A Paced Auditory Serial Addition Task evokes stress and differential effects on masseter-muscle activity and haemodynamics.

This study aimed to determine autonomic and jaw-muscle activities, and haemodynamic responses, to acute experimental mental stress in humans. Eleven healthy men (25.2 ± 3.0 years of age) and five healthy women (23.0 ± 3.7 years of age) performed a standardized mental stress task, the Paced Auditory Serial Addition Task (PASAT). Autonomic function, such as heart rate variability (HRV), and haemodynamic changes were recorded simultaneously. The success rate of the PASAT decreased with increased pace and duration. Low-frequency (5.8 ± 1.1 ms(2)) and high-frequency (5.3 ± 0.6 ms(2)) components of HRV decreased during the PASAT (to 5.0 ± 0.9 ms(2) and 4.6 ± 1.1 ms(2), respectively) as an indication of acute stress. Oxygenated haemoglobin in the masseter muscle (14.6 ± 2.2 10(4) units mm(-3)) remained at an elevated level during the PASAT (15.5 ± 2.5 10(4) units mm(-3)), whereas deoxygenated haemoglobin (7.8 ± 2.3 10(4) units mm(-3)) showed a consistent decrease (to 6.8 ± 2.1 10(4) units mm(-3)). Total haemoglobin and jaw-muscle electromyographic (EMG) activity did not change during the PASAT. Thus, PASAT-induced mental stress changed the parasympathetic/sympathetic balance of the heart and had an acute influence on jaw-muscle haemodynamics, but not on jaw-muscle EMG activity. This non-invasive experimental set-up can be applied to study the effects of repeated or longer-lasting mental stress in order to further the understanding of pathophysiological mechanisms in craniofacial pain conditions.