Hemoglobin Oxygen Saturation with Mild Hypoxia and Microgravity.

INTRODUCTION: Microgravity (G) exposure and even early recovery from G in combination with mild hypoxia may increase the alveolar-arterial oxygen (02) partial pressure gradient. METHODS: Four male astronauts on STS-69 (1995) and four on STS-72 (1996) were exposed on Earth to an acute sequential hypoxic challenge by breathing for 4 min 18.0%, 14.9%, 13.5%, 12.9%, and 12.2% oxygen-balance nitrogen.The 18.0% 02 mixture at sea level resulted in an inspired 02 partial pressure (P(l)o(2)) of 127 mmHg. The equivalent PlO2 was also achieved by breathing 26.5% O-2 at 527 mmHg that occurred for several days in G on the Space Shuttle. A Novametrix CO2SMO Model 7100 recorded hemoglobin (Hb) oxygen saturation through finger pulse oximetry (S(p)o(2),%).There were 12 in-flight measurements collected. Measurements were also taken the day of (R+0) and 2 d after (R+2) return to Earth. Linear mixed effects models assessed changes in Spo2 during and after exposure to G. RESULTS: Astronaut Spo2 levels at baseline, R+0, and R+2 were not significantly different from in flight, about 97% given a P1o2 of 127 mmHg. There was also no difference in astronaut Spo2 levels between baseline and R+0 or R+2 over the hypoxic challenge. CONCLUSIONS: The multitude of physiological changes associated with G and during recovery from G did not affect astronaut Spo2 under hypoxic challenge.