Biomedical Engineering and Bioengineering Commons^™

Prolonged Quadriceps Activity Following Imposed Hip Extension: A Neurophysiological Mechanism For Stiff-Knee Gait?, Michael D. Lewek, T. George Hornby, Yasin Y. Dhaher, Brian D. Schmit

Biomedical Engineering Faculty Research and Publications

The biomechanical characteristics of stiff knee gait following neurological injury include decreased knee flexion velocity at toe-off, which may be due to exaggerated quadriceps activity. The neuromuscular mechanism underlying this abnormal activity is unclear, although hyperexcitable heteronymous reflexes may be a source of impaired coordination. The present study examines the contribution of reflex activity from hip flexors on knee extensors following stroke and its association with reduced swing-phase knee flexion during walking. Twelve individuals poststroke and six control subjects were positioned in supine on a Biodex dynamometer with the ankle and knee held in a static position. Isolated hip extension …

Separate Adaptive Mechanisms For Controlling Trajectory And Final Position In Reaching, Robert A. Scheidt, Claude Ghez

Biomedical Engineering Faculty Research and Publications

We examined control of the hand's trajectory (direction and shape) and final equilibrium position in horizontal planar arm movements by quantifying transfer of learned visuomotor rotations between two tasks that required aiming the hand to the same spatial targets. In a trajectory-reversal task (“slicing”), the hand reversed direction within the target and returned to the origin. In a positioning task (“reaching”), subjects moved the hand to the target and held it there; cursor feedback was provided only after movement ended to isolate learning of final position from trajectory direction. We asked whether learning acquired in one task would transfer to …

Different Learned Coordinate Frames For Planning Trajectories And Final Positions In Reaching, Claude Ghez, Robert A. Scheidt, Hank Heijink

Biomedical Engineering Faculty Research and Publications

We previously reported that the kinematics of reaching movements reflect the superimposition of two separate control mechanisms specifying the hand's spatial trajectory and its final equilibrium position. We now asked whether the brain maintains separate representations of the spatial goals for planning hand trajectory and final position. One group of subjects learned a 30° visuomotor rotation about the hand's starting point while performing a movement reversal task (“slicing”) in which they reversed direction at one target and terminated movement at another. This task required accuracy in acquiring a target mid-movement. A second group adapted while moving to—and stabilizing at—a single …

Mechanical Behavior And Failure Analysis Of Prosthetic Retaining Screws After Long‐Term Use In Vivo. Part 1: Characterization Of Adhesive Wear And Structure Of Retaining Screws, Youssef S. Al Jabbari, Raymond Fournelle, Gerald J. Ziebert, Jeffrey M. Toth, Anthony Iacopino

Biomedical Engineering Faculty Research and Publications

Purpose: The general aim of this study and those presented in Parts 2–4 of this series was to characterize the structure, properties, wear, and fracture of prosthetic retaining screws in fixed detachable hybrid prostheses after long‐term use in vivo. This part of the overall investigation addresses whether there are differences in thread wear between the screws closest to the fulcrum and those that are farthest from the fulcrum in fixed detachable hybrid prostheses.

Materials and Methods: The total number of prosthetic retaining screws used in this study was 100 (10 new and 90 used). New screws (controls) from Nobel Biocare …

Mechanical Behavior And Failure Analysis Of Prosthetic Retaining Screws After Long‐Term Use In Vivo. Part 2: Metallurgical And Microhardness Analysis, Youssef S. Al Jabbari, Raymond Fournelle, Gerald J. Ziebert, Jeffrey M. Toth, Anthony Iacopino

Biomedical Engineering Faculty Research and Publications

Abstract

Purpose: This study involved testing and analyzing multiple retrieved prosthetic retaining screws after long‐term use in vivo to: (1) detect manufacturing defects that could affect in‐service behavior; (2) characterize the microstructure and alloy composition; and (3) further characterize the wear mechanism of the screw threads.

