PubMed Health⌕ Search

Biomedical subjects

R K Simpson

Publications and source records attributed to R K Simpson.

90 records · Page 5Linked to original sources
PubMed1983

The effects of spinal cord injury on somatosensory evoked potentials produced by interactions between afferent pathways.

The purpose of the present study was to determine the utility of somatosensory evoked potentials (SEPs) produced by interaction between afferent pathways for spinal cord injury evaluation. Interaction was measured as alterations in SEP configuration compared to controls. Monkeys anesthetized with N2O were used. Stimulus intensities were sufficient to excite all nerve fibers. The conditioning stimulus (CS) was applied to the left peroneal nerve and test stimulus (TS) to the left radial nerve. CS-TS intervals were 100 msec in duration. SEPs were recorded from primary cortical receiving area for the forelimb. Different surgical lesions were made at spinal cord level T3-T4. Amplitudes of TS-produced-SEPs remained unchanged postlesion. CS-produced-SEPs were found to be dependent upon the integrity of anterolateral column pathways. Accentuated interaction was observed following dorsal column ablation. Interaction was slightly enhanced after left hemisection but diminished after right hemisection or central cord lesion. Interaction between spatially separate afferent inputs as measured by SEP alteration was determined to be a sensitive indicator of spinal cord injury.

Afferent Pathways↗
PubMed1983

Far-field potentials as a method of monitoring acute and chronic spinal cord injury.

Far-field potentials (FFPs) were studied in monkeys to determine the utility of such responses in evaluating acute and chronic spinal cord injury. Monkeys (Macaca fascicularis) were anesthetized with 70% N2O 30% O2, immobilized with pancuronium bromide, and maintained on a respirator. Spinal cord transections were made at level T3-T4 and included bilateral dorsal columns or anterolateral columns, right or left hemisection, or central cord lesions. Percutaneous stimulation of both posterior tibial nerves was performed at a frequency of 3 Hz using 3-4 mA for 0.3 msec duration. Potentials were recorded from chronically implanted epidural electrodes (right ear reference) through a 300-3,000 Hz band pass filter. Each far-field potential represents the average of 256 individual responses recorded for a duration of 25 msec before and after cord lesion for up to 8 weeks. Seven reproducible components in the far-field potential could be identified. Following dorsal column transection all components were reduced in amplitude. After anterolateral column transection only latencies were altered. Right or left hemisections caused both attenuation of component amplitudes and latency alteration. Central cord lesions resulted in no detectable amplitude or latency disturbances. Control records likewise showed no changes. No major alterations, following day 1 posttransection, were observed, attesting to the relative stability of far-field potentials over long periods of time. Far-field potentials therefore may be useful in monitoring spinal cord injury.

Animals↗
PubMed1982

Classification of somatic evoked potentials through maximum entropy spectral analysis.

Maximum entropy (ME) spectra are currently considered to be superior to spectra calculated by means of Fast Fourier Transforms (FFT) because the former offer higher resolution. However, in terms of classification of somatic evoked potentials (SEPs), FFT spectra are found to be better than ME spectra. An even better set of parameters for discriminating SEPs is the set of reflection coefficients derived in the process of calculating the ME spectra. They permit separation of SEPs obtained from monkeys with dorsal column lesion from SEPs obtained from normal monkeys, as well as distinguishing between SEPs obtained from large nerve fiber stimulation and SEPs from stimulation of all nerve fibers.

Animals↗
PubMed1981

Velar stretch as a function of task.

This study examined velar stretch in 20 young, normal adults during the production of /alpha/,/epsilon/, and /u/, and during blowing. Velar length was measured from cephalometric x-rays in two ways: (1) along the nasal surface of the velum and (2) along the velar midline. Results show no significant differences in velar stretch between males and females. Using nasal surface measures, there was significantly greater stretch for /u/ and for blowing than for /alpha/ and /epsilon/. For midline measures, the only differences which reached statistical significance were between blowing and /alpha/ or /epsilon/, which were not different from each other. Correlations between need ratio and percentage of stretch were significant as were correlations between percentage of velar stretch (nasal surface measure) and velar height. Comparisons of the two methods of measuring velar length are presented followed by a discussion concerning the significance of the findings.

Adolescent↗
PubMed1980

A cephalometric study of velar stretch in adolescent subjects.

Cephalometric x-rays were used to evaluate velar stretch in 20 normal adolescents during the production of /s/. Radiopaque markers were used so that the behaviors of both the anterior and posterior portions and the total velum cound be evaluated. Velar stretch was found in each of the subjects with the average stretch (15.19%) greater than the amount reported for 10-year-old subjects but less than the average stretch for adults. The correlation between amount of velar stretch and need ratio was not significant. The different stages of involution of adenoid tissue, which is characteristic of this age group, resulted in varying configurations of the naso-pharynx were postulated as one possible explanation for this unexpected finding. Normative data and clinical implications are presented.

Adolescent↗
PubMed1975

A roentgencephalometric investigation of the effect of adenoid removal upon selected measures of velopharyngeal function.

Pre-and postoperative lateral x-rays were taken of 15 candidates for adenoid removal, ranging in age from four to seven years. Cephalometric measurements were taken during rest and during function (/s/). The postoperative group acquired pharyngeal dimensions of C.P.I. proportions as a result of adenoid removal. However, all subjects achieved velopharyngeal closure and displayd no hypernasality following this surgical procedure, indicating success in terms of speech. The success in their adaptation can be attributed to the following: 1) increased velar mobility; 2) increased height of velopharyngeal closure; 3) increased percent of velar stretch; and 4) anterior movement of the posterior pharyngeal wall when amount of velopharyngeal contact became tenuous. The normal velopharyngeal mechanism has the capacity to successfully overcome the imbalance between pharyngeal dimensions and velar length caused by adenoid removal. The normal mechanism overcomes this imbalance by means of compensations, some of which are typical of the inadequate mechanism.

Adenoidectomy↗
PubMedDate not supplied

Scalp hamartoma in identical twins.

Identical twin male infants had scalp hamartomas removed from the occipital region. The histologic features and genetic implications of these unusual lesions are discussed.

Diseases in Twins↗
PubMedDate not supplied

Early component changes in corticomotor evoked potentials following experimental stroke.

Corticomotor evoked potentials have recently been used in experimental animals and patients as a measure of neurologic function after stroke. However, little is known about the fundamental electrophysiologic properties contributing to the formation of these potentials. To define some of these properties, corticomotor evoked potentials were recorded from the contralateral hindlimb in response to transcortical stimulation in cats anesthetized with halothane. These potentials were obtained hourly for 6 hours after middle cerebral artery occlusion. Four major identifiable components were recorded in control responses. Immediately after infarction, all component amplitudes were significantly attenuated. However, after approximately 5 hours, the early latency components exceeded control values; late latency components were also increased. Corresponding somatosensory evoked potentials were abolished and did not return throughout the recording session. Based on classic neurophysiologic studies, the amplitude increment can be explained as combined activation of low-threshold brainstem facilitatory centers and/or direct activation of subcortical axonal pathways. With further study, corticomotor evoked potentials may be a valuable adjunct to current electrophysiologic monitoring techniques, particularly with regard to defining the extent and location of an infarct, as well as to assessing functional recovery.

Animals↗