Positive emotion inducement modulates cardiovascular responses caused by mental work
© The Author(s). 2016
Received: 11 July 2016
Accepted: 31 October 2016
Published: 16 November 2016
Positive emotion is considered as an important factor related to health-relevant biological processes, including cardiovascular responses. To explore the possibility of using positive emotion as a tool to manage cardiovascular response of white-collar workers, we examined the influence on cardiovascular response of positive emotion inducement before a mental work.
Seventeen healthy males participated and performed a 10-min, PC-based Stroop color word task as their mental work. Before the task, 60 pleasant pictures chosen from the International Affective Picture System were presented in a random order under a positive emotion inducement condition while a gray screen was presented under a control condition. A 30-min relaxation period after completing the task was provided to examine the aftereffects of positive emotion inducement. Throughout these periods, systolic and diastolic blood pressure, mean arterial blood pressure, heart rate, stroke volume, cardiac output, and total peripheral resistance were measured continuously.
Blood pressure and total peripheral resistance were lower during the picture presentation period under the positive emotion inducement period compared to the control condition. All indices did not differ during the color word task period. During the relaxation period after the task, however, blood pressure and total peripheral resistance were lower under the positive emotion inducement condition compared to the control condition.
Positive emotion inducement before a mental work beneficially modulates cardiovascular responses, suggesting that positive emotion inducement may be a useful tool to manage the cardiovascular response to mental work.
KeywordsPositive emotion Mental work Blood pressure Total peripheral resistance
White-collar workers at risk for cardiovascular disorders (e.g., hypertension and ischemic heart disease) can be identified from their chronic exaggerated cardiovascular responses to mental work and delayed recovery after the work [1–4]. Some previous studies have reported that white-collar workers who have been exposed to cumulative work-related mental stress had a significant increase in systolic blood pressure (SBP), which is considered to be a long-term predictor of incident hypertension [2, 3]. Inhibition of exaggerated responses to mental work and promotion recovery of these responses are significantly important to manage work-related cardiovascular responses.
Cardiovascular responses include not only blood pressure but also the underlying hemodynamic aspects in increasing blood pressure. The hemodynamics are that mean arterial pressure (MAP) is elevated by cardiac output (CO) and/or total peripheral resistance (TPR) (MAP = CO × TPR), and CO is changed by heart rate (HR) and/or stroke volume (SV) (CO = HR × SV). The cardiac and vascular responses in increasing blood pressure are also considered to be risk factors of cardiovascular disorders, and exaggerated response in TPR was associated with high risk of hypertension [4–6]. Therefore, not only the magnitude of increasing blood pressure but also the underlying hemodynamics in increasing blood pressure should also be considered when examining prevention countermeasures of cardiovascular disorders.
As important factors for increasing hemodynamic responses (especially increases in MAP and TPR), negative emotions (such as anger, anxiety, and depression) are well documented [7, 8]. In recent years, some researchers began to pay attention to positive emotion as an important factor related to health-relevant biological processes, such as reduced hypothalamic-pituitary-adrenal (HPA) reactivity and promotion of a faster recovery of cardiovascular responses [9–14]. For example, Fredrickson and colleagues reported that low-arousal positive emotion (contentment and amusement) promoted heart rate return to baseline after a negative emotion-elicited task, and this effect was called the “undoing effect” [12, 13]. However, it is still unclear how positive emotion influences hemodynamic responses to mental work.
The previous studies about positive emotion mainly focused on the functions of positive emotions without a detailed classification of them, because positive emotions are not associated with specific actions and it is difficult to clearly classify a certain positive emotion from others [11, 12, 15–17]. Previous studies have reported some methods to induce positive emotions, such as presenting pleasant pictures or videos, listening to music and recalling happy experiences [12, 13, 15, 18]. In the present study, we presented low-arousal pleasant pictures to induce positive emotion before a mental work in order to investigate the influences of positive emotion inducement on cardiovascular responses. We examined cardiovascular responses using hemodynamic indices and hypothesized that positive emotion inducement before a mental work would beneficially modulate hemodynamic responses to a mental work.
Seventeen healthy males participated in this study. The ages, weights, heights, and BMIs of the participants (mean ± standard deviation (SD)) were 23.1 ± 1.7 years, 62.5 ± 10.0 kg, 172.4 ± 5.0 cm, and 21.0 ± 3.1, respectively. The participants were requested to refrain from exercise and alcohol intake on the night prior to the experiment and were prohibited from drinking caffeinated beverages or smoking during the 2-h period immediately preceding the experiment. After receiving a detailed description of the study, all participants gave written informed consent before taking part in this study. This study was approved by the Research Ethics Committee of the National Institute of Occupational Safety and Health in Japan (No. H24023).
