Genetic influences on baroreflex sensitivity during rest and mental stress

Spontaneous baroreflex sensitivity and its association with age, sex, obesity indices and hypertension: a population study

BACKGROUND

Low baroreflex sensitivity (BRS) was an established risk factor for cardiovascular disorders. We investigated determinants of BRS in a large sample from general population.

METHODS

In a population-based study (n = 901), data were collected on BRS, arm cuff blood pressure (BP), and obesity indices including body mass index, waist-to-hip ratio, waist circumference, and percentage body fat (%BF). BRS was calculated by spectral analysis software based on continuously recorded spontaneous fluctuations in beat-to-beat finger BP for 10-15 minutes. Correlations and multivariable regression analyses were used to test associations of age, sex, obesity indices, and hypertension with BRS while considering effects of lifestyle factors (smoking, alcohol consumption, and physical activity).

RESULTS

In multivariable analysis, age, sex, %BF, and hypertension were independently associated with BRS. BRS decreased with -0.10 (95% confidence interval: -0.15 to -0.06) ms/mm Hg with each year of increase in age. Women had -1.55 (95% confidence interval: -2.28 to -0.73) ms/mm Hg lower mean BRS than men. The effects of %BF (per 10% increase) and hypertension on BRS were -0.55 (95% confidence interval: -0.97 to -0.13) ms/mm Hg and -1.23 (95% confidence interval: -1.92 to -0.46) ms/mm Hg, respectively. There was no evidence of associations between BRS and lifestyle factors. Age, age2, sex, and their interactions plus %BF and hypertension contributed 16.9% of total variance of BRS.

CONCLUSIONS

In this large general population study, we confirmed prior findings that age and sex were important factors associated with BRS and found %BF was more strongly related to less favorable BRS levels than body mass index.

Higher Anxiety Is Associated with Lower Cardiovascular Autonomic Function in Female Twins

Anxiety symptoms co-occur with cardiovascular health problems, with increasing evidence suggesting the role of autonomic dysfunction. Yet, there is limited behavior genetic research on underlying mechanisms. In this twin study, we investigated the phenotypic, genetic and environmental associations between a latent anxiety factor and three cardiovascular autonomic function factors: interbeat interval (IBI, time between heart beats), heart rate variability (HRV, overall fluctuation of heart-beat intervals) and baroreflex sensitivity (BRS, efficiency in regulating blood pressure [BP]). Multivariate twin models were fit using data of female twins (N = 250) of the Twin Interdisciplinary Neuroticism Study (TWINS). A significant negative association was identified between latent anxiety and BRS factors (r = -.24, 95% CI [-.40, -.07]). Findings suggest that this relationship was mostly explained by correlated shared environmental influences, and there was no evidence for pleiotropic genetic or unique environmental effects. We also identified negative relationships between anxiety symptoms and HRV (r = -.17, 95% CI [-.34, .00]) and IBI factors (r = -.13, 95% CI [-.29, .04]), though these associations did not reach statistical significance. Findings implicate that higher anxiety scores are associated with decreased efficiency in short-term BP regulation, providing support for autonomic dysfunction with anxiety symptomatology. The baroreflex system may be a key mechanism underlying the anxiety-cardiovascular health relationship.

Heritability and genetic and environmental correlations of heart rate variability and baroreceptor reflex sensitivity with ambulatory and beat-to-beat blood pressure

This family study from Oman (n = 1231) explored the heritability and genetic and environmental correlations of heart rate variability (HRV) and baroreceptor reflex sensitivity (BRS) with ambulatory and beat-to-beat blood pressure (BP). Ambulatory BP was measured for 24 hours to calculate mean values for daytime and sleep separately. Time and frequency domain HRV indices, BRS, office beat-to-beat BP, and heart rate (HR) were measured for 10 minutes at rest. SOLAR software was used to perform univariate and bivariate quantitative genetic analyses adjusting for age, age², sex, their interactions and BMI. Heritability of SBP and DBP ranged from 16.8% to 40.4% for daytime, sleeping, 24-hour and office beat-to-beat measurements. HR and BRS showed a heritability of 31.9% and 20.6%, respectively, and for HRV indices heritability ranged from 11.1% to 20.5%. All HRV measurements and BRS were found to be negatively correlated with BP, but phenotypic correlation coefficients were relatively weak; HR was positively correlated with BP. None of the genetic correlations were statistically significant while environmental factors explained most of the correlations for all HRV indices with BP. Our study found consistent but weak correlations among HRV, HR, BRS and ambulatory/office beat-to-beat BP. However, environmental rather than genetic factors contributed most to those correlations.

