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Biomedical subjects

D G Lloyd

Publications and source records attributed to D G Lloyd.

29 records · Page 2Linked to original sources
PubMed1996

Selective muscle activation following rapid varus/valgus perturbations at the knee.

Knee muscles are generally divided into groups based on their function as flexors or extensors. In this study we sought to determine if muscles were selectively activated according to their potential roles as varus or valgus stabilizers following rapid loads to the knee. While subjects were supine, varus or valgus moments were applied to the knees of 10 human subjects using a servomotor-driven perturbation device. During the experiments, electromyograms (EMG) were recorded from seven muscles, four of which had medial moment arms relative to the knee center, and three of which had lateral moment arms. It was observed that, for all medial muscles, a statistically significant increase in muscle activation followed valgus loads as compared with varus loads. All lateral muscles except the vastus lateralis showed the opposite response (as expected). These results suggest that muscles can be reflexively activated independent of their roles as flexors or extensors to provide stability to the human knee during varus or valgus loads. The timing of the reflex is consistent with that arising from joint mechanoreceptors, although polysynaptic stretch reflex may also be involved.

Electromyography↗
PubMed1996

A model of load sharing between muscles and soft tissues at the human knee during static tasks.

In this study, we have subjects voluntarily generate various forces in a transverse plane just above their ankles. The contributions of their muscles and soft tissues to the support of the total external knee joint moment were determined by analyzing the experimental data using a biomechanical model of the knee. In this model, muscle forces were estimated using the recorded EMGs. To account for subject variability, various muscle parameters were adjusted using a nonlinear least-squares fit of the model's estimated flexion and extension joint moments to those recorded externally. Using the estimated muscle forces, the contributions from the muscles and other soft tissues to the total joint moment were obtained. The results showed that muscles were primarily used to support flexion and extension loads at the knee, but in so doing, were able to support some part of the varus or valgus loads. However, soft tissue loading was still required. Soft tissues supported up to an average maximum of 83 percent of the external load in pure varus and valgus. Soft tissue loading in pure varus and valgus was less than 100 percent of the external load as the muscles, on average, were able to support 17 percent of the external load. This muscle support was by virtue of muscle cocontraction and/or specific muscle activation.

Adult↗
PubMed1996

A technique for the measurement of cadence using walkway vibrations.

A new method has been developed to measure cadence while walking. The method uses instrumentation to detect the vibrations transmitted in the walkway surface. These vibrations are produced when a subject's foot makes initial contact with the walking surface. The method was tested against heel switches and was found to measure stride duration with RMS errors of around 1%. The vibration method requires no instrumentation to be attached to the subject, can be used with bare feet or any other footwear, is simple to use and is very robust and reliable.

Acceleration↗
PubMed1995

Muscle activity is different for humans performing static tasks which require force control and position control.

Muscle activation levels in humans were examined during two different static tasks which required the same joint angles and the same joint moments. In the isometric case, joint angles were fixed and subjects were required to match forces. In the isoinertial case, a constant load was imposed across the joint and the subject was required to match position. It was observed that for a specified posture and for specified load conditions, EMG activity varied depending on whether the limb was loaded isometrically or isoinertially. That is, different co-activation relationships were observed for position control versus force control tasks during otherwise similar conditions. These results imply that the neural command for static tasks depends on more than joint angles and load magnitude.

Electromyography↗
PubMed1990

Quantitative shape analysis of the temporal and prefrontal lobes of schizophrenic patients: a magnetic resonance image study.

In a recent quantitative neuroimaging study, the authors reported significant reduction in the gray matter volume of both temporal lobes of schizophrenic (SC) patients. In order to better elucidate the nature of this finding (i.e., diffuse vs. focal), we analyzed the shape of the temporal lobes of 17 SC patients and an equal number of age-sex matched controls. Our shape analysis was able to discriminate between a significant number of SC and control patients based on the Fourier harmonic amplitudes of both the middle and posterior levels of the temporal lobes. These results are consistent with bilateral focal or multifocal distortions of the temporal lobes of SC patients. A similar shape analysis of the prefrontal lobes showed no significant conformational differences between the groups. The basis of this quantitative shape analysis (the Fourier expansion series) and the method by which it can be applied are explained in detail.

Atrophy↗
PubMed1989

Changes in neuronal size and neurotransmitter marker in hereditary canine spinal muscular atrophy.

Hereditary canine spinal muscular atrophy (HCSMA) is a dominantly inherited motor neuron disease that produces muscle weakness and atrophy. Immunocytochemical and computer-imaging morphometric methods were used to compare early changes that occurred in dogs with HCSMA (n = 4) versus controls (n = 2). The size and number of neurons in the ventral horn and the number of motor neurons expressing choline acetyltransferase were quantitated. The density of all ventral horn neurons per micrometer squared in dogs with HCSMA was greater than controls, and there were more small neurons than in controls. Immunocytochemical methods revealed more small cholinergic neurons and fewer large cholinergic neurons in HCSMA than in controls, suggesting growth arrest in HCSMA or a shift in size class from large cholinergic neurons to small ones. The density of cholinergic neurons per micrometer squared was not significantly different between the two groups. Analysis of predicted distributions of cholinergic and noncholinergic neurons revealed that HCSMA cholinergic neurons were smaller and that, in some size classes, fewer neurons expressed choline acetyltransferase. These observations indicate that in HCSMA the motor neuron fails to achieve normal size and/or undergoes atrophy.

Animals↗
PubMed1987

Parallels between sexual strategies and other allocation strategies.

Allocation strategies in which a limited resource is apportioned among alternative activities are applicable to diverse structural, genetical and behavioral topics, including male versus female investments. In a model of sex allocation strategies, the absolute fitnesses of individuals are calculated by summing the production of male and female gametes or offspring, each weighted by its reproductive value. The ESS is obtained by examining the fitness advantage of one phenotype over another. An analogous method is used to obtain a general model of allocation strategies that incorporates some widespread features. Allocation strategies are affected by the sizes and shapes of the reward curves, stochastic factors, and constraints on the allocations permitted. A number of parallels among diverse types of allocation strategies, including the occurrence of fixed, conditional and mixed strategies, and matching rules, are discussed.

Models, Genetic↗
PubMed1985

Parallels between sexual strategies and other allocation strategies.

Allocation strategies in which a limited resource is apportioned among alternative activities are applicable to diverse structural, genetical and behavioral topics, including male versus female investments. In a model of sex allocation strategies, the absolute fitness of individuals are calculated by summing the production of male and female gametes or offspring, each weighted by its reproductive value. The ESS is obtained by examining the fitness advantage of one phenotype over another. An analogous method is used to obtain a general model of allocation strategies that incorporates some widespread features. Allocation strategies are affected by the sizes and shapes of the reward curves, stochastic factors, and constraints on the allocations permitted. A number of parallels among diverse types of allocation strategies, including the occurrence of fixed, conditional and mixed strategies, and matching rules, are discussed.

Animals↗
PubMedDate not supplied

Imaging receptors by autoradiography: computer-assisted approaches.

Receptor autoradiography is one of the first fields where 'desktop' computer-assisted image analysis has been applied. Less than 10 years ago, the first image analysis systems were commercially marketed. Improvements on these early systems have been substantial and there are currently a wide variety of systems available for investigators. These systems dramatically reduce the time required for analysis, improve accuracy and increase the willingness to work in these areas. New techniques allowing autoradiography without emulsion will further expand opportunities for image analysis. While great strides have been made, significant affordable improvements are likely in the near future.

Animals↗