Genetic and environmental influences on blood pressure variability: a study in twins

Cardiovascular variability, sociodemographics, and biomarkers of disease: the MIDUS study

Introduction: Like heart rate, blood pressure (BP) is not steady but varies over intervals as long as months to as short as consecutive cardiac cycles. This blood pressure variability (BPV) consists of regularly occurring oscillations as well as less well-organized changes and typically is computed as the standard deviation of multiple clinic visit-to-visit (VVV-BP) measures or from 24-h ambulatory BP recordings (ABPV). BP also varies on a beat-to-beat basis, quantified by methods that parse variation into discrete bins, e.g., low frequency (0.04-0.15 Hz, LF). However, beat-to-beat BPV requires continuous recordings that are not easily acquired. As a result, we know little about the relationship between LF-BPV and basic sociodemographic characteristics such as age, sex, and race and clinical conditions. Methods: We computed LF-BPV during an 11-min resting period in 2,118 participants in the Midlife in the US (MIDUS) study. Results: LF-BPV was negatively associated with age, greater in men than women, and unrelated to race or socioeconomic status. It was greater in participants with hypertension but unrelated to hyperlipidemia, hypertriglyceridemia, diabetes, elevated CRP, or obesity. LF-diastolic BPV (DBPV), but not-systolic BPV (SBPV), was negatively correlated with IL-6 and s-ICAM and positively correlated with urinary epinephrine and cortisol. Finally, LF-DBPV was negatively associated with mortality, an effect was rendered nonsignificant by adjustment by age but not other sociodemographic characteristics. Discussion: These findings, the first from a large, national sample, suggest that LF-BPV differs significantly from VVV-BP and ABPV. Confirming its relationship to sociodemographic risk factors and clinical outcomes requires further study with large and representative samples.

Visit-to-visit blood pressure variability and mortality and cardiovascular outcomes after acute myocardial infarction

The relationship between visit-to-visit blood pressure variability (BPV) and cardiovascular outcomes remains unclear. Our study assessed the prognostic implications of visit-to-visit BPV in patients after acute myocardial infarction (AMI). The present study enrolled 7,375 patients who underwent percutaneous coronary intervention for AMI and at least five measurements of blood pressure after hospital discharge. Visit-to-visit BPV was estimated as variability independent of mean. The primary endpoint was all-cause mortality. The secondary endpoints were major cardiovascular events (the composite of cardiovascular death, myocardial infarction, and ischemic stroke) and hospitalization for heart failure. During a median follow-up of 5.8 years, adjusted risks of all-cause mortality, major cardiovascular events, and hospitalization for heart failure continuously increased as systolic BPV and diastolic BPV increased. Patients in the highest quartile of systolic BPV (versus lowest) had increased risk of all-cause mortality (adjusted hazard ratio (aHR) 1.51 [95% confidence interval (CI) 1.23-1.85]), major cardiovascular events (aHR 1.31 [95% CI 1.1-1.55]), and hospitalization for heart failure (aHR 2.15 [95% CI 1.49-3.1]). Patients in the highest quartile of diastolic BPV was also associated with all-cause mortality (aHR 1.39 [95% CI 1.14-1.7]), major cardiovascular events (aHR 1.29 [95% CI 1.08-1.53]), and hospitalization for heart failure (aHR 2.01[95% CI 1.4-2.87]). Both systolic and diastolic BPV improved the predictive ability of the GRACE (Global Registry of Acute Coronary Events) risk score for both all-cause mortality and major cardiovascular events. Higher visit-to-visit BPV was associated with increased risks of mortality and cardiovascular events in patients after AMI.

The genetic architecture of blood pressure variability: A genome-wide association study of 9370 participants from UK Biobank

