A Novel Method to Measure Transient Impairments in Cognitive Function During Acute Bouts of Hypoxia

INTRODUCTION: Exposure to low oxygen environments (hypoxia) can impair cognitive function; however, the time-course of the transient changes in cognitive function is unknown. In this study, we assessed cognitive function with a cognitive test before, during, and after exposure to hypoxia. METHODS: Nine participants (28 6 4 yr, 7 women) completed Conner’s Continuous Performance Test (CCPT-II) during three sequential conditions: 1) baseline breathing room air (fraction of inspired oxygen, FIo2 5 0.21); 2) acute hypoxia (FIo2 5 0.118); and 3) recovery after exposure to hypoxia. End-tidal gas concentrations (waveform capnography), heart rate (electrocardiography), frontal lobe tissue oxygenation (near infrared spectroscopy), and mean arterial pressure (finger photoplethysmography) were continuously assessed. RESULTS: Relative to baseline, during the hypoxia trial end-tidal (-30%) and cerebral (-9%) oxygen saturations were reduced. Additionally, the number of commission errors during the CCPT-II was greater during hypoxia trials than baseline trials (2.6 6 0.4 vs. 1.9 6 0.4 errors per block of CCPT-II). However, the reaction time and omission errors did not differ during the hypoxia CCPT-II trials compared to baseline CCPT-II trials. During the recovery CCPT-II trials, physiological indices of tissue hypoxia all returned to baseline values and number of commission errors during the recovery CCPT-II trials was not different from baseline CCPT-II trials. DISCUSSION: Oxygen concentrations were reduced (systemically and within the frontal lobe) and commission errors were increased during hypoxia compared to baseline. These data suggest that frontal lobe hypoxia may contribute to transient impairments in cognitive function during short exposures to hypoxia.