Development of equipment for automatic diagnosis of the neuromuscular condition

Abstract

Electrically evoked muscle contraction has become a relevant therapeutic strategy in the rehabilitation practice and in the research field. In Intensive Care Unit (ICU), for instance, critical ill patients can present significant muscle weakness and neuromuscular electrophysiological disorders due to long periods of immobility. Neuromuscular Electrical Stimulation (NMES) has been shown an important tool to avoid such problems. However, in crically-ill patients with neuromuscular electrophysiological disorders the assessment of neuromuscular excitability is essential for improving NMES efficacy. Neuromuscular excitability has been assessed by Stimulus Electrodiagnosis Test (SET) which measures: rheobase, chronaxie and accommodation. However, SET is a time demanding procedure and depends on the subjective visual detection of each examiner. The objective of this work was to develop an equipment capable to automating SET, making it feasible accurate and reliable. Such equipment is capable of generating the electrical stimuli with the parameters necessary for SET, modify these parameters in real time and stop the stimulation when the contraction is detected. This detection is possible through a biofeedback system implemented using an accelerometer placed on the muscle in which contraction will occur due to electrostimulation. Through the workbench tests it was possible to generate biphasic electric stimuli up to 225 mA with load of 1 kΩ and monophasic up to 104 mA with load of 1 kΩ too. It was possible to vary the pulse width of the stimuli from 20 µs to 50 ms with steps of 20 µs. Tests performed on biofeedback algorithm showed it was capable to detect automatically voluntary muscle contractions.