Long-term blood pressure variability (BPV) is a risk factor for cardiovascular diseases, dementia, and stroke. However, its genetic architecture is not fully understood. This study aims to explore its genetic factors and provide more evidence on the mechanisms and further pathological study of BPV. The genome-wide association study (GWAS) is based on the UK Biobank cohort. There were four data collection rounds from 2006 to 2020, and 9370 participants with more than three blood pressure measurements were included. They had a median age of 55 and a male percentage of 50.1%. The phenotypes (BPV) were calculated by four methods and the genetic data contains 6 884 260 single nucleotide polymorphisms (SNPs) after imputation and quality control. A linear regression model was performed with adjustments for sex, age, genotype array, and a significant principal component. Subgroup analysis was performed on hypertension-free participants. The significant and suggestive significant P thresholds were set as 5 × 10-8 and 1 × 10-6 . Six genetic loci (BAD, CCDC88B, GPR137, PLCB3, RPS6KA4 for systolic BPV, and WWC2 for diastolic BPV) were identified by coding region SNPs at the suggestive significant P threshold (1 × 10-6 ). Among them, gene CCDC88B and RPS6KA4 reached the significant P threshold (5 × 10-8 ), with the strongest signal of SNP rs1229536170 (P = 6.36 × 10-8 , β = -.29). The annotation results indicate that genes CCDC88B, GPR137, RPS6KA4, and BAD are associated with long-term SBPV. Their functions of inflammation, epithelial dysfunction, and apoptosis are related to artery stiffness, which was reported as potential mechanisms of BPV.

Blood pressure variability and structural brain changes: a systematic review

BACKGROUND

Blood pressure variability (BPV) has been linked with cognitive impairment and dementia. However, the pathophysiological mechanisms by which BPV affects cognition are unclear. This systematic review aims to assess the links between different BPV measures and white and grey matter structures.

METHODS AND RESULTS

The following databases were searched from inception through to January 2021; EMBASE, MEDLINE, EMCARE and SCOPUS. Studies that reported on the relationship between within-individual BPV (short, medium or long-term variability) or a circadian blood pressure (BP) measurement and MRI assessed brain structures were included. Overall, 20 studies met the criteria and were included, of which 11 studies looked at short-term BPV, eight articles investigated visit-to-visit BPV and one study looked at a compositional BPV measurement. Due to heterogeneity in study samples, meta-analysis was not possible. Across the included studies, associations between MRI indices and BP dipping patterns were mixed; higher long-term BPV and higher sleep systolic BPV was found to be associated with lower whole brain volume and hippocampal volume.

CONCLUSION

Increased BPV, in particular systolic long-term and systolic night-time BPV, appears to be associated with lower brain volume and hippocampal volume. This highlights the adverse effect that increased BPV has upon the brain, potentially contributing to cognitive decline, including dementia, in late-life.

High blood pressure in children and adolescents: current perspectives and strategies to improve future kidney and cardiovascular health

Hypertension is one of the most common causes of preventable death worldwide. The prevalence of pediatric hypertension has increased significantly in recent decades. The cause of this is likely multifactorial, related to increasing childhood obesity, high dietary sodium intake, sedentary lifestyles, perinatal factors, familial aggregation, socioeconomic factors, and ethnic blood pressure (BP) differences. Pediatric hypertension represents a major public health threat. Uncontrolled pediatric hypertension is associated with subclinical cardiovascular disease and adult-onset hypertension. In children with chronic kidney disease (CKD), hypertension is also a strong risk factor for progression to kidney failure. Despite these risks, current rates of pediatric BP screening, hypertension detection, treatment, and control remain suboptimal. Contributing to these shortcomings are the challenges of accurately measuring pediatric BP, limited access to validated pediatric equipment and hypertension specialists, complex interpretation of pediatric BP measurements, problematic normative BP data, and conflicting society guidelines for pediatric hypertension. To date, limited pediatric hypertension research has been conducted to help address these challenges. However, there are several promising signs in the field of pediatric hypertension. There is greater attention being drawn on the cardiovascular risks of pediatric hypertension, more emphasis on the need for childhood BP screening and management, new public health initiatives being implemented, and increasing research interest and funding. This article summarizes what is currently known about pediatric hypertension, the existing knowledge-practice gaps, and ongoing research aimed at improving future kidney and cardiovascular health.

Association Between Visit-to-Visit Blood Pressure Variability in Early Adulthood and Myocardial Structure and Function in Later Life

Importance

Long-term blood pressure (BP) variability has emerged as a reproducible measure that is associated with heart failure independent of systemic BP. Visit-to-visit BP variability may be associated with the risk of heart failure early in the life course and thus may be reflected in subclinical alterations in cardiac structure and function.

Objective

To evaluate the association between visit-to-visit BP variability in early adulthood and myocardial structure and function in middle age.

