Near infra-red spectroscopy combined with transcranial direct current stimulation in FPGA-based hardware for point of care testing of cerebral vascular status - A stroke study

Cerebral vascular status can be evaluated with cerebrovascular reactivity (CVR) that reflects the capacity of blood vessels to dilate, and is an important marker for brain vascular reserve. Here, transcranial direct current stimulation (tDCS) can up- and down- regulate cortical excitability depending on current direction, and anodal tDCS can increase regional cerebral blood flow during stimulation. Impairments in CVR have been associated with increased risk of ischemic events. Here, near-infrared spectroscopy (NIRS) is a cerebral monitoring method that can be used for non-invasive and continuous measurement of cerebral vascular status under various clinical conditions. This paper describes the development of a 4-channel continuous wave NIRS combined with tDCS in an FPGA-based hardware that captured the hemodynamic changes in the frontal cortex of the brain, as a measure of CVR, before and after anodal tDCS. We recruited 14 patients with established and acute ischemic stroke (<;1 month) localized to a single hemisphere (10 male and 4 females from age 42 to 73). The affected hemisphere with impaired circulation showed significantly less (0.26 +/- 0.28), p<;0.01, change in cerebral hemoglobin oxygenation than the healthy side (3.43+/- 0.86) in response to anodal tDCS. Thus, combining NIRS with tDCS can lend to low-cost point of care testing of cerebral vascular status so we present a NIRS-tDCS based adaptive neuro-fuzzy inference system implemented in a FPGA-based hardware.