Interactive effects of physical work and carbon monoxide on cognitive task performance

The simple and interactive effects of carbon monoxide (CO) exposure and prior physical work on cognitive performance were evaluated in 11 men and 7 women. Three levels of carboxyhemoglobin (HbCO) (0, 7, 10%) and three workloads (rest, 35%, 60% Vo2max) were crossed resulting in nine repeated measures conditions for each subject. Following bolus administration of CO, subjects exercised or rested for 50 min, then performed five cognitive tasks: Manikin spatial processing, Sternberg memory, Stroop word-color interference, visual search, and dual-axis tracking, with and without a secondary mathematics task. Carboxyhemoglobin levels were assessed after bolus administration and again following completion of the last task. Ambient CO levels were set to maintain the required HbCO levels in each condition. Performance on the second of two sequentially presented Stroop interference tasks (using identical stimuli but with instructions reversed) was impaired with increasing HbCO level, suggesting a reduced ability to adapt to a new response set. An interaction between HbCO level and exercise level was seen for visual search performance: in rest conditions, performance was improved with increasing HbCO level; by contrast, performance was impaired with increasing HbCO levels following 60% work. Elevated HbCO had no effect on spatial processing, short-term memory, simple reaction time, or psychomotor tracking.