Heart Rate Variability as a Correlate of Trauma Symptom Expression,Psychological Well-Being,and Emotion Regulation in African Americans With Traumatic Spinal Cord Injury

Abstract

This study examined the relationship between heart rate variability, trauma symptom expression, and psychological distress in a sample (N = 28) of African Americans with traumatic spinal cord injury. Participants’ heart rate (R-R interval) was recorded at baseline, during a mental arithmetic task, and then again at recovery. Heart rate variability was indexed as the root mean square of successive difference (rMSSD) of participants’ R-R interval. Following this procedure, participants were administered a battery of surveys to assess levels of trauma and psychological distress. Findings indicated that there was a statistically significant relationship between heart rate variability, trauma symptoms, and psychological distress. Implications of the study’s findings are discussed in the context of future research and clinical interventions.

Keywords

health psychology trauma stress coping

The psychological consequences secondary to traumatic spinal cord injury (TSCI) have been well documented in the rehabilitation psychology literature. For example, several studies have reported increased levels of anxiety and depression following TSCI (e.g., Dryden et al., 2005; Krause, Broderick, & Broyles, 2004; Migliorini, Tonge, & Taleporos, 2008). Moreover, a study by Beedie and Kennedy (2002) found that suicide rates were as much as six times higher among individuals with TSCI than in able-bodied populations. Although this growing body of empirical research has influenced both clinical work and policy regarding individuals with TSCI, there remain significant gaps in this literature. Specifically, despite the fact that African Americans account for 24% of all new TSCI cases each year (National Spinal Cord Injury Statistical Center, 2013), a rate of incidence disproportionate to their representation in the overall population (13%; U.S. Census Bureau, 2005), the majority of studies have been conducted with predominantly White samples. In light of the disparity in the incidences of new TSCI cases among African Americans researchers have an ethical duty to extend their examination of the psychological and emotional sequelae of TSCI to this population.

Despite being at increased risk for injury little is known about the impact of TSCI on the psychological and emotional functioning of African Americans. According to Cohen et al. (1998), exposure to major traumatic events may produce behavioral changes and alterations in physiological functioning that can persist for extended periods of time following the event. Belgrave (1991) conducted a study examining psychosocial predictors of adjustment in a sample of African Americans with disabilities. She found that perception of disability severity, self-esteem, and social support accounted for 50% of the variance in adjustment to disability. Krause (1998) found that African Americans with TSCI scored poorly on indicators of subjective well-being, specifically those related to career, finances, living arrangements, and family relations. With regard to mental health functioning, Krause et al. (2004) found that African American women with TSCI reported significantly more negative affect and depressive symptoms than other racial and gender groups with TSCI. It is unclear, however, whether there are physiological markers of risk for adverse psychological outcomes related to trauma symptoms and adjustment to disability. The purpose of this study was to explore the relationship between trauma symptom expression, emotional affect, psychological symptoms (anxiety and depression), and heart rate variability as a physiological marker of stress adaptation in African Americans with TSCI. It is important to note that TSCI is distinguished from other forms of spinal cord injury (congenital, progressive, and disease-related) and is the focus of this study.

Heart Rate Variability

Heart rate variability (HRV) is the beat-to-beat alteration (R-R intervals) in heart rate and is considered an indicator of a person’s capacity to respond adaptively to stress (Appelhans & Luecken, 2006). The body’s stress responses are regulated by the autonomic nervous system (ANS), which includes the sympathetic (SNS) and parasympathetic (PNS) subdivisions The vagus nerve regulates resting heart rate fluctuation and consequently, the body’s response to a stressor. The quality, or level, of vagal regulation of resting heart rate is termed vagal tone (McEwen & Lasley, 2002; Porges, 1995). During a stress response the SNS increases heart rate (arousal) in preparation for a fight or flight response; the PSN slows the heart rate (inhibition) once the threat has dissipated (McEwen & Lasley, 2002). Resting heart rate fluctuates in relation to the respiration cycle; inspiration increases heart rate and expiration decreases heart rate (Appelhans & Luecken, 2006). Respiratory sinus arrhythmia is the mechanism by which respiration influences heart rate. When heart rate varies considerably for each respiratory cycle (high HRV), it is said to demonstrate good vagal tone. When there is little variability (low HRV), vagal tone is said to be poor (Thayer & Lane, 2007). Higher HRV is generally reflective of autonomic balance between subsystems of the ANS and is associated with more positive health outcomes, including psychological well-being. This is theorized to be the result of more effective and efficient physiological adaptation to chronic stress (McEwen & Lasley, 2002; Porges, 1995). Berntson and Cacioppo (2004) posited that resting HRV is determined by individual differences in neural, neurochemical, and physiological mechanisms of ANS function. Hence, resting HRV can be viewed as a relatively stable trait that does not vary across time.

