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Biomedical subjects

N Hogan

Publications and source records attributed to N Hogan.

At least 37 records · Page 2Linked to original sources
PubMed1999

Nitric oxide donors can increase heart rate independent of autonomic activation.

Administration of nitric oxide (NO) donors in vivo is accompanied by a baroreflex-mediated increase in heart rate (HR). In vitro, however, NO donors can increase HR directly by stimulating a pathway that involves NO, cGMP, and the hyperpolarization-activated current (I(f)). The aim of this study was to assess the functional significance of this pathway in vivo by testing whether NO donors can increase HR in the anesthetized rabbit independent of the autonomic nervous system. New Zealand White rabbits were vagotomized, cardiac sympathectomized, and treated with propranolol (0.3 mg/kg iv). The NO donor molsidomine (0.2 mg/kg iv) caused a progressive increase (Delta) in HR (DeltaHR, 14 +/- 3 beats/min; P < 0.01). This effect was significantly reduced by the I(f) blocker ZD-7288 (0.2 mg/kg iv; DeltaHR, 2 +/- 3 beats/min; P = not significant). Similar results were seen with sodium nitroprusside. The positive chronotropic effect of sodium nitroprusside (50 microM) was confirmed in the isolated working rabbit heart preparation (DeltaHR, 17 +/- 3 beats/min; P < 0.01). In conclusion, NO donors exert a small, but significant, positive chronotropic effect in vivo that is independent of the autonomic nervous system. These results are also consistent with data in sinoatrial node cells that show that NO donors increase HR by stimulating I(f).

Adrenergic beta-Antagonists↗
PubMed1999

Overview of clinical trials with MIT-MANUS: a robot-aided neuro-rehabilitation facility.

We are applying robotics and information technology to assist, enhance, and quantify neuro-rehabilitation. Our goal is a new class of interactive, user-affectionate clinical devices designed not only for evaluating patients, but also-for delivering meaningful therapy via engaging "video games". Notably, the novel robot MIT-MANUS has been designed and programmed for clinical neurological applications, and has undergone extensive clinical trials for more than four years at Burke Rehabilitation Hospital - White Plains, NY. This paper will review results of the first clinical trial of 20 patients, which showed that: - Stroke patients treated daily with additional robot-aided therapy during acute rehabilitation had improved outcome in motor activity at hospital discharge, when compared to a control group that received only standard acute rehabilitation treatment. - This improved outcome was sustained after three years. - The neuro-recovery process continued far beyond the commonly accepted 3 months post-stroke interval.

Double-Blind Method↗
PubMed1998

Influence of joint angle on the calibration and performance of EMG amplitude estimators.

Multiple-channel electromyogram (EMG) amplitude estimators incorporating temporal whitening filters and/or spatial uncorrelation filters contain a characterization of the EMG waveform (specifically, auto- and cross-correlation information) which may vary with joint angle. This paper reports on an experimental study which investigated the influence of joint angle on these EMG amplitude estimators. It was found that little or no relative improvement in estimator performance resulted from altering either temporal whitening or spatial uncorrelation filters as a function of joint angle. Also, the absolute performance level of these estimators did not vary with joint angle.

Adult↗
PubMed1998

Robot-aided neurorehabilitation.

Our goal is to apply robotics and automation technology to assist, enhance, quantify, and document neurorehabilitation. This paper reviews a clinical trial involving 20 stroke patients with a prototype robot-aided rehabilitation facility developed at the Massachusetts Institute of Technology, Cambridge, (MIT) and tested at Burke Rehabilitation Hospital, White Plains, NY. It also presents our approach to analyze kinematic data collected in the robot-aided assessment procedure. In particular, we present evidence 1) that robot-aided therapy does not have adverse effects, 2) that patients tolerate the procedure, and 3) that peripheral manipulation of the impaired limb may influence brain recovery. These results are based on standard clinical assessment procedures. We also present one approach using kinematic data in a robot-aided assessment procedure.

Aged↗
PubMed1998

Issues in impedance selection and input devices for multijoint powered orthotics.

We investigated the applicability of impedance controllers to robotic orthoses for arm movements. We had tetraplegics turn a crank using their paralyzed arm propelled by a planar robot manipulandum. The robot was under impedance control, and chin motion served as command source. Stiffness varied between 50, 100, or 200 N/m and damping varied between 5 or 15 N/m/s. Results indicated that a low stiffness and high viscosity provided better directional control of the tangential force exerted on the crank.

