Biomedical subjects

Laura A Miller

Publications and source records attributed to Laura A Miller.

6 recordsLinked to original sources

PubMed2006

Improved myoelectric prosthesis control accomplished using multiple nerve transfers.

BACKGROUND: The control of shoulder-level disarticulation prostheses is significantly more difficult than that of prostheses for more distal amputations. Amputees have significant difficulties coordinating the separate functions of prosthetic shoulder, elbow, wrist, and hand/hook components. The user must lock one joint at a particular position in space before subsequently moving a different joint. METHODS: A patient with bilateral humeral disarticulations after an electrical injury underwent a novel nerve transfer procedure designed to improve the control of a myoelectric prosthesis. The median, radial, ulnar, and musculocutaneous nerves were transferred to the nerves of segments of the pectoralis major and minor muscles. Those muscles then act as bioamplifiers of peripheral nerve signals when the normal upper extremity nerves are activated by the patient's brain. Therefore, when the patient thinks "flex elbow," the transferred musculocutaneous nerve fires, and a segment of the pectoralis major contracts. An electromyographic signal is then detected transcutaneously and causes the prosthetic elbow to flex. RESULTS: Three of the four nerve transfers were successful. One of the nerve transfers unexpectedly yielded two separate controllable muscle segments. Standardized testing using a "box-and-blocks" apparatus was performed with the patient's previous myoelectric device and the current device after nerve transfers. The patient's performance improved by 246 percent. CONCLUSIONS: Nerve transfers to small muscle segments are capable of creating a novel neural interface for improved control of a myoelectric prosthesis. This is done using standard techniques of nerve and flap surgery, and without any implantable devices.

Arm↗

PubMed2006

Distinct contributions of vaccine-induced immunoglobulin G1 (IgG1) and IgG2a antibodies to protective immunity against influenza.

Vaccination represents the most effective form of protection against influenza infection. While neutralizing antibodies are typically measured as a correlate of vaccine-induced protective immunity against influenza, nonneutralizing antibodies may contribute to protection or amelioration of disease. The goal of this study was to dissect the individual contributions of the immunoglobulin G1 (IgG1) and IgG2a antibody isotypes to vaccine-induced immunity against influenza virus. To accomplish this, we utilized an influenza vaccine regimen that selectively enhanced IgG1 or IgG2a antibodies by using either DNA or viral replicon particle (VRP) vectors expressing influenza virus hemagglutinin (HA) (HA-DNA or HA-VRP, respectively). After HA-DNA vaccination, neutralizing antibodies were detected by both in vitro (microneutralization) and in vivo (lung viral titer) methods and were associated with increased IgG1 expression by enzyme-linked immunosorbent assay (ELISA). Vaccination with HA-VRP did not strongly stimulate either neutralizing or IgG1 antibodies but did induce IgG2a antibodies. Expression of IgG2a antibodies in this context correlated with clearance of virus and increased protection against lethal influenza challenge. Increased induction of both antibody isotypes as measured by ELISA was a better correlate for vaccine efficacy than neutralization alone. This study details separate but important roles for both IgG1 and IgG2a expression in vaccination against influenza and argues for the development of vaccine regimens that stimulate and measure expression of both antibody isotypes.

Animals↗

PubMed2005

Structural dynamics and resonance in plants with nonlinear stiffness.

Although most biomaterials are characterized by strong stiffness nonlinearities, the majority of studies of plant biomechanics and structural dynamics focus on the linear elastic range of their behavior. In this paper, the effects of hardening (elastic modulus increases with strain) and softening (elastic modulus decreases with strain) nonlinearities on the structural dynamics of plant stems are investigated. A number of recent studies suggest that trees, crops, and other plants often uproot or snap when they are forced by gusting winds or waves at their natural frequency. This can be attributed to the fact that the deflections of the plant, and hence mechanical stresses along the stem and root system, are greatest during resonance. To better understand the effect of nonlinear stiffness on the resonant behavior of plants, plant stems have been modeled here as forced Duffing oscillators with softening or hardening nonlinearities. The results of this study suggest that the resonant behavior of plants with nonlinear stiffness is substantially different from that predicted by linear models of plant structural dynamics. Parameter values were considered over a range relevant to most plants. The maximum amplitudes of deflection of the plant stem were calculated numerically for forcing frequencies ranging from zero to twice the natural frequency. For hardening nonlinearities, the resonant behavior was 'pushed' to higher frequencies, and the maximum deflection amplitudes were lower than for the linear case. For softening nonlinearities, the resonant behavior was pushed to lower frequencies, and the maximum deflection amplitudes were higher than for the linear case. These nonlinearities could be beneficial or detrimental to the stability of the plant, depending on the environment. Damping had the effect of drastically decreasing deflection amplitudes and reducing the effect of the nonlinearities.