Materials and Methods: Two new (control) screws from Nobel Biocare (NB) and 18 used (in service 18–120 months) retaining screws [12 from NB and 6 from Sterngold (SG)] were: (1) metallographically examined by light microscopy and scanning electron microscopy (SEM) to determine the microstructure; (2) analyzed by energy dispersive X‐ray (EDX) microanalysis to determine …

Airway Strain During Mechanical Ventilation In An Intact Animal Model, Scott W. Sinclair, Robert C. Molthen, Steven Thomas Haworth, Christopher A. Dawson, Christopher M. Waters

Biomedical Engineering Faculty Research and Publications

Rationale: Mechanical ventilation with large tidal volumes causes ventilator-induced lung injury in animal models. Little direct evidence exists regarding the deformation of airways in vivo during mechanical ventilation, or in the presence of positive end-expiratory pressure (PEEP).

Objectives: To measure airway strain and to estimate airway wall tension during mechanical ventilation in an intact animal model.

Methods: Sprague-Dawley rats were anesthetized and mechanically ventilated with tidal volumes of 6, 12, and 25 cm³/kg with and without 10–cm H₂O PEEP. Real-time tantalum bronchograms were obtained for each condition, using microfocal X-ray imaging. Images were …

Chronic Hypoxia-Induced Pulmonary Hypertension Does/Does Not Lead To Loss Of Pulmonary Vasculature, Marlene Rabinovitch, Naomi Chesler, Robert C. Molthen

Biomedical Engineering Faculty Research and Publications

No abstract provided.

Role Of Mitochondrial Electron Transport Complex I In Coenzyme Q1 Reduction By Intact Pulmonary Arterial Endothelial Cells And The Effect Of Hyperoxia, Marilyn P. Merker, Said H. Audi, Brian J. Lindemer, Gary S. Krenz, Robert D. Bongard

Biomedical Engineering Faculty Research and Publications

The objective was to determine the impact of intact normoxic and hyperoxia-exposed (95% O(2) for 48 h) bovine pulmonary arterial endothelial cells in culture on the redox status of the coenzyme Q(10) homolog coenzyme Q(1) (CoQ(1)). When CoQ(1) (50 microM) was incubated with the cells for 30 min, its concentration in the medium decreased over time, reaching a lower level for normoxic than hyperoxia-exposed cells. The decreases in CoQ(1) concentration were associated with generation of CoQ(1) hydroquinone (CoQ(1)H(2)), wherein 3.4 times more CoQ(1)H(2) was produced in the normoxic than hyperoxia-exposed cell medium (8.2 +/- 0.3 and 2.4 +/- 0.4 microM, …

Pulmonary Microvascular Injury Resulting From A Single Exposure To Low-Dose Thoracic Radiation, Q. Wu, G. Schmirler, John E. Moulder, Elizabeth R. Jacobs, Meetha Medhora, Robert C. Molthen

Biomedical Engineering Faculty Research and Publications

No abstract provided.

Soleus H-Reflex Excitability Changes In Response To Sinusoidal Hip Stretches In The Injured Human Spinal Cord, Maria Knikou, Brian D. Schmit, Debjani Chaudhuri, Elizabeth Kay, William Zev Rymer

Biomedical Engineering Faculty Research and Publications

Imposed static hip stretches substantially modulate the soleus H-reflex in people with an intact or injured spinal cord while stretch of the hip flexors affect the walking pattern in lower vertebrates and humans. The aim of this study was to assess the effects of dynamic hip stretches on the soleus H-reflex in supine spinal cord injured (SCI) subjects. Sinusoidal movements were imposed on the right hip joint at 0.2 Hz by a Biodex system. H-reflexes from the soleus muscle were recorded as the leg moved in flexion or extension. Stimuli were sent only once in every hip movement cycle that …

D-4f Does Not Mitigate Key Parameters In Rat Model Of Severe Pulmonary Hypertension, Robert C. Molthen, Shelley Baumgardt, K. A. Pritchard Jr

Biomedical Engineering Faculty Research and Publications

No abstract provided.

