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Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 73 records · Page 4Linked to original sources
PubMed1994

Plasma cholesteryl ester transfer in patients with non-insulin dependent diabetes mellitus.

Plasma newly synthesised cholesteryl ester transfer (NCET) rates from high density lipoproteins (HDL) to very low density lipoproteins (VLDL) and low density lipoproteins lipoproteins (LDL) were measured in 26 patients with non-insulin dependent diabetes mellitus (NIDDM), 26 healthy subjects with closely matching plasma triglyceride (TG) levels and 10 normolipidaemic healthy individuals. In addition, insulin mediated glucose uptake was measured in the NIDDM patients and the normolipidaemic subjects. Rates of NCET were significantly (P < 0.05) elevated in NIDDM patients compared with healthy normolipidaemic individuals but were similar to rates in healthy subjects with closely matching TG levels. In all groups of subjects plasma NCET was significantly (P < 0.001) correlated with plasma TG concentration. In NIDDM patients correlations between NCET and plasma glucose (r = 0.489, P = 0.011) independently of plasma TG levels, and glycated haemoglobin levels (r = 0.430, P = 0.028) were also recorded. Insulin mediated glucose uptake was unrelated to plasma NCET rates in the study. These data suggest that in NIDDM patients under good diabetic control elevated plasma NCET rates are mainly due to hypertriglyceridaemia and a specific and possibly stimulatory effect of diabetes on these rates may be seen only in patients with poorly controlled diabetes.

Adult↗
PubMed1994

The effect of acute hyperinsulinemia on plasma cholesteryl ester transfer protein activity in patients with non-insulin-dependent diabetes mellitus and healthy subjects.

The effect of acute hyperinsulinemia on plasma cholesteryl ester (CE) transfer protein (CETP) activity was determined in 11 patients with non-insulin-dependent diabetes mellitus (NIDDM) and 10 healthy subjects. Plasma CETP activity was reduced significantly in NIDDM patients (-37 +/- 59 nmol/mL/h, P < .05) but not in healthy subjects (-7 +/- 37 nmol/mL/h) during insulin infusion. Saline infusion did not alter plasma CETP activity significantly. The change in plasma CETP activity was correlated significantly with the baseline plasma triglyceride (TG) concentration (r = -.523, n = 21, P = .01) and marginally with the concomitant decrease in these levels with acute hyperinsulinemia (r = .413, n = 21, P = .06) in NIDDM patients and healthy subjects combined. These data indicate that acute hyperinsulinemia reduces plasma CETP activity and probably plasma CETP concentration in NIDDM patients, and suggest coordinated regulation of CETP levels and TG metabolism by insulin.

Adult↗
PubMed1994

Absolute pitch--electrophysiological evidence.

People who have the ability to label or to produce notes without any reference are considered to possess Absolute Pitch (AP). Others, who need a reference in order to identify the notes, possess Relative Pitch (RP). The AP ability is assumed to reflect a unique, language-like representation of non-lexical musical notes in memory. The purpose of this study was to examine this assumption by comparing Event Related Potentials (ERP) of musicians with and without AP, to lexical and non-lexical representation of musical material. Subjects were eighteen young adult musicians. Seven were AP and eleven RP. Auditory stimuli, presented through earphones, were piano notes (non-lexical) or a voice saying the note's name (lexical). Visual stimuli, presented on a computer display were note symbols (non-lexical) or letters (lexical). Subjects performed a number of tasks, combining the two modalities (visual and auditory) and stimulus types (lexical and non-lexical), and reaction times (RT), performance accuracy and evoked potentials were recorded. The tasks forced the subjects to transfer mental representations of musical material from one mode to another. Our most important findings were the differences, between groups, in the scalp distribution of P300 amplitudes. We conclude that absolute pitch possessors use the same internal language as relative pitch possessors, when possible, but the distribution of the underlying brain activity is different between AP and RP subjects.

Acoustic Stimulation↗
PubMed1994

Machine scoring of somatosensory evoked potentials.