Design, Setting, and Participants

This cohort study used data from the Coronary Artery Risk Development in Young Adults (CARDIA) study, a community-based cohort study of 5115 participants aged 18 to 30 years at baseline (year 0; March 25, 1985, to June 7, 1986) and followed up over a 30-year interval. A total of 2400 CARDIA study participants underwent evaluation at 4 field sites (Birmingham, Alabama; Oakland, California; Chicago, Illinois; and Minneapolis, Minnesota). Blood pressure was measured at 8 visits over a 25-year interval and participants received echocardiograms at year 25 (June 1, 2010, to August 31, 2011). Data analysis was conducted from June 7, 1986, to August 31, 2011.

Exposures

Visit-to-visit systolic and diastolic BP variability measures included SD, average real variability, and variability independent of the mean.

Main Outcomes and Measures

Echocardiographic indices of myocardial structure, systolic function, and diastolic function at the year 25 examination.

Results

Of the 2400 participants, 1024 were men (42.7%) and 976 were African American (40.7%); mean (SD) age at the year 25 examination was 50.4 (3.6) years. Per 1-SD increment, greater visit-to-visit systolic BP variability independent of the mean was associated with higher left-ventricular (LV) mass index (β [SE], 2.66 [0.4] g/m2, P < .001), worse diastolic function (early peak diastolic mitral annular velocity [é]) (β [SE], -0.40 [0.1] cm/s, P < .001), higher LV filling pressures (mitral inflow velocity to early diastolic mitral annular velocity [E/é]) β [SE], 0.37 [0.1] cm/s, P < .001), and worse global longitudinal strain (β [SE], 0.17 [0.1], P = .002). Similarly, greater visit-to-visit diastolic BP variability was associated with higher LV mass index (β [SE], 3.21 [0.5] g/m2, P < .001), worse diastolic function (é: β [SE], -0.24 [0.1] cm/s [P < .001]; E/é: β [SE], 0.23 [0.1] cm/s [P < .001]), and worse global longitudinal strain (β [SE], 0.13 [0.1], P = .02). The findings remained consistent when other BP variability measures were used (SD and average real variability).

Conclusions and Relevance

In this cohort study using data from the CARDIA study, greater visit-to-visit systolic and diastolic BP variability have been associated with adverse alterations in cardiac structure as well as systolic and diastolic function independent of mean BP levels.

Blood Pressure Variability and Dementia: A State-of-the-Art Review

Accumulating evidence demonstrates that blood pressure variability (BPV) may contribute to target organ damage, causing coronary heart disease, stroke, and renal disease independent of the level of blood pressure (BP). Several lines of evidence have also linked increased BPV to a higher risk of cognitive decline and incident dementia. The estimated number of dementia cases worldwide is nearly 50 million, and this number continues to grow with increasing life expectancy. Because there is no effective treatment to modify the course of dementia, targeting modifiable vascular factors continues as a top priority for dementia prevention. A clear understanding of the role of BPV in dementia may shed light on the etiology, early prevention, and novel therapeutic targets of dementia, and has therefore gained substantial attention from researchers and clinicians. This review summarizes state-of-art evidence on the relationship between BPV and dementia, with a specific focus on the epidemiological evidence, the underlying mechanisms, and potential intervention strategies. We also discuss challenges and opportunities for future research to facilitate optimal BP management and the clinical translation of BPV for the risk assessment and prevention of dementia.

Chiropractic care for hypertension: Review of the literature and study of biological and genetic bases

BACKGROUND AND AIM

Hypertension is a multifactorial condition that is among the leading causes of mortality worldwide. Regulation of blood pressure greatly depends upon the activity of the autonomic nervous system. Alterations in the autonomic nervous system can lead to hypertension. In addition to nervous system control and individual physiologic state, various genes can directly influence autonomic responses. The complexity of blood pressure control is reflected in the 20-30% of individuals resistant to traditional pharmacological treatment, this indicates the need for alternative interventions. This article provides an integrative review and discussion of the key neurophysiologic and genetic factors that contribute to blood pressure regulation, the autonomic nervous system (ANS) and manual therapy literature, and the manual therapy and blood pressure literature.

METHODS

To assess the effects of chiropractic on the management of hypertension we searched articles published from 1980 to 2019 in PubMed, the Index to Chiropractic Literature and CINAHL, using the keywords: chiropractic, spinal manipulation, hypertension, and blood pressure.

