Sistema para avaliação da capacidade de discriminação sensorial de corrente elétrica senoidal em diferentes frequências : uma prova de conceito

Abstract

Several studies have discussed the use of electrical stimulation in the diagnosis of peripheral neuropathies that selectively or progressively affect nerve fibers, like diabetes mellitus, leprosy, and carpal tunnel syndrome. This technique is a neuroselective, quantitative and non-invasive alternative to conventional methodologies. However, there are no records in literature about quantitative and non-invasive methodologies that are used to assess impairments to central nervous system, like multiple sclerosis or the effects of stroke sequelae. This work aims to present the development of a new electrical somatosensory stimulator, with two channels, and propose a new electrical stimulation methodology, called Sensory Discrimination, to assess cognitive loss generated by central nervous system impairments. The new stimulator, called EELS (acronym for Portuguese Estimulador Elétrico Somatossensorial), is composed of new hardware, a graphic interface software for mobile devices (mobile application), and by a WEB server integrated to a cloud database. It was included in EELS the methodologies of Current Perception Threshold (CPT) and reaction time determination, already presented by literature. It was additionally developed a new protocol to assess the Sensory Discrimination, which is based on the ability of the subject to differentiate electrical stimuli at different frequencies, which predominantly activate different types of peripheral somatosensory fibers. Workbench tests were conducted to validate the EELS and to compare it against its predecessor system, the NeuroStim. It was also conducted functional tests in 11 voluntaries without neurological impairments, of either sex and in age range from 23 to 56 years old. The data were compared against a Current Perception Threshold sample of 10 volunteers obtained with NeuroStim. Also, the Sensory Discriminant results were assessed to observe the influence of distractors in the hit rate and error type of the individuals, verifying the relation between the distractors and the affected fiber type. The workbench tests show that the new equipment presents advantages over the NeuroStim, like 7.6 times lower harmonic distortions, and larger bandwidth (0 Hz to 10 kHz). The data obtained during the tests in volunteers reveal that the Current Perception Threshold and Reaction Time values are according to literature and it was not possible to proof the existence of statistically significant difference between the data obtained by both systems. The Sensory Discrimination data reinforces the data found in the literature about the neuroselectivity of the electrical stimulation, and the hypothesis of the stimuli at 250 Hz activate both thick and thin mielinized fibers, working as a good distractor. It is concluded that the EELS attends to all recommended requisites, being technically able to replace the NeuroStim in researches involving sinusoidal electrical stimulation, allowing the implementation of new stimulation protocols; and that the technique of Sensory Discrimination seems to be a functional and promising methodology for studies about central nervous system impairments, and different types of distractors may be studied.