Arm↗
PubMed1998

Intermittency in preplanned elbow movements persists in the absence of visual feedback.

It has been observed for nearly 100 years that visually guided human movements appear to be composed of submovements, intermittently executed overlapping segments. This paper presents experiments to investigate the pervasiveness of movement intermittency and, in particular, whether it is exclusively due to visual feedback. With and without visual feedback, human subjects were asked to 1) move with constant velocity and 2) draw elliptical figures on a phase-plane display (showing velocity vs. position) that required cyclic movements at different frequencies. In both tasks, we found that removal of visual feedback did not significantly change movement intermittency. Subjects were unable to generate movements at constant speed. In addition, subjects moved less smoothly when drawing slower phase-plane ellipses. Furthermore, elliptical phase-plane figures were not always drawn at the frequency suggested by the center of the display. Instead, subjects moved more slowly than the tall (fast) ellipse displays suggested, and faster than the wide (slow) displays suggested. These results show that 1) movement intermittency is not exclusively due to visual feedback and 2) may in fact be a fundamental feature of movement behavior.

Adult↗
PubMed1998

Robot-aided functional imaging: application to a motor learning study.

The purpose of this study was to examine the neural activity underlying an implicit motor learning task. In particular, our goals were to determine whether initial phases of procedural learning of a motor task involve areas of the brain distinct from those involved in later phases of learning the task, and what changes in neural activity coincide with performance improvement. We describe a novel integration of robotic technology with functional brain imaging and its use in this study of implicit motor learning. A portable robotic device was used to generate forces that disturbed the subjects' arm movements, thereby generating a "virtual mechanical environment" that the subjects learned to manipulate. Positron emission tomography (PET) was used to measure indices of neural activity underlying learning of the motor task. Eight health, right-handed male subjects participated in the study. Results support the hypothesis that different stages of implicit learning (early and late implicit learning) occur in an orderly fashion, and that distinct neural structures may be involved in these different stages. In particular, neuroimaging results indicate that the cortico-striatal loop may play a significant role during early learning, and that the cortico-cerebellar loop may play a significant role during late learning.

Adult↗
PubMed1997

The effect of robot-assisted therapy and rehabilitative training on motor recovery following stroke.

BACKGROUND: We used MIT-Manus, a robot designed to provide interactive, goal-directed motor activity for clinical neurologic applications. OBJECTIVE: To test whether this robotic manipulation of the impaired limb influenced motor recovery in patients with hemiplegia. METHODS: Sequential patients with a history of a single stroke and hemiplegia (N = 20) hospitalized on the same acute care rehabilitation floor were enrolled in a standard rehabilitation program supplemented by either robot-aided therapy or sham robot-aided therapy. These 2 groups were comparable in age, initial physical impairment, and time between onset of the stroke and enrollment in the trial. Patients, clinical team members, and the clinical evaluator were blinded to the treatment group assignments. Standardized assessment tools measured outcomes. RESULTS: Impairment and disability declined in both groups between hospital admission and discharge. The robot-treated group showed a greater degree of improvement in all 3 measures of motor recovery, and the change in motor status measured in the proximal upper limb musculature was significant (P = .002). No adverse events resulted from robot-assisted therapy. CONCLUSIONS: These results suggest that robotic manipulation of the impaired limb may favorably add to recovery following stroke and that robotics may provide new strategies for neurologic rehabilitation.

Adult↗
PubMed1997

Relating agonist-antagonist electromyograms to joint torque during isometric, quasi-isotonic, nonfatiguing contractions.

This paper describes an experimental study which relates simultaneous elbow flexor-extensor electromyogram (EMG) amplitude to joint torque. Investigation was limited to the case of isometric, quasi-isotonic (slowly force-varying), nonfatiguing contractions. For each of the flexor and extensor muscle groups, the model relationship between muscle group torque contribution and EMG amplitude was constrained to be a sum of basis functions which had a linear dependence on a set of fit parameters. With these constraints, the problem of identifying the EMG-to-torque relationship was reduced to a linear least squares problem. Surface EMG's from elbow flexors and extensors, and joint torque were simultaneously recorded for nonfatiguing, quasi-isotonic, isometric contractions spanning 0-50% maximum voluntary contraction. Single-/multiple-channel unwhitened/whitened/adaptively whitened EMG amplitude processors were used to identify an EMG-to-torque relation, and then estimate joint torque based on this relation. Each unwhitened multiple-channel EMG-to-torque estimator had a standard error (SE) approximately 70% of its respective single-channel estimator. The adaptively whitened multiple-channel joint torque estimator had an SE approximately 90% of the unwhitened multiple-channel estimator, providing an estimation error approximately 3% of the combined flexion/extension torque range. The experimental studies demonstrated that higher fidelity EMG amplitude processing led to improved joint torque estimation.

