A cerebral oximeter is a device that uses light to measure the amount of oxygen within the brain. It is similar to the device that measures the level of oxygen in the tip of the finger, known as a pulse oximeter. The cerebral oximeter consists of a sensor placed on the forehead that both emits and detects the amount of light absorbed. This study will determine how accurate the device is by comparing the displayed value on the monitor with blood samples taken simultaneously from the arterial blood in the wrist and venous blood in the neck. In order to test the device over a suitable range, the level of oxygen within the blood will be reduced in a controlled manner by reduction of the inspired oxygen concentration. This is the equivalent of ascending to an altitude of 16,000 feet. The study will be conducted in healthy volunteers.

This is a calibration and validation study of a near-infrared spectroscopy (NIRS) device designed to measure the cerebral tissue oxygen saturation non-invasively. This is achieved by comparing NIRS-derived cerebral tissue oxygen saturation with a calculated value derived from simultaneous arterial and jugular venous blood samples.

At present the FDA have adopted the standards published in 2005 by the International Organization for Standardization (ISO), entitled ISO 9919. This is a set of technical specifications and guidelines for pulse oximeters, which share certain technical similarities to cerebral oximeters. In particular, Annex EE details the conduct of a controlled desaturation study for the calibration of pulse oximeter equipment. Specifically, the fraction of inspired oxygen delivered to test subjects is varied to achieve a series of targeted steady state saturation periods over a range of arterial oxygen saturation of 70 - 100%.

While cerebral oximeters differ from pulse oximeters in terms of the what is being measured (brain tissue versus arterial blood) the FDA have maintained the requirement to examine data from human volunteer studies in which the arterial oxygen saturation ranges from 70 - 100%. Several FDA-approved cerebral oximeters were validated in a similar manner.

The device controlling the inspired gas concentration is the RespirAct, which permits precise reduction in the arterial oxygen saturation while also maintaining the arterial carbon dioxide level at a precise level.

The study consists of 2 sequences:

• First sequence: reduction in arterial oxygen saturation in approximately 5% increments from 100 to 70%, while maintaining the arterial carbon dioxide level at 40 mmHg, followed by return to room air and then a period of supplemental oxygen.
• Second sequence: reduction in arterial oxygen saturation in approximately 5% increments from 100 to 70%, while maintaining the arterial carbon dioxide level at a different level, followed by return to room air and then a period of supplemental oxygen.

Inclusion Criteria:

1. Body Mass Index (BMI) of 18 to 30, inclusive
2. No anticoagulant or platelet inhibitor use
3. Oxygen saturation (SpO2) ≥ 95% on room air
4. Able to tolerate breathing mask apparatus

Exclusion Criteria:

1. Female with positive pregnancy test
2. Beard or history of or anatomy suggestive of difficult airway
3. Lab values outside normal range for the clinical site
4. History of cigarette smoking or currently a cigarette smoker
5. Current drug or alcohol abuse
6. History of sleep apnea, high blood pressure (HBP), cardiac or pulmonary disease, gastroesophageal reflux, hemoglobinopathy, or coagulation abnormality
7. Known allergy to lidocaine or heparin
8. Abnormal electrocardiogram (ECG)