The participants performed a 10-min, PC-based Stroop color word (CW) task as their mental work. The CW task involved a target word, the name of a color (e.g., green), which was printed in a different color from the meaning of the word (e.g., yellow). Around the target word (green), six buttons marked with the name of colors were presented (green, yellow, black, red, blue, and purple). The participants were instructed to press the button corresponding to the name of the target word’s color within 3 s (in the case of the example, the correct reaction would be to press the button marked “yellow”). If the participants pressed a wrong button or took over 3 s to press a button, the trial was recorded as an error, and then a new trial started automatically. The total number of trials was also recorded to examine task performance.
Positive emotion inducement
The IAPS number of each picture and their valence and arousal scores
Present study (male)
Present study (male)
Protocol and parameters
The mean values of each period were calculated, while the final relaxation period was divided into three 10-min periods (R1, R2, and R3) in order to investigate the aftereffect as a function of the same time window. To avoid the influence of differences in the baselines, a change rate was calculated for each cardiovascular index by dividing a value in a period by its baseline (B). Two-way repeated measures ANOVAs [conditions × measurement periods] were conducted for all cardiovascular indices and emotion states. If Mauchly’s sphericity test was significant, Greenhouse-Geisser correction was used to estimate epsilon in order to correct the degree of freedom of the F value. Measures of effect size (partial η 2 ) and power were also reported. Multiple comparisons with the Bonferroni method were conducted to further examine the significant results. Paired t tests were conducted to compare task performances between conditions. The level of significance was set at 0.05 and significant tendency was set at 0.1. Statistical analysis was carried out using IBM SPSS Statistics 19 (IBM Corp.).
The total number of trials (mean ± SD) under the positive emotion inducement condition and under the control condition was 494.83 ± 77.31 and 492.61 ± 87.20, respectively. Error rates (error trials/total trials, by percent) (mean ± SD) under the positive emotion inducement condition and under the control condition were 2.01 ± 3.92, and 2.90 ± 4.76, respectively. There were no significant differences between conditions.
Evaluation of emotion states
For MAP, the main effects of the measurement period (F(2.23, 35.75) = 27.67, p < 0.001, η p 2 = 0.63, power = 1.00) and condition (F(1, 16) = 6.27, p < 0.05, η p 2 = 0.28, power = 0.65) were significant. Interaction between factors was also significant (F(5, 80) = 4.04, p < 0.01, η p 2 = 0.20, power = 0.94). SBP and DBP showed the same tendency as MAP and interaction between factors were also significant (SBP: F(5, 80) = 4.33, p < 0.01, η p 2 = 0.21, power = 0.95; DBP: F(5, 80) = 3.55, p < 0.01, η p 2 = 0.18, power = 0.90).
The cardiac responses did not significantly differ between conditions, and the interaction between factors was not significant (Fig. 4). The main effect of the measurement period was significant for HR (F(2.07, 33.19) = 5.31, p < 0.01, η p 2 = 0.25, power = 0.81), SV (F(2.46, 39.28) = 3.56, p < 0.05, η p 2 = 0.18, power = 0.69), and CO (F(2.79, 44.58) = 4.82, p < 0.01, η p 2 = 0.23, power = 0.86). Multiple comparisons showed that compared to the baseline, HR increased during the task period (T > B, p < 0.10) but decreased during the relaxation periods (R2 and R3 < B, p < 0.05); SV decreased during task period and the first relaxation period (T and R1 < B, p < 0.05) and CO decreased during relaxation periods (R1, R2, and R3 < B, p < 0.05).
Previous studies suggested that positive emotion inducement promoted heart rate returning to baseline after a negative emotion-elicited task [12, 13]. Based on these, we hypothesized that positive emotion inducement before a mental work would beneficially modulate hemodynamic responses. The results of the present study showed that MAP were lower during the picture presentation period and suggested that the blood pressure was modulated by positive emotion inducement before the mental task. During the task period, however, MAP increased significantly for both conditions and did not differ between conditions. This result was considered that the influences of positive emotion inducement may be masked by the task itself because the task performance was not different between conditions. In contrast, MAP during the relaxation period after the task was significantly lower under the positive emotion inducement condition compared to the control condition. Under the control condition, MAP did not change during the relaxation periods after the task, and this tendency agreed with our previous studies, which suggested that blood pressure did not show a decreased tendency immediately after mental tasks [23–25]. Under the positive emotion inducement condition, however, MAP decreased immediately after the task and TPR showed a similar response tendency, although they did not return to the baseline during the last measurement periods. These results suggested that positive emotion inducement before a mental task beneficially modulated the hemodynamic responses during the relaxation period after the task, resulting in a quicker recovery in hemodynamic responses compared to control condition without affecting task performance.
