Inspired carbon dioxide during hypoxia: effects on task performance and cerebral oxygen saturation.
BACKGROUND
Exposure to a hypoxic environment has a deleterious effect on physiological and mental functions. We studied the effect of added inspired CO2 during artificially induced hypoxic normobaric hypoxia (oxygen saturation approximately 80%) on complex task performance.


METHODS
In random order, 22 healthy volunteers were exposed to 3 gas mixtures for 50 min each: sham hypoxia (SH, PetO2 103 mmHg without inspired CO2); isocapnic hypoxia (IH, PetO2 approximately 40 mmHg, PetcO2 clamped to 0.4 mmHg above resting values); and poikilocapnic hypoxia (PH, PetO2 approximately 40 mmHg; no inspired CO2). Brain oxygenation was measured using near infrared spectroscopy. During minutes 25-45 of hypoxia, subjects performed vigilance and task performance tests used in aviation research: the Vigilance and Tracking test and the Multi-Attribute Task battery (MAT-bat). The tests varied in difficulty with the tracking tests considered most difficult.


RESULTS
PetCO2 levels differed significantly among groups: IH 42.8 +/- 0.7, SH 39.0 +/- 0.7, and PH 36.8 +/- 0.7 mmHg. Brain oxygenation levels were significantly higher during IH than PH (62.2 +/- 1.0 vs. 59.1 +/- 1.3%). The results of the performance tests indicated a negative effect of PH vs. SH on most function tests. For the Tracking test of the MAT-bat, performance was worst during PH, but returned to baseline during IH.


CONCLUSIONS
We demonstrate the ability of added inspired CO2 to improve performance during hypoxia by preventing PH-associated hypocapnia-induced vasoconstriction of brain blood vessels. Our results are relevant to aerospace medicine and other circumstances in which complex tasks are performed in a hypoxic environment such as mountain climbing and working in confined spaces.
Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands.
Eveline
E
Van Dorp
Michel
M
Los
Perjan
P
Dirven
Elise
E
Sarton
Pierre
P
Valk
Luc
L
Teppema
Rudolf
R
Stienstra
Albert
A
Dahan
D000293:Adolescent; D000328:Adult; D000337:Aerospace Medicine; D001921:Brain / Q000378:metabolism*; D002245:Carbon Dioxide / Q000008:administration & dosage*; D002560:Cerebrovascular Circulation / Q000502:physiology; D003071:Cognition / Q000502:physiology*; D005260:Female; D006801:Humans; D002534:Hypoxia, Brain / Q000378:metabolism*; D008297:Male; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism*; D012123:Pulmonary Ventilation / Q000502:physiology; D019265:Spectroscopy, Near-Infrared; D013647:Task Performance and Analysis; D013990:Tidal Volume / Q000502:physiology
D002245:Carbon Dioxide; D010100:Oxygen