A machine-scoring algorithm was developed for automatic identification and measurement of the positive and negative peaks of short-latency somatosensory evoked potentials (SEPs). The algorithm enables objective and consistent identification and naming of specific components with minimal operator involvement, avoiding inaccuracies and variability resulting from differences in the criteria used by different operators, or by the same operator at different times. The algorithm is based on finite impulse response filtering of wave forms from 4 conventional recording channels at a bandpass of 90-240 Hz. The bandpass was based on the major lobe in power spectra of multiple records and was verified as effective by application to numerous wave forms. Peak identification is based on identifying the peak at its optimal channel and verifying its consistency with corresponding peaks in the other channels. The machine-scoring algorithm was validated on SEPs from 120 subjects. The machine-scored peak latencies obtained with this procedure were significantly correlated with their manually measured counterparts.

Adult↗
PubMed1994

Three-channel Lissajous' trajectory of the binaural interaction components in human auditory brain-stem evoked potentials.

The 3-channel Lissajous' trajectory (3-CLT) of the binaural interaction components (BI) in auditory brain-stem evoked potentials (ABEPs) was derived from 17 normally hearing adults by subtracting the response to binaural clicks (B) from the algebraic sum of monaural responses (L + R). ABEPs were recorded in response to 65 dB nHL, alternating polarity clicks, presented at a rate of 11/sec. A normative set of BI 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivations of BI and of ABEP L + R and B. 3-CLT measures included: apex latency, amplitude and orientation, as well as planar segment duration and orientation. The results showed 3 apices and associated planar segments ("BdII," "Be" and "Bf") in the 3-CLT of BI which corresponded in latency to the vertex-mastoid and vertex-neck peaks IIIn, V and VI of ABEP L + R and B. These apices corresponded in latency and orientation to apices of the 3-CLT of ABEP L + R and ABEP B. This correspondence suggests generators of the BI components between the trapezoid body and the inferior colliculus output. Durations of BI planar segments were approximately 1.0 msec. Apex amplitudes of BI 3-CLT were larger than the respective peak amplitudes of the vertex-mastoid and vertex-neck recorded BI, while their intersubject variabilities were comparable.

Adolescent↗
PubMed1994

A high-intensity, goggle-mounted flash stimulator for short-latency visual evoked potentials.

The few studies that have been done on short-latency, subcortical visual evoked potentials (SVEPs) have all used stroboscopic flashes as the evoking stimulus. The dimensions of the stimulator, the acoustical artifacts and the photic spread to the examination room limited the use of SVEPs to research laboratories. With the advent of high-efficiency light-emitting diodes (LEDs), high-intensity flashes can now be generated from goggle-mounted LEDs. In this study, a goggle-mounted high-intensity stimulator was constructed and its flashes used to evoke SVEPs. The reproducibility of SVEPs across subjects and the ease of using the high-intensity LED flash stimulator make them a promising candidate for testing subcortical visual pathway function in the operating room.

Cerebral Cortex↗
PubMed1994

Three-channel Lissajous' trajectory of human middle latency auditory evoked potentials.

OBJECTIVE: We provide the normative values for middle latency auditory evoked potentials (MLAEPs) measures (three-channel Lissajous' trajectories or 3-CLT) in response to clicks and tone pips, which are the stimuli most widely used in MLAEP clinical testing. The relationship of 3-CLT measures to the more widely used latency and amplitude characteristics of the single-channel MLAEP of the same subjects was also evaluated. We further relate the 3-CLT findings to the question of MLAEP generators. DESIGN: 3-CLT of MLAEPs were derived from 12 humans (24 ears) in response to 65 dB nHL, rarefaction clicks as well as tone pips (1000 Hz), presented at a rate of 3.3/sec. A normative set of 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivation of MLAEP. RESULTS: Apex latencies of 3-CLT were comparable to peak latencies of the vertex-neck record, both in absolute values and in intersubject variability. Durations of planar segments were approximately 5.0 msec. Size and shape measures of planar segments were variable across subjects, making their clinical use, in their present form, questionable. CONCLUSIONS: The results showed two apices and associated planar segments (i1 and i2) in the 3-CLT of MLAEP which corresponded to the vertex-neck component Pa. These results and earlier studies that indicated a dual set of generators for Pa are compatible with a primary auditory cortex generator for i1 and ascending subcortical generators for i2.

Adolescent↗
PubMed1993

Critical ages in brainstem development revealed by neonatal 3-channel Lissajous' trajectory of auditory brainstem evoked potentials.