Adult↗
PubMed1995

Stability properties of human reaching movements.

Through an experimental study of the stability properties of the human neuromuscular system while it performs simple point-to-point arm movements, this paper evaluates the concepts of equilibrium and virtual trajectories as a means of executing movement of the arm. Human subjects grasped the instrumented handle of a two-link robot manipulandum and performed specified point-to-point planar arm trajectories. Computer-controlled brakes were used to subtly change the movements by constraining the trajectory along an arc of radius equal to the length of one link of the manipulandum. Target points were arranged to lie along the arc so that the subject could complete the movement even when constrained. These situations were tested: (1) unconstrained throughout the movement, (2) constrained through the entire movement, and (3) initially constrained and then released during movement. Experimental results showed that the constraint evoked significant forces strongly oriented so as to restore the hand to the unconstrained hand path. In addition, when released from the constraint, these forces caused a strong tendency to return the hand to the unconstrained path before the end of the movement was reached. Such strong positional stability properties of the arm reinforce the notion that a moving attractor point dominates the dynamics of the arm during movement. Additionally, bounds on the shape of the virtual trajectory were found which indicate that the equilibrium point remains close to the actual movement produced. These results, showing that a controlled equilibrium point may be used for planning and coordinating multijoint movements, are consistent with an equilibrium point hypothesis.

Adult↗
PubMed1995

Multiple site electromyograph amplitude estimation.

Temporal whitening of individual surface electromyograph (EMG) waveforms and spatial combination of multiple recording sites have separately been demonstrated to improve the performance of EMG amplitude estimation. This investigation combined these two techniques by first whitening, then combining the data from multiple EMG recording sites to form an EMG amplitude estimate. A phenomenological mathematical model of multiple sites of the surface EMG waveform, with analytic solution for an optimal amplitude estimate, is presented. Experimental surface EMG waveforms were then sampled from multiple sites during nonfatiguing, constant-force, isometric contractions of the biceps or triceps muscles, over the range of 10-75% maximum voluntary contraction. A signal-to-noise ratio (SNR) was computed from each amplitude estimate (deviations about the mean value of the estimate were considered as noise). Results showed that SNR performance: 1) increased with the number of EMG sites, 2) was a function of the sampling frequency, 3) was predominantly invariant to various methods of determining spatial uncorrelation filters, 4) was not sensitive to the intersite correlations of the electrode configuration investigated, and 5) was best at lower levels of contraction. A moving average root mean square estimator (245-ms window) provided an average +/- standard deviation (A +/- SD) SNR of 10.7 +/- 3.3 for single site unwhitened recordings. Temporal whitening and four combined sites improved the A +/- SD SNR to 24.6 +/- 10.4. On one subject, eight whitened combined sites were achieved, providing an A +/- SD SNR or 35.0 +/- 13.4.

Adult↗
PubMed1995

Performance of above elbow body-powered prostheses in visually guided unconstrained motion tasks.

The "classical" body-powered above elbow arm prosthesis continues to be used by a large majority of arm prosthesis users, even though many more modern devices are available. This paper presents a set of experiments designed to compare performance of unimpaired arms and body-powered prostheses of six unilateral amputees. The experiments were designed to measure quantitatively how well the body-powered prosthesis can be used to perform free-motion tasks, as well as to study the qualitative features of movement common to both the prosthesis and unimpaired arm. It was found that regular peaks in velocity were common to both the unimpaired arm and prosthesis movements, suggesting that movements were composed of a sequence of successive actions. In addition, it was found that the body-powered prosthesis generally required more movements than the unimpaired arm to meet an accuracy constraint and could not keep up with the unimpaired arm when a speed constraint was imposed, even though the body-powered prosthesis was able to match the unimpaired arm in a simple nondynamic task.

Adult↗
PubMed1994

Single site electromyograph amplitude estimation.

