Simultaneous collection of continuous cerebral oximeter values from the NIRS devices under test will be captured electronically via a computer or other methods. Event marks will be placed in the computer log at the point of sampling SaO2 and SjvO2 blood specimens taken at controlled steps of blood oxygenation in healthy adult volunteers. During the study period, vital signs via a clinical care monitor will be captured into the computer. After catheters are placed in the radial artery and jugular bulb, the cerebral oximeter sensors are placed on the subject’s forehead. An oral breathing circuit is fitted to the subject and the subject breathes a mixture of oxygen and nitrogen gasses. Carbon dioxide (CO2) gas is added to the inspired gas mixture to maintain normocarbia and independently for the management of hyper- and hypo-carbia challenges. Inhaled oxygen is reduced or increased to bring the subject near target levels. Desaturation to the lowest arterial oxygenation level (~70 % SaO2) and highest arterial saturation (near 100% SaO2) is conducted in a stepwise process, per the ISO 80601-2-85:2021 standard. 1 The number of saturation plateaus is typically 5 in increments of ~6%, e.g., 100 to 97, 97 to 92, 92 to 85, 84 to 78, 78 to 70.

A reference pulse oximeter (SpO2 values) will be used to continuously monitor the settling of each plateau (as a continuous estimate of SaO2). Within each saturation plateau level, two specimens of arterial and jugular venous blood will be sampled, analyzed by co-oximetry, and the values entered in a case report form (CRF). The desaturation to oxygenation process is repeated for a total of two series. During the first series of desaturation plateaus, hyper- and hypo-carbia challenges. 3 will occur at plateaus 3 and 5 of the first series (i.e., ,92 to 85 and 78 to 70) and at plateaus 2 and 4 of the 2nd series (i.e., 97 to 92 and 84 to 78). The catheters are removed, and the subject is observed for at least 30 minutes by the medical staff before determining they can be discharged. Subjects are followed-up by study staff via phone call within 24 hours and again at 30 days (±5 days) after completion of their study and their condition noted in the CRF.