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Biomedical subjects

Todd A Kuiken

Publications and source records attributed to Todd A Kuiken.

13 recordsLinked to original sources
PubMed2007

Neural machine interfaces for controlling multifunctional powered upper-limb prostheses.

This article investigates various neural machine interfaces for voluntary control of externally powered upper-limb prostheses. Epidemiology of upper limb amputation, as well as prescription and follow-up studies of externally powered upper-limb prostheses are discussed. The use of electromyographic interfaces and peripheral nerve interfaces for prosthetic control, as well as brain machine interfaces suitable for prosthetic control, are examined in detail along with available clinical results. In addition, studies on interfaces using muscle acoustic and mechanical properties and the problem of interfacing sensory information to the nervous system are discussed.

Amputation, Surgical↗
PubMed2006

Eliminating cardiac contamination from myoelectric control signals developed by targeted muscle reinnervation.

The electrocardiogram (ECG) artifact is a major noise contaminating the myoelectric control signals when using shoulder disarticulation prosthesis. This is an even more significant problem with targeted muscle reinnervation to develop additional myoelectric sites for improved prosthesis control in a bilateral amputee at shoulder disarticulation level. This study aims at removal of ECG artifacts from the myoelectric prosthesis control signals produced from targeted muscle reinnervation. Three ECG artifact removal methods based on template subtracting, wavelet thresholding and adaptive filtering were investigated, respectively. Surface EMG signals were recorded from the reinnervated pectoralis muscles of the amputee. As a key parameter for clinical myoelectric prosthesis control, the amplitude measurement of the signal was used as a performance indicator to evaluate the proposed methods. The feasibility of the different methods for clinical application was also investigated with consideration of the clinical speed requirements and memory limitations of commercial prosthesis controllers.

Adult↗
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

Simulation of intramuscular EMG signals detected using implantable myoelectric sensors (IMES).

The purpose of this study was to test the feasibility of recording independent electromyographic (EMG) signals from the forearm using implantable myoelectric sensors (IMES), for myoelectric prosthetic control. Action potentials were simulated using two different volume conductor models: a finite-element (FE) model that was used to explore the influence of the electrical properties of the surrounding inhomogeneous tissues and an analytical infinite volume conductor model that was used to estimate the approximate detection volume of the implanted sensors. Action potential amplitude increased progressively as conducting electrodes, the ceramic electrode casing and high resistivity encapsulation tissue were added to the model. For the muscle fiber locations examined, the mean increase in EMG root mean square amplitude when the full range of material properties was included in the model was 18.2% (+/-8.1%). Changing the orientation of the electrode with respect to the fiber direction altered the shape of the electrode detection volume and reduced the electrode selectivity. The estimated detection radius of the IMES electrode, assuming a cylindrical muscle cross section, was 4.8, 6.2, and 7.5 mm for electrode orientations of 0 degree, 22.5 degrees, and 45 degrees with respect to the muscle fiber direction.

Action Potentials↗
PubMed2005

Phantom limb pain treatment with mirtazapine: a case series.

OBJECTIVES: To pilot the efficacy of mirtazapine for relief of phantom limb pain (PLP); to correlate the putative drug mechanism with theoretical PLP mechanisms; and to develop a rationale for further study of mirtazapine in this population. DESIGN: Open-label case series. SUBJECTS/PATIENTS: Four individuals with PLP for at least 3 months after amputation. METHODS: All subjects received oral mirtazapine between 7.5 and 30 mg/day. An 11-point numeric rating scale (0 to 10) measured pain intensity and relief during monitored outpatient follow-up visits. RESULTS/DISCUSSION: Mirtazapine use improved the PLP experienced by these subjects by at least 50%. Subjects with PLP-related sleeping difficulties reported the greatest pain relief concomitant with improved sleep quality. One subject was able to eliminate the use of a selective serotonin reuptake inhibitor antidepressant while using mirtazapine for PLP and depression without change in mood or affect. Mirtazapine enhances noradrenergic and serotonergic activity and may modulate PLP by central mechanisms. Current concepts of the proposed pathophysiology of PLP and the hypothetical impact of mirtazapine are discussed. CONCLUSION: Mirtazapine may be an effective treatment for PLP that can also potentially enhance sleep and mood. This information provides preliminary reinforcement for more formal, controlled studies concerning mirtazapine use in PLP.