On the other hand, cardiac responses (HR, SV, and CO) did not differ between conditions. A previous study has reported that positive emotion inducement after a negative emotion-elicited task promoted heart rate return to baseline . The present study presented pleasant low-arousal pictures to induce positive emotion before a mental task and we think that the different timing and characteristic of task may influence the effects on cardiac responses. Previous studies have reported that positive emotion inducement may influence automatic nervous and endocrine system responses [9, 11, 18, 26–28], but the physiological mechanism of influences of positive emotion inducement on hemodynamic response is not clear yet, and we think further examination is necessary in the future.
To induce positive emotion, we presented 60 pleasant with low-arousal pictures chosen from IAPS during a 6-min period before a mental task in the present study. The pictures were also evaluated as pleasant with low-arousal by the participants of the present study. Fredrickson et al. used films of waves breaking on a beach and a small dog playing with a flower, and they defined the elicited emotions as contentment and amusement . We think that the pictures used in the present study also included contentment, amusement, and so on. In contrast, the emotion state evaluated by the Two-dimensional Mood Scale was not significantly different for pleasure between conditions. The Two-dimensional Mood Scale did not evaluate positive emotion directly but calculated pleasure and arousal scores from eight adjectives about vitality and stability . The indirect evaluation structure may influence the sensitivity of detecting changes of positive emotion. On the other hand, the influence of positive emotion inducement on cardiovascular responses may not always depend on the subjective sensation of participants.
As an initial-stage study investigating the effects of positive emotion inducement on cardiovascular responses, the results of the present study demonstrated that a short-term positive emotion inducement (6 min) before a mental task beneficially modulated hemodynamic responses without affecting task performance. These results suggested the possibility of inducing positive emotion (i.e., looking at pleasant and relaxing pictures) during short breaks or rests during working hours may beneficially modulate cardiovascular responses. On the other hand, because the experiment design was different so far from the real work situation, there are also many works to do before using positive emotion inducement as a tool to manage cardiovascular response of white-color workers, including examination longer task periods.
There are also some limitations in the present study. First, because we used pleasure pictures with low-arousal to elicit positive emotion, the results of the present study may be limited and did not apply for positive emotions with high arousal. Second, only one task was used in the present study. Our previous study reported that different types of tasks have different hemodynamic response characteristics: a negative emotion-elicited task caused a higher vascular response, but the intellectual mental task caused both cardiac and vascular responses . The effects of positive emotion inducement may vary among different types of tasks, and more tasks should be examined in the future. Finally, whether other positive inducement methods also have similar effects and whether there is interaction between the inducement methods and tasks, are unknown. All of these factors should be examined further in the future.
The present study demonstrated that positive emotion inducement before mental work beneficially modulates hemodynamic responses without affecting task performance, suggesting the possibility of using positive emotion inducement as a tool to manage cardiovascular responses to mental work.
Analysis of variance
Stroop color word task
Diastolic blood pressure
Positive emotion inducement condition
The International Affective Picture System
Mean arterial pressure
A 6-min picture or gray screen presentation
A 30-min relaxation period after the task
The first 10-min relaxation period
The second 10-min relaxation period
The third 10-min relaxation period
The Self-Assessment Manikin
Systolic blood pressure
A 10-min color word task period
Two-dimensional Mood Scale
Total peripheral resistance
This study was partly supported by a Grant-in-Aid for Young Scientists (B) (No. 24700746) from the Japan Society for the Promotion of Science.
This study was partly supported by a Grant-in-Aid for Young Scientists (B) (No. 24700746) from the Japan Society for the Promotion of Science. This funding partly supported the measuring equipment and necessary materials.
Availability of data and materials
The individual raw data will not be shared publicly because of the ethics policy.
XL collected the funds, designed the experiments, carried out the measurement, analyzed data and drafted the manuscript. KIs contributed to the design of protocol, participated in the data analysis and revised the manuscript. MS and KIw contributed to the experiment, participated in the data analysis, revised the manuscript. All authors read and approved the final approval.
The authors declare that they have no competing interests.
Ethics approval and consent to participate
This study was approved by the Research Ethics Committee of the National Institute of Occupational Safety and Health in Japan (No. H24023). After receiving a detailed description of the study, all participants gave written informed consent for participation and publication before taking part in this study.
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