Heritability and Temporal Stability of Ambulatory Autonomic Stress Reactivity in Unstructured 24-Hour Recordings

OBJECTIVE

Measurements of ambulatory autonomic reactivity can help with our understanding of the long-term health consequences of exposure to psychosocial stress in real-life settings.

METHODS

In this study, unstructured 24-hour ambulatory recordings of cardiac parasympathetic and sympathetic control were obtained in 1288 twins and siblings, spanning both work time and leisure time. These data were used to define two ambulatory baseline (sleep, leisure) and four stress conditions (wake, work, work_sitting, work_peak) from which six ambulatory stress reactivity measures were derived. The use of twin families allowed for estimation of heritability and testing for the amplification of existing or emergence of new genetic variance during stress compared with baseline conditions.

RESULTS

Temporal stability of ambulatory reactivity was assessed in 62 participants and was moderate to high over a 3-year period (0.36 < r < 0.91). Depending on the definition of ambulatory reactivity used, significant heritability was found, ranging from 29% to 40% for heart rate, 34% to 47% for cardiac parasympathetic control (indexed as respiratory sinus arrhythmia), and 10% to 19% for cardiac sympathetic control (indexed as the preejection period). Heritability of ambulatory reactivity was largely due to newly emerging genetic variance during stress compared with periods of rest. Interestingly, reactivity to short standardized stressors was poorly correlated with the ambulatory reactivity measures implying poor laboratory-real-life correspondence.

CONCLUSIONS

Ambulatory autonomic reactivity extracted from an unstructured real-life setting shows reliable, stable, and heritable individual differences. Real-life situations uncover a new and different genetic variation compared with that seen in resting baseline conditions, including sleep.

Identifying genetic variants for heart rate variability in the acetylcholine pathway

Heart rate variability is an important risk factor for cardiovascular disease and all-cause mortality. The acetylcholine pathway plays a key role in explaining heart rate variability in humans. We assessed whether 443 genotyped and imputed common genetic variants in eight key genes (CHAT, SLC18A3, SLC5A7, CHRNB4, CHRNA3, CHRNA, CHRM2 and ACHE) of the acetylcholine pathway were associated with variation in an established measure of heart rate variability reflecting parasympathetic control of the heart rhythm, the root mean square of successive differences (RMSSD) of normal RR intervals. The association was studied in a two stage design in individuals of European descent. First, analyses were performed in a discovery sample of four cohorts (n = 3429, discovery stage). Second, findings were replicated in three independent cohorts (n = 3311, replication stage), and finally the two stages were combined in a meta-analysis (n = 6740). RMSSD data were obtained under resting conditions. After correction for multiple testing, none of the SNPs showed an association with RMSSD. In conclusion, no common genetic variants for heart rate variability were identified in the largest and most comprehensive candidate gene study on the acetylcholine pathway to date. Future gene finding efforts for RMSSD may want to focus on hypothesis free approaches such as the genome-wide association study.

Concepts of scientific integrative medicine applied to the physiology and pathophysiology of catecholamine systems

This review presents concepts of scientific integrative medicine and relates them to the physiology of catecholamine systems and to the pathophysiology of catecholamine-related disorders. The applications to catecholamine systems exemplify how scientific integrative medicine links systems biology with integrative physiology. Concepts of scientific integrative medicine include (i) negative feedback regulation, maintaining stability of the body's monitored variables; (ii) homeostats, which compare information about monitored variables with algorithms for responding; (iii) multiple effectors, enabling compensatory activation of alternative effectors and primitive specificity of stress response patterns; (iv) effector sharing, accounting for interactions among homeostats and phenomena such as hyperglycemia attending gastrointestinal bleeding and hyponatremia attending congestive heart failure; (v) stress, applying a definition as a state rather than as an environmental stimulus or stereotyped response; (vi) distress, using a noncircular definition that does not presume pathology; (vii) allostasis, corresponding to adaptive plasticity of feedback-regulated systems; and (viii) allostatic load, explaining chronic degenerative diseases in terms of effects of cumulative wear and tear. From computer models one can predict mathematically the effects of stress and allostatic load on the transition from wellness to symptomatic disease. The review describes acute and chronic clinical disorders involving catecholamine systems-especially Parkinson disease-and how these concepts relate to pathophysiology, early detection, and treatment and prevention strategies in the post-genome era.

