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Free Content Elevated End-Tidal Pco2 During Long-Duration Spaceflight

BACKGROUND: Elevated ambient Pco2 in the International Space Station (ISS) has been cited as a potential contributor to the vision impairment intracranial pressure syndrome (VIIP), a significant health risk for astronauts during long-duration space missions. The elevation in ambient Pco2 is rather modest and normal respiratory compensation could minimize the impact on arterial Pco2.

METHODS: In nine male astronauts, breaths measured prior to a rebreathing maneuver were examined to assess inspired and end-tidal Pco2 during upright seated preflight and in-flight conditions.

RESULTS: Inspired Pco2 increased from preflight baseline (0.6 ± 0.1 mmHg) to in flight (3.8 ± 0.4 mmHg). End-tidal Pco2 also increased from preflight baseline (36.0 ± 3.2 mmHg) to in flight (42.1 ± 3.7 mmHg). The difference between end-tidal Pco2 comparing in flight to preflight (6.1 ± 1.6 mmHg) was greater than the difference between inspired Pco2 comparing preflight to in flight (3.3 ± 0.5 mmHg).

DISCUSSION: The greater increase in end-tidal vs. inspired Pco2 might reflect alveolar hypoventilation due to differences in ventilatory control with spaceflight. These data suggest that further studies should focus on arterial Pco2 and acid-base balance to determine if CO2 dilates cerebral and retinal vessels and might contribute to the incidence of VIIP in astronauts.

Hughson RL, Yee NJ, Greaves DK. Elevated end-tidal Pco2 during long-duration spaceflight. Aerosp Med Hum Perform. 2016; 87(10):894–897.

Keywords: arterial Pco2; astronaut; respiratory control; vision impairment intracranial pressure syndrome

Document Type: Short Communication

Publication date: October 1, 2016

More about this publication?
  • This journal (formerly Aviation, Space, and Environmental Medicine), representing the members of the Aerospace Medical Association, is published monthly for those interested in aerospace medicine and human performance. It is devoted to serving and supporting all who explore, travel, work, or live in hazardous environments ranging from beneath the sea to the outermost reaches of space. The original scientific articles in this journal provide the latest available information on investigations into such areas as changes in ambient pressure, motion sickness, increased or decreased gravitational forces, thermal stresses, vision, fatigue, circadian rhythms, psychological stress, artificial environments, predictors of success, health maintenance, human factors engineering, clinical care, and others. This journal also publishes notes on scientific news and technical items of interest to the general reader, and provides teaching material and reviews for health care professionals.

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