Heart Rate Variability and Mental Health

A number of scholars conducting research in the area of psychophysiology have linked individual differences in emotion regulation, physiological arousal, and the onset of psychopathology (Appelhans & Luecken, 2006). Emotion regulation is an individual’s ability to regulate physiological arousal and modulate their emotional state in the context of the situational demands of environmental stress (Gross & Thompson, 2007). This ability represents a dynamic balance between SNS and PNS on heart rate and can be measured directly by HRV (Thayer & Lane, 2007). Moreover, there is increasing empirical support for HRV as a marker of individual differences in emotion regulation (Appelhans & Lueken, 2006).

Scholars have proposed that decreased HRV is linked to emotional stress and psychological symptoms. For example, studies have found that decreased HRV was predictive of depression and anxiety disorders(Friedman, & Thayer, 1998; Hughes & Stoney, 2000; Kawachi, Sparrow, Vokonas, & Weiss, 1995). A study by Gorman and Sloan (2000) found that low HRV was related to hostility, anxiety, and depressive symptoms. Movius and Allen (2005) found that vagal tone (HRV) moderated the relation between induced stress and anxiety, induced stress and behavioral activation, and induced stress and defensiveness. A study by O’Connor, Allen, and Kaszniak (2002) found that HRV moderated the relation between bereavement and positive psychological outcomes. Taken together these studies demonstrate that the relationship between exposure to stress and psychological symptoms may be affected by HRV. This preliminary study examines the link between HRV, emotional regulation, and psychological symptoms in African Americans with TSCI.

Conceptual Framework

The conceptual framework undergirding the current study is grounded in the theoretical model proposed by Appelhans and Luecken (2006) that views HRV as a physiological marker of individual differences in emotion regulation. The ability to regulate emotions is a function of the degree to which the SNS and PNS systems are in dynamic balance (Thayer & Lane, 2007). Flexibility of the ANS is represented by balance between its two branches and has been linked to mental health (Gross & Muñoz, 1995). This is especially true in trauma patients. Research has demonstrated that HRV can be used as a marker of physiological changes in the autonomic function of individuals exposed to extreme traumatic events (Cohen et al., 1998). Consequently, individuals who experience TSCI manifest hyperarousal and dysregulation of the ANS (Cohen et al., 1998). Therefore, it is anticipated that HRV, as a physiological marker of ANS hyperarousal and dysregulation, will be inversely correlated with scores on measures of negative affect, anxiety, and depression. Specifically, it is hypothesized that individuals in the current study with lower HRV will have higher scores on measures of negative affect, anxiety, and depression.

The aim of this preliminary investigation is to examine whether autonomic balance (as measured by HRV) correlates with negative affect and psychological symptoms in African Americans with TSCI. This study has implications related to addressing health disparities specific to the mental health functioning and overall quality of life of African Americans with TSCI. Specifically, assessing the degree to which HRV influences emotional and psychological well-being in this population could inform how rehabilitation medicine professionals screen individuals with TSCI for psychosocial predictors of adjustment. In addition, this study has the potential to inform recommendations made for the treatment and care of factors related to emotional and psychological well-being.

Method

Participants

Participants consisted of 28 African Americans with TSCIs who were patients at a Level-1 trauma center between 2000 and 2005. Individuals of African American descent were identified from the archival records of this program and sent a letter informing them of their eligibility to participate in the study. Persons interested in participating in the study contacted the lead investigator to schedule an appointment.

Participants were 21 (75%) men and 7 (25%) women between the ages of 19 and 67 years (M = 40.89 years, SD = 14.30). Eleven participants were either married or cohabiting, 13 were single, 2 were in long-term relationships, and 2 were widowed. Levels of education varied with 7 participants having less than a high school education, 4 completed their GED, 11 were high school graduates, 4 had at least some college, 1 had a bachelor’s degree, and 1 had a graduate education. Participants varied in their level of injury with 15 reporting cervical injuries, 8 reporting thoracic injuries, and 5 reporting lumbar injuries. Although 15 participants reported having cervical injuries, none required ventilator support for breathing. Of the 28 total participants in the study, 17 were motor vehicle accident victims and 11 were injured as the result of a gunshot wound. The mean time from injury to date was 34 months (SD = 22.74 months). Four individuals were excluded from the sample due to missing or incomplete data.

Instruments

Positive and Negative Affect Schedule

The Positive and Negative Affect Schedule (PANAS; Watson, Clark, & Tellegen, 1988) is a 20-item measure of positive and negative affectivity. The PANAS asks participants to indicate the degree to which they experience certain feelings and emotions within a given time-frame (e.g., today, past few days, past week). Ten items assess positive affect and 10 items assess negative affect. Study participants were asked to describe their feelings and emotions “at the present moment.” Higher scores on the PANAS indicate greater expression of positive or negative emotions. However, for purposes of the current study only the Negative Affect scale of the PANAS was used in the analyses. The current study’s Cronbach’s alpha coefficient for the PANAS’ Negative Affect scale was .87.

