Development of NIRS Based Noninvasive Cerebrovascular Regulation Assessment

Abstract

Alterations to cerebral blood flow (CBF) have been implicated in diverse neurological conditions, including mild traumatic brain injury, microgravity induced intracranial pressure (ICP) and intraocular pressure (IOP) increases, and mild cognitive impairment. 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, CO2-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 usedto 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 rSO2, partial pressure of end tidal CO2(PETCO2), and vital signs were continuously monitored. Change in rSO2measurements from pre-to intra-challenge (ΔrSO2) detected periods of hypercapnic challenges. Subjects were grouped into three exercise factor levels (hr/wk), 1: 0, 2:>0 and <10, and 3:>10. Exercise factor level 3 subjects showed significantly greater ΔrSO2responses to CO2challenges than level 2 and 1 subjects. No significant difference in ΔPETCO2 existed between these factor levels. Establishing baseline values of rSO2and cerebrovascular reactivity (CVR) to CO2in clinical practice may be useful in early detection of CBF changes. This is the first reported use of a COTS device to monitor changes inrSO2in response to hypercapnia and correlate these responses with frequency of routine exercise in healthy young adults at rest.