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Biomedical subjects

J T Murphy

Publications and source records attributed to J T Murphy.

At least 55 records · Page 3Linked to original sources
PubMed1986

Measurements of human forearm viscoelasticity.

In human subjects, stiffness of the relaxed elbow was measured by three methods, using a forearm manipulandum coupled to a.d.c. torque motor. Elbow stiffness calculated from frequency response characteristics increased as the driving amplitude decreased. Step displacements of the forearm produced restoring torques linearly related to the displacement. The stiffness was very similar to that calculated from natural frequencies at amplitudes above 0.1 rad. Thirdly, elbow stiffness was estimated from brief test pulses, 120 ms in duration, by mathematically simulating the torque-displacement functions. Stiffness values in the limited linear range (under +/- 0.1 rad) were higher than in the linear range of the first two methods. A major component of elbow stiffness appears to decay within 1 s. The coefficients of viscosity determined from the simulation were, however, very similar to those calculated from the frequency response. Test pulse simulation was then used to determine joint impedance for different, actively maintained elbow angles. Joint stiffness and viscosity increased with progressive elbow flexion.

Adult↗
PubMed1985

Properties of visual cue responses in primate precentral cortex.

Monkeys were trained to perform a visuomotor task involving the alignment of a cursor over a vertical target line on a videomonitor by flexion or extension movements of the wrist. The forelimb area of the contralateral precentral cortex was thoroughly explored during the task. Intracortical microstimulation was employed to classify the forelimb region into wrist flexion--extension and non-wrist flexion--extension populations. Unit recording revealed an initial response to the cue for movement, viz. the appearance of the cursor and target line on the videomonitor, while visual signals not related to the task failed to evoke any response. The mean latency of these visual cue responses was approximately 150 ms. A great majority of the responses (96%) were bidirectional in character, in that they did not correlate with the directional information embedded in the visual cue, nor were they good predictors for the direction or timing of the subsequent movement. They were uniformly distributed in both the wrist and non-wrist regions of the forelimb area; the non-forelimb areas were devoid of the cue response. Further, when the variability of response to the visual cue for the wrist and non-wrist populations was compared, no significant difference was observed. These observations are consistent with an interpretation that the visually triggered cue responses provide a generalized activation over the task-related area of precentral cortex, paving the way for later and more specific activations leading to the execution of the task.

Animals↗
PubMed1985

The selected use of ultrasound mammography to improve diagnostic accuracy in carcinoma of the breast.

Our initial experience with diagnostic ultrasound mammography (UM) showed it to be of high diagnostic accuracy and improved specificity when compared with x-ray mammography (XRM) in certain categories of patients. To evaluate this modality further, we reviewed our experience with 600 consecutive patients who underwent ultrasound mammography as part of their initial evaluation for breast disease. Five categories of patients were reviewed: I: age 35 or less--129; II: DY or P-2 pattern on XRM--174; III: negative XRM but symptoms requiring additional evaluation--81; IV: high risk remaining breast in patients previously having mastectomy--48; V: refusal of repeat XRM because of pregnancy, lactation, or fear of radiation exposure--168. Fifty-five solid lesions were diagnosed, including 36 carcinomas. Seventeen of these were not diagnosed on x-ray mammography, giving an improved pick-up of carcinoma in this overall group of 2.83%. Of particular interest was that, of the 27 carcinomas that were found in the group having XRM, 8 or 29.6% were missed on that modality alone. Five of these (62.5%) were patients having a DY pattern. All patients have been followed carefully and re-examined at 3-month intervals, with no evidence of a false negative examination. Overall, we feel diagnostic ultrasound mammography is a valuable adjunct to x-ray mammography and recommend its continued use in selected groups of patients where it has a superior diagnostic accuracy over x-ray mammography alone.

Adolescent↗
PubMed1985

Evoked potentials from passive elbow movements. I. Quantitative spatial and temporal analysis.