Design And Validation Of A Mr-Compatible Pneumatic Manipulandum, Aaron J. Suminski, Janice L. Zimbelman, Robert A. Scheidt

Biomedical Engineering Faculty Research and Publications

The combination of functional MR imaging and novel robotic tools may provide unique opportunities to probe the neural systems underlying motor control and learning. Here, we describe the design and validation of a MR-compatible, 1 degree-of-freedom pneumatic manipulandum along with experiments demonstrating its safety and efficacy. We first validated the robot's ability to apply computer-controlled loads about the wrist, demonstrating that it possesses sufficient bandwidth to simulate torsional spring-like loads during point-to-point flexion movements. Next, we verified the MR-compatibility of the device by imaging a head phantom during robot operation. We observed no systematic differences in two measures of MRI …

Parallel Facilitatory Reflex Pathways From The Foot And Hip To Flexors And Extensors In The Injured Human Spinal Cord, Maria Knikou, Elizabeth Kay, Brian D. Schmit

Biomedical Engineering Faculty Research and Publications

Spinal integration of sensory signals associated with hip position, muscle loading, and cutaneous sensation of the foot contributes to movement regulation. The exact interactive effects of these sensory signals under controlled dynamic conditions are unknown. The purpose of the present study was to establish the effects of combined plantar cutaneous afferent excitation and hip movement on the Hoffmann (H) and flexion reflexes in people with a spinal cord injury (SCI). The flexion and H-reflexes were elicited through stimulation of the right sural (at non-nociceptive levels) and posterior tibial nerves respectively. Reflex responses were recorded from the ipsilateral tibialis anterior (TA) …

Reach Adaptation And Final Position Control Amid Environmental Uncertainty After Stroke, Robert A. Scheidt, Tina M. Stoeckmann

Biomedical Engineering Faculty Research and Publications

We characterized how hemiparetic stroke survivors and neurologically intact individuals adapt reaching movements to compensate for unpredictable environmental perturbations. We tested the hypotheses that like unimpaired subjects, hemiparetic stroke survivors adapt using sensory information obtained during only the most recent movements and that the reliability of target acquisition decreases as the degree of sensorimotor impairment increases. Subjects held the handle of a two-joint robotic arm that applied forces to the hand while reaching between targets in a horizontal plane. The robot simulated a dynamic environment that varied randomly in strength from one trial to the next. The trial sequence of …

Neural And Electromyographic Correlates Of Wrist Posture Control, Aaron J. Suminski, Stephen M. Rao, Kristine M. Mosier, Robert A. Scheidt

Biomedical Engineering Faculty Research and Publications

In identical experiments in and out of a MR scanner, we recorded functional magnetic resonance imaging and electromyographic correlates of wrist stabilization against constant and time-varying mechanical perturbations. Positioning errors were greatest while stabilizing random torques. Wrist muscle activity lagged changes in joint angular velocity at latencies suggesting trans-cortical reflex action. Drift in stabilized hand positions gave rise to frequent, accurately directed, corrective movements, suggesting that the brain maintains separate representations of desired wrist angle for feedback control of posture and the generation of discrete corrections. Two patterns of neural activity were evident in the blood-oxygenation-level-dependent (BOLD) time series …

Quantifying Kinematics Of Purposeful Movements To Real, Imagined, Or Absent Functional Objects: Implications For Modelling Trajectories For Robot-Assisted Adl Tasks, Kimberly J. Wisneski, Michelle J. Johnson

Biomedical Engineering Faculty Research and Publications

Background

Robotic therapy is at the forefront of stroke rehabilitation. The Activities of Daily Living Exercise Robot (ADLER) was developed to improve carryover of gains after training by combining the benefits of Activities of Daily Living (ADL) training (motivation and functional task practice with real objects), with the benefits of robot mediated therapy (repeatability and reliability). In combining these two therapy techniques, we seek to develop a new model for trajectory generation that will support functional movements to real objects during robot training. We studied natural movements to real objects and report on how initial reaching movements are affected by …