Design and Modeling of a Passive Hydraulic Device for Muscle Spasticity Simulation1

2018 Design of Medical Devices Conference

Zallek

et al. 2018

Self Cite

Spasticity is a common abnormal muscle behavior associated with neurological disorders and is characterized by speed-dependent increased tone in the affected muscle when induced by passive movement [1]. During the passive stretch of the muscle, additional unique clinical signs that accompany spasticity are (a) sudden increase in muscle tone at a certain joint position (catch angle), called the “catch”, (b) after the “catch”, a quick drop of muscle resistance, called the “release”, where (a) and (b) together are usually referred to as the “catch-release” behavior, and (c) limited range of motion (ROM) [1,2]. With the evolution of spasticity, these symptoms will worsen.

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Revised Design of a Passive Hydraulic Training Simulator of Biceps Spasticity

2018 Design of Medical Devices Conference

Zallek

et al. 2018

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Passive Hydraulic Training Simulator for Upper Arm Spasticity

Liang

Journal of Mechanisms and Robotics

et al. 2020

Spasticity is a hypertonic muscle behavior commonly observed in patients with multiple sclerosis, cerebral palsy, stroke, etc. Clinical assessment for spasticity is done through passive stretch evaluations of various joints using qualitative clinical scales, such as the Modified Ashworth Scale (MAS). Due to the subjective nature of this evaluation method, diagnostic results can have poor reliability and inconsistency. A few research groups have developed electromechanical training simulators of upper arm spasticity with the intent of providing healthcare students practical training opportunities. This paper presents a novel, purely mechanical (nonpowered) training simulator as an alternative design approach. This passive design utilizes a hydraulic damper with selectable viscous effect to simulate the speed-dependent spastic muscle tone and a Scotch-Yoke linkage system to create the “catch-release” behavior of spasticity. An analytical fluid model was developed to systematically design the hydraulic damper. The error residuals between model prediction and experimental damping force were found within ±2.0 N and percent errors within ±10% across various testing speeds (i.e., 250, 500, 750, and 1000 mm/min). The performance of the fully assembled simulator was tested under slow (ω ≤ 60 deg/s), medium (60 deg/s < ω < 150 deg/s), and fast (ω ≥ 150 deg/s) stretch speeds, where ω is the joint angular speed. Preliminary bench-top results suggested the feasibility of replicating five distinct levels of spasticity behaviors (MAS levels 0–4), where resistive torque increased with higher stretch speed and peak resistive torque ranged from 1.3 to 6.7 N · m under the fast stretch speed.

Design Framework and Clinical Evaluation of a Passive Hydraulic Patient Simulator for Biceps Spasticity Assessment Training

Journal of Mechanisms and Robotics

Zallek

et al. 2021

This paper presents the framework for developing a passive (unpowered) mechanical training simulator for replication of biceps spasticity to complement current clinical assessment training. The passive training simulator was developed to mimic three main behavioral features of spasticity, i.e., abnormal muscle tone, catch-release behavior, and range of motion (ROM) reduction. The simulator can replicate varied levels of spasticity (Modified Ashworth Scale (MAS) levels 0-4) using a combination of three adjustable mechanical design features, i.e., resistance level, catch angle, and ROM selectors. Bench-top evaluation examined the performance of individual mechanical design features, as well as their combined performance. Spastic muscle resistance profiles generated by the simulator qualitatively agreed with the clinical descriptions of spasticity in the MAS. Mean peak simulated resistive torque fell within the clinical measures from actual spasticity patients for MAS 1-4, but was lower for MAS 0 (0.9, 3.5, 4.2, 6.9, 9.8 Nm for MAS 0-4, respectively). Seven clinicians were invited to validate the simulator performance. They were asked to identify the simulated MAS level during a blinded assessment and to score the realism of each simulation feature using a five-point scale, where 3 was “about right”, during a disclosed assessment. The mean percent agreement of clinicians‘ judgments was 76 ± 12%. The mean realism score throughout MAS 0-4 were 2.82 ± 0.15. Preliminary results suggested good potential for this simulator in helping future healthcare practitioners learn and practice the basics of spasticity assessment.