Evoked potentials following perturbations of the forearm were recorded monopolarly at 8 scalp sites. Successive 10 msec bins of individual EPs were compared across subjects to determine intervals of consistent potential change. From this analysis it was possible to objectively sort subjects into two subpopulations with different common wave forms. Spatial vectors (potential gradient between two adjacent leads) were computed as well as Laplacian derivatives, to identify electrodes closest to source activity. Subsequently, temporal derivatives of the vectors were computed to define the timing of statistically significant response phases. To more precisely localize the largest potential gradients, component vectors (or their derivatives) in the Laplacians were resolved algebraically on a scaled representation of the scalp. Convergence of these resultant vectors from adjacent areas, identified zones of significant potential change which corresponded to known somatosensory areas. The two subpopulations had initial responses of similar topography localized to the central sulcal region. Subsequently, for one group the area of activated cortex expanded to include posterior parietal and more frontal areas. Prestimulus negative potential shifts had different distributions for the two groups and are described in relation to the poststimulus differences.

Adult↗
PubMed1985

Cross correlation studies in primate motor cortex: synaptic interaction and shared input.

Awake, unrestrained monkeys were trained to reach out with the forelimb and touch a button. Extracellular spike trains were recorded from pairs of neurons in contralateral precentral cortex with the same or separate microelectrodes. The neurons were located in the same or different functional columns as defined by intracortical microstimulation and passive sensory stimulation. Cross correlation analysis showed patterns consistent with synaptic excitation and/or inhibition between members of the cell pairs during the voluntary movement. The strength of correlation was inversely related to distance between columns, with the strongest correlations found between cells within the same column. Inhibitory correlations were virtually restricted to cell pairs within a single column. Temporal analysis showed that direct synaptic interaction and shared input patterns could be clearly distinguished in this physiologic setting. Spatial analysis indicated that shared input was concentrated among columns in the same and adjacent joint controlling zones as well as within a single column. No directional preference of shared input was present, a finding which was consistent with the observed nested organization of the forelimb area.

Action Potentials↗
PubMed1985

Cross correlation studies in primate motor cortex: event related correlation.

Simultaneous extracellular unit recordings were made from each cell of 237 pairs in two awake monkeys, during a voluntary reaching movement of the forelimb. The cells were located in contralateral precentral cortex and functionally coupled to single forelimb joints, as indicated by intracortical microstimulation and passive sensory stimulation. Cross correlation analysis showed that 72 of these pairs exhibited significant event-related correlation over periods of up to 780 ms, comparable to and coincident with the forelimb movement. Spatial analysis showed that such correlation extended across contiguous portions of all four forelimb joint zones of precentral cortex, over distances up to 3.5 mm. No preferred direction of correlation was observed. The data confirm the previously described nested organization of the forelimb area of precentral cortex. Findings are discussed in terms of mechanisms by which columns of neurons in motor cortex participate in the reaching movement.

Animals↗
PubMed1985

Sequential activation of neurons in primate motor cortex during unrestrained forelimb movement.

We trained monkeys to perform an unrestrained, reaching movement of the arm. Electromyogram (EMG) recordings of forelimb muscles revealed sequential activation, proximal to distal, of muscle groups involved in the task. The delay in onset of EMG activity between proximal (shoulder and elbow) and distal (wrist and finger) muscles was approximately 60 ms. We identified the neurons in the forelimb area of the contralateral motor cortex as controlling particular joints by previously defined criteria involving responses to somatosensory stimulation and effects of intracortical microstimulation. Many cells discharged prior to the onset of EMG activity acting on the appropriate joint, whereas others began firing at a later phase of the movement. The population of all proximal cells altered discharge patterns approximately 60 ms earlier than the population of distal cells. A small percentage of cells showed an initial inhibitory change in discharge frequency, and this inhibition typically occurred prior to the excitatory changes seen in the majority of cells. The results are discussed in terms of the "nested-zone" model of the forelimb motor cortex. The data support one of the predictions of this model, namely that discharges of identified cells within the cortical zones are causally related to voluntary movement at appropriate forelimb joints.

Animals↗
PubMed1985

Cross-correlation analysis of thalamic neurons and EMG activity in parkinsonian tremor.

