Patterns of sympathetic responses induced by different stress tasks

Abstract

Stress tasks are used to induce sympathetic nervous system (SNS) arousal. However, the efficacy and the patterns of SNS activation have not been systematically compared between different tasks. Therefore, we analyzed SNS activation during the following stress tasks: Presentation of negative, positive, and - as a control - neutral affective pictures, Color-Word interference test (CWT), mental arithmetic under time limit, singing a song aloud, and giving a spontaneous talk. We examined 11 healthy subjects and recorded the following SNS parameters: Activation of emotional sweating by quantitative sudometry, skin vasoconstriction by laser-Doppler flowmetry, heart rate by ECG, blood pressure by determination of pulse wave transit time (PWTT), and electromyographic (EMG) activity of the trapezius muscle. Moreover, subjective stress ratings were acquired for each task using a visual analog scale. All tasks were felt significantly stressful when compared to viewing neutral pictures. However, SNS activation was not reliable: Affective pictures did not induce a significant SNS response; singing, giving a talk and mental arithmetic selectively increased heart rate and emotional sweating. Only the CWT globally activated the SNS. Regarding all tasks, induction of emotional sweating, increase of heart rate and blood pressure significantly correlated with subjective stress ratings, in contrast to EMG and skin vasoconstriction.Our results show that the activation of the SNS widely varies depending on the stress task. Different stress tasks differently activate the SNS, which is an important finding when considering sympathetic reactions - in clinical situations and in research.

Fig. (1)

Mean +/- SEM of subjective stress ratings are presented. Compared to neutral pictures all tasks induced more stress.neutr: neutral affective pictures; pos: positive affective pictures;sing: singing task; neg: negative affective pictures; CWT: Color-Word interference test; talk: hold a talk; calc: mental arithmetic;*: p < 0.05 vs neutr; **: p < 0.01 vs neutr.

Fig. (2) All data are presented as mean +/- SEM.

1. Emotional sweating is expressed as area under the sweating curve (AUC). Singing (p < 0.05), CWT (p <0.01), giving a talk (p <0.05) and mental arithmetic (p < 0.05) induced significant emotional sweating as compared to baseline. Significant differences to neutral affective pictures are indicated by stars.

2. Skin blood flow vasoconstriction (differences of flux values, FV). Compared to baseline, presentation of positive (p < 0.05) and negative pictures (p < 0.05), singing (p < 0.05), CWT (p < 0.05) and mental arithmetic (p < 0.05) led to significant vasoconstriction. Significant differences to neutral affective pictures are indicated by stars.

3. Heart rate increase as compared to baseline (bpm). Singing (p < 0.01), CWT (p < 0.05), giving a talk (p < 0.05) and mental arithmetic (p < 0.01) induced significant increase of heart rate as compared to baseline. Significant differences to neutral affective pictures are indicated by stars.

4. Reduction of PWTT (ms). Singing (p < 0.01), CWT (p < 0.01), giving a talk (p < 0.01) and mental arithmetic (p < 0.05) caused significant reduction of PWTT as compared to baseline. Significant differences to neutral affective pictures are indicated by stars.

5. Activity in trapezius muscle EMG (µV). Singing (p <0.05), CWT (p < 0.05) and giving a talk (p < 0.05) significantly increased trapezius muscle EMG activity as compared to baseline. Significant differences to neutral affective pictures are indicated by stars.

   neutr: neutral affective pictures; pos: positive affective pictures; sing: singing; neg: negative affective pictures; CWT: Color-Word interference test; talk: giving a talk; calc: mental arithmetic; *: p < 0.05; **: p < 0.01.

Fig. (3)

Correlation analyses between mean subjective stress ratings during different tasks and the corresponding mean of sympathetic responses. Stress ratings were significantly correlated to emotional sweating (p < 0.01), increase of heart rate (p < 0.01) and reduction of PWTT (p < 0.05, Spearman rank order correlation).