Method: 15 healthy participants performed, in one session, a series of five minutes modified PASAT with a digit presentation pace set at either 3.6-s, 2.4-s, 1.6-s, or 1.2-s between digits in each of the four five minutes tasks, to evoke acute stress. The order of the paces and control (2.4-s pace, digits repeated without calculation) was randomized. The percentage correct PASAT scores were calculated for each pace. Heart rate variability and hemodynamic measures were recorded non-invasively (Task Force® Monitor). Participants scored on a 0-10 numeric rating scale (NRS) the extent of difficulty, annoyance, stress, and motivation at each pace. Analyses of variance (ANOVA) and Students t-test were used to test the data.
Result: Percentage correct answers decreased and subject-based scores increased with increasing PASAT pace (P<0.001) except motivation levels which did not differ between paces (P>0.05). Heart rate increased during all PASAT paces compared with baseline (P<0.05). Root mean square successive difference and high frequency power decreased during 2.4-s, 1.6-s, and 1.2-s compared with baseline (P<0.05), whereas low frequency power (except at 1.6-s) and total power decreased during all paces (P<0.05). Systolic and diastolic blood pressure and cardiac output increased during all PASAT paces (P<0.05).
Conclusion: Significant differences between the different PASAT paces were revealed from both the subjective evaluations of conducting PASAT and the objective responses of the autonomic nervous system. As a standardized human experimental acute mental stress task, modified paces of PASAT affect cardiovascular function at different levels. Therefore, it may be of benefit to choose a suitable pace according to a particular purpose.