Auditory brainstem evoked potentials (ABEPs) were recorded from 91 newborns from 7 age groups between 26 to 43 weeks of gestation. In addition to the widely used vertex-mastoid derivation, potentials were recorded from three orthogonal electrode configurations, and represented in 3 dimensional voltage-space as three-channel Lissajous' trajectories (3CLTs). ABEPs were evoked by alternating polarity, monaural 75 dBnHL clicks presented at rates of 10/s, 55/s and 80/s. Potentials were also recorded to 45 dBnHL and 15 dBnHL clicks presented at 10/s. 3CLT point by point (apex latencies, amplitudes and orientation) as well as planar segment (planar segment position and duration) descriptors, along with peak latencies of the vertex-mastoid peaks, were followed for effects of age, stimulus intensity and rate. ABEPs began to appear consistently at 29 weeks of gestation to high stimulus intensities, with a rapid decrease of ABEP thresholds up to 34 weeks. At 35 weeks, thresholds stabilized approximately at adult values. The results indicate a significant effect of stimulus rate and intensity as well as of gestational age group on apex latencies. The findings also showed changes in apex orientations associated with stimulus rate and intensity interacting with gestational age. 3CLT descriptors enhanced the understanding of these results in relation to developmental and maturational aspects of the auditory system. The results may be explained by maturational change in relative contributions of constituents of the complex ABEP generators.

Analysis of Variance↗
PubMed1993

Upper limb somatosensory evoked potentials as a predictor of rehabilitation progress in dominant hemisphere stroke patients.

BACKGROUND AND PURPOSE: The aim of this study was to determine the predictive yield of upper limb short latency somatosensory evoked potential (USEP) in patients with first stroke in the dominant hemisphere. METHODS: Nineteen patients (average age, 58 years) were evaluated twice: on arrival at the rehabilitation center, approximately 3 weeks after the stroke, and again approximately 10 weeks later. The clinical assessment included a quantitative evaluation of motor ability, independence in activities of daily living, and communication ability. USEP was recorded during the week of the initial clinical evaluation. Special attention was paid to the relations between USEP parameters and the dynamics of the clinical condition. RESULTS: The seven patients in whom no cortical potential could be detected showed the worst outcomes; however, the existence of cortical potentials in the remaining 12 patients did not provide a precise prediction of their "rehabilitative capacity" (ie, the extent of their progress). A correlation was established between the amplitude of the potentials recorded over both hemispheres and changes in communication ability. Additional findings included an association between shortened central conduction time over the damaged hemisphere during the first month after stroke and improvement in motor ability. CONCLUSIONS: USEP can serve as an adjuvant tool for predicting the recovery progress of stroke patients.

Adult↗
PubMed1993

Computational waveform analysis and classification of auditory brainstem evoked potentials.

The widely used quantitative descriptors of amplitude and latency of evoked potentials, for peaks and troughs along the waveform, relate to only a limited number of points along the waveform, ignoring the interposed data. Moreover, these descriptors are typically determined manually, rendering them susceptible to user bias. We propose and demonstrate a machine-scoring algorithm for the identification and measurement of Auditory Brainstem Evoked Potentials (ABEP) peaks I, III and V. We further introduce an algorithm for the quantitative analysis of ABEP by waveform, and for clustering records according to waveform characteristics. The results of computerized peak identification and measurement, without user intervention, were correlated with manual measurements of the same peaks in a large number of waveforms. The waveform analysis and classification procedure differentiated waveforms to monaural left, monaural right and binaural stimulation, as well as according to the recording montage. These results underscore the advantages of using information in the waveform of ABEP, which has so far been overlooked. The automated algorithms for evaluation of ABEP by waveform hold the promise of a more comprehensive and consistent evaluation, and hence improved sensitivity.

Adult↗
PubMed1993

Blinking in patients with memory disorders during short term memory tasks.

