Comparing standard blood oxygen measures to a new device in humans under changing oxygen conditions

This is a single-arm, non-crossover study, in which participants will act as their own control within a single testing phase via the collection of baseline data. This protocol will involve rebreathing a predetermined gas mixture that matches the participants personal end-tidal gasses to induce cyclical reductions or increases in body/brain oxygenation. Studies will take place at the Centre of Translational Physiology, University of Otago Wellington. The study will last roughly 90 minutes, if not otherwise ceased. This study uses a baseline recording as a control and so only one trial is required. A researcher will also be present with the participant for the duration of the study. Participants will also be asked to change into an Equivital vest for non-invasive monitoring of vital signs (ECG, breathing rate, temperature). They will be instrumented with a 23 gauge butterfly needle catheter in either the left or right Median Cubital Vein for intermittent blood draws, which will be used for intermittent blood gas analysis (a total of 9mL over 90 minutes). This will be performed by a medical doctor. Participants will then be instrumented with a plastic nasal gas sampling line, and asked to relax for three minutes to ascertain their average end-tidal respiratory gasses. This instrumentation will be performed by a researcher. This average measurement of their end-tidal gasses will be used to fill the Douglas bag. Full instrumentation with (i) a plastic face mask with gas sampling line; (ii) a finger SpO2 clip; and a (iii) finger blood pressure cuff will then be performed by a researcher. The participant will lie supine on a clinic bed with their head in the cavity of our device. Their head will be lightly restrained to limit movement. All of these readings are continuous. Intermittent blood draws (1mL) at the start and end of each phase will be performed by a medical doctor. A baseline recording under normal atmospheric conditions will take 7 minutes; this will act as our control. The first blood draw will then occur. The first rebreathing phase will then start: a one-way 13 L douglas bag with a mixture matching the end-tidal gasses as determined by the short pre-recording will be placed over the gas mask. In this instance, this is a closed circuit, and the bag will progressively fill with expired air, which the participant will breath in (e.g. continuously falling O2 and rising CO2). This will induce continuous global deoxygenation in the participant. Rebreathing will continue until the participant displays 70% SpO2 (roughly 6-9 minutes). A blood draw will then occur. Participants will then be returned to atmospheric breathing for 7 minutes, repeating the cycle a further 2 times (total 3 rebreathing phases), including blood draws. After a final atmospheric breathing phase, participants will breath from a two-way 13L douglas bag that is continuously supplied with pure O2; i.e. exhaled gasses return to the atmosphere while inhaled gasses (pure O2) come directly from the bag. This hyperoxic phase will last for 7 minutes, and be followed by a washout until the participant’s SpO2 falls to baseline levels. A graph of the approximate timings is seen below. Participants will be informed of the protocol and risks over email and in-person on the day of the study by the researchers. They will be free to ask questions and withdraw without any repercussions, both before and within the trial. Fidelity to the intervention will be monitored using check-sheets which will be completed by the operating researcher.