Journal Article↗
PubMed2004

Computerized biofeedback knee goniometer: acceptance and effect on exercise behavior in post-total knee arthroplasty rehabilitation.

OBJECTIVE: To assess device accuracy, patient acceptance, and effect of a computerized biofeedback knee goniometer (CBG), on patients' compliance with active range of motion (AROM) exercises after total knee arthroplasty (TKA). DESIGN: Two-stage study: measurement validation on asymptomatic controls and an unblinded, multiple crossover trial. SETTING: Inpatient rehabilitation. PARTICIPANTS: Asymptomatic controls (n=14) and post-TKA inpatients (n=11). INTERVENTIONS: For measurement validation, CBG-angle measurements were compared with manual, clinician-obtained angles. To assess motivational effect, the CBG was worn after TKA; on alternating days, it either monitored AROM silently (no feedback) or provided audiovisual feedback about reaching preset range of motion (ROM) goals and prompted the patients to exercise when idle. MAIN OUTCOME MEASURES: To assess accuracy, the device's readings were compared with manual measurements. Patient satisfaction was determined by a self-report questionnaire; exercise compliance was assessed by calculating activity rate and stratified interactivity intervals. RESULTS: CBG readings reproduced clinician measurements reliably between 0 degrees and 100 degrees (eta(2)=98.5%). Auditory feedback was more helpful than visual feedback for motivating exercise. During feedback-on days, the mean total activity rate +/- standard deviation was 15.1+/-10.9 activity counts per hour, and the interactivity interval was 6.7+/-5.7 minutes. The activity rate was higher on feedback-off days-22.5+/-11.1 counts/hour (P=.11)-and the mean interactivity interval was 3.6+/-2.7 minutes (P=.07). CONCLUSIONS: The CBG provided reliable, unbiased estimates of clinician measurements of joint angle within the range of 0 degrees to 100 degrees. The CBG was accepted well by most patients. Surprisingly, slightly more ROM activity was noted during feedback-off days than feedback-on days.

Analysis of Variance↗
PubMed2004

Volume conduction in an anatomically based surface EMG model.

A finite-element model to simulate surface electromyography (EMG) in a realistic human upper arm is presented. The model is used to explore the effect of limb geometry on surface-detected muscle fiber action potentials. The model was based on magnetic resonance images of the subject's upper arm and includes both resistive and capacitive material properties. To validate the model geometry, experimental and simulated potentials were compared at different electrode sites during the application of a subthreshold sinusoidal current source to the skin surface. Of the material properties examined, the closest approximation to the experimental data yielded a mean root-mean-square (rms) error of the normalized surface potential of 18% or 27%, depending on the site of the applied source. Surface-detected action potentials simulated using the realistic volume conductor model and an idealized cylindrical model based on the same limb geometry were then compared. Variation in the simulated limb geometry had a considerable effect on action potential shape. However, the rate of decay of the action potential amplitude with increasing distance from the fiber was similar in both models. Inclusion of capacitive material properties resulted in temporal low-pass filtering of the surface action potentials. This effect was most pronounced in the end-effect components of action potentials detected at locations far from the active fiber. It is concluded that accurate modeling of the limb geometry, asymmetry, tissue capacitance and fiber curvature is important when the specific action potential shapes are of interest. However, if the objective is to examine more qualitative features of the surface EMG signal, then an idealized volume conductor model with appropriate tissue thicknesses provides a close approximation.

Action Potentials↗
PubMed2003

Independence of myoelectric control signals examined using a surface EMG model.

The detection volume of the surface electromyographic (EMG) signal was explored using a finite-element model, to examine the feasibility of obtaining independent myoelectric control signals from regions of reinnervated muscle. The selectivity of the surface EMG signal was observed to decrease with increasing subcutaneous fat thickness. The results confirm that reducing the interelectrode distance or using double-differential electrodes can increase surface EMG selectivity in an inhomogeneous volume conductor. More focal control signals can be obtained, at the expense of increased variability, by using the mean square value, rather than the root mean square or average rectified value.

Action Potentials↗
PubMed2003

Finite-element time-domain algorithms for modeling linear Debye and Lorentz dielectric dispersions at low frequencies.

