Non-communicable diseases such as cardiovascular disease account for two-thirds of the mortality rates globally (Mayor, 2016). Hypertension, as well as elevated blood pressure (BP) within the normal range, are major risk factors for the development of cardiovascular disorders (Pei et al., 2011). Due to these dangerous and potentially fatal consequences, there is an urgent need to explore the mechanisms underlying elevated blood pressure, so that suitable interventions might be developed. Amongst other factors, the role of psychological factors in the pathogenesis of hypertension has received ample support from clinical, epidemiological and laboratory research (Esler & Parati, 2004). However, most of the studies linking emotion and emotional processes with elevated blood pressure/hypertension have focused disproportionately on the link with negative emotional states (e.g., anxiety, depression, stress, etc.) (e.g., Lerman et al., 1989; Markovitz et al., 1993; Lal et al., 1982). Researchers have found that elevated blood pressure is also associated with a reduced responsiveness to (and processing of) emotions, termed ‘cardiovascular emotional dampening’ (e.g., McCubbin et al., 2011; McCubbin et al., 2014). However, these studies have focussed only on exploring how BP variations are associated with reduced recognition of emotions, including identification of emotional content in auditory and/or visual emotional stimuli (Jain et al., 2017; McCubbin et al., 2011, 2014; Pury et al., 2004; Shukla et al., 2018, 2019). None of the studies, to our knowledge, have explored how BP elevations vary with behavioural reactivity or motivational tendencies. The present study addresses this gap.

Cardiovascular emotional dampening or blood pressure-associated emotional dampening was first recognised by Pury and colleagues (2004). In their study, participants’ systolic blood pressure (SBP) was significantly negatively correlated with their valence ratings of both positive and negative emotion-inducing scenes from the International Affective Picture System (IAPS). A second study then reported that resting diastolic blood pressure (DBP) also correlated inversely with emotion recognition accuracy (in faces and written statements) (McCubbin et al., 2014), thus providing evidence for cardiovascular emotional dampening. More recent studies have built on these initial evidences by showing reduced emotion responsivity in experimental tasks using more implicit instructions to probe emotion processing. One study reported that isolated increases in either systolic or diastolic blood pressure in normotensive individuals were associated with poorer labelling and matching of different facial emotions (Shukla et al., 2019) – a finding that also generalized to clinically-hypertensive and prehypertensive individuals (Shukla et al., 2018). It is noteworthy that even normotensives at-risk for developing high BP due to a parental history of hypertension demonstrate reduced responsiveness to both positive and negative emotions in comparison to individuals with normotensive parents (Wilkinson & France, 2009).

While the previous studies exploring the phenomenon of emotional dampening have reported a reduced recognition of emotions with elevation in blood pressure in the normotensive, prehypertesnive, and the hypertensive ranges, very few studies explored BP-linked dampening effects on emotional behaviour or motivational tendencies. One recent study (McCubbin et al., 2020) found preliminary evidence that elevated resting BP is predictive of risky behaviour among women in a simulated driving environment, suggesting that emotional dampening is associated with reduced threat appraisal. However, the presence of the reward (positive stimulus) and threat (negative stimulus) in this study was more implicit within the simulated driving game. Thus, it remains to be seen if a reduced recognition to emotions (both positive and negative), as manifested in BP-associated emotional dampening, transforms into actual action tendencies towards explicit positive and negative stimuli. According to the motivational reflex model (Bradley et al., 1990, 2001; Lang et al., 1990), a stimulus, such as a facial expression, is immediately classified as either positive or negative, which then instantly triggers a motivational system associated with either approach or avoidance, respectively. As BP elevations are already known to link to poorer emotion recognition, it is possible that these may cascade to influence motivational deficits (or deficits in approach and avoidance tendencies to affective stimuli).

