Objective: To develop a method to detect freezing of gait in real time

Background: Freezing of gait (FOG) is a major debilitating symptom and cause of falls in many patients with Parkinson’s disease (PD). FOG consists of sudden interruptions of the gait cycle of highly variable duration. It often does not respond to treatments given on steady basis, like medications, pacing sounds, and  patterned visual backgrounds (“open-loop” interventions). We therefore plan to develop “closed-loop” interventions triggered by the onset of FOG episodes. This approach requires real-time detection of FOG onset. 

Methods: We introduce a new method of detection of FOG episodes based on ground forces recorded by custom-built instrumented sandals (Solesound system). This system measures foot pressure and relays it in real-time to a laptop via wi-fi while a human subject walks freely in a 20-m range. We introduce a new variant of gait phase representation based on the binary on-the-ground/off-the-ground state of the heel and ball of the foot. We studied such representations of foot pressure patterns during freezing and non-freezing portions periods of walking in four patients with PD and FOG. 

Results: Analysis of gait phase transitions revealed unique reversals of transition directions at the onset of FOG episodes. These transitions were different from those observed during gait initiation, walking, and turning. 

Conclusions: This finding allowed accurate detection of FOG onset using a look-up table comparison of the present and previous two gait phases. This method is suitable for future implementation of rapid real-time detection of FOG, possibly as quickly as 500 ms after FOG onset. The unique signature of FOG in gait phase space may hold clues to the nature of the gait control abnormality that underlies FOG

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MDS Abstracts - https://www.mdsabstracts.org/abstract/freezing-of-gait-in-parkinsons-disease-consists-of-unique-pressure-based-gait-phase-transitions/