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Biomedical subjects

L E Miller

Publications and source records attributed to L E Miller.

At least 55 records · Page 3Linked to original sources
PubMed1994

The relation between the direction dependence of electromyographic amplitude and motor unit recruitment thresholds during isometric contractions.

The activation of muscles can be studied by measuring the activity of a representative set of single motor units in a muscle or by measuring the surface electromyographic (EMG) activity of a muscle that results from the contribution of a large number of motor units. In this study we have developed a model showing how the direction dependence of the amplitude of the EMG activity during isometric contractions can be understood from the recruitment thresholds of single motor units when force is applied in various directions within a plane. The model predicts that the direction with the largest EMG activity (called the "preferred direction") corresponds to the direction in which the largest number of motor units is recruited. If one assumes homogeneous activation of a population of motor units, this preferred direction can be shown to be equivalent to the direction in which the recruitment threshold of the motor units is smallest. The experimental data show that, for most muscles in the human arm, the amplitude of surface EMG activity for a constant, isometric force at the wrist was proportional to the cosine of the angle between the muscle's preferred direction and the direction of force. As predicted by the model, the preferred direction coincided with the direction in which the recruitment threshold of motor units was smallest. Musculus deltoideus anterior had a more complicated directional sensitivity for surface EMG activity that could not be well fit by a single cosine function. This effect could be explained by the finding of two subpopulations of motor units within that muscle, each with a different recruitment behavior.

Adult↗
PubMed1993

Correlation of primate red nucleus discharge with muscle activity during free-form arm movements.

1. We recorded from 239 neurons located in the magnocellular division of the red nucleus of four alert macaque monkeys. At the same time, we recorded electromyographic (EMG) signals from as many as twenty electrodes chronically implanted on muscles of the shoulder, arm, forearm and hand. We recorded EMG signals for periods ranging from several months to a year. 2. The monkeys were trained to perform three free-form food retrieval tasks, each of which activated all of the recorded muscles and most of the neurons. The 'prehension' task required simply that the monkey grasp a piece of food from a fixed point in space. The 'barrier' task required the monkey to reach around a small barrier to obtain the food, and the 'Kluver' task required that food be removed from small holes. During the prehension task, we found approximately equal numbers of neurons that were strongly active while the hand was being moved toward the target (70% of units), and while the food was being grasped (60%). Relatively few units were active as the hand was returned to the mouth (15%). 3. Data files of 1-2 min duration were collected while the monkey performed a single behavioural task. Whenever possible, we recorded files for all three tasks from each neuron. For each file we calculated long time-span analog cross-correlations (+/- 1.28 s) between instantaneous neuronal firing rate and each of the full-wave rectified, low-pass filtered EMG signals. We used the peak correlation and the time of the peak as two summary measures of the functional relation between modulation of neuronal activity and EMG. 4. The magnitude of the strongest correlations was between 0.4 and 0.5 (normalized to a perfect correlation of +/- 1.0). Distal muscles were the most frequently correlated, and extensors were more frequently correlated than flexors. For all monkeys, the lags for well correlated muscles were distributed broadly about a uni-modal value near 0 ms. Eighty five per cent of the correlations larger than or equal to 0.25 had peaks between -150 and 200 ms. 5. The activity of each neuron was represented in a muscle co-ordinate system by an n-dimensional 'functional linkage vector', each element of which was the peak correlation with one of n muscles. The vector for any given neuron points in a particular direction in muscle space, depending on the similarity between the activity of the neuron and the activity of each muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

The control of arm pointing movements in three dimensions.

In this study we investigated pointing movements made with an extended arm. Despite the large number of mechanical degrees of freedom, limb orientation adopted during pointing could be described by rotation axes contained on a two-dimensional curved surface. As a result of the curvature, the orientation of a linear plane approximating a small region of the curved surface was dependent on the location of the movements within the full workspace. These results account for earlier suggestions that limb orientation could be described by coplanar rotation vectors and that the orientation of the plane moved with the workspace. Despite the additional complexity, our results indicate that the number of degrees of freedom used to position the extended forearm is reduced from four to two for normal pointing movements. Contributions to orientation of the wrist and hand by supination/pronation of the forearm were minor for changes in shoulder yaw angle. However, supination/pronation added significantly to orientation of the hand for changes in shoulder pitch angle.