The occurrence of blinking during short term memory tasks was analyzed for 32 subjects divided into three groups: 12 memory impaired patients, 10 elderly normals (age-matched to the patients), and 10 young normals. The subjects were participating in a study of brain evoked potentials accompanying memory activities. They were instructed not to blink during the performance of the memory tasks for reasons related to the quality of the recorded potentials. In this context, the withholding of blinking can be considered a secondary task. Blinking during the short term memory tasks was inversely related to performance accuracy (r = -.57). Age, mini-mental score and reaction time were also significantly related to the frequency of blinking. Dividing the memory patients into two groups according to the incidence of blinking, ("high-blinking" and "low-blinking"), revealed a significant difference in overall task accuracy with the high-blinking group performing more poorly than the low-blinking group.

Adult↗
PubMed1993

Bipolar cochlear nerve recording technique: a preliminary report.

To preserve hearing during vestibular neurectomy and acoustic neuroma removal, the cochlear nerve must be identified. Present techniques, including monitoring eighth nerve action potentials, help the surgeon identify those maneuvers that increase the risk of nerve injury but do not help in the anatomic identification of the cochlear nerve or the cochlear-vestibular cleavage plane. The purpose of this study was to demonstrate an electrophysiologic method of identifying the cochlear portion of the eighth cranial nerve. A flush-tipped, bipolar electrode recording probe was used to directly record responses to monaural click stimuli from the cochlear nerve but not from surrounding tissue. It was also used to delineate the cochlear-vestibular cleavage plane. Stimulus intensity levels over 25 dB sensation level tended to reduce the accuracy of nerve identification, and lower levels prolonged recording time. This technique and its application to posterior fossa surgery is discussed.

Adolescent↗
PubMed1993

Real-time monitoring of visual evoked potentials.

Steady-state visual evoked potentials (SSVEP) were recorded in response to flashes from eyepatch-mounted light-emitting diodes during neurological surgery and in the intensive care unit. SSVEP were detected and measured with a microprocessor-based waveform correlator. The system enabled a continuous display, in real time, of SSVEP amplitude and latency. SSVEP amplitude and latency changes were monitored throughout a variety of surgical procedures. Some of these procedures directly affect the central visual pathway, some affect the central nervous system as a whole, while others do not affect central nervous system function. In addition, intensive care unit patients with a variety of intracranial pressures were monitored. The results of this study indicate that SSVEP recorded with this method showed changes in SSVEP within seconds of surgical and/or medical decompression of intracranial pressure and were sensitive to specific changes in the visual pathway. Surgical procedures that directly affected the visual system, or elevation of intracranial pressure, resulted in changes in SSVEP. In contrast, procedures that did not affect the functional integrity of the visual system did not affect the recordings.

Adenoma↗
PubMed1992

Contralateral effects of cerebello-pontine angle exposure on human auditory brain-stem evoked potentials.

Auditory brain-stem evoked potentials (ABEPs) were recorded during surgical procedures which exposed the cerebello-pontine angle (CPA) in humans. Recordings made with the CPA contralateral to stimulus exposed were compared with those obtained with the skin sutured at the end of surgery. Single-channel as well as 3-channel Lissajous' trajectory (3-CLT) analyses were used to evaluate the effect of the surgical exposure on ABEP. The results suggest that exposure of the CPA contralateral to the stimulated ear did not affect dipole equivalent orientation nor magnitude, but did affect timing of the recorded activity being more pronounced for segments 'd'-'e' (corresponding to waves IV-V) than for 'a'-'b' (waves I-II). The results imply that the effects of disrupting the volume conductor may have been overwhelmed by other effects, such as local temperature changes. These changes, although not associated with clinical sequella, should be accounted for when analyzing subtle quantitative changes involving surgical exposures.

Acoustic Stimulation↗
PubMed1992

Auditory event related potentials during lexical categorization in the oddball paradigm.

Event related potentials (ERPs) and reaction times (RTs) were recorded from 18 subjects, performing lexical categorization of words and nonwords. Three sets of monosyllable utterances, differentiated in semantic and rhyming attributes, were presented using the "oddball paradigm." ERPs included a sustained negativity which began approximately 100 msec after stimulus onset and peaked at approximately 400 mses (SN4) poststimulus, in response to target as well as to nontarget word stimuli. Semantic effects on SN4 latency were observed only for target utterances. Nonmeaningful word targets were associated with longer SN4 peak latencies as well as slower RTs compared to meaningful word targets. It is suggested that these longer latencies are due to a longer time required for an exhaustive search in permanent memory before categorizing a stimulus as a nonmeaningful word.

Adult↗