Brief Symptom Inventory–18

The Brief Symptom Inventory–18 (BSI-18; Derogatis & Savitz, 2000) is an 18-item self-report measure of anxiety, depression, somatization, and a global severity index of overall psychological distress. Higher scores on the BSI-18 scales indicate greater intensity of symptom expression in the aforementioned domains. Participants complete the BSI-18 by indicating the degree to which they are bothered or distressed by the thoughts, feelings, and experiences described by the items. Only the anxiety, depression, and somatization scales were used in the analyses of the current study. BSI Cronbach’s alpha coefficients for the current study were as follows: anxiety, .84; depression, .76; and somatization, .84.

Trauma Symptom Inventory

The Trauma Symptom Inventory (TSI; Briere, 1995) is a 100-item measure of acute and chronic trauma symptoms. The measure is used to assess symptoms commonly experienced by individuals with posttraumatic stress disorder. Participants are asked to indicate the frequency with which they have experienced the symptoms described in the TSI items. The TSI consists of three summary subscales, they are as follows: (a) Trauma, (b) Dysphoria, and (c) Self (which assesses impaired self-reference, such as low self-esteem or identity issues). Higher TSI factors scores indicate greater symptom expression in a given trauma domain. TSI Cronbach’s alpha coefficients for the current study were as follows: Trauma, .84; Dysphoria, .86; and Self, .89.

Polar S810i Heart Rate Monitor

The Polar S810i Heart Rate Monitor (Polar Electro, n.d.) is a noninvasive measure of ANS activity (PNS) that collects heart rate data via an adjustable transmitter that is placed around the participant’s rib cage. The device remotely transmits the heart rate reading to a wrist watch receiver. Data from the receiver were saved on the watch as a file that can be uploaded to a computer. HRV was measured as an individual’s beat-to-beat alterations (R-R intervals) in heart rate (McEwen & Lasley, 2002). Although several indices of HRV are generated by the Polar S810i software, the root mean square of successive differences (rMSSD) was used for purposes of the current study’s analyses.

Procedure

Participants were provided information regarding the study’s purpose and procedures and reviewed an institutional review board–approved consent form. Once consented, they were seated comfortably and the Polar S810i chest sensor transmitter was attached to their chest. Following the 5-minute baseline reading of cardiovascular function, participants were given a nonverbal arithmetic task, commonly used in stress and cardiovascular risk research (see, Ruddel, Langewitz, Schachinger, Schieder, & Schulte, 1988). The task required participants to add, in a cumulative sequence, 10 rows of 9 integers between 1 and 20. During the arithmetic task, HR was continuously recorded for 5 minutes. Following the arithmetic task, participants were allowed to rest for a 15-minute recovery period after which a final HR reading was recorded. Immediately following the recovery period, participants completed study questionnaires, were debriefed, allowed to ask additional questions regarding the study, and compensated $50 for their participation.

Results

Descriptive Analysis

Means and standard deviations were calculated for the study’s measures (see Table 1). Moreover, the data were examined for missing values, outliers, and any violation of assumptions that might affect the primary analysis.

Table 1.

Means, Standard Deviations, and Spearman’s Correlation Coefficients for Trauma Symptom and Psychological Distress Variables.

Variable	M	SD	1	2	3	4	5	6	7	8
1. rMSSD	6.00	23.51	—	−.15	−.24	−.34*	−.27	−.58**	−.54**	−.64**
2. SOM	12.46	5.33	—	—	.26^†	.58**	.32*	.32^†	.25.	.45*
3. DEP	10.75	4.29	—	—	—	.64**	.78**	.68**	.51**.	.62**
4. ANX	9.78	4.61	—	—	—	—	.66**	.60**	.49**	.68**
5. NEGAFF	19.42	8.11	—	—	—	—	—	.67**	.44*	.68**
6. TRAUMA	63.41	18.46	—	—	—	—	—	—	.82**	.87**
7. SELF	57.52	16.16	—	—	—	—	—	—	—	.90**
8. DYSPHOR	42.88	11.70	—	—	—	—	—	—	—	—

Note: rMSSD = root mean square of successive differences; SOM = Brief Symptom Inventory (BSI) somatization scores; DEP = BSI depression scores; ANX = BSI anxiety scores; NEGAFF = Positive and Negative Affect Schedule (PANAS) Negative Affect scores; TRAUMA = Trauma Symptom Inventory (TSI) trauma symptom scores; SELF = TSI Self scores; DYSPHOR = TSI Dysphoria scores.

†

p< .10. *p< .05. **p< .01.