RESULTS

We found 38 original studies that analyzed the effect of chiropractic therapy on hypertension. Of these studies, 10 were case reports and the statistical significance of the effects of chiropractic on blood pressure was not evaluated on these articles, so we focused on the remaining 28 articles.

CONCLUSIONS

The results of the review relative to chiropractic care were promising, but often contradictory, suggesting more research should be done. In consideration of the complexity of ANS blood pressure control, an evaluation of patient presenting physiologic and genetic characteristics is recommended and could provide valuable insight relative to the likelihood of patient blood pressure related responsiveness to care.

Genetic and Environmental Effects on Gene Expression Signatures of Blood Pressure: A Transcriptome-Wide Twin Study

Recently, 2 transcriptome-wide studies identified 40 genes that were differentially expressed in relation to blood pressure. However, to what extent these BP-related gene expression signatures and their associations with BP are driven by genetic or environmental factors has not been investigated. In this study of 391 twins (193 twin pairs and 5 singletons; age 55-69 years; 40% male; 57% monozygous) recruited from the Finnish Twin Cohort, transcriptome-wide data on peripheral leukocytes were obtained using the Illumina HT12 V4 array. Our transcriptome-wide analysis identified 1 gene (MOK [MAPK/MAK/MRK overlapping kinase], P=7.16×10-8) with its expression levels associated with systolic BP at the cutoff of false-discovery rate <0.05. This association was further replicated in the Framingham Heart Study (P=1.02×10-5). Out of the 40 genes previously reported, 12 genes could be replicated in the twin cohort with false-discovery rate <0.05 and consistent direction of effect. Univariate twin modeling showed that genetic factors contributed to the expression variations of 12 genes with heritability estimates ranging from 6% to 65%. Bivariate twin modeling showed that 53% of the phenotypic association between systolic BP and MOK expression, and 100% of the phenotypic association of systolic and diastolic BP with CD97 (cluster of differentiation 97), TIPARP (TCDD-inducible poly[ADP-ribose] polymerase), and TPPP3 expression could be explained by genetic factors shared in common. In this study of adult twins, we identified one more gene, MOK, with its expression level associated with BP, and replicated several previously identified signals. Our study further provides new insights into the genetic and environmental sources of BP-related gene expression signatures.

Body Size Predicts Cardiac and Vascular Resistance Effects on Men's and Women's Blood Pressure

Key Points Summary We report how blood pressure, cardiac output and vascular resistance are related to height, weight, body surface area (BSA), and body mass index (BMI) in healthy young adults at supine rest and standing.Much inter-subject variability in young adult's blood pressure, currently attributed to health status, may actually result from inter-individual body size differences.Each cardiovascular variable is linearly related to height, weight and/or BSA (more than to BMI).When supine, cardiac output is positively related, while vascular resistance is negatively related, to body size. Upon standing, the change in vascular resistance is positively related to size.The height/weight relationships of cardiac output and vascular resistance to body size are responsible for blood pressure relationships to body size.These basic components of blood pressure could help distinguish normal from abnormal blood pressures in young adults by providing a more effective scaling mechanism. Introduction: Effects of body size on inter-subject blood pressure (BP) variability are not well established in adults. We hypothesized that relationships linking stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) with body size would account for a significant fraction of inter-subject BP variability. Methods: Thirty-four young, healthy adults (19 men, 15 women) participated in 38 stand tests during which brachial artery BP, heart rate, SV, CO, TPR, and indexes of body size were measured/calculated. Results: Steady state diastolic arterial BP was not significantly correlated with any index of body size when subjects were supine. However, upon standing, the more the subject weighed, or the taller s/he was, the greater the increase in diastolic pressure. Systolic pressure strongly correlated with body weight and height both supine and standing. Diastolic and systolic BP were more strongly related to height, weight and body surface area than to body mass index. When supine: lack of correlation between diastolic pressure and body size, resulted from the combination of positive SV correlation and negative TPR correlation with body size. The positive systolic pressure vs. body size relationship resulted from a positive SV vs. height relationship. In response to standing: the positive diastolic blood pressure vs. body size relationship resulted from the standing-induced, positive increase in TPR vs. body size relationship. The relationships between body weight or height with SV and TPR contribute new insight into mechanisms of BP regulation that may aid in the prediction of health in young adults by providing a more effective way to scale BP with body size.

