title: Development of a computer controlled stimulation and recording system for trans-spinal electrical stimulation
Creators: name: Eickhoff, Steffen
Publisher: name: TU Wien
Year: 2017
Subjects: subject: Functional Electrical Stimulation
subject: FES
subject: posterior root reflex
subject: spinal cord stimulation
subject: assessment
subject: reflex response recording

description: Spinal cord injury (SCI) causes impairment of the neuronal connection of the brain with the spinal cord as well as with the peripheral nervous system. This impairment can lead to partial (incomplete) or complete loss of motoric and / or sensory functions of anatomical structures, innervated below the spinal lesion. Electrical spinal cord stimulation (SCS) is able to elicit posterior root muscle (PRM) reflexes in subjects with SCI classified as motoric complete. While this was originally observed using epidurally implanted electrodes, numerous studies find non-invasive transcutaneous spinal cord stimulation (tSCS) capable of evoking similar spinal reflexes. Recent studies in this field are approach selective stimulation and modulation of spinal excitability, which often employs the use of sub-threshold conditioning pulses prior to the stimulation. In this thesis a two-channel stimulation system, also capable of recording muscle reflexes, is developed and technically evaluated. This evaluation under laboratory conditions verified that the system fulfills the specific requirements of research investigations in the area of neuromodulation in SCS and is safe to be applied in a preliminary clinical study. The initial results of this study suggest that spinal cord excitability can be modified incorporating peripheral nerve stimulation prior to eliciting PRM reflexes. The recording system for electromyographic (EMG) signals has 16 channels of which eight are used to measure the PRM reflexes bilaterally in the four big synergistic muscle groups of the lower limb. These EMG signals are amplified with a gain of 590 V/V and filtered at a bandwidth of 30 – 590 Hz. Furthermore, the system has 4 digital markers, which allow to manually mark specific events during the stimulation procedure. Marker and EMG amplifier are connected to a National Instruments™ data acquisition card (NI USB 6221 OEM) to visualize and store the measurement data. The stimulation system is composed of two BIOPAC® STMISOLA linear isolated stimulators, which are connected to the NI USB 6221 OEM. As a protective measure against DC currents being applied to the subject, high pass filters with cut-off frequencies of 2.2 Hz are placed between NI-card and stimulators. The output is generated via a LabVIEW™ program in which stimulation modes, specifically designed for the relevant type of SCS studies, are contained. The system is capable of emitting rectangular single or double pulses, as well as different types of stimulation patterns in a range of +/- 100mA. Phase durations of up to 1 ms have been evaluated and verified as being free from distorting effects of the filter circuitry. The system is further tested in the course of a preliminary study in a clinical environment with one spinal cord injured subject. The first channel applies stimulation impulses to the posterior roots of the subject, which elicit PRM reflexes that serve as a probe. The second stimulation channel delivers different patterns of stimulation to the sural nerve, a purely afferent peripheral nerve, at the subjects left ankle. A comparison of the PRM reflex peak-to-peak response magnitudes, with and without stimulation of the sural nerve prior to spinal cord stimulation, shows a strong suppressive conditioning effect in the ipsilateral leg. These preliminary results are in good accordance to recent literature.