The effects of 7.5% carbon dioxide inhalation on task performance in healthy volunteers

Studies have shown that anxiety can positively or negatively affect performance with respect to focusing of attention or distractibility, subjective workload and effort (Humphreys and Revelle, 1984). The inhalation of carbon dioxide (CO2) is associated with physiological and psychological effects of anxiety (Bailey et al., 2005) but its effects on performance have rarely been reported. The studies reported here looked at the effects of CO2 inhalation on physiological and subjective measures and performance on two tasks. Eight healthy male participants completed a tracking task with a reaction time component, and 12 healthy participants (six male) completed a complex target identification task. Tasks were performed during 20-min inhalations of 7.5% CO2/21% O2/71.5% N2 mixture or medical air. Continuous heart rate and blood pressure measures were taken, in addition to subjective measures of mood and workload. In comparison with air, CO2 increased heart rate and blood pressure, increased subjective scores of panic, anxiety, fear, and tension, and reduced subjective scores of relaxation and happiness. Attention was focussed when inhaling CO2 during the simple task, and central demand was greater when inhaling CO2 during the complex task. Therefore, inhalation of 7.5% CO2 produces effects on task performance which are consistent with anxiety.