LaBarron K. Hill

Ethnic Differences in Resting Heart Rate Variability : A Systematic Review and Meta-Analysis

Background Ethnic disparities in cardiovascular morbidity and mortality are widely documented in the literature. Recently, research has shown that decreased parasympathetic cardiac modulation is associated with the established and emerging risk factors for cardiovascular disease (CVD) and stroke. In consideration of the disproportionate CVD risk and disease profile of African Americans (AAs), it is plausible that decreased cardiac parasympathetic functioning may partially explain these disparities. In the present systematic review and meta-analysis, we assess the available evidence for a reliable ethnic difference in tonic vagally mediated heart rate variability (HRV), an indicator of parasympathetic cardiac modulation. Methods A systematic literature search was conducted yielding studies comparing tonic HRV in AAs and European Americans. Adjusted standardized effect sizes (Hedges g) were calculated using a mixed-effects model, with restricted maximum likelihood estimation for 17 studies containing appropriate measures of vagally mediated HRV. Results Meta-analysis results suggest that AAs have greater HRV than do European Americans (Hedges g = 0.93, 95% confidence interval = 0.25–1.62), even after consideration of several covariates including health status, medication use, and subgroup stratification by sex and age. Conclusions These findings suggest that decreased vagally mediated HRV is not likely to account for the persistent health disparities experienced by AAs with respect to CVD risk and burden. These disparities underscore the need for continued research addressing socioethnic cardiovascular differences and the biobehavioral mechanisms involved.

Perceived Racism and Ambulatory Blood Pressure in African American College Students

Experiences with racial discrimination may contribute to stress-induced blood pressure (BP) elevations among African Americans. It was reported that perceived racism was associated with ambulatory BP (ABP) during waking hours. This study examined perceived racism and ABP among 40 African American college students, who completed an ABP assessment from which daytime and nighttime averages were computed. Perceived frequency of experiences with racism and racial discrimination was measured using the Perceived Racism Scale. Controlling for gender and body mass index, perceived racism in academic settings was associated with higher diastolic BP (DBP) during waking hours and nighttime sleep. Systolic BP (SBP) was unrelated to perceived racism, and perceived racism in the public realm and in statements from Whites was unrelated to ABP. Perceived racism in academic settings predicted ambulatory DBP among college students. Previous laboratory research has found stronger effects of perceived racism for DBP than SBP. The hemodynamic regulation of BP may explain this phenomenon. Future laboratory and ambulatory studies should assess the contributions of vascular resistance and cardiac output to BP elevations associated with perceived racism.

Depression, Suicidal Ideation, and Attempts in Black Patients With Sickle Cell Disease

There is a strong relationship between suicidal ideation, suicide attempts, and depression. Rates of successful suicides are relatively high among the chronically ill compared to other populations but are reduced with treatment. Depression and suicide rates also often differ among blacks as compared to other populations. Using survey methods, we evaluated self-reported rates of depression, suicidal ideation, and suicide attempts in 30 male and 37 female black patients with sickle cell disease (SCD). SCD is a condition characterized by chronic, unpredictable pains and psychosocial distress. Thirty-six percent of the sample self-reported depression in the past 30 days, while 22 percent of the sample exhibited scores on the Beck Depression Inventory indicative of mild or greater depression (mean BDI, 8.31 +/- 7.79). Twenty-nine percent of patients indicated an episode of suicidal ideation and 8%, a suicidal attempt in their lifetime. Thirty-three percent reported treatment by a mental health professional. We conclude that there is a continuing need for mental health services in the management of depressed affect and risk for suicide among patients with SCD. Standards of clinical care must remain flexible to accommodate the mental health needs of this population of patients.

Neuropsychological effects and attitudes in patients following electroconvulsive therapy

The current study examined the effects of electroconvulsive therapy (ECT) on neuropsychological test performance. Forty-six patients completed brief neuropsychological and psychological testing before and after receiving ECT for the treatment of recalcitrant and severe depression. Neuropsychological testing consisted of the Levin Selective Reminding Test (Levin) and Wechsler Memory Scale-Revised Edition (WMS-R). Self-report measures included the Beck Depression Inventory (BDI), the Short-Term Memory Questionnaire (STMQ), and several other measures of emotional functioning and patient attitudes toward ECT. The mean number of days between pre-ECT and post-ECT testing was 24. T-test revealed a significant decrease in subjective ratings of depression as rated by the BDI, t(45) = 9.82, P < 0.0001 (Pre-BDI = 27.9 ± 20.2; post-BDI = 13.5 ± 9.7). Objective ratings of memory appeared impaired following treatment, and patients’ self-report measures of memory confirmed this decline. More specifically, repeated measures MANOVA [Wilks Lambda F(11,30) = 4.3, p < 0.001] indicated significant decreases for measures of immediate recognition memory (p < 0.005), long-term storage (p < 0.05), delayed prose passage recall (p < 0.0001), percent retained of prose passages (p < 0.0001), and percent retained of visual designs (p < 0.0001). In addition, the number of double mentions on the Levin increased (p < 0.02). This study suggests that there may be a greater need to discuss the intermittent cognitive risks associated with ECT when obtaining informed consent prior to treatment. Further that self-reports of cognitive difficulties may persist even when depression has remitted. However, patients may not acknowledge or be aware of changes in their memory functioning, and post-ECT self-reports may not be reliable.

