END-TIDAL PCO2 AS AN INDEX OF PSYCHOPHYSIOLOGICAL ACTIVITY DURING VDTDATA-ENTRY WORK AND RELAXATION

The present study was designed to assess the utility of end-tidal PCO2 (peak concentration of carbon dioxide in a single breath of exhaled a ir) as an index of psychophysiological activity during performance of a computer-based task and during relaxation. Eleven data-entry operato rs were monitored continuously for three consecutive, 6 hour work days under the following conditions: (a) during a self-relaxation baseline period; (b) during an abbreviated progressive muscle relaxation perio d; and (c) during a period of computer-based data-entry work. End-tida l PCO2, respiration frequency, and cardiac inter-beat interval (a meas ure of heart rate and its variability) were monitored continuously dur ing the three conditions of the study. Self-ratings of relaxation and tension were also monitored at periodic intervals. Consistent with a d ecrease in psychophysiological arousal, end-tidal PCO2 and self-rating s of relaxation were significantly higher during progressive muscle re laxation than during baseline relaxation. Consistent with an increase in psychophysiological arousal, end-tidal PCO2, cardiac inter-beat int erval, and relaxation ratings during data-entry work were significantl y lower than during either baseline relaxation or progressive muscle r elaxation, while respiration frequency and tension ratings were higher . The findings indicate that end-tidal PCO2 discriminates among differ ent psychophysiological states, and that end-tidal PCO2 may be useful in indexing the stress-hearth effects of human-computer interactions.