Heritability of cardiac vagal control in 24-h heart rate variability recordings: influence of ceiling effects at low heart rates

This study estimated the heritability of 24-h heart rate variability (HRV) measures, while considering ceiling effects on HRV at low heart rates during the night. HRV was indexed by the standard deviation of all valid interbeat intervals (SDNN), the root mean square of differences between valid, successive interbeat intervals (RMSSD), and peak-valley respiratory sinus arrhythmia (pvRSA). Sleep and waking levels of cardiac vagal control were assessed in 1,003 twins and 285 of their non-twin siblings. Comparable heritability estimates were found for SDNN (46%-53%), RMSSD (49%-54%), and pvRSA (48%-57%) during the day and night. A nighttime ceiling effect was revealed in 10.7% of participants by a quadratic relationship between mean pvRSA and the interbeat interval. Excluding these participants did not change the heritability estimates. The genetic factors influencing ambulatory pvRSA, RMSSD, and SDNN largely overlap. These results suggest that gene-finding studies may pool the different cardiac vagal indices and that exclusion of participants with low heart rates is not required.

The Twin Interdisciplinary Neuroticism Study

The Twin Interdisciplinary Neuroticism Study (TWINS) is a three-wave study including >800 twin pairs from the northern part of the Netherlands. The aim of the study is to unravel why neuroticism reflects vulnerability to mental disorders. In this study, we focus on possible mechanisms underlying this vulnerability and their genetic and environmental origins. In total, 125 female twin pairs visited our psychophysiological laboratory. From these twin pairs DNA was isolated and both candidate gene and genome-wide genotyping were conducted. Future work includes studies of candidate genes. The study also participates in several meta-genome-wide association study (GWAS) consortia.

Reproducibility of heart rate variability and baroreflex sensitivity measurements in children

Despite their extensive use, the reproducibility of cardiac autonomic measurements in children is not well-known. We investigated the reproducibility of short-term continuous measurements of heart rate (HR), heart rate variability (HRV, time and frequency domain), and spontaneous baroreflex sensitivity (BRS, frequency domain) in the supine and standing position in 57 children (11.2+/-0.7 years, 52.6% boys). Reproducibility between two sessions within a two-week interval was evaluated by intraclass correlation coefficients (ICCs), standard error of measurement, coefficients of variation (CVs), limits of agreement, and Bland-Altman plots. HR and HRV were moderately-to-highly (ICC=.63-.79; CV=5.7%-9.7%) and BRS moderately (ICC=.49-.63; CV=11.4%-14.0%) reproducible. While the BRS measurements were slightly less reproducible than the HR and HRV measurements, all can be reliably applied in research, thus implicating sufficient capacity to detect real differences between children. Still, clinical studies focusing on individual changes in cardiac autonomic functioning need to address the considerable random variations that may occur between test-retest measurements.

Rejection sensitivity relates to hypocortisolism and depressed mood state in young women

Rejection sensitivity and the associated fear of negative social evaluation (FNSE) trait are characteristics of hypocortisolemic syndromes such as atypical depression. However, a meta-analysis showed that acute FNSE evokes strong cortisol responses in humans. This is consistent with suggestions that hypocortisolism reflects a protective adaptation to a history of high cortisol responses. This leads us to hypothesize that measures of trait FNSE relate to hypocortisolism. Moreover, because FNSE relates positively to depressed mood state, but negatively to cortisol, we expect that the positive relationship between depressed mood state and cortisol will show up most clearly when controlling for the confounding effect of FNSE on this relationship. In the present study we measured salivary cortisol awakening response and psychological variables in 194 community women aged 18-30 years. The results confirmed our hypotheses. We propose that dispositional FNSE is associated with a history of frequent high cortisol responses, leading to long-term protective inhibition of further cortisol and energy mobilization. The present results have special relevance for mental health problems that have high prevalence among young women.