Oxytocin receptor gene polymorphism modulates the effects of social support on heart rate variability

A large body of empirical research has demonstrated stress-buffering effects of social support. However, recent studies suggest that genetic variation of the oxytocin system (specifically, a common single nucleotide polymorphism, rs53576, of the oxytocin receptor gene) modulates the efficacy of social support. The timing and neurobiological basis of this genetic modulation were investigated using a standardized, laboratory-based psychological stress procedure (Trier Social Stress Test for Groups, TSST-G). To index potential stress buffering effects of social support mediated by the oxytocin system, heart rate variability (HRV) was obtained before and during the TSST-G from 40 healthy participants. Results indicate that social support is associated with higher HRV only in G allele carriers. Specifically, social support increased heart rate variability during direct social interaction and only in individuals with at least one copy of the G allele of rs53576. These findings support the idea that the stress-attenuating effects of social support are modulated by genetic variation of the oxytocin system.

Capturing the cardiac effects of racial discrimination: Do the effects "keep going"?

Racial discrimination negatively impacts cardiac functioning, but few studies examine the more distal cardiac effects of racial discrimination experiences. The present study examined the momentary and prolonged impact of lab-based intergroup and intragroup racial discrimination on heart rate variability (HRV) and heart rate (HR) in a sample (N = 42) of African American (AA) women across two days. On day one, the women were exposed to simulated racial discrimination from either a European American (EA) or AA confederate in the lab. On day two, the women returned to the lab for additional physiological recording and debriefing. Women insulted by the EA confederate exhibited lower HRV on day one and marginally lower HRV on day two. These women also exhibited marginally higher HR on day two. The HRV and HR effects on day two were not mediated by differences in perseveration about the stressor. The findings indicate that racial discrimination - particularly intergroup racial discrimination - may have both momentary and prolonged effects on cardiac activity in AAs.

Autonomic dysregulation in burnout and depression: evidence for the central role of exhaustion

Objectives Given the important role of the autonomic nervous system (ANS) in stress regulation, astonishingly little is known about ANS functioning in burnout, a condition arising after prolonged exposure to work-related stress. The current study sought to investigate ANS modulation, as indexed by vagally-mediated heart rate variability (HRV), in relation to burnout symptomatology to (i) distinguish associations between the three dimensions of burnout [emotional exhaustion (EE), cynicism, reduced personal accomplishment] and (ii) investigate overlap in associations with depressive symptomatology. Methods Assessments of vagally-mediated HRV (ie, root mean square of successive differences, RMSSD) were conducted in a large population-based sample from the Dresden Burnout Study [N=410, mean age 42.2, standard deviation (SD) 11.2 years; 33.4% male]. Vagally-mediated HRV was assessed for 90 seconds during an emotionally-arousing situation (venipuncture, recumbent), a 335-second recumbent recovery period, and a 335-second seated resting condition. Results Results from multiple linear regression analyses revealed that EE was negatively related to RMSSD during venipuncture (=β -0.11, P=0.03) and the seated rest (β= -0.09, P=0.04) even after accounting for established ANS modulators (eg, age, body mass index). This pattern was not observed for the other dimensions of burnout. Exploratory analyses of depressive symptomatology further revealed that RMSSD was significantly and inversely associated with burnout-related symptoms but not with the core criteria of depression (eg, depressed mood). Conclusions This study presents evidence for a link between exhaustion and reduced vagal function, both in burnout and depression, suggesting that ANS modulations may not be disorder-specific but rather a psychophysiological correlate of an underlying feature shared by both conditions.

Examining the association between perceived discrimination and heart rate variability in African Americans.