Previous investigators have experimentally demonstrated and/or analytically predicted that temporal whitening of the surface electromyograph (EMG) waveform prior to demodulation improves the EMG amplitude estimate [1]-[6]. However, no systematic study of the influence of various whitening filters upon amplitude estimate performance has been reported. This paper describes a phenomenological mathematical model of a single site of the surface EMG waveform and reports on experimental studies which examined the performance of several temporal whitening filters. Surface EMG waveforms were sampled during nonfatiguing, constant-force, isometric contractions of the biceps or triceps muscles, over the range of 10-75% maximum voluntary contraction. A signal-to-noise ratio (SNR) was computed from each amplitude estimate (deviations about the mean value of the estimate were considered as noise). A moving average root mean square estimator (245ms window) provided an average +/- standard deviation (A +/- SD) SNR of 10.7 +/- 3.3 for the individual recordings. Temporal whitening with one fourth-order whitening filter designed per site improved the A +/- SD SNR to 17.6 +/- 6.0.

Adult↗
PubMed1993

Quantitative assessment of four men using above-elbow prosthetic control.

We studied the relationship between kinematically unconstrained activities of daily living (ADL) tasks and a kinematically constrained task in above-elbow (AE) amputee subjects using myoelectrically controlled prostheses. Four men, 24 to 49 years old, with unilateral AE amputation wore a prosthesis interfaced to a programmable controller to emulate two different elbow control schemes, conventional velocity and a new "natural" controller. Subjects were timed during three ADL tasks--cutting meat, donning socks, and rolling dough--with both controllers. The prosthesis emulator was then connected to a crank device with a handle, and the subjects turned the crank from bottom to top positions in a vertical plane using each controller. Synergistic shoulder-elbow joint coordination required for crank turning was quantified as the maximum slope of the change in elbow torque versus the change in crank-angle. Performance between the two controllers differed significantly for the crank test but not for ADL tasks. One subject did not complete all crank turning tests. Positive canonical correlation of 0.77 was found between time and crank domain measures. We conclude that biomechanical assessments should be integrated with time-based clinical tests to comprehensively evaluate performance of AE amputee subjects with a myoelectric device.

Activities of Daily Living↗
PubMed1991

Apparent unilateral visual neglect in MPTP-hemiparkinsonian monkeys is due to delayed initiation of motion.

Monkeys made hemiparkinsonian by infusion of a solution of MPTP into one carotid artery appeared to ignore food presented from the contralateral side. Initial observations suggested neglect of visual stimuli presented as fruit treats by automated delivery system in the half-field contralateral to MPTP treatment. Further studies in which fruit treats were left in the 'neglected' visual field indicated that this apparent neglect, unlike neglect attending cortical lesions, was rather a marked delay in initiating movements (unilateral hypokinesia). These observations may explain apparent subcortical neglect and are consistent with the known role of nigrostriatal dopaminergic neurones in movement regulation. This is a useful animal model in which difficulties in initiation of movement (hypokinesia). a cardinal symptom of Parkinson's disease, can be studied separately from other deficits in motor performance.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1991

Development of substantive theory in nursing.

The lack of a comprehensive, substantive theory base has resulted in the profession of nursing borrowing theoretical assumptions, concepts, and research instruments from other disciplines to examine nursing phenomena. Nurse researchers have focused their attention primarily on applied research leaving the development of substantive theory to others. If the nursing profession is to develop a scientifically-based practice, nurses will need to engage in debates about the need for and methods of generating substantive theory and shift from the use of borrowed knowledge and methods to original nursing research. In order to broaden the theoretical conceptualisations and directions of nursing research for the development of a substantive theory base, multi-method perspectives are necessary. Triangulation of qualitative and quantitative methods is one way to design research that will allow for development of substantive theory through the use of multiple methodology. This paper describes one method of preparing doctoral nurse students for triangulation of methods and to develop substantive theory for nursing practice.

Humans↗
PubMed1990

Functional assessment of control systems for cybernetic elbow prostheses--Part II: Application of the technique.

This paper (Part II of II) presents application of the technique described in Part I to functional assessment of two myoelectric elbow-prosthesis controllers: the controller implemented in the Boston Elbow, a state-of-the-art elbow prosthesis, and a proposed control scheme that, to a crude degree, mimics control of the intact elbow. Assessment of the controllers was achieved by evaluating an amputee subject's functional capability as he performed a constrained motion task with a prosthesis that implemented each control scheme. Evaluation of the amputee's capability was accomplished off line using sampled values of his myoelectric activity, his limb kinematics, and the interface forces at the constraint. Superior performance was observed with the proposed scheme. Namely, the subject exhibited better synergy among his elbow and shoulder muscles. Furthermore, when using the proposed controller, he exhibited some natural patterns of muscle coordination.

Amputation, Surgical↗