Creating tactile feedback with intelligent electrical stimulation to compensate for sensory impairment.

Abstract

Performing daily life activities can be more challenging as a result of peripheral neuropathy in the feet and can lead to an increased risk of falls and injuries. Biofeedback, in the form of electrocutaneous stimulation, can be used as a means to transmit information about the force and pressure applied to the feet, and this can help people determine their body position in relation to the ground and the amount of sway movements. The motivation for the present work was to explore whether a wearable electrotactile feedback system (EFS) could improve life quality by supporting people with balance instability as a result of this condition. In this study a wearable EFS was designed to estimate the magnitude of pressure applied to the feet during standing and walking. The study also aimed to determine whether the EFS had an effect on posture control in standing and confidence in walking among individuals suffering from peripheral neuropathy. A wearable EFS has been developed in this work including the hardware design for an electrocutaneous stimulation and a processing unit to compute the sensor data. The EFS uses a sensor system with piezoresitive force sensors that has been developed and tested beforehand. The proposed system considers aspects of safety and portability, as well as meeting individual parameters. The latter one was assured by implementing and testing a novel calibration method for the detection of sensory thresholds and device parameters. A software for magnitude estimation and force and pressure feedback based on the centre of pressure (COP) movement was programmed and a psychophysical transfer function involving sensory thresholds and sensor system variables was implemented. A pilot study with 11 participants was carried out to evaluate the suitability of the EFS for magnitude estimation. Magnitude estimation with the EFS showed high accuracy and sensitivity and it was found that the design proposed in this work is beneficial over other solutions. The upper leg was identified as a suitable location for electrotactile feedback. A proof of concept study was undertaken among 14 individuals suffering with peripheral neuropathy and five controls in a clinical environment, testing the effects of the EFS on balancing and walking in different scenarios. It was shown that, when used by patients with neuropathy, the EFS helped improving posture control in certain scenarios and did not hinder patients during walking. A longer learning period might be necessary so that users can fully benefit from the EFS. The findings of the study contribute to the understanding of electrotactile feedback and are valuable for further developments of wearable EFS to compensate for sensory impairment and improve activities of daily life for people with sensation loss in their feet.