Arm↗
PubMed1991

Effects of moon phase and other temporal variables on absenteeism.

Previous research on the effects of lunar phase on deviant behavior has produced weak and inconsistent results and has been criticized for failing to use appropriate statistical controls. This study examined the effects of the full moon on daily absenteeism rates in a large organization while correcting for autocorrelation and controlling for the effects of the day of the week, month, and proximity to a holiday. Contrary to expectations, the full moon was associated with a significant (but very slight) decrease in absenteeism. Reasons for persistent beliefs in the effects of the full moon are discussed.

Absenteeism↗
PubMed1989

Modeling awareness of feelings: a needed tool in the therapeutic communication workbox.

Feelings are the focus of much therapeutic time with clients. This article reviews the reasons for encouraging clients to explore feelings and provides a therapeutic communication tool. Clients who are reluctant or unable to acknowledge their feelings present a challenge. One way around this impasse is for the nurse to model feelings--directly or indirectly.

Communication↗
PubMed1987

Soluble interleukin 2 receptors are elevated in patients with AIDS or at risk of developing AIDS.

Utilizing an enzyme-linked immunosorbent assay, we detected elevated serum levels of soluble interleukin 2 receptors (SIL-2R) in 73% of patients with acquired immunodeficiency syndrome (AIDS), 80% of AIDS-related complex patients, 78% of anti-HIV-positive lymphadenopathy syndrome patients, 85% of HIV-antibody-positive hemophiliacs, and 80% of anti-HIV-positive asymptomatic homosexual males, iv drug abusers, and heterosexual contacts. Of the subjects with no demonstrable antibody to HIV, 29% of hemophiliacs, 12% of adult homosexual males and iv drug abusers, and none of the patients with lymphadenopathy had elevated SIL-2R. Overall, only 5 of 40 antibody-negative "high-risk" individuals had SIL-2R values greater than the reference interval whereas 108 of 138 antibody-positive individuals had elevated values (chi 2 = 57.85, P less than 0.001).

AIDS-Related Complex↗
PubMed1987

Correlation and spectral analysis of relations between single unit discharge and muscle activities.

Correlation and spectral analysis was used to study functional linkages between single-cell discharge in the magnocellular red nucleus and the electromyographic activity of several limb muscles. Long sequences of unit discharge and EMG activity were recorded while feline subjects performed a food retrieval task. Unit discharge and muscle activity were patterned in bursts that corresponded to different phases of the task. There was sufficient variability in the parameters of these bursts to regard the signals as pseudorandom variables, thus facilitating a correlation analysis. Cross-correlation functions computed between unit discharge and each muscle EMG served to characterize the strength and reliability of linkages between a single unit and various limb muscles. Auto-correlation and auto-spectral density functions provided summary measures of the temporal and frequency characteristics of the signals. Power in the signals was concentrated in a behaviorally relevant range (0.2-8 Hz). Coherence functions showed peaks that indicated which frequency components were well correlated with unit discharge. Two-sided impulse responses served to characterize the dynamic properties of the linkages. These methods are shown to be valuable in characterizing noncausal, as well as causal, linkages through multisynaptic pathways in the nervous system.

Action Potentials↗
PubMed1986

Repair of a coccygeal vertebral fracture in a dog, using a four-hole finger plate.

A 7-year-old Pointer was referred with a transverse fracture of the 12th coccygeal vertebra. A 4-hole 2-mm finger plate was applied to the dorsolateral aspect of the vertrebra, and the tail was placed in a protective splint. This case presents an alternate method of fixation of coccygeal fractures, and is recommended when the nerve and blood supplies to the tail are intact, and when a cosmetic appearance with minimal callus formation is desired.

Animals↗
PubMed1985

Effects of exercise conditioning on semen characteristics from hyper- and hypotensive lines of turkeys.