Bursting activity in cells cross-correlated with electromyographic (EMG) activity during parkinsonian tremor. Statistically significant evidence of cross-correlation was found for 49% of cells located at the lesion target for relief of tremor. Statistically significant correlation was found for 90% of cells having tremor frequency power greater than twice 'average power' at nontremor frequencies. This population of cells may be involved in the generation of parkinsonian tremor.

Electromyography↗
PubMed1985

Celiac disease and spinocerebellar degeneration with normal vitamin E status.

We studied a 47-year-old man with spinocerebellar degeneration and malabsorption due to celiac enteropathy; the serum vitamin E level was normal. The neurologic disorder initially deteriorated despite improvement of small bowel histology on a gluten-free diet and vitamin E therapy, but later stabilized. The etiology of the neurologic disorder in adult celiac disease has not been identified and does not appear to be vitamin E deficiency.

Celiac Disease↗
PubMed1985

Use of a highly sensitive assay to analyze the excision repair of dimer and nondimer DNA damages induced in human skin fibroblasts by 254-nm and solar ultraviolet radiation.

The excision repair of nondimer DNA damages induced in normal human skin fibroblasts exposed to the Mylar-filtered UV produced by a fluorescent sunlamp was investigated. This work was accomplished through the development of a modification of the bromodeoxyuridine photolysis assay that greatly increases the sensitivity of this assay. This enhancement in sensitivity was achieved through use of alkaline elution to measure the DNA strand breakage produced by the photolysis of bromodeoxyuridine incorporated into the DNA through excision repair. Using this modified bromodeoxyuridine photolysis assay, it was found that the solar UV-induced nondimer DNA damages appear to have been repaired by a short patch repair mechanism in which a small number of nucleotides (two to four) were inserted into the repaired site. This is in contrast to the long patch repair process involved in the excision of cyclobutane pyrimidine dimers in which approximately 40 nucleotides were inserted into each repaired region.

Bromodeoxyuridine↗
PubMed1984

Human U2 and U1 RNA genes use similar transcription signals.

We have analyzed the requirements for human U2 RNA transcription by injection of cloned U2/6 RNA genes into nuclei of Xenopus laevis oocytes. Two forms of human U2 RNAs accumulate, a major species corresponding to mature-sized U2 RNA and a minor species corresponding to a 3'-extended precursor. This RNA polymerase II transcription requires only 258 and 94 bp of 5'- and 3'-flanking region sequences, respectively. Efficient U2 RNA synthesis depends on a promoter element located between positions -258 and -198. This region contains a 12-bp direct repeat which strongly resembles a comparable upstream promoter element of the human U1 RNA genes. Sequences between -258 and -198 also confer on the U2 RNA template the ability to complete with co-injected U1 RNA templates for a snRNA gene-specific transcription factor(s). Transcription of U2 RNA is reduced off templates containing an active RNA polymerase III transcription unit, presumably because of relaxation or sequestration of the DNA. In vitro transcription of the U2 RNA gene, like that of the U1 RNA gene, is initiated upstream of the point corresponding to the 5' end of in vivo synthesized RNA.

Amanitins↗
PubMed1984

Synthesis of human U1 RNA. II. Identification of two regions of the promoter essential for transcription initiation at position +1.

We have analyzed the requirements for human U1 RNA transcription catalyzed by RNA polymerase II. In Xenopus laevis oocytes, a human U1 RNA gene with only 231 and 35 nucleotides of the 5' and 3' flanking regions, respectively (Lund, E. and Dahlberg, J. E. (1984) J. Biol. Chem. 259, 2013-2021), is able to support accumulation of human U1 RNA. We show that the point in the template corresponding to the 5' end of U1 RNA is a site of transcription initiation. That result rules out the possibility that the 5' end of U1 RNA is generated by cleavage and capping of a precursor RNA. The accumulation of correctly initiated human U1 RNA transcripts requires at least two essential upstream elements. The region between positions -231 and -203 is indispensable for transcription both in oocytes and in vitro. The other region, between positions -105 and -6, fixes the location of the 5' ends of the U1 RNA transcripts in oocytes while not altering the overall level of transcription. This latter region contains a sequence located around position -50, which we propose serves as the analog of the T-A-T-A sequence in U1 and U2 RNA genes.

