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Cleveland FES Center

the cleveland FeS center is a consortium

of three nationally recognized institutions:

the Louis Stokes cleveland VA medical

center, case Western Reserve University,

and metroHealth medical center. the

cleveland FeS center is dedicated to the

advancement and clinical deployment of

technologies that generate or suppress

activity in the nervous system, including

technology that produces and controls the

movement of otherwise paralyzed limbs.

FeS devices send electrical impulses to electrodes—implanted in the body, worn on the skin, or operating through the skin—to produce and control movement. While a great deal is known about how electrical stimulation affects paralyzed nerves and muscles, until now a challenge has been the need to customize each de-vice for the individual patient’s abilities and disabilities.

in this article, researchers at case West-ern University describe how they devel-oped the Universal external control Unit (UecU), a flexible, configurable system technology platform for FeS applications. With UecU, engineers in the clinic can change an FeS controller and immediately see the results, enabling them to make im-provements up to ten times faster than they could do before. >>

In developing the UECU, we had three pri-mary goals. First, we wanted the UECU hardware and software to be modular and flexible enough to be used for a wide variety of FES applications. Second, the design envi-ronment had to enable researchers and reha-bilitation engineers—not expert program-mers—to develop rapid prototypes and quickly translate basic research into actual clinical systems. Third, the UECU had to work effectively in several disparate settings: in the laboratory, where basic research is the focus and rapid turnaround is important; in the clinic, where applications are customized for each patient; and in the patient’s home, where the key requirements are portability, robustness, and ease of use.

Developing the UECU BlocksetWe used Simulink® from the very start of the project. As a proof of concept, we connected a Freescale microcontroller evaluation board to a prototype implant control module and wrote S-functions to control this hardware. We were able to create a simple FES control-

For individuals with neurological impairments, functional

electrical stimulation (FES) can help make real what was once

only imagined: the restoration of movement to paralyzed

arms and legs. Depending on the location and severity of

the disability, FES can significantly improve quality of life by

enabling the individual to regain capabilities such as walking,

grasping objects, or maintaining bladder control.

Using Functional Electrical Stimulation to Restore Movement to Individuals with Neuromuscular Disabilities By Stephen Trier, Tina Vrabec, and Jeff Weisgarber Cleveland FES Center and Case Western Reserve University Department of Biomedical Engineering

Products Used ■ MATLAB®

■ Simulink®

■ Signal Processing Blockset™

■ Stateflow®

■ Real-Time Workshop®

■ xPC Target™

■ xPC Target™ Embedded Option™

MATLAB Digest | AcAdemic edition

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ler in Simulink and generate code from the model with Real-Time Workshop®. The proof-of-concept system worked, and demonstrated that we could get real-time control of stimula-tion pulses from a Simulink model.

From there, we developed and refined the software. While the hardware engineers de-signed the electronics, the software devel-opers divided the UECU’s capabilities into functional building blocks that researchers can use to assemble FES applications. We included these blocks in a custom Simulink blockset. The UECU Blockset provides more than 75 blocks, including individual blocks for accessing input from analog de-vices, joint angle transducers, myoelectric signals, and simple buttons, as well as blocks for generating simulation pulses and pro-ducing sounds, lights, and other feedback from the control unit.

Along with the blockset, we developed a custom Real-Time Workshop target for the UECU. An adaptation of the generic real-time target provided in the package, our tar-get configures the C compiler and other tools to correctly compile for the UECU. With the target, a clinical engineer can use a single Build command to turn a Simulink model into a compiled program downloaded to a UECU and ready to run.

Accelerating Development of FES ApplicationsBecause applications are assembled from Simulink blocks, our researchers can build FES control software up to ten times faster than before.

FES applications used to be developed in C by dedicated programmers. The development group supported multiple clinical groups, each of which specialized in a different dis-ability. When a clinical group needed a new feature or capability, they sent a request to the programmers, waited for a new version of the software, and then tested it in the clinic. While

coding in C was very flexible, the overall pro-cess was slow, limiting how quickly we could move from idea to reality. Worse, because the programmers might not understand what was needed, it often took several iterations be-fore the clinical group had a change that met their needs.

The Simulink based UECU has enabled our central development group to focus on building and maintaining a single system. The system’s flexibility and ease of use make it possible for each clinical group to rapidly de-velop and refine their own FES applications (Figure 1).

Figure 1. Application developed by a clinician to provide arm and hand control using an implanted stimulator.

FeS devices help restore movement to paralyzed muscles by controlling the electrical

signals used to stimulate nerves and muscle tissue. the devices translate input from

transducers or other devices that the patient can control into complex stimulus pat-

terns that produce the desired motion in paralyzed or uncontrollable muscles.