Sympathetic Nerve Activity in Monozygotic Twins

Microneurographic recordings of human muscle sympathetic nerve activity responses to sudden sensory stimuli (ie, arousal) have revealed 2 intraindividually reproducible response profiles in healthy young males that predict different neural and blood pressure responses to more sustained stress. Approximately 50% of subjects inhibit muscle sympathetic nerve activity during arousal, whereas the remaining 50% do not, and the latter group displays a markedly greater blood pressure increase in response to arousal, as well as during and after 3 minutes of mental arithmetic. Studying a group of monozygotic twins (10 pairs, 2 excluded from analysis), the aim of the present study was to evaluate the degree of genetic determination of these sympathetic response profiles. Muscle sympathetic burst incidence at rest was similar in twins, with a within-pair burst incidence ratio of 0.87±0.02 (SEM) compared with 0.73±0.07 found in unrelated pairs ( P =0.002), confirming a previous study from our laboratory. In contrast, the sympathetic responses to arousal showed large twin within-pair variance (arousal inhibition ratio 0.56±0.11), which did not significantly differ ( P =0.939) from the variance in pairs of unrelated subjects (0.46±0.11). The finding that human muscle sympathetic nerve responses to arousal are less determined by genotype than the resting level of corresponding sympathetic nerve activity suggests that the arousal response pattern is more prone to be altered by environmental factors. This raises the possibility that these intraindividually reproducible sympathetic neural response profiles can be modified in a positive direction from a cardiovascular risk perspective.

Maternal undernutrition and excessive body weight and risk of birth and health outcomes

BACKGROUND

Overweight and obesity are increasing in low- and middle-income countries, while underweight remains a significant health problems. However, the association between double burden of nutrition and risk of adverse birth and health outcomes is still unclear in Bangladesh. The aim of this study was to determine the effect of maternal undernutrition and excessive body weight on a range of maternal and child health outcomes.

METHODS

In this study, we used Bangladesh Demographic and Health Survey (BDHS) 2011 and 2014 data sets to cover the maternal, child and non-communicable diseases related health outcomes. The study considered a range of outcome variables including pregnancy complication, cesarean delivery, diabetes, hypertension, stunting, and wasting, low birth weight, genital discharge, genital sore/ulcer, stillbirth, early neonatal mortality, perinatal mortality, preterm birth and prolonged labor. The key exposure variable was maternal body mass index. Multilevel regression analysis was performed to examine the association between outcomes and exposure variables.

RESULTS

Maternal overweight and obesity has increased from 10% in 2004 to 24% in 2014, a 240% increase in 10 years. Between 2004 and 2014, maternal undernutrition declined from 33% to 18%, a reduction rate of only 54% in 10 years. Compared to normal-weight women, overweight and obese women were more likely to have experienced pregnancy complication, cesarean delivery, diabetes, and hypertension. Underweight women were 1.3 times more likely to have children with stunting and 1.6 times more likely to experience wasting compared to normal weight women. Maternal BMI was not significantly associated with increased risk of genital sore or ulcer, genital discharge, menstrual irregularities, or low birth weight though in certain cases risk was higher.

CONCLUSIONS

High maternal overweight and obesity were observed to have significant adverse effects on health outcomes, while underweight was a risk factor for newborn health. The findings show that weight management is necessary to prevent adverse birth and health outcomes in Bangladesh.

TRIAL REGISTRATION

Data related to health was collected by following the guidelines of ICF international and Bangladesh Medical Research Council. The registration number of data collection is 132989.0.000 and the data-request was registered on March 11, 2015.

Characteristic enhancement of blood pressure V-shaped waves in sinoaortic-denervated rats in a conscious and quiet state