Primary Analysis

A series of analyses of variance were conducted to evaluate gender and level of injury differences with regard to HRV. Findings from this analysis indicated that HR (R-R interval) recovery scores did not significantly differ across gender, F(1, 25) = 0.17, p = .68, or level of injury, F(1, 25) = 0.91, p = .35.

A manipulation check was conducted to establish that mean HR would vary with exposure to stress in individuals with spinal cord injury. We conducted a general linear model repeated-measures analysis of variance to test for the equality of mean scores for average R-R interval (mean HRV) scores at baseline, during arithmetic task, and at recovery. Findings indicated that there was a statistically significant effect between mean HRV scores at baseline, during arithmetic task, and at recovery, F(2, 24) = 7.60, p< .01. A test of within-subjects contrasts indicated that there was a statistically significant quadratic effect for mean HRV scores from baseline, during arithmetic task, and at baseline, F(1, 25) = 15.57, p< .01. As anticipated, mean R-R interval scores declined from baseline (790.23 ms) to the arithmetic task (760.92 ms) and then increased at recovery (806.42 ms). These findings indicate that the stress associated with the mental arithmetic task reduced the HRV of participants.

Given the relatively small sample size, a nonparametric statistical approach was used to examine the relationship between variables in the study. Specifically, Spearman correlation coefficients were calculated to examine the relationship between HRV recovery scores and indicators of psychological distress. An HRV recovery score was calculated by taking the difference between baseline rMSSD scores and rMSSD scores at recovery. An examination of Table 1 would indicate that HRV recovery scores were significantly correlated with scores on the Trauma and Dysphoria scales of the TSI, the Depression subscale of the BSI-18, and the Negative Affect subscale of the PANAS. A trend was observed for the Self Factor subscale of the TSI. Other notable findings include a statistically significant negative correlation between time since injury and scores on the Negative Affect subscale of the PANAS. Time since injury was measured in months. These findings would suggest that as time passed, there was a statistically significant decline in negative emotions.

Discussion

Our findings support previous research indicating that lower HRV is associated with stress (Appelhans & Luecken, 2006; Katz & Gottman, 1995). Specifically, we found that low to moderate HRV correlated with the presence of trauma symptomology and that mean R-R interval scores varied at baseline, during the presentation of a stressful task, and at recovery. This indicates that, for African Americans with TSCI, HRV is sensitive to the presence of a stressor, adapts accordingly, and may be a viable indicator of stress vulnerability for this population, and potentially others. Furthermore, our results suggest that HRV recovery is related to feelings of depression, negative affect, and dysphoria for African Americans with TSCI. This finding is consistent with other research implicating HRV as a predictor of psychopathology (Gorman & Sloan, 2000; Miyawaki & Salzman, 1991) and supports studies suggesting that African Americans experience significant mental health consequences as a result of TSCI (Belgrave, 1991; Krause, 1998; Krause et al., 2004). Our data demonstrate that for African Americans with TSCI, there are physiological consequences to the presence of a chronic stressor, albeit mental or physical, and may be a viable indicator of coping or general mental health functioning. These findings have important diagnostic implications for African Americans with TSCI and other groups experiencing chronic stressors.

Our study found no differences in HRV by gender or by injury type. Although studies have found that women report more negative affect and depressive symptoms there is evidence that the two groups are somewhat similar in terms of subjective well-being (Krause, 1998; Krause et al., 2004). However, the present study’s sample size may have limited the ability to detect these differences. Similarly, in terms of injury type, although no significant differences in HRV recovery were found, other studies have found that HRV has been able to differentiate between various injury types, such as incomplete and complete SCI (Grimm, De Meersman, Almenoff, Spungen, & Bauman, 1997). This inconsistency may be indicative of several methodological differences. For example, the number of differences in methodology among existing studies makes it difficult to ascertain whether the relationship is weak or whether the small sample size of the current study limits the ability to replicate those results.

Little research has examined the utility of HRV as an indicator of stress vulnerability in a sample of African American individuals with SCI. Scholars have proposed that the status of the autonomic system prior to exposure to a stressor may affect HRV (O’Connor et al., 2002). Furthermore, evidence supports that African Americans are likely to have lower HRV than Whites (Lampert, Ickovics, Horwitz, & Lee, 2005). Given this potential for lower baseline HRV, it may be more challenging to detect changes in this population, suggesting that HRV may be less sensitive to detecting small variations of stress within populations with significant prior exposure to stress. Use of an experimental comparison group in future research may be useful in further exploring group differences and in identifying the degree to which chronic stress and low resting HRV influence change in HRV during stress.

Measurement of HRV may help scientists better understand the impact of mental and physical distress and may be used to assess mental health symptomology, (e.g., severity of symptoms, level of coping, or overall mental health functioning). The implications of clinical use of this tool are many as well. These data suggest that HRV may be useful in detecting the level of coping or global mental health functioning in African Americans with TSCI and may generalize to African Americans.

Footnotes

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

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