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, 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 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 rSO2, partial pressure of end
tidal CO2 (PETCO2), and vital signs were continuously monitored. Change in rSO2 measurements from pre- to intrachallenge
(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 ΔrSO2 responses to
CO2 challenges than level 2 and 1 subjects. No significant difference in ΔPETCO2 existed between these factor levels.
Establishing baseline values of rSO2 in clinical practice may be useful in early detection of CBF changes.