstinence rates in an alcoholism treatment program.

Treatment outcome studies of alcoholism have historically had innumerable difficulties and controversy. Few investigators ever have reported a replication of their initial study results, let alone the crossvalidation of such initial results. This article provides results of a four-year replication study of a medical behavioral treatment approach. Comparisons of patients receiving a uniform treatment were made at yearly intervals. A few variables are identified to clarify who will or will not achieve and maintain follow-up sobriety, although it is admitted that our knowledge in this area is still rudimentary. These results affirm for the practitioner today that the alcoholic patient is treatable with a high probability of success. When the outcome of treatment is positive, the diagnosis and referral become crucial for alcoholism just as for other treatable diseases.

Adult↗

PubMed1982

Auditory brain stem potentials evoked by clicks in notch-filtered masking noise.

Auditory brain stem evoked potentials (ABEPs) were recorded in response to wide-band clicks in notch-filtered masking noise. Notches (1/2 octave wide, 96 dB/octave slopes) were centered on the audiometric frequencies. Without the notches, masking noise intensity was adjusted to obliterate ABEPs. Intensity series, with both clicks and masking noise attenuated by the same 10 dB steps, were obtained for clicks masked by notched noise, in addition to unmasked clicks. Absolute latencies and interpeak latency differences of ABEPs to clicks in notched noise did not change with notch frequency. Absolute latencies were longer for ABEPs to clicks with notched noise than to unmasked clicks. For all stimuli, latencies were prolonged when stimulus intensity decreased. The findings suggest that ABEPs to clicks in notched noise are initiated by low threshold cochlear activation which may account for the independence of component latency from 'travelling wave' propagation time. These potentials may be representative of only one subset of the constituents of ABEPs to wide-bank unmasked clicks. The clinical application of these potentials must await elucidation of their relevance to the process of hearing.

Acoustic Stimulation↗

PubMed1982

Analog delay line artifact rejector for evoked potential studies.

A true artifact rejector which utilizes a bucketbrigade delay line is described. The delay line enables scanning of all the data in the analysis period prior to its inclusion in the average. The device is small in size, independent of the averager, and the total cost of components is under $100. This artifact rejector is compatible with any averager. Artifact rejection can be according to excessive amplitude, as described in this version, or according to externally applied signals. In addition, by a minor change in the interference detector module, rejection could be according to other criteria, such as frequency contents. The utility of the device is demonstrated on records of auditory brain stem evoked potentials.

Analog-Digital Conversion↗

PubMed1982

Short latency visual evoked potentials in man.

Contrary to auditory and somatosensory evoked potentials, surface recorded visual evoked potentials which arise in subcortical neural elements have rarely been described. Considerable disagreement exists between the reports in the literature on such visual potentials. In this study, flash stimuli were used to evoke the potentials which were recorded from the skin overlying the infra-orbital ridge, outer canthus, middle of the forehead, vertex, mastoid ipsilateral to the stimulated eye and inion, using a non-cephalic reference. The potentials were amplified in a band which was chosen to omit slow retinal and cortical potentials, and to enhance activity which might include compound neural activity. Potentials were recorded from 9 subjects (13 eyes), and for each one the effects of eye position and stimulus intensity were studied. The results indicate that the series of components recorded within the first 100 msec following photic stimulation were volume-conducted activity generated by a subset of the visual system which is activated by luminosity changes. The generators of the first 4 or 5 components seem to be situated within the retina, the subsequent components seem to be generated in the optic nerve or tracts, and the later components may be thalamo-cortical in origin. These potentials may complement pattern evoked potentials in a more accurate definition of sites of lesions along the visual pathway.

Adult↗

PubMed1982

Hospital treatment of alcoholism: a profile of middle income Americans.

3,411 first admissions for alcoholism treatment to nine proprietary hospitals were studied with standardized questionnaire and diagnostic instruments. Despite the patients' relative economic and social stability, severe patterns of addictive alcohol use had developed and persisted for many years with a high incidence of alcohol-related and intercurrent medical disorders which required prompt medical intervention. Although most patients had a personal physician, less than 9% of referrals for hospital treatment for alcoholism were made by physicians; most patients responded to television outreach programs, recommendations by former patients or were self or family referred. This survey shows that persons who are neither socially disadvantaged nor economically deprived may have severe alcohol-related problems. Such patients constitute a significant challenge to the medical profession to develop strategies for early intervention and more efficacious treatment.

Adolescent↗