We present what we believe to be the first algorithms that use a simple scalar-potential formulation to model linear Debye and Lorentz dielectric dispersions at low frequencies in the context of finite-element time-domain (FETD) numerical solutions of electric potential. The new algorithms, which permit treatment of multiple-pole dielectric relaxations, are based on the auxiliary differential equation method and are unconditionally stable. We validate the algorithms by comparison with the results of a previously reported method based on the Fourier transform. The new algorithms should be useful in calculating the transient response of biological materials subject to impulsive excitation. Potential applications include FETD modeling of electromyography, functional electrical stimulation, defibrillation, and effects of lightning and impulsive electric shock.

Algorithms↗
PubMed2002

A simulation study to examine the use of cross-correlation as an estimate of surface EMG cross talk.

Cross-correlation between surface electromyogram (EMG) signals is commonly used as a means of quantifying EMG cross talk during voluntary activation. To examine the reliability of this method, the relationship between cross talk and the cross-correlation between surface EMG signals was examined by using model simulation. The simulation results illustrate an increase in cross talk with increasing subcutaneous fat thickness. The results also indicate that the cross-correlation function decays more rapidly with increasing distance from the active fibers than cross talk, which was defined as the normalized EMG amplitude during activation of a single muscle. The influence of common drive and short-term motor unit synchronization on the cross-correlation between surface EMG signals was also examined. While common drive did not alter the maximum value of the cross-correlation function, the correlation increased with increasing motor unit synchronization. It is concluded that cross-correlation analysis is not a suitable means of quantifying cross talk or of distinguishing between cross talk and coactivation during voluntary contraction. Furthermore, it is possible that a high correlation between surface EMG signals may reflect an association between motor unit firing times, for example due to motor unit synchronization.

Adipose Tissue↗
PubMed2002

A multiple-layer finite-element model of the surface EMG signal.

The effect of skin, muscle, fat, and bone tissue on simulated surface electromyographic (EMG) signals was examined using a finite-element model. The amplitude and frequency content of the surface potential were observed to increase when the outer layer of a homogeneous muscle model was replaced with highly resistive skin or fat tissue. The rate at which the surface potential decreased as the fiber was moved deeper within the muscle also increased. Similarly, the rate at which the surface potential decayed around the surface of the model, for a constant fiber depth, increased. When layers of subcutaneous fat of increasing thickness were then added to the model, EMG amplitude, frequency content, and the rate of decay of the surface EMG signal around the limb decreased, due to the increased distance between the electrodes and the active fiber. The influence of bone on the surface potential was observed to vary considerably, depending on its location. When located close to the surface of the volume conductor, the surface EMG signal between the bone and the source and directly over the bone increased, accompanied by a slight decrease on the side of the bone distal to the active fiber. The results emphasize the importance of distinguishing between the effects of material properties and the distance between source and electrode when considering the influence of subcutaneous tissue, and suggest possible distortions in the surface EMG signal in regions where a bone is located close to the skin surface.

Action Potentials↗
PubMed2002

Frequency- and time-domain FEM models of EMG: capacitive effects and aspects of dispersion.

Electromyography (EMG) simulations have traditionally been based on purely resistive models, in which capacitive effects are assumed to be negligible. Recent experimental studies suggest these assumptions may not be valid for muscle tissue. Furthermore, both muscle conductivity and permittivity are frequency-dependent (dispersive). In this paper, frequency-domain and time-domain finite-element models are used to examine the impact of capacitive effects and dispersion on the surface potential of a volume conductor. The results indicate that the effect of muscle capacitance and dispersion varies dramatically. Choosing low conductivity and high permittivity values in the range of experimentally reported data for muscle can cause displacement currents that are larger than conduction currents with corresponding reduction in surface potential of up to 50% at 100 Hz. Conductivity and permittivity values lying toward the middle of the reported range yield results which do not differ notably from purely resistive models. Also, excluding dispersion can also cause large error-up to 75% in the high frequency range of the EMG. It is clear that there is a need to establish accurate values of both conductivity and permittivity for human muscle tissue in vivo in order to quantify the influence of capacitance and dispersion on the EMG signal.

Computer Simulation↗