Autonomic responses to stress in Black versus Caucasian Africans: the SABPA study

Heart rate variability, the dynamic nature of the retinal microvasculature and cardiac stress: providing insight into the brain-retina-heart link: the SABPA study

BACKGROUND AND AIMS

Decreased heart-rate-variability (HRV) indicates increased sympathetic nervous system (SNS) activity and modulation with a shift in the sympatho-vagal balance towards SNS predominance. Increased SNS activity may precede volume-loading hypertension, contribute to increases in cardiac troponin T (cTnT), endothelial dysfunction and small vessel disease. Therefore, we investigated the retinal vasculature, HRV during flicker-light-induced-provocation (FLIP) and systemic cTnT, a marker of cardiac stress, to provide further evidence in support of the brain-retina-heart link.

METHODS

Cross-sectional observations were obtained from a bi-ethnic cohort (N = 264), aged 23-68 years. Fasting serum samples for cTnT were obtained. Retinal vascular calibres were quantified from mydriatic eye fundus images and dynamic retinal vessel calibre responses were determined during FLIP. Time-and frequency domain parameters of HRV were calculated during FLIP for each participant.

RESULTS

Africans had wider venules and attenuated time domain parameters during FLIP. In Africans, inverse associations emerged between arteriolar dilation and both cTnT and root-mean squared of the standard deviations of successive RR-intervals (rMSSD) (p = 0.030), and between arteriolar constriction and both low-frequency expressed in normalised units (LFnu) (p = 0.003) and high-frequency expressed in normalised units (p = 0.021). Wider venules inversely associated with standard deviation of the NN intervals (SDNN) as well as LFnu (p = 0.009) in Africans. An opposite profile was observed in Caucasians with both time-and frequency domain parameters of HRV in relation to retinal vessel structure and function.

CONCLUSION

FLIP elicited increased SNS activity and modulation in this bi-ethnic cohort. In Africans, decreased HRV during FLIP accompanied arteriolar and venular responses and elevated systemic levels of cTnT, implying that the SNS exerted a significant effect on the smooth muscle tone of the retinal vasculature. Disrupted retinal autoregulation may imply general autonomic nervous system dysfunction; exemplifying central control by the brain on all systemic regulatory functions, across different vascular beds.

Spectral Analysis of Heart Rate Variability: Time Window Matters

Spectral analysis of heart rate variability (HRV) is a valuable tool for the assessment of cardiovascular autonomic function. Fast Fourier transform and autoregressive based spectral analysis are two most commonly used approaches for HRV analysis, while new techniques such as trigonometric regressive spectral (TRS) and wavelet transform have been developed. Short-term (on ECG of several minutes) and long-term (typically on ECG of 1–24 h) HRV analyses have different advantages and disadvantages. This article reviews the characteristics of spectral HRV studies using different lengths of time windows. Short-term HRV analysis is a convenient method for the estimation of autonomic status, and can track dynamic changes of cardiac autonomic function within minutes. Long-term HRV analysis is a stable tool for assessing autonomic function, describe the autonomic function change over hours or even longer time spans, and can reliably predict prognosis. The choice of appropriate time window is essential for research of autonomic function using spectral HRV analysis.

Cardiovascular reactivity and oxidative stress in young and older adults: the African-PREDICT and SABPA studies

Background: Oxidative stress and increased cardiovascular reactivity are associated with endothelial dysfunction and cardiovascular disease development. These factors along with early vascular compromise are more pronounced in black populations. We aimed to compare cardiovascular reactivity and investigate associations thereof with oxidative stress in two bi-ethnic cohorts (younger: 25.0 ± 3.19yrs; older: 44.7 ± 9.61yrs). Methods: Cardiovascular reactivity using the color-word conflict test was measured with the Finometer device. Oxidative stress markers included superoxide dismutase (SOD), γ-glutamyl transferase (γ-GT) and reactive oxygen species (ROS). Results: Black groups displayed greater cardiovascular responses to stress than white groups. In younger white participants, diastolic blood pressure (DBP) (β = 0.31; p = 0.001) and mean arterial blood pressure (MAP) (β = 0.28; p = 0.002) associated with ROS. In older black participants, DBP (β = 0.23; p = 0.009), MAP (β = 0.18; p = 0.033), stroke volume (β = -0.20; p = 0.023) and arterial compliance (β = -0.25; p = 0.005) associated with γ-GT. In older white participants, systolic blood pressure (β = -0.20; p = 0.006) and MAP (β = -0.19; p = 0.009) associated with SOD. Conclusions: In the older black group, cardiovascular reactivity associated with markers of glutathione metabolism, suggesting a possible compensatory up-regulation thereof in order to correct their heightened responses to stress. Independent of age, findings in the white groups support a regulatory role of ROS to maintain vascular tone during stress.