Animals↗
PubMed1983

Stretch reflex modulation during a cyclic elbow movement.

Small torque pulses were delivered to the forearm in order to test the stretch reflex of the brachialis and triceps arm muscles in 11 normal subjects performing a cyclic movement about the elbow in the horizontal plane. The flexion-extension movement was paced by a metronome and performed under various loading conditions. Reflexes for each muscle were tested either in each 50 msec segment of the 2 sec cycle period, or in a smaller number of selected phases. A late reflex, appearing at a latency of about 60 msec (measured from the onset of the torque increment), was modulated extensively during the movement cycle. The amplitude of the late reflex increased markedly at the onset of a muscle contraction. In many of the subjects reflex responsiveness began to increase as early as 200 msec prior to the onset of voluntary muscle activity. Peak reflex responses were elicited by stimuli delivered 100-150 msec prior to the peak rate of increase of dynamic load (composed of inertial, viscous and elastic forces). The increase in responsiveness was followed by a drop which was generally coincident in time with the peak rate of increase of the load opposing muscle contraction. The modulation of the late reflex is appropriately timed for reflex-generated tension to help counteract dynamic loads, intrinsic to the movement.

Adult↗
PubMed1983

Development of a total parenteral nutrition program in a community hospital.

The article outlines a Total Parenteral Nutrition (TPN) program now existing in a community hospital which could be introduced in other community hospitals. It also describes the role of the pharmacist as the instigator in the formation of a TPN Committee and as a contributing member of the TPN Committee.

Hospital Bed Capacity, 300 to 499↗
PubMed1982

Participation of precentral neurons in somatically and visually triggered movements in primates.

Monkeys were trained to perform somatically and visually triggered wrist flexion-extension (F-E) movements. Extracellular unit recordings were made in the contralateral precentral forelimb area. These neurons were identified as being best related to particular single forelimb joints by their responses to passive somatosensory stimulation and to the determining effects of local intracortical microstimulation. It was found that almost 60% of single-joint related cells participated in both somatically and visually triggered movements. All wrist (F-E) neurons responded reciprocally while non-wrist (F-E) neurons had reciprocal as well as bidirectional responses to the oppositely directed visual and somatic perturbations. Somatically related responses and visually related responses were both uniformly distributed throughout the vertical layers of precentral cortex. With respect to horizontal spatial arrangements, multiple clusters of reciprocally and bidirectionally responsive neurons were intermingled. This latter finding supports the concept of a context-sensitive organization for motor control within precentral cortex.

Animals↗
PubMed1982

Activity of primate precentral neurons during voluntary movements triggered by visual signals.

Awake, intact monkeys were trained to perform discrete flexion or extension movements of the hand about the wrist in response to visual signals. The object of the movement was to align a cursor, coupled to a manipulandum, on a target line. Cursor and target lines are displayed on a video monitor placed in front of the monkey. The target line was stepped to the right or left, randomly with regard to direction and timing, with each step implying an instruction for the monkey to make a voluntary movement for alignment. Single unit recording was made in the forelimb area of contralateral precentral cortex. Neurons were classified by their responses to passive sensory stimulation and the effects of local intracortical microstimulation into two populations; wrist flexion-extension (F-E) neurons, and all other forelimb neurons (non-wrist (F-E)). A significantly higher proportion of wrist (F-E) neurons as compared to non-wrist (F-E) neurons were task-related. Moreover the wrist (F-E) neurons exhibited exclusively reciprocal responses to the oppositely directed visual signals, whereas the non-wrist (F-E) neurons showed both reciprocal and bidirectional responses. No significant differences in mean latencies of responses, either in respect to the visual signals or to movement onset, were observed between the two populations of neurons. However the range of latencies in both instances was greater in the non-wrist (F-E) populations. The wrist (F-E) population showed significantly less response variability than the non-wrist (F-E) population with regard to response latencies to visual signals and movement onsets, and the degree of correlation between duration of response and reaction time.

Animals↗