Essential Tremor Measuring Device

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Essential Tremor Measuring Device

Designers: Kailash Bohra, Jonathan Cayce, Eric DuBois, Ingrid Menegazzo
Client Coordinator: Dr. Leon Dure, Division of Pediatric Neurology

 

Tremor exists in humans both physiologically and pathologically. While physiological tremor is a normal tremor observed in the body that helps maintain tone and steadiness of the extremities to perform complex tasks, pathological tremors are the most commonly observed neurological illnesses.  The tremors are categorized depending on the frequency of oscillation and trigger.  Essential tremor (ET) is one of the most frequently occurring tremor disorders and is commonly observed in limbs or the head during the performance of an action, and in certain postures [1]. When observed in children, diagnosis is crucial to improve the quality of life and ensure the ability to develop needed skills. With this in mind the present device was developed to measure ET in children and to create a database for comparative analysis, as to further investigate and improve diagnosis for this disease.

The design constraints were established by which the device should measure ET of the hand and arm (5 to 12 Hz) with the capability to measure physiological tremor (up to 30 Hz) [2] and expand to other tremors. It would be used in small examination rooms (12 ft by 12 ft); therefore the device should be simple, compact, portable, and easy to set up. Based on these constraints, the client required the device to interface with a laptop system. Due to the patients’ range of ages (5-18 years) it also had to be adjustable to different sized arms. The device was to have a shock resistant rating – for the measuring elements it must be at least 1000 g to ensure adequate protection from misuse, fall, and sustainability of the device. It must be made of materials that can be cleaned using antiseptics to ensure sterile use for each patient. The software associated with the device was to provide graphs of frequency, display the value of the tremor frequency, and store data to be used for later analysis. The client supplied the design team with a $10,000 budget to augment NSF support of $1,500. The time frame to design and construct the device was 15 weeks.

TECHNICAL DESCRIPTION

 

Three tri-axial accelerometers (Kistler 8690C5 PiezoBEAM) were interfaced with three separate Dynamic Signal Acquisition modules (National Instruments USB-9233), which connected directly to the laptop (Dell Inspiron 680m).  The assembly of the prototype can be seen in Figure 2 (left).  The materials used for the strapping system were elastic bands with Velcro strips sewed on to firmly attach the strap to the patient with the finger accelerometer being attached using bandaging tape.  A third elastic band was constructed to hold wires running from the accelerometers against the patient to allow more patient mobility.  Accelerometer mounting brackets were mounted to the hand and forearm straps using fabric glue to create a firm interface between the straps and the accelerometers.   The set up of the strapping system can be seen in Figure 2 (right).

The Dynamic Signal Acquisition module contained built-in filtering, which consisted of a passband filter, stopband filter, and alias free filter.  The software design incorporated LabVIEW (National Instruments), which uses block diagram programming to build user-defined applications where there are numerous tools and functions predefined to acquire and analyze data, called Visual Interface modules or VIs.  The prototype’s software was initialized using a visual interface, named Introduction, where the user can select to test the patient, compare data, cancel or quit the program by clicking on the appropriate VI button.  When the Test patient or Compare data buttons are pushed, a new visual interface is displayed to the user where two separate sets of code are used to accomplish appropriate tasks.

The test patient interface functions by first prompting the user to enter information.  The user then selects the type of test (postural, finger to nose, or nose to target) and then clicks start in the visual interface window to begin data acquisition.  A built in module in LabVIEW named data acquisition assistant module is called three times simultaneously to collect data from the accelerometers at a rate of 2,000 samples per second and converts the signal from volts to acceleration.  The data acquisition assistant module outputs a clustered signal that contains data for the x, y, and z axes of the accelerometer, which allows for easier processing in the LabVIEW environment.  The acceleration data is plotted onto three separate viewgraphs and is sent to the FFT spectral analysis module and the frequency and amplitude module for the extraction of frequency measurements.  The frequency spectrum is then sent to three separate viewgraphs to display the peak frequencies of the data set to the user.

The acquired data is saved using a built in write to file module that creates an Excel data sheet that contains patient and test information and the mean frequencies for each axes of the three accelerometers.  A second method uses LabVIEW’s built in database connectivity to transfer data collected in the Test Patient VI to an Access Database named Acceleration data.  Once the data has been entered into the database, the user can then perform other tests on the patient or exit out back to the introduction interface by clicking on the appropriate button.  To protect the device during transport, the design team purchased a hard case (Pelican) with foam padding.  The total cost associated with the system was $9,199.

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Figure 22. (left) Laptop, data acquisition modules, accelerometers, clip, velcro straps and non adherent bandage; (right) Lateral and top views of the mounted accelerometers on the arm, using a non adherent bandage on the finger, velcro on the forearm and hand, as well as to secure the cables to the upper arm.

References:
[1] Deuschi G., Krack P., “Tremor: Differential Diagnosis, Neurophysiology, and Pharmacology.” Parkinson’s Disease and Movement Disorders, 419.
[2] Cohen, O., Pullman, S., Jurewicz, E., Watner, D., Louis, E.D., “Rest Tremor in Patients with Essential Tremor.” Arch Neurol 2003, 60: 405-410.