One way to study the action tendencies towards positive and negative affective stimuli is the use of the Approach-Avoidance Task (AAT). The AAT is based on extensive findings that positive stimuli activate action tendencies of approach while negative ones result in avoidance tendencies (e.g., Chen & Bargh, 1999; Czeszumski et al., 2021; Ernst et al., 2013; Neumann et al., 2003). Operationally, these action tendencies of approach and avoidance are assessed by the AAT in terms of reaction times of arm movements pulling or pushing positive and negative stimuli towards or away from the individual (Marsh et al., 2005). While unpleasant/negative stimuli (such as an angry facial expression) evoke avoidance, pleasant/positive stimuli (like a happy facial expression) triggers approach (Marsh et al., 2005), tapping into the inherent human urge to avoid things we detest and approach things we like (van Peer et al., 2007; Davidson, 1998; Carver & White, 1994). In fact, it is argued that perceiving facial expressions is a two-step process, the first being rapid approach-avoidance response, and second, later categorisation of the stimulus into a particular emotion (such as happiness, anger) given contextual information (Ikeda, 2022). Thus, approach and avoidance are considered the fundamental action intentions associated with emotion perception (Davidson & Hugdahl, 1996). How closely linked are emotional valence and motivational action tendencies of approach and avoidance is also evidenced by the fact that left-hemispheric lateralisation is noted for positive emotions and approach tendencies while right-hemispheric lateralisation has been reported for both negative emotions and avoidance behavioural intentions (Harmon-Jones, 2003).

Altered approach-avoidance tendencies have been noted in depression, social anxiety and even, psychopathy (Heuer et al., 2007; Radke et al., 2016; Roelofs et al., 2010; Seidel et al., 2010; Von Borries et al., 2010). Specifically, individuals suffering from depression demonstrate no approach or avoidance tendencies (Radke et al., 2016) and lesser behavioural approach overall (Seidel et al., 2010) in explicit rating tasks. However, they demonstrate stronger or no avoidance of angry faces when processing the emotional stimuli implicitly (Derntl et al., 2011; Seidel et al., 2010). Individuals with depression also demonstrate facial emotion recognition biases in that they have heightened sensitivity to negative (Leppänen, 2006) and reduced sensitivity to positive emotional cues (Bourke et al., 2010). Socially anxious individuals show behavioural avoidance tendencies towards happy faces, even though they evaluate such faces as being pleasant (Heuer et al., 2007). A recent study indicates that among individuals with high trait anxiety, an increase in state anxiety is linked to an increased bias towards perceiving anger (Dyer et al., 2022). Since, anxiety and depression are both strongly associated with elevations in blood pressure (Cai et al., 2022; Eloseily et al., 2022), similar behavioural tendencies and perceptual biases towards (or away from) emotions may likely be observed among people with elevated BP. Similar to these affective difficulties, patients of schizophrenia show weaker approach-avoidance action tendencies, and compared to controls, demonstrate less approach to happy faces as well as less avoidance of angry faces (Radke et al., 2015).

Based on previous studies of altered approach-avoidance motivation among affective disorders, the present study aimed to explore how the action tendencies of approach and avoidance are affected in cardiovascular emotion dampening, a BP-associated affective difficulty. We used the approach-avoidance task (AAT) developed by Rinck and Becker (2007) to assess participants’ behavioural responses to affective facial stimuli. Typically, pulling positive stimuli towards oneself and negative stimuli away from oneself (‘congruent’ trials) involve quicker response times than pulling negatively-valenced stimuli towards oneself and pushing positively-valenced away (‘incongruent’ trials). On the basis of studies of cardiovascular emotional dampening, which indicate dampened emotion recognition among individuals with elevated BP (Pury et al., 2004; McCubbin et al., 2011, 2014) and findings of less pronounced approach and avoidance tendencies among individuals with depression and schizophrenia, it was hypothesised that in individuals with elevated BP, an aberrant approach-avoidance would be noted towards faces depicting anger and happiness.