Researchers at the cleveland FeS center have developed FeS devices for a diverse

range of applications, including:

• Restoring hand and arm function to persons with quadriplegia

• enabling paraplegic patients to stand and walk

• improving motor control and gait after stroke

• Restoring bladder and bowel function

• improving tissue health by preventing pressure sores

each application uses a combination of one or more implanted

stimulators, percutaneous electrodes, or surface electrodes to

produce movement.

Functional Electrical Stimulation

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Building a Rapid Prototype Once a design is completed, researchers

use Real-Time Workshop to generate code from their Simulink model. Often researchers test new ideas by building a rapid prototype with xPC Target™. This approach enables them to use simpler floating-point designs to validate ideas on PC-compatible hardware before committing the design to portable, fixed-point target hardware.

Once a basic controller design has been de-veloped, we must still fine-tune the stimulus parameters that it uses to control the patient’s muscles (Figure 2).

We designed the UECU with non-volatile memory in which we store a table of stimu-lus data. In an arm control application, for example, this table is used to translate a sca-lar control signal into a vector of 8 to 16 numbers that control the pulses sent to nerves and muscles in the patient’s arm. To optimize the stimulus patterns, we set the signal levels at an initial starting point, see how they perform with the patient’s arm, then adjust the levels in an iterative process (Figure 3). Because muscles grow stronger or weaker over time, we have to repeat this pro-cess every so often to keep the FES system performing at its best.

From Idea to Implementation in a Single DayA case involving an early version of a myo-electric control highlights the speed with which clinicians can now implement new ideas. A patient had come in from out of town, and would be the first to use this form of control, in which the electrical activity of a fully functional muscle is used to control muscles that are paralyzed. At that time, the controller did not work as well as it does today, and we were unable to get the system running to our satisfaction.

We all wanted to send the patient home with a system that he could use to control his hands. On the last day of the patient’s visit, one of the rehabilitation engineers had an idea: Why not use the sip-and-puff control, a straw that the patient blows or suck to control his wheelchair? In one day, the engineer developed an algorithm that incorporated this unique feature into the control software. Using Simulink and the UECU Blockset, he had the algorithm test-ed and working by the time the patient left the clinic. Previously, this kind of effort would have taken a week or more.

The UECU in ResearchAt present, the UECU is used primarily for

restoring limb movement, but research groups also use it to develop other applications. In one initiative, a Biomedical Engineering graduate student used Simulink and the UECU to de-velop an experimental application for bladder control. Because only a limited amount of hardware was available for testing, he modeled, simulated, and tested the control logic entirely in Simulink. When hardware was available, we needed less than an hour to get his model working on the actual UECU.

Another group of graduate students used the UECU to develop a slip detector that can sense when an object is slipping from some-one’s hand. Using a piezoelectric sensor and signal processing developed in Simulink, a slip detector like this may eventually provide valuable feedback for those who have no sense of touch in their hands.

Figure 3. The pattern editor enables clinicians to rapidly create new stimulus patterns and fine-tune FES applications.

Figure 2. A clinician adjusts the stimulus parameters on a paralyzed patient’s FES device.

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Continuing to Improve Quality of LifeWith UECU, our clinical teams can build increasingly sophisticated applications that let patients have more control than before. We can, for example, control two implants with a single external controller, providing the patient with greater function and bet-ter portability. Using our rapid prototyping environment, clinical engineers have built neuro-prosthetic applications for many dif-ferent types of injury. More than 30 UECUs are currently in use by patients.

We continue to develop new modules for the UECU. We expect to deploy a radio module with multiple RF transceivers that will interface to a wireless transducer sys-tem developed at the Cleveland FES Cen-ter, as well as a surface electromyogram (EMG) module for measuring muscular activity from the surface of the skin.

We are also planning a multi-channel transducer module that will collect data from a wide variety of transducers, and a DSP module that will significantly increase the computing power of the UECU, allowing the system to handle more computationally intense applications. These advances will en-able patients to more naturally control their arms and legs—by directing multiple joints at once, for example—and as a result, to re-sume a more active life.

In the next five to ten years, we aim to replace the UECU and its companion im-plants with a new, fully internal system. Having an FES system completely inside the body will improve independence in places UECU cannot go today, such as in the shower or the pool, and will provide a more natural experience in any setting. The lab prototypes of the new system are al-ready running programs created with Simulink and Real-Time Workshop. ■

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For More Information ■ Cleveland FES Center

http://fescenter.case.edu

■ Department of Biomedical Engineering, Case Western Reserve University http://bme.case.edu

■ The MathWorks in Academia www.mathworks.com/academia