Hemoglobin Oxygen Saturation with Mild Hypoxia and Microgravity.

Area of Science:

• Aerospace Medicine
• Human Physiology
• Space Exploration

Background:

• Microgravity (μG) exposure and early recovery can increase the alveolar-arterial oxygen partial pressure gradient.
• This physiological change may impact oxygen saturation under hypoxic conditions.

Purpose of the Study:

• To investigate the effect of microgravity and recovery on astronaut hemoglobin oxygen saturation (SpO2) during hypoxic challenges.
• To assess if physiological changes in space affect the body's ability to maintain oxygen saturation.

Main Methods:

• Four astronauts on two Space Shuttle missions (STS-69 and STS-72) underwent sequential hypoxic challenges.
• Inspired oxygen partial pressure (PiO2) was reduced by breathing progressively lower oxygen-nitrogen mixtures.
• Hemoglobin oxygen saturation (SpO2) was measured using finger pulse oximetry, both in-flight and on Earth (R+0 and R+2 days post-flight).

Main Results:

• Astronaut SpO2 levels remained stable at approximately 97% during a PiO2 of 127 mmHg, both in-flight and during terrestrial testing.
• No significant differences in SpO2 were observed between in-flight measurements and post-flight assessments (R+0, R+2) under hypoxic conditions.

Conclusions:

• Physiological adaptations to microgravity and the recovery process did not impair astronaut SpO2 response to mild hypoxia.
• Astronauts maintain stable hemoglobin oxygen saturation despite microgravity exposure and early recovery phases.