The Na+K+-ATPase Inhibitor Marinobufagenin and Early Cardiovascular Risk in Humans: a Review of Recent Evidence

PURPOSE OF REVIEW

This review synthesizes recent findings in humans pertaining to the relationships between marinobufagenin (MBG), a steroidal Na+/K+-ATPase inhibitor and salt-sensitivity biomarker, and early cardiovascular risk markers.

RECENT FINDINGS

Twenty-four-hour urinary MBG strongly associates with habitual salt intake in young healthy adults (aged 20-30 years). Furthermore, in young healthy adults free of detected cardiovascular disease, MBG associates with increased large artery stiffness and left ventricular mass independent of blood pressure. These findings in human studies corroborate mechanistic data from rat studies whereby stimulation of MBG by a high salt intake or MBG infusion increased vascular fibrosis and cardiac hypertrophy. Twenty-four-hour urinary MBG may be a potential biomarker of early cardiovascular risk. Adverse associations between MBG-which increases with salt consumption-and early cardiovascular risk markers support the global efforts to reduce population-wide salt intake in an effort to prevent and control the burden of non-communicable diseases.

Autonomic activity and its relationship with the endogenous cardiotonic steroid marinobufagenin: the African-PREDICT study

Aim: Marinobufagenin (MBG), a cardiotonic steroid and a natriuretic hormone, is elevated in response to high salt diet consumption. In animal models salt intake stimulates adrenocortical MBG secretion via increased angiotensin II, sympathetic activity and aldosterone. No evidence in humans exists to suggest the involvement of the angiotensinergic-sympatho-excitatory pathway in MBG production. We investigated whether MBG is related to indices of autonomic activity in men and women. Methods: This cross-sectional study included 680 black and white, men and women from the African-PREDICT study (aged 20-30 years). Continuous 24 hr ECG recordings were used to obtain low and high frequency (LF, HF) heart rate variability (HRV). We measured 24 hr urinary MBG excretion and serum aldosterone. Results: We found a positive association of MBG excretion with estimated salt intake (P < 0.001) and aldosterone (P < 0.001) in women and men. In women only, a positive relationship was evident between MBG excretion and LF HRV in multivariate adjusted regression analyses (Adj. R ²= 0.33; β = 0.11; P = 0.030). In men, MBG excretion associated positively with HF HRV in similar regression analyses (R ² = 0.36; β = 0.12; P = 0.034). Sex-specific results were corroborated only in blacks, namely, a positive association of MBG excretion with LF HRV in black women (R ² = 0.38; β = 0.13; P = 0.036), and negative association with HF HRV in black men (R ² = 0.40; β = 0.18; P = 0.045). No relationships were evident in white women (P = 0.58) or men (P = 0.27). Conclusion: Our findings in this human cohort support suggested mechanisms whereby MBG is elevated as a result of increased salt intake, including autonomic activity, previously demonstrated in Dahl salt-sensitive hypertension.

Hemodynamic profile and compensation deficit in African and European Americans during physical and mental stress

Increased vascular reactivity to stress has been suggested to contribute to the greater risk for developing hypertension in African Americans. Here, we examined the way (hemodynamic profile) and the extent to which (compensation deficit) cardiac output and total peripheral resistance compensate for each other in determining blood pressure responses to a physical (orthostasis) and a mental (anger recall) stress task, in normotensive African American (AA, n = 30) and European American (EA, n = 48) college students. Blood pressure stress reactivity did not differ as a function of race. However, AAs showed a prominent vascular hemodynamic profile and a significant compensation deficit in response to both tasks, while EAs showed no hemodynamic response to orthostasis and a mixed profile in response to anger recall. The present findings demonstrate a more prominent vascular hemodynamic reactivity to stress in AAs, which could contribute to the pathogenesis of hypertension in this ethnic group.

Defensive coping facilitated a smaller cortisol-to-estradiol ratio and a higher hypertension risk: the SABPA study

OBJECTIVES

Taxing psychosocial stress and defensive coping have been associated with hypoactivity in cortisol, a vasoconstrictive agent. Estradiol has vasodilatory properties with cardio- and neuroprotective effects. It can however also induce α₁-adrenergic vasoconstrictive responsiveness. We aimed to determine whether the cortisol-to-estradiol ratio (Cort:E2) may augment α₁-adrenergic responsiveness and hypertension risk when habitually using defensive coping.

METHODS

African (n = 168) and Caucasian (n = 207) men and women (46 ± 9 years) were included. Preferential use of defensive coping was determined from Coping Strategy Indicator questionnaire scores. 24h Ambulatory blood pressure was obtained. Fasting serum estradiol and cortisol samples were collected before 09h00 and Cort:E2 was calculated.

