Effects of Inertia and Wrist Oscillations on Contralateral Neurological Postural Tremor Using the Wristalyzer, a New Myohaptic Device

Abstract

Upper limb postural tremor consists of mechanical-reflex and central-neurogenic oscillations, superimposed upon a background of irregular fluctuations in muscle force. Muscle spindles play key-roles in the information flow to supra-spinal and spinal generators. Oscillations were delivered using a new generation portable myohaptic device, called ldquowristalyzer,rdquo taking into account the ergonomy of upper limbs and allowing a fine adjustment to each configuration of upper limb segments. The nominal torque of the first generation device is 4 Nm, with a maximal rotation velocity of 300 degrees/s and a range of motion of plusmn45 degrees. Reliability was assessed in basal condition and during loading conditions. We assessed the effects of the addition of inertia on postural tremor of the finger in a group of 26 neurological patients and the effects of wrist oscillations upon contralateral postural tremor in 6 control subjects and in 7 neurological patients exhibiting a postural tremor. Patients showed two different behaviors in response to inertia and exhibited an increased variability of postural tremor during fast oscillations (13.3 Hz). One patient with overactivity of the olivocerebellar pathways exhibited a drop in the peak frequency of more than 20%. The relative power of the 8-12 Hz subband was significantly higher in controls both in basal condition and during oscillations (p = 0.028 and p = 0.015, respectively). The second generation wristalyzer allows to investigate the effects of mechanical oscillations up to frequency of 50 Hz. This mechatronic device can assess the responsiveness of tremor generators to stimulation of muscle spindles and biomechanical loading. Potential applications are the monitoring of dysmetria under various inertial or damping conditions, the assessment of rigidity in Parkinson's disease and the characterization of voluntary muscle force.

A New Myohaptic Instrument to Assess Wrist Motion Dynamically

“…We show an inability of cerebellar patients to tune appropriately the intensities of muscle discharges in a task requiring a sequential activation of muscles. As compared to previous works [ 6 – 12 ], the present paper extends the application of the wristalyzer to a group of cerebellar patients and shows for the first time (1) how kinematic and electromyographic data correlate with clinical observations, and (2) the assessment of stretch reflexes in cerebellar disorders.…”

“…Other applications include the evaluation of upper limb tremor in various damping conditions and rehabilitation of wrist disorders [ 12 ]. The advantages of the instrument are its robustness, the comfort during testing and the reliability of the procedures [ 12 ].…”

“…In assessing metrics of motion in neurological patients, the selection of the instrumentation is critical [ 12 ]. Indeed, assessment of joint properties and voluntary motion in neurological patients remains a challenge in daily practice.…”

Neurological Tremor: Sensors, Signal Processing and Emerging Applications

“…The haptic tools are also proposed as future therapeutical methods for rehabilitation [ 47 ]. These instruments record angular motion, torques and corresponding EMG activities (in case of combination with EMG sensors), and can be used to obtain real-time spectral analysis, to apply loads and mechanical oscillations as well as characterize the effects of damping on voluntary motion in neurological patients [ 48 ]. Comparison with conventional accelerometers has demonstrated a high accuracy in terms of reproducibility of frequency and amplitudes of imposed oscillations [ 49 ].…”

Tremor: From Pathogenesis to Treatment

“…The device characterizes the effects of damping on voluntary motion in neurological patients (Grimaldi et al, 2008). The wristalyzer's features are the following:…”