Twenty-one male Broad Breasted White turkeys which had been selected for high or low blood pressure were put on an exercise regimen to determine its effect on semen quality. Eleven were from the hypertensive line and 10 from the hypotensive line. Eleven (6 hypertensive and 5 hypotensive) turkeys were placed on an exercise regime of walking (herding) about 1 mile daily for 6 weeks before the experiment began, and then for a further 6 weeks during semen collection. Semen was collected from 11 turkeys on the exercise regime and 10 nonexercised control birds which were kept in their experimental pens during the trial. Both hypertensive and exercised groups showed an improved semen colour score at the first collection period (P less than or equal to 0.09). Only the exercised group showed a significantly (P less than or equal to 0.05) better score than the control group during periods 2 and 3. The hypertensive line showed significantly higher spermatozoa count than the hypotensive line during the first collection period. There was no effect of either exercise or selection for high or low blood pressure on semen volume.

Animals↗
PubMed1985

Effects of caponization on body weight, atherosclerosis, and cardiovascular variables in hypertensive and hypotensive turkey lines.

Effects of caponization and blood pressure selection on serum lipids, severity of atherosclerosis, body weight, hematocrit, and relative ventricular weight in hypertensive and hypotensive lines of turkeys were evaluated in two trials. At 8 weeks of age, half the turkeys from each line were caponized. Body weights, blood pressure, and blood samples were obtained from each treatment at 8, 20, and 30 weeks of age. A total of 56 and 72 birds were used in Trials 1 and 2, respectively. Birds were necropsied at 30 weeks of age. Hypertensive turkeys had significantly greater serum cholesterol and total lipid than hypotensive turkeys only at 30 weeks of age in Trial 1. Lower relative ventricular weights were observed in hypotensive turkeys within both trials. Hypertensive birds exhibited a more severe degree of atherosclerosis and higher relative heart weight than hypotensive turkeys. Caponization significantly increased total serum lipid only at 20 weeks of age in Trial 2. Average body weight of caponized turkeys was significantly lower (1.2) than the control turkeys at 30 weeks of age. Caponized turkeys exhibited lower relative ventricular weight in Trial 1 but not Trial 2 and an increase in blood pressure only in Trial 2. Caponization suppressed body weight, decreased hematocrit values, and had no significant effect upon plaque severity. The presence or absence of male sex hormones had virtually no effect on proposed atherogenic stimuli thereby suggesting another mechanism by which the female is afforded a higher degree of protection.

Animals↗
PubMed1984

Viscoelastic properties of the wrist motor servo in man.

Viscoelastic properties play an important role in posture and movement. Such properties arise from muscle mechanics and from stretch-reflex actions. We describe experiments designed to characterize both linear and nonlinear elastic and viscous properties of the wrist motor servo in human subjects. First, we describe a trial comparison method for the identification of reflex responses that are unmodified by triggered reaction-time movements. Elastic properties were studied by applying step changes in load force that stretched or released the wrist flexor and extensor muscles. The properties were basically spring-like, but there was a short-range enhancement of stiffness that gave rise to a prominent hysteresis. Viscous properties were studied by applying ramp stretches at different velocities. Both EMG and force responses showed a weak fractional-power dependence on velocity similar to that described recently for muscle spindle receptors. Consideration is given to the possible advantages of this type of nonlinear feedback in the damping of postural responses and movements.

Biomechanical Phenomena↗
PubMed1983

Effect of exercise on aortic atherosclerosis and other cardiovascular variables among hyper- and hypotensive turkeys.

Two experiments were conducted to determine the effects of physical training on the turkey cardiovascular system. Sexually mature (Experiment 1) and immature (Experiment 2) Large White turkeys were used. Equal numbers of genetically hypertensive and hypotensive birds were used in each experiment. In each experimental group, birds were randomly divided into exercise and control treatments. Assessments were made with regard to training effects and differences associated with genetic blood pressure strain. Exercise had no significant effect on the severity of atherosclerosis or serum lipid levels in either experiment. Significantly greater hematocrits were recorded among birds exercised in Experiment 1; however, hemoglobin concentration did not follow this trend. Exercise was also associated with increased cardiac dimensions (Experiment 1) and increased body weight (Experiment 2). Genetic hypertension was associated with accelerated atherogenesis and higher serum cholesterol levels in immature birds, and in mature birds cardiac enlargement was associated with hypertension. Differences in behavior response to exercise were observed between the two experiments. Sexually mature hypertensive turkeys showed less endurance to the walking regimen than the hypotensive turkeys, but no such differences were observed in immature hypertensive or hypotensive birds.

Animals↗