Cerebral and muscle near-infrared spectroscopy during lower-limb muscle activity – volitional and functional electrical stimulation

Abstract Chronic venous insufficiency (CVI) can lead to blood clotting in the deep veins of the legs, a disease known as deep vein thrombosis. An estimated 40 percent of people in the United States have venous insufficiency that may be ameliorated with functional electrical stimulation (FES). Near-infrared spectroscopy (NIRS) is a non-invasive optical imaging method for monitoring hemodynamics. NIRS being an optical technique can be combined with FES for a theranostics application without suffering stimulation artefact. In this study, we combined muscle NIRS with electromyogram (EMG) of the calf muscles to detect blood volume changes (based on total hemoglobin concentration) in the muscle during volitional tiptoe movements at different frequencies as well as during FES (using geko™) with different stimulation intensity. In muscle NIRS+FES study, we also measured the cerebral hemodynamics using functional NIRS (fNIRS). Muscle NIRS was conducted using a frequency domain (FD) method (called FDNIRS) that used a multi-distance method to isolate muscle hemodynamics. FDNIRS-EMG study in ten healthy humans found a statistically significant (p<0.05) effect of the tiptoe frequencies on the EMG magnitude (and power) that increased with tiptoe frequency. Also, the muscle blood volume (standing/rest) decreased p<0.01) with increasing tiptoe frequency and increasing stimulation intensity that was statistically significantly (p<0.05) different for males and females. Moreover, increasing stimulation intensity led to a statistically significant (p<0.01) increase in cerebral blood volume measured with fNIRS. Therefore, combined muscle NIRS and fNIRS with FES can provide a theranostics application in CVI.