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Inspired Carbon Dioxide During Hypoxia: Effects on Task Performance and Cerebral Oxygen Saturation

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Author: Dorp, E. van · Los, M. · Dirven, P. · Sarton, E. · Valk, P. · Teppema, L. · Stienstra, R. · Dahan, A.
Type:article
Date:2007
Institution: TNO Defensie en Veiligheid
Source:Aviation, Space, and Environmental Medicine, 7, 78, 666-672
Identifier: 20074
Keywords: Aviation · Complex task performance · Isocapnia · Poikilocapnia · Simulation of piloting · Vigilance · Carbon dioxide · Alertness · Infrared spectroscopy · Multi attribute task battery · Oxygen saturation · Task performance · Vasoconstriction · Vigilance and tracking test · Carbon Dioxide · Cerebrovascular Circulation · Cognition · Brain · Oximetry · Oxygen · Pulmonary Ventilation · Spectroscopy, Near-Infrared · Task Performance and Analysis · Tidal Volume

Abstract

Introduction: 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 ∼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 ∼40 mmHg, PetCO2 clamped to 0.4 mmHg above resting values); and poikilocapnic hypoxia (PH, PetO2 ∼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. Discussion: 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. Copyright © by Aerospace Medical Association.