Objective: Previous research attempting to delineate the role of discrimination in racial/ethnic disparities in hypertension has focused largely on blood pressure, which is chiefly governed by the sympathetic branch of the autonomic nervous system. Consequently, few studies have considered the role of the parasympathetic branch and particularly its regulation of the heart via the vagus nerve. Method: In the present cross-sectional study, we employed hierarchical linear regressions to examine associations between perceived ethnic discrimination and resting heart rate variability (HRV), an important biomarker of parasympathetic cardiac modulation and overall health, in a sample (N = 103) of young, healthy African American participants (58% female, Mage = 19.94 years, SD = 2.84). Results: After accounting for demographic factors and health status characteristics, lifetime discrimination emerged as an inverse predictor of HRV. When subdomains of discrimination were considered, discrimination attributable to threats or actual acts of aggression was also predictive of lower HRV. Conclusions: Our findings suggest that a greater lifetime burden of discrimination and discriminatory harassment and/or assault is associated with lower resting HRV in African Americans. The implications of these findings are discussed in the context of past, present and emerging research emphasizing biological linkages between discrimination and health.

Race and sex differences in cardiovascular α-adrenergic and β-adrenergic receptor responsiveness in men and women with high blood pressure

Objective: Hypertension is associated with unfavorable changes in adrenergic receptor responsiveness, but the relationship of race and sex to adrenergic receptor responsiveness in the development of cardiovascular disease is unclear. This study examined &agr;-adrenergic and ß-adrenergic receptor responsiveness in African-American and white men and women with untreated high blood pressure (BP) (HBP) and with normal BP. Methods and results: The study sample comprised 161 African-American and white men and women in the age range 25–45 years. Isoproterenol, a nonselective ß-adrenergic receptor agonist, was administered intravenously to determine the bolus dose required to increase heart rate by 25 bpm, an index of &bgr;-adrenergic receptor responsiveness. Similarly, phenylephrine, an &agr;1-adrenergic receptor agonist, was administered to determine the bolus dose required to increase BP by 25 mmHg, an index of vascular &agr;1-adrenergic receptor responsiveness. HBP (P < 0.01), male sex (P = 0.04), and higher BMI (P < 0.01) were all associated with reduced &bgr;-adrenergic receptor responsiveness, with a similar trend observed for African-American race (P = 0.07). Conversely, &agr;1-adrenergic receptor responsiveness was increased in association with HBP (P < 0.01), female sex (P < 0.01), and African-American race (P < 0.01). Conclusion: In the early stages of hypertension, cardiovascular &bgr;-adrenergic receptors demonstrate blunted responsiveness, whereas conversely &agr;1-adrenergic receptors exhibit increased responsiveness. This pattern of receptor changes is especially evident in men and African-Americans, is exacerbated by obesity, and may contribute to the development of cardiovascular disease.

Resting Heart Rate Variability, Facets of Rumination and Trait Anxiety: Implications for the Perseverative Cognition Hypothesis

The perseverative cognition hypothesis (PCH) posits that perseveration, defined as the repetitive or sustained activation of cognitive representations of a real or imagined stressor, is a primary mechanism linking psychological (or stress) vulnerability with poor health and disease. Resting vagally mediated heart rate variability (vmHRV) is an important indicator of self-regulatory abilities, stress vulnerability and overall health. Those with lower resting vmHRV are more vulnerable to stress, and thus more likely to engage in perseverative cognition and experience subsequent negative mental health outcomes such as anxiety. Recent research suggests that rumination—one of the core mechanisms underlying perseveration—is a construct containing (at least) two maladaptive (depressive and brooding) and one adaptive (reflective) types of rumination. However, to date, research has not examined how the association between resting vmHRV may differ between these three facets of rumination, in addition to these facets’ mechanistic role in linking lower resting vmHRV with greater trait anxiety. The current cross-sectional study explores these relationships in a sample of 203 participants (112 females, 76 ethnic minorities, mean age = 19.43, standard deviation = 1.87). Resting vmHRV was assessed during a 5-min-resting period using an Electrocardiogram (ECG). Both trait rumination (including the three facets) and anxiety were assessed via self-report scales. Significant negative associations were found between resting vmHRV and maladaptive, but not adaptive, forms of perseveration. Similarly, mediation analyses showed a significant indirect relationship between resting vmHRV and anxiety through maladaptive, but not adaptive, facets of rumination. Our findings support the PCH such that those with stress vulnerability, as indexed by lower resting vmHRV, are more likely to engage in maladaptive perseverative cognition and thus experience negative outcomes such as anxiety. Our data also lend a novel outlook on the PCH; resting vmHRV is not related to reflective rumination and thus, this facet of perseveration may be a neutral, but not beneficial, factor in the link between stress vulnerability and psychological well-being.