RESULTS

Estradiol was higher in ethnic-coping groups. Smaller Cort:E2, higher estradiol levels, self-reported emotional stress (19.05% vs. 9.66%) and 24h blood pressure reaching hypertensive status (65% vs. 24%) were evident in African compared to Caucasian men (p ≤ .05). A smaller Cort:E2 was associated with augmented 24h SBP and 24h DBP in African men [Adj R² 0.21-0.29 (p ≤ .05)], and especially when utilizing defensive coping [Adj R² 0.34-0.38 (p ≤ .001)].

CONCLUSIONS

A smaller Cort:E2 was associated with raised blood pressure in defensive coping African men. Defensive coping, possibly via highly activated α₁-adrenergic vasoconstrictive responses, may facilitate neuro-endocrine dysfunction and hypertension in African men.

Cohort Profile: Sympathetic activity and Ambulatory Blood Pressure in Africans (SABPA) prospective cohort study

Adapting to an over-demanding stressful urban environment may exhaust the psychophysiological resources to cope with these demands, and lead to sympathetic nervous system dysfunction. The evidence that an urban-dwelling lifestyle may be detrimental to the cardiometabolic health of Africans motivated the design of the Sympathetic activity and Ambulatory Blood Pressure in African Prospective cohort study. We aimed to determine neural mechanistic pathways involved in emotional distress and vascular remodelling. The baseline sample included 409 teachers representing a bi-ethnic sex cohort from South Africa. The study was conducted in 2008–09 and repeated after 3-year follow-up in 2011–12, with an 87.8% successful follow-up rate. Seasonal changes were avoided and extensive clinical assessments were performed in a well-controlled setting. Data collection included sociodemographics, lifestyle habits, psychosocial battery and genetic analysis, mental stress responses mimicking daily life stress (blood pressure and haemostatic, cardiometabolic, endothelial and stress hormones). Target organ damage was assessed in the brain, heart, kidney, blood vessels and retina. A unique highly phenotyped cohort is presented that can address the role of a hyperactive sympathetic nervous system and neural response pathways contributing to the burden of cardiometabolic diseases in Africans.

Efficacy of exercise for menopausal symptoms: a randomized controlled trial

OBJECTIVE

This study aims to determine the efficacy of exercise training for alleviating vasomotor and other menopausal symptoms.

METHODS

Late perimenopausal and postmenopausal sedentary women with frequent vasomotor symptoms (VMS) participated in a randomized controlled trial conducted in three sites: 106 women randomized to exercise and 142 women randomized to usual activity. The exercise intervention consisted of individual facility-based aerobic exercise training three times per week for 12 weeks. VMS frequency and bother were recorded on daily diaries at baseline and on weeks 6 and 12. Intent-to-treat analyses compared between-group differences in changes in VMS frequency and bother, sleep symptoms (Insomnia Severity Index and Pittsburgh Sleep Quality Index), and mood (Patient Health Questionnaire-8 and Generalized Anxiety Disorder-7 questionnaire).

RESULTS

At the end of week 12, changes in VMS frequency in the exercise group (mean change, -2.4 VMS/d; 95% CI, -3.0 to -1.7) and VMS bother (mean change on a four-point scale, -0.5; 95% CI, -0.6 to -0.4) were not significantly different from those in the control group (-2.6 VMS/d; 95% CI, -3.2 to -2.0; P = 0.43; -0.5 points; 95% CI, -0.6 to -0.4; P = 0.75). The exercise group reported greater improvement in insomnia symptoms (P = 0.03), subjective sleep quality (P = 0.01), and depressive symptoms (P = 0.04), but differences were small and not statistically significant when P values were adjusted for multiple comparisons. Results were similar when considering treatment-adherent women only.

CONCLUSIONS

These findings provide strong evidence that 12 weeks of moderate-intensity aerobic exercise do not alleviate VMS but may result in small improvements in sleep quality, insomnia, and depression in midlife sedentary women.

Effects of acute and chronic stress on the L-arginine nitric oxide pathway in black and white South Africans: the sympathetic activity and ambulatory blood pressure in Africans study

OBJECTIVE

This study investigated the impact of stress on effectors of the L-arginine/nitric oxide (NO) system including the endogenous inhibitor asymmetric dimethylarginine (ADMA).

METHODS

Black (n = 168) and white (n = 206) South African teachers were exposed to a mental and a physical stressor for 1 minute, respectively. Serum samples for determination of l-arginine, NO metabolites, ADMA, and symmetric dimethylarginine (SDMA) were obtained at rest and during stress exposure. Perception of task stressfulness was assessed on a 7-point Likert scale, and psychological distress was estimated by the General Health Questionnaire.

