Effects of mechanical vibration on tremor in Essential Tremor patients

- Brief name. Effects of mechanical afferent stimulation on tremor in Essential Tremor patients - Materials. In order to apply mechanical afferent stimuli and assess the ongoing tremor in patients, a device was designed and built which is able to deliver vibratory stimuli with different frequencies to the forearm and the hand and simultaneously record the movement of the wrist. Vibratory stimuli were delivered using piezoelectric actuators (model QP-10W, for the fingertips; PPA-4011 for the hand; PPA-1022 for the forearm; all from Mide Technology, US), which were controlled at 5 kHz through piezoelectric haptic drivers (DRV8662, Texas Instruments, US) via a data acquisition card (DAQ) (NI USB 6003, National Instrument, US) connected to a consumer laptop. The amplitude of the mechanical vibration was left constant during the experiment, and set to the maximum. Wrist movement was monitored at 100 Hz using inertial sensors (TechMCS, Technaid, SP). - Procedures The experiments are performed in the arm most affected by tremor, which is identified by a neurologist at the beginning of the experimental session. During the experiments, patients are comfortably seated in front of a desk. Piezoelectric actuators were located over the fingertips, the hand and the forearm, the areas where Pacinian corpuscle density is higher (Bruce Goldstein, 2010). To measure wrist movement, inertial sensors are strapped to the dorsal side of the hand and forearm. Patients perform a standard postural task, while their proximal arm rests on a purposely-built support which not constrain hand or forearm movements. The support decreases muscle fatigue and ensures repeatability across trials. During the trials, patients are instructed to hold the arm, forearm and hand outstretched against gravity, to trigger their tremor. The experimental protocol consists of four 4-min trials in which different stimulation strategies are applied. These trials are interleaved with 10 min long resting periods. The experimental session lasts for ~90 minutes. 1. Stimulation at 50 Hz: vibration was delivered at 50 Hz, a frequency which should minimally recruit Pacinian corpuscles. 2. Stimulation at 250 Hz stimulation: vibration was delivered at 250 Hz, a frequency which should maximally recruit Pacinian corpuscles. 3. Increasing stimulation frequency: vibration was delivered in 50 Hz steps (increasingly, from 50Hz to 450Hz); each frequency was applied during 13.33 s. This trial was designed to test the frequency-dependency of the stimulation. 4. Random stimulation frequency: vibration was delivered at the same frequencies as during the IncreasingFreq trials, but their order was randomized; each frequency was again applied during 13.33 seconds. This trial was designed any potential adaptation to the stimulation from the frequency-dependent effects. These trials are divided into four 60 s epochs: during the first epoch (Pre-stim) the patient’s basal tremor is assessed; during epochs 2 and 3 (Stim1 and Stim2), we apply vibratory stimuli as defined by the corresponding strategy; during the last epoch (Post-stim), the tremor is assessed to detect potential after-effects. - Intervention providers A neurologist and an engineer are present during the trials. The first is responsible of assessing the basal tremor of the patient and evaluating his/her state while the stimulation is applied. The engineer is responsible of managing the device and recording the data. Both researchers monitor fidelity to the intervention by direct supervision. - Modes of delivery The protocol is provided to one participant at a time. Each patient completes the protocol once. - Location Hospital Universitario 12 de Octubre (Madrid, Spain) - Tailoring and modifications The protocol remains unaltered across applications. The only adaptation to patients is the choice of the arm most affected by tremor.