Method

Participants

The study was approved by an Ethics Committee based at King’s College London (Ref: HR-16/17-3826). The study was conducted before the COVID-19 pandemic. The same group of participants (N = 71) as reported in the study by Shukla et al. (2020) were called for the approach-avoidance task. Participants who were able to give informed consent and were in the age range of 18–60 years were included. Participants were excluded from the study if they reported the presence of any present or past history of mental illness, drinking, smoking, and/or any medical illness such as thyroid, renal, or cardiovascular problems, including hypertension or hypotension. Participants reporting impaired eyesight or hearing, routine prescriptions, pregnancy, and breastfeeding were also excluded from the study. This was done using a self-reported screening form developed for the research. Of 71 research volunteers showing an interest in participation, nine did not fulfill the criteria for recruitment, leaving a total of 62 individuals who participated in the study. Three participants’ data were omitted for a variety of reasons (e.g., leaving more than 50% of the study incomplete). A further three participants were considered outliers (based on the RT) during the data analysis and were excluded. Thus, the results are reported on a sample of 56 participants.

The SBP and the DBP of the participants were assessed thrice immediately prior to beginning the study, with an inter-assessment interval of one minute. The SBP and DBP of all the participants were in the normotensive range (i.e., SBP < 120 mmHg and DBP < 80 mmHg) as per the criteria laid down in the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-7; Chobanian et al., 2003). To combine the information of SBP and DBP into one factor, a latent BP factor model was tested using structural equation modeling approach, with the three measures of SBP and DBP as indicators. This model included all the three measurements of SBP and DBP as indicators of the latent factor of BP. This model was tested using AMOS and after allowing the errors of SBP to correlate, the model (see Supplementary Fig. 1) yielded a good fit to the data.

The various indices of goodness of fit of structural equation model met the contemporary criteria of a good fit [χ2/df = 1.18, GFI = 0.961, TLI = 0.985, CFI = 0.994, SRMR = 0.062 and RMSEA = 0.057]. Since the measurement model representing BP as a latent factor was found a very good fit to the data, the score of the latent BP factor was estimated using the data imputation feature of AMOS. Based on the estimated latent BP score (that comprised information of both SBP and DBP), two BP groups: Low BP group and High BP group were created using median split. The Low BP group comprised 27 participants whereas the High BP group consisted of 29 participants.

Measures

The approach-avoidance task (Rinck & Becker, 2007)

In this task, a joystick is used to move a happy or angry face towards or away from the participant as quickly as they can. There are two conditions: in the Congruent condition, the happy face is required to be moved towards the participant (a Pull movement of the joystick) and the angry face needs to be moved away (a Push movement of the joystick), while in the Incongruent condition, the happy face is pushed away and the angry face is pulled towards the participants. It is assumed that positive emotion initiates appetitive reactions and therefore approaching it is the natural tendency, therefore the RT taken in pulling the happy face towards oneself would be lesser than when it is required to push the happy face away. Similarly, negative emotion from the angry face causes aversive reactions resulting in quicker push movement of the joystick than the pull ones. Every new trial on the task can be initiated by pressing the ‘start’ button at the top of the joystick, making a face appear on the screen. In accordance with the joystick’s pull or push motion, the emotional face zooms in and out, giving a sense of the face moving closer to or farther away from the participant, respectively. Once the picture is fully pushed or pulled in the appropriate direction, the picture disappears from the screen. The joystick then needs to be brought back to the centre position and the start button clicked again for a new face to appear. The computer records the time difference between the appearance and disappearance of the picture from the screen.

Rinck and Becker (2007) adapted the original AAT and modified it to include a zooming-in and zooming-out function. Thus, in this version of the AAT, when the participants are instructed to pull a joystick closer to themselves, the face (expressing either happy or angry expression) gradually keeps on increasing in size until it fills the screen, giving the impression of the face approaching the participant. When the participants push the joystick away, the face keeps on diminishing in size until it disappears.