RESULTS

Black South Africans exhibited higher resting levels of NO metabolites (adjusted mean [standard error of the mean] = 11.3 [1.3] versus 3.9 [1.1] μmol/l, p < .001) but lower circulating ADMA (0.62 [0.02] versus 0.70 [0.02] μmol/l, p = .004) and SDMA (0.41 [0.01] versus 0.53 [0.01] μmol/l, p < .001) than did white South Africans. Ethnicity-by-psychological distress interaction was observed for resting levels of ADMA (p = .002), SDMA (p = .038), and L-arginine (p = .048). Ethnic differences in responses to experimental stress were evident for NO metabolites (blacks versus whites: 5.94 [1.55] versus -0.74 [1.25] μmol/l, p = .004) and SDMA (blacks versus whites: -0.02 [0.01] versus 0.02 [0.01] μmol/l, p = .004). Ethnicity-by-psychological distress interaction for stress responses was found for l-arginine/ADMA ratio (p = .027).

CONCLUSIONS

The l-arginine/NO system is affected by psychosocial distress with higher susceptibility in black South Africans. This interaction may contribute to the higher cardiovascular disease risk in black South Africans.

Trigonometric regressive spectral analysis: an innovative tool for evaluating the autonomic nervous system

Biological rhythms, describing the temporal variation of biological processes, are a characteristic feature of complex systems. The analysis of biological rhythms can provide important insights into the pathophysiology of different diseases, especially, in cardiovascular medicine. In the field of the autonomic nervous system, heart rate variability (HRV) and baroreflex sensitivity (BRS) describe important fluctuations of blood pressure and heart rate which are often analyzed by Fourier transformation. However, these parameters are stochastic with overlaying rhythmical structures. R-R intervals as independent variables of time are not equidistant. That is why the trigonometric regressive spectral (TRS) analysis--reviewed in this paper--was introduced, considering both the statistical and rhythmical features of such time series. The data segments required for TRS analysis can be as short as 20 s allowing for dynamic evaluation of heart rate and blood pressure interaction over longer periods. Beyond HRV, TRS also estimates BRS based on linear regression analyses of coherent heart rate and blood pressure oscillations. An additional advantage is that all oscillations are analyzed by the same (maximal) number of R-R intervals thereby providing a high number of individual BRS values. This ensures a high confidence level of BRS determination which, along with short recording periods, may be of profound clinical relevance. The dynamic assessment of heart rate and blood pressure spectra by TRS allows a more precise evaluation of cardiovascular modulation under different settings as has already been demonstrated in different clinical studies.

A biobehavioral approach to understanding obesity and the development of obesogenic illnesses among Latino immigrants in the United States

The prevalence of obesity and obesity-related illnesses is higher among Hispanics (Latinos) than other racial and ethnic groups, and rates increase exponentially with the number of years living in the United States. Mounting evidence suggests that the origins of many chronic illnesses among disadvantaged minority groups may lie with cumulative exposure to chronic psychological and physiological stressors through the biobehavioral process of allostatic load (AL). Among immigrant Latinos, acculturation stress may contribute to an increase in AL and thus may be an independent risk factor for the development of obesity and obesogenic illnesses. The purpose of this theoretical article is to present a proposed model of the effects of acculturation stress on AL and obesity among Latino immigrants. Such a model can be useful to guide intervention efforts to decrease obesity among immigrant Latinos by adding education, skill building, and social integration strategies to healthy eating and physical activity to reduce the deleterious impact of acculturation stress.

Double product and end-organ damage in African and Caucasian men: the SABPA study

BACKGROUND

Increasing urbanisation in sub-Saharan African countries is causing a rapid increase in cardiovascular disease. Evidence suggests that Africans have higher blood pressures and a higher prevalence of hypertension-related cardiovascular morbidity and mortality, compared to Caucasians. We investigated double product (systolic blood pressure × heart rate), a substantial measure of cardiac workload, as a possible cardiovascular risk factor in African and Caucasian men.

MATERIAL AND METHODS

The study consisted of 101 urbanised African and 101 Caucasian male school teachers. We measured 24h ambulatory blood pressure and the carotid cross-sectional wall area, and determined left ventricular hypertrophy electrocardiographically by means of the Cornell product. Urinary albumin and creatinine were analysed to obtain the albumin-to-creatinine ratio.

RESULTS

Africans had higher 24h, daytime and nighttime systolic- and diastolic blood pressure, heart rate and resultant double product compared to the Caucasians. In addition, markers of end-organ damage, albumin-to-creatinine ratio and left ventricular hypertrophy were higher in the Africans while cross-sectional wall area did not differ. In Africans after single partial and multiple regression analysis, 24h systolic blood pressure, but not double product or heart rate, correlated positively with markers of end-organ damage (cross-sectional wall area: β=0.398, P=0.005; left ventricular hypertrophy: β=0.455, P<0.001; albumin-to-creatinine ratio: β=0.280, P=0.012). No associations were evident in Caucasian men.

CONCLUSIONS

Double product may not be a good marker of increased cardiovascular risk when compared to systolic blood pressure in African and Caucasian men.