NIRS-based noninvasive cerebrovascular regulation assessment

Alterations to cerebral blood flow (CBF) have been implicated in diverse neurological conditions, including mild traumatic brain injury, microgravity induced intracranial pressure (ICP) increases, mild cognitive impairment, and Alzheimer’s disease. Near infrared spectroscopy (NIRS)-measured regional cerebral tissue oxygen saturation (rSO2) provides an estimate of oxygenation of the interrogated cerebral volume that is useful in identifying trends and changes in oxygen supply to cerebral tissue and has been used to monitor cerebrovascular function during surgery and ventilation. In this study, CO 2 -inhalation-based hypercapnic breathing challenges were used as a tool to simulate CBF dysregulation, and NIRS was used to monitor the CBF autoregulatory response. A breathing circuit for the selective administration of CO2-compressed air mixtures was designed and used to assess CBF regulatory responses to hypercapnia in 26 healthy young adults using non-invasive methods and real-time sensors. After a 5 or 10 minute baseline period, 1 to 3 hypercapnic challenges of 5 or 10 minutes duration were delivered to each subject while rSO 2 , partial pressure of end tidal CO 2 (PETCO 2 ), and vital signs were continuously monitored. Change in rSO 2 measurements from pre- to intrachallenge (ΔrSO 2 ) detected periods of hypercapnic challenges. Subjects were grouped into three exercise factor levels (hr/wk), 1: 0, 2:>0 and 10. Exercise factor level 3 subjects showed significantly greater ΔrSO 2 responses to CO 2 challenges than level 2 and 1 subjects. No significant difference in ΔPETCO2 existed between these factor levels. Establishing baseline values of rSO 2 in clinical practice may be useful in early detection of CBF changes.