This task is divided into two halves of congruent and incongruent condition by a small rest pause in between. The order of presentation of these two task conditions is counterbalanced across participants. All the participants are presented the facial emotion photographs (Happy and Angry faces) in the same pseudo-random order ensuring that no more than three photographs of the same valence are presented in a sequence. Each trial is formed of a single picture appearing at the centre of the black screen. Each half of the task begins with a practice session on 16 trials, followed by the main task session comprising of 64 trials.

Procedure

All participants were told to avoid caffeine and excessive activity 2 hours before their session. This was done to avoid external effects on blood pressure readings. Upon arriving at the lab, participants were encouraged to rest for 15 min to normalise their blood pressure. They were handed the study’s information page. They were asked to read the document and ask questions or voice concerns, if any. If they were happy with the responses and consented to participate, participants were requested to sign an informed consent form.

During blood pressure measurements, participants sat with straight backs and flat feet. Blood pressure was measured using the Kinetic Health Fully Automatic Blood Pressure Monitor from the dominant arm of the participants. Each of the three blood pressure readings were one minute apart. Participants sat facing the computer monitor. To administer the approach-avoidance task, the joystick was centred on the table. The joystick was 12 cm from the screen and 40 cm from the participant. The screen resolution was 1024 × 768 pixels. The participant was randomly allocated to Group 1 or Group 2, and depending on the group, they started with the congruent (Happy-Pull and Angry-Push) or incongruent condition (Happy-Push and Angry-Pull). Depending on the condition, the screen displayed directions, which were also read aloud. Participants were told to respond as swiftly and as accurately as they could. They completed the first half of the task after practising on 16 faces. Before continuing, they could relax and hit any key when they were ready to continue. They were then given another practice session for the second half of the task on 16 faces, before they began with the main task trials. The task took 15 min on an average. Participants were debriefed after the task. In addition to travel expenses, all participants received £5 for participating.

Statistical analysis

A mixed-design 2 (BP group: Low, High) x 2 (Emotion: Happy, Angry) x 2 (Condition: Congruent, Incongruent) ANOVA was performed on (reaction time RT) data to explore variations in approach and avoidance action tendencies between individuals with low and high BP in the normotensive range.

Results

The average resting SBP and DBP values along with age, gender, and BMI values for study participants are presented in Table 1. Twenty-one participants described their ethnicity as Asian, twenty-five as Caucasian, three as African, one as Turkish, and three as Mixed ethnicity. The rest of the participants (n = 3) refused to state their ethnicity. There was no significant effect of age, gender, ethnicity, or BMI on the outcome variable (RTs in AAT conditions).

Table 1 Overall and group-wise demographic information of the participants
Full size table

The 2 (BP group: Low & High) x 2 (Emotion: Happy & Angry) x 2 (Condition: Congruent & Incongruent) ANOVA showed no significant main effect of BP group (F(1, 54) = 0.022, p = .88) or Emotions (F(1, 54) = 0.004, p = .95) on RTs. However, the main effect of Condition was significant (F(1, 54) = 8.56, p = .005). Irrespective of Emotions or BP groups, significantly lesser time was required by the participants in the congruent (M = 787.16 ms, SE = 14.02 ms) than the incongruent (M = 815.90 ms, SE = 13.16 ms) condition. The Emotion x BP groups interaction was significant, F(1, 54) = 7.65, p = .008. Following up this significant interaction effect with simple-effects analysis, we found significant differences in the average RT taken in responding to Happy (M = 812.90 ms, SE = 18.29 ms) and Angry faces (M = 793.88 ms, SE = 18.14 ms), p = .046 by the High BP group. However, this difference in the average RT in responding to Happy (M = 790.60 ms, SE = 18.96 ms) and Angry faces (M = 808.73 ms, SE = 18.80 ms), p = .066 was not significant for the Low BP group. These results indicate that irrespective of whether the participants were required to pull or push the emotional faces toward and away from themselves (i.e., regardless of congruent or incongruent conditions), those with high BP were quicker to react to angry compared to happy faces, while those with low BP responded to happy and angry faces similarly. The two BP groups, however, did not differ significantly in their RT to happy as well as angry faces.

