Protective stepping response in Parkinsonian patients and the effect of vibrotactile feedback

Abstract

The objectives of this study were (1) to characterize protective stepping responses to unpredictable forward/backward postural perturbation in Parkinson's disease (PD) and (2) to assess whether vibrotactile cues of the impending fall improve the stepping response. Twenty mild PD patients, 7 advanced PD patients, and 17 age-matched controls stood on a platform moving unpredictably forward and backward, requiring a protective step to maintain balance. Direction-coded vibrotactile cues, triggered by leg tilt, were provided to prompt step generation. All subjects showed quicker reaction time, shorter steps, and smaller total trunk displacement when stepping backward than when stepping forward. Advanced PD patients took shorter, slower, and an increased number of protective steps. The only abnormality observed in mild PD patients was slightly slower backward steps. Vibrotactile feedback reduced the amount of trunk displacement observed before taking a protective step but did not improve any abnormality in PD patients. Early PD patients had near-normal protective stepping responses to unpredictable perturbations, but advanced patients made slow and short steps both forward and backward. Given that latencies were preserved even in unpredictable conditions, step slowness and hypometria are the primary abnormalities of the stepping response in PD. As voluntary locomotor stepping in PD is reported to improve with sensory feedback, the lack of such improvement in our study implies that additional sensory cues cannot help automatic reflex-like stepping reactions in PD patients.

Characterization of Compensatory Stepping in People With Multiple Sclerosis

“…CoM displacement represents extent of disequilibrium induced by the perturbations, and serves as an overall measure of performance 16, 17 . Step latency was chosen because delayed feet-in-place postural responses are characteristic of prolonged somatosensory conduction delays in PwMS 3 , and similar delays in postural stepping responses may contribute to falls 6 .…”

Vibrotactile Feedback for Human Balance Improvement: Experimental Investigation of Optimal Feedback Location

“…A consistent way for measuring the effectiveness of a biofeedback system in decreasing tilt should be developed and a set of testing procedures should be performed by all of the research groups in this field. [7] Varying number of tactor columns on the waist showed no significant performance difference Presenting ML and AP tilt in conjunction reduces tilt more than providing feedback on ML and AP tilt independently Tactor spatial resolution bears no effect on sway reduction…”

“…Although some research exists to determine the best type of information coding method to be use in balance feedback, no study has compared in depth various feedback locations on the body to determine the feedback location that lends itself to improved balance measures. Instead, the choice of location for feedback in most studies was often not supported or justified [6] [7].…”

“…With regards to tactor type, one study compared C2 (voice-coil type linear actuators) and Tactaid (electromagnetic inertial transducer) tactors' effects on natural body sway [7]. It was found that the C2 tactors created greater postural shift vector magnitudes, possibly because of its greater stimulus amplitude.…”

“…In order to eventually compare the effectiveness of providing feedback on various body locations, it is important to first understand the mechanical properties associated with the feedback to be provided and to determine which type of actuator should be used in feedback applications. There is very little in the way of research on which type of tactor is best sensed by the wearer; the only study involved in this type of research found that voice-coil type actuators were more easily sensed than electromagnetic inertial transducers [7]. There is also no research conducted on the ability to predict whether or not participants will be able to sense feedback, an ability which could prove useful when first setting-up a feedback device for a user; it could allow for customization of the device to ensure that all vibrations provided to the user could be felt.…”