Elasticity↗

PubMed2005

Expression of groups I and II metabotropic glutamate receptors in the rat brain during aging.

Age-dependent changes in the expression of group I and II metabotropic glutamate (mGlu) receptors were studied by in situ hybridization, Western blot analysis and immunohistochemistry. Male Fisher 344 rats of three ages (3, 12 and 25 months) were tested. Age-related increases in mGlu1 receptor mRNA levels were found in several areas (thalamic nuclei, hippocampal CA3) with parallel increases in mGlu1a receptor protein expression. However, a slight decrease in mGlu1a receptor mRNA expression in individual Purkinje neurons and a decline in cerebellar mGlu1a receptor protein levels were detected in aged animals. In contrast, mGlu1b receptor mRNA levels increased in the cerebellar granule cell layer. Although mGlu5 receptor mRNA expression decreased in many regions, its protein expression remained unchanged during aging. Compared to the small changes in mGlu2 receptor mRNA levels, mGlu3 receptor mRNA levels showed substantial age differences. An increased mGlu2/3 receptor protein expression was found in the frontal cortex, thalamus, hippocampus and corpus callosum in aged animals. These results demonstrate region- and subtype-specific, including splice variant specific changes in the expression of mGlu receptors in the brain with increasing age.

Aging↗

PubMed2005

A computational fluid dynamics of 'clap and fling' in the smallest insects.

In this paper, we have used the immersed boundary method to solve the two-dimensional Navier-Stokes equations for two immersed wings performing an idealized 'clap and fling' stroke and a 'fling' half-stroke. We calculated lift coefficients as functions of time per wing for a range of Reynolds numbers (Re) between 8 and 128. We also calculated the instantaneous streamlines around each wing throughout the stroke cycle and related the changes in lift to the relative strength and position of the leading and trailing edge vortices. Our results show that lift generation per wing during the 'clap and fling' of two wings when compared to the average lift produced by one wing with the same motion falls into two distinct patterns. For Re=64 and higher, lift is initially enhanced during the rotation of two wings when lift coefficients are compared to the case of one wing. Lift coefficients after fling and during the translational part of the stroke oscillate as the leading and trailing edge vortices are alternately shed. In addition, the lift coefficients are not substantially greater in the two-winged case than in the one-winged case. This differs from three-dimensional insect flight where the leading edge vortices remain attached to the wing throughout each half-stroke. For Re=32 and lower, lift coefficients per wing are also enhanced during wing rotation when compared to the case of one wing rotating with the same motion. Remarkably, lift coefficients following two-winged fling during the translational phase are also enhanced when compared to the one-winged case. Indeed, they begin about 70% higher than the one-winged case during pure translation. When averaged over the entire translational part of the stroke, lift coefficients per wing are 35% higher for the two-winged case during a 4.5 chord translation following fling. In addition, lift enhancement increases with decreasing Re. This result suggests that the Weis-Fogh mechanism of lift generation has greater benefit to insects flying at lower Re. Drag coefficients produced during fling are also substantially higher for the two-winged case than the one-winged case, particularly at lower Re.

Animals↗

PubMed2004

When vortices stick: an aerodynamic transition in tiny insect flight.

We have used computational fluid dynamics to study changes in lift generation and vortex dynamics for Reynolds numbers (Re) between 8 and 128. The immersed boundary method was used to model a two-dimensional wing through one stroke cycle. We calculated lift and drag coefficients as a function of time and related changes in lift to the shedding or attachment of the leading and trailing edge vortices. We find that the fluid dynamics around the wing fall into two distinct patterns. For Re> or =64, leading and trailing edge vortices are alternately shed behind the wing, forming the von Karman vortex street. For Re< or =32, the leading and trailing edge vortices remain attached to the wing during each 'half stroke'. In three-dimensional studies, large lift forces are produced by 'vortical asymmetry' when the leading edge vortex remains attached to the wing for the duration of each half stroke and the trailing edge vortex is shed. Our two-dimensional study suggests that this asymmetry is lost for Re below some critical value (between 32 and 64), resulting in lower lift forces. We suggest that this transition in fluid dynamics is significant for lift generation in tiny insects.

Animals↗