Discussion

The findings of the present study revealed that elevation in BP, even in the normotensive range, results in valence-specific altered behavioural approach-avoidance tendency. More specifically, the findings revealed that the normotensive individuals with relatively elevated BP showed a quicker response time to angry facial expressions than happy ones, irrespective of the nature of response (pull or push of the joystick) when compared with low BP group (who responded similarly to happy and angry facial expressions in terms of action tendencies). These findings contrast with most of the earlier findings that reported dampened emotional responding, irrespective of emotional valence, in relation to elevated BP (McCubbin et al., 2011, 2014; Shukla et al., 2018, 2019). The observed enhanced behavioural reactivity towards angry relative to happy facial expressions among individuals with elevated BP brings a novel insight into the nature of emotional responding in relation to BP levels. While earlier studies document elevation in BP- associated emotional dampening in terms of conscious (McCubbin et al., 2011, 2014; Shukla et al., 2018, 2019) as well as more automatic processing (recognition) of emotions, such as affective modulation of eye-blink startle reflex (Shukla et al., 2020), the present findings show an increased sensitivity of individuals with elevated BP towards anger/aggression at the level of voluntarily-controlled behavioural responses to emotions.

The presence of significant blood pressure and emotion interaction suggests that the basic appetitive and aversive motivations towards emotional valence do not remain intact in individuals with high blood pressure. The findings revealed that irrespective of whether the participants were required to approach or avoid the valenced facial stimuli, participants in the low BP group reacted similarly (showed similar reaction time) to happy and angry faces, while those in the high BP group showed significantly quicker responses (both in congruent and incongruent conditions) to angry as compared to happy faces. These preliminary findings may imply an unimpaired and quicker recognition of anger, or a behavioural over-reactivity towards angry facial expressions, or both among individuals with elevated BP.

Some evidence from previous research suggests the former possibility of a quicker recognition of anger among those with elevated BP. For instance, Aftanas et al. (2013) report that a bias towards preconscious and quick recognition of anger may indicate a risk of developing essential hypertension. Similarly, Wilner (2004) administered anger-management strategies to a patient of essential hypertension and noted lowering of BP, decreased anger, lower arousal levels and better problem-solving in the patient. Thus, hypervigilance for anger may be a cause for increase in blood pressure. Individuals with elevated blood pressure and hypertension have been reported to experience more state anger and also possess more trait anger than normal individuals (Mushtaq & Najam, 2014; Player et al., 2007; Schum et al., 2003; Williams et al., 2002). Specifically, with respect to facial expressions of emotions, a recent study showed that people with hypertension demonstrate an anger recognition bias in that they more frequently recognise anger expressions in the faces of others (Auer et al., 2022). In comparison to normotensive controls, hypertensive participants overrated anger expressions in facial displays of mixed emotions. Similarly, another study noted an association between elevated mean BP and elevated sensitivity for recognition of emotional expressions of anger (Zuccarella et al., 2013). They concluded that hypertensive patients are quicker to recognize the facial expressions of anger compared to normotensives, if anger is shown. Our findings, however, go contrary to the findings of cardiovascular emotional dampening, which suggest a reduced recognition of both pleasant and unpleasant emotions amongst individuals with elevated BP (Jain et al., 2017; McCubbin et al., 2014; Shukla et al., 2019).

Recent research demonstrating behavioural risk-taking tendencies (in other words, approach tendencies towards unpleasant/threatening stimuli) to be associated with dampened recognition of emotions that comes with elevated BP (McCubbin et al., 2020) may provide partial support to the possibility of aberrant approach-avoidance action tendencies among those with elevated BP. The research by McCubbin and colleagues (2020) might explain why no difference in rection time in approaching and avoiding happy as well as angry facial expressions was seen among those with elevated BP in our study. However, since this was also true for the low BP group, dampened recognition of emotions associated with elevated BP does not seem to be the driving factor behind lack of significant difference in reaction time across congruent and incongruent conditions. Similarly, it fails to explain why quicker reactivity was noted for angry than happy expressions among those with elevated BP.

