This study is designed to calibrate and determine the accuracy for SpO2, pulse rate and respiratory rate of the newly in-house build Test Device wrist 1 (TDw1, or EVA) at Philips.

SpO2, pulse rate and respiratory rate during hypoxia will be calculated by using data of well-known reference devices, including:

• A reference SpO2 sensor of Nellcor placed at a fingertip, that reflects also continuously the pulse rate Will be used to compare with the test device.
• A reference respiratory rate device that calculates the respiratory rate based on detection of end-tidal CO2 peaks by capnography.
• Oxygen saturation in arterial blood samples (SaO2), determined by a co-oximeter will be used to calculate the accuracy of the test device.

During the study the following devices will be additionally used by the volunteers:

• AppleWatch 7
• TDw2, watch build by philips, using the PPG and software technology developed by Philips
• A smartphone that detects reflected PPG signals from the reflected screen at the handpalm, by the build in frontfacing camera (TDc) of the smartphone

Volunteers will undergo progressive hypoxia (9 min/% O2) from 21 to 10% O2 in an altitude room, resulting in a volunteer's SpO2 of 73%. During this deliberated hypoxia, the volunteers wear the test and reference devices.

This study consists of 4 sub-studies (NI = non-invasive; IN = invasive with an arterial line):

• NI (Fast-Sitting): volunteers are seated in the hypoxia room in which the ambient oxygen concentration decreases at a speed of 9 min/% O2. If the volunteer reached a SpO2 ≤73% for more than 1 minute, he/she leaves the hypoxia room. And will breath air with 21% oxygen. Volunteers wear TDw1 and TDw2 and the reference devices.
• NI(Fast-Lying): identical to NI(Fast-Sitting) but volunteers lay on a mattress. Volunteers wear TDw1 and AppleWatch 7 and the reference devices.
• NI (Slow-Sitting): identical to NI (Fast-Sitting), but after one of the volunteers reaches a SpO2 ≤73% for more than one minute, oxygen in the room increases at a speed of 9 min/% O2 until normal ambient air oxygen concentration of 21%. Volunteers wear TDw1 and AppleWatch 7 and the reference devices.
• IN(Fast-Sitting): identical to NI(Fast-Sitting) but the volunteer's oxygen saturation in blood samples withdrawn via an arterial line is measured in the laboratory.

The NI studies include 18 healthy participants in each sub-study. After the first volunteers have completed the study, small adaptations in the software of the study devices is still possible, e.g. to increase the quality of the PPG-signals. After the three sub-studies are completed, the algorithm for conversion of raw PPG signals to SpO2, pulse rate and respiratory rate will be defined and fixed for the test devices.

During the IN-study, which can only be started after completion of all NI studies, an arterial catheter will be inserted in the radial artery of the 12 participating volunteers, in order to take several blood samples to measure oxygen saturation in the blood (25 samples at well-defined moments during the study per volunteer). Using these results of arterial oxygen saturation, the accuracy of the test devices can be calculated.

Inclusion Criteria:

• Healthy subjects (ASA 1 and ASA 2) between 18 and 65 years of age upon signing the informed consent. (ASA: American Society of Anesthesiologist's health score). In each group, at least 30% of one gender need to be present, and at least 15% of participants have a Fitzpatrick's skin color scale of 5 or 6.

Exclusion Criteria:

• Heavy smokers or individuals exposed to high levels of carbon monoxide that result in elevated carboxyhemoglobin levels.
• Individuals subject to conditions that result in elevated levels of methemoglobin.
• Individuals with low SpO2 or SaO2 (<95%) at FiO2 = 0,21
• Moderate to severe claustrophobia for small rooms
• Severe obesity (BMI > 35 kg/m2)
• Hemoglobinopathies
• Arteriopathies, including Raynaud disease
• ASA 3 to 5 subjects
• Tattoo's, skin lesions,use of skin lotions or use of nail polish/fake nails at the region of interest for TDw and TDc
• Pregnancy