Elevated End-Tidal Pco2During Long-Duration Spaceflight.
BACKGROUND
Elevated ambient Pco2in 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 Pco2is 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 Pco2during upright seated preflight and in-flight conditions.


RESULTS
Inspired Pco2increased from preflight baseline (0.6 ± 0.1 mmHg) to in flight (3.8 ± 0.4 mmHg). End-tidal Pco2also increased from preflight baseline (36.0 ± 3.2 mmHg) to in flight (42.1 ± 3.7 mmHg). The difference between end-tidal Pco2comparing in flight to preflight (6.1 ± 1.6 mmHg) was greater than the difference between inspired Pco2comparing preflight to in flight (3.3 ± 0.5 mmHg).


CONCLUSIONS
The greater increase in end-tidal vs. inspired Pco2might reflect alveolar hypoventilation due to differences in ventilatory control with spaceflight. These data suggest that further studies should focus on arterial Pco2and acid-base balance to determine if CO2dilates cerebral and retinal vessels and might contribute to the incidence of VIIP in astronauts. Hughson RL, Yee NJ, Greaves DK. Elevated end-tidal Pco2during long-duration spaceflight. Aerosp Med Hum Perform. 2016; 87(10):894-897.
Schlegel-University of Waterloo Research Institute for Aging, Waterloo, Ontario, Canada.
Richard L
RL
Hughson
Nicholas J
NJ
Yee
Danielle K
DK
Greaves
D000328:Adult; D018480:Astronauts; D001944:Breath Tests; D002245:Carbon Dioxide / Q000032:analysis*; D006801:Humans; D019586:Intracranial Hypertension; D008297:Male; D008875:Middle Aged; D010313:Partial Pressure; D013026:Space Flight; D013577:Syndrome; D014786:Vision Disorders
D002245:Carbon Dioxide