Emotions serve as motivational states or action tendencies (Montag & Panksepp, 2017). As per the motivational priming theory (Lang et al., 1990), neural networks have a readiness or are ‘primed’ to respond to the stimuli in accordance with the currently active motivational system of the individual. Since individuals with elevated BP possess more state and trait anger than those with normal BP (Mushtaq & Najam, 2014; Player et al., 2007; Williams et al., 2002), this dispositional negative affectivity may ‘prime’ them towards negative affect-inducing stimuli (such as an angry facial expression), leading to a quicker response or higher reactivity to angry facial expressions. However, future studies are required to establish the salience of this hypothesis, while also addressing the limitations of the present study. An important limitation of the present study is the small sample size. For the purposes of generalization and to gain more confidence in these findings, future research studies with larger samples are required. Another limitation is that the resting blood pressure of the participants was measured using an automated blood pressure monitor on the single occasion of their visit to the laboratory. For a more accurate assessment of the resting blood pressure of the participants, the blood pressure readings should be averaged over two or more visits or an ambulatory blood pressure measurement should be undertaken. A third limitation is the unequal gender distribution of our sample. Although the gender distribution did not differ significantly between the Low and High BP groups, a comparable number of male and female participants could have allowed for a gender-wise analysis of the differences in blood pressure-related deficits in behavioural tendencies towards affective stimuli. Finally, since very few participants belonged to certain ethnic backgrounds, this precluded any comparisons across ethnicities. This caveat needs to be taken into account when understanding the findings and future research should aim to include culture/ethnicity as an important variable in their study design.

The findings of the present study tentatively imply that the behavioural over-responsiveness towards stimuli connoting anger among individuals with elevated BP may dispose them towards later development of high blood pressure since anger is strongly associated with elevation in BP and being highly reactive to anger may lead to chronic elevations in blood pressure and development of hypertension. Over-reactivity to anger is also likely to create distancing in social relationships, which may be an additional factor leading to increase in stress and feelings of isolation, which can subsequently cause further elevations in blood pressure. Moreover, though not studied here directly, a heightened recognition of negative emotion of anger among individuals with elevated blood pressure may have implications for the experience and expression of emotions in such individuals. Rapid Facial Reactions (RFRs) are believed to be very quick, bottom-up, and automatic facial responses to facial expressions of others which may play a role in sharing the affect of other people (Datyner et al., 2017) and are supposedly present since birth (van Baaren et al., 2009). It can be hypothesized that a quick recognition and response to angry emotion may reflect in RFRs of individuals with elevated BP. However, this would have to be explored in future research. Stressful situations can lead to the development of hypertension (Spruill et al., 2019) and the COVID-19 pandemic has likely brought about unprecedented stress for people. The impact of COVID-19-related lockdown on lifestyle habits and behavioural (e.g., psychological distress and mood symptoms) risk factors also cannot be ignored (Odone et al., 2020) and may contribute to blood pressure elevation and/or development of hypertension. Thus, exploring the pandemic-specific stress factors among individuals with elevated BP and hypertension and how this affects their approach-avoidance reactions can be an important area for future investigations during the post-pandemic phase as well as during the pandemic where new wave of COVID-19 has started to emerge. Relatedly, studies may seek to examine how psychological symptoms associated with long COVID (Davis et al., 2023) influence the emotion-linked motivational tendencies among individuals with elevated BP.

Conclusion

The findings of this study reveal an enhanced behavioural reactivity towards angry facial expressions among individuals with elevated blood pressure. Awaiting verification from future researches, the present findings tentatively indicate that an enhanced negative affectivity as well as state and trait anger frequently associated with individuals having elevated BP may prime them towards a quicker recognition of and subsequent behavioural reactivity towards a facial expression of anger. These findings imply that a behavioural over-reactivity towards anger may further lead to chronic elevations in BP resulting in the development of hypertension.