Desenvolvimento e validação funcional de hardware para estimulação elétrica somatossensorial baseado em topologia de fonte de corrente de Howland

Abstract

The skin is widely innervated by primary afferent nerve fibers responsible for carrying information from the skin’s somatic sensory receptors to the central nervous system (CNS). Different disorders of the peripheral nervous system (PNS) affect these nerve fibers, compromising, partially or integrally, the quality of the information that reaches the CNS. Some of these neuropathies act selectively on nerve fibers; others gradually compromisse the SNP. In both cases, the evaluation of peripheral nerves provides information about the progress of diseases, indicating the need for therapeutic interventions to improve patients’ quality of life. Among the techniques available to assess nerve fibers’ integrity, the sinusoidal current is one of the main tools for screening and monitoring somatosensory disorders. This method is quantitative, non-invasive, and neuroselective, allowing the differentiation of the nerve fibers affected. Systems such as Neurometer and NeuroStim are widely used in studies of the somatosensory system. However, both devices have complex hardware architecture, requiring at least three voltage-raising stages and presenting offset values that compromise the test results, requiring periodic calibration of the system. Seeking to expand the transcutaneous electrical stimulation applications with sinusoidal current, the present work aims to present new multichannel hardware for the electrical stimulation system EELS (Somatosensory Electrical Stimulator). The Howland current source topology was used in combination with a bootstrapping power scheme, making it possible to simplify the design of the power circuit, using only one voltage lift stage. The modernization and simplification of the hardware enabled the implementation of a calibration circuit in real-time and the construction of a multichannel system, which opens up new possibilities for clinical research, including assessing disorders in the CNS. The new system is controlled by a graphical interface software and generates current stimuli with constant intensity, maximum amplitude of 8.63 mA, frequency between 1 Hz and 3 kHz in two independent channels. The hardware features high output linearity, stable load regulation, total harmonic distortion (THD) less than 1%, and automatic offset control. The tests carried out indicated that the EELS could be used in threshold tests of sensitivity to electrical current and the Neurometer and NeuroStim, and it also brings new resources to carry out different protocols.