A hemodynamic feature of chronic sinoaortic-denervated (SAD) rats is the increase in blood pressure variability (BPV) without significant changes in the average level of blood pressure (BP). The current study was designed to investigate the changes in BP V-shaped waves (V waves) in SAD rats. Sprague-Dawley (SD) rats were divided into 2 groups: SAD rats and sham-operated rats (n=13). Hemodynamics measurements were obtained in conscious, freely moving rats, four weeks after sinoaortic denervation or sham operation. V wave indices were evaluated in rats in both conscious and quiet states. Additionally, normal and high BPV was simulated by the production of V waves with different amplitudes. The results showed that the V wave amplitude was dramatically increased, with a significantly prolonged duration and reduced frequency in SAD rats. V wave BPV in SAD rats was significantly increased, though BP remained unchanged. The twenty-four hour BPV in all rats was positively correlated with amplitude, duration time and V wave BPV and negatively correlated with frequency. The systolic BP spectral powers in the low frequency range (0.38-0.45 Hz) were significantly reduced in the V waves of SAD rats. Moreover, there was a remarkable increase in mean BPV and a normal mean BP after simulating high BPV in SAD rats. These results suggest that enhancement of V waves might be a waveform character of BP in SAD rats in both the conscious and quiet states. These types of V waves appear to be related to a depression of sympathetic regulation of BP induced by sinoaortic denervation.

Maternal body mass index and risk of birth and maternal health outcomes in low- and middle-income countries: a systematic review and meta-analysis

We conducted a systematic review and meta-analysis of population-based cohort studies of maternal body mass index (BMI) and risk of adverse birth and health outcomes in low- and middle-income countries. PubMed, Embase, CINAHL and the British Nursing Index were searched from inception to February 2014. Forty-two studies were included. Our study found that maternal underweight was significantly associated with higher risk of preterm birth (odds ratio [OR], 1.13; 95% confidence interval [CI], 1.01-1.27), low birthweight (OR, 1.66; 95% CI, 1.50-1.84) and small for gestational age (OR, 1.85; 95% CI, 1.69-2.02). Compared with mothers with normal BMI, overweight or obese mothers were at increased odds of gestational diabetes, pregnancy-induced hypertension, pre-eclampsia, caesarean delivery and post-partum haemorrhage. The population-attributable risk (PAR) indicated that if women were entirely unexposed to overweight or obesity during the pre-pregnancy or early pregnancy period, 14% to 35% fewer women would develop gestational diabetes, pre-eclampsia or pregnancy-induced hypertension in Brazil, China, India, Iran or Thailand. The highest PAR of low birthweight attributable to maternal underweight was found in Iran (20%), followed by India (18%), Thailand (10%) and China (8%). Treatment and prevention of maternal underweight, overweight or obesity may help reduce the burden on maternal and child health in developing countries.

Effect of genome and environment on metabolic and inflammatory profiles

Twin and family studies have established the contribution of genetic factors to variation in metabolic, hematologic and immunological parameters. The majority of these studies analyzed single or combined traits into pre-defined syndromes. In the present study, we explore an alternative multivariate approach in which a broad range of metabolic, hematologic, and immunological traits are analyzed simultaneously to determine the resemblance of monozygotic (MZ) twin pairs, twin-spouse pairs and unrelated, non-cohabiting individuals. A total of 517 participants from the Netherlands Twin Register, including 210 MZ twin pairs and 64 twin-spouse pairs, took part in the study. Data were collected on body composition, blood pressure, heart rate, and multiple biomarkers assessed in fasting blood samples, including lipid levels, glucose, insulin, liver enzymes, hematological measurements and cytokine levels. For all 51 measured traits, pair-wise Pearson correlations, correcting for family relatedness, were calculated across all the individuals in the cohort. Hierarchical clustering techniques were applied to group the measured traits into sub-clusters based on similarity. Sub-clusters were observed among metabolic traits and among inflammatory markers. We defined a phenotypic profile as the collection of all the traits measured for a given individual. Average within-pair similarity of phenotypic profiles was determined for the groups of MZ twin pairs, spouse pairs and pairs of unrelated individuals. The average similarity across the full phenotypic profile was higher for MZ twin pairs than for spouse pairs, and lowest for pairs of unrelated individuals. Cohabiting MZ twins were more similar in their phenotypic profile compared to MZ twins who no longer lived together. The correspondence in the phenotypic profile is therefore determined to a large degree by familial, mostly genetic, factors, while household factors contribute to a lesser degree to profile similarity.

Specific genetic influences on nighttime blood pressure

OBJECTIVES

Nighttime blood pressure (BP) has been shown to be superior to daytime BP in predicting hypertension related target organ damage and cardiac mortality. In our Georgia Cardiovascular Twin Study, we showed that apart from the genes that also influence daytime BP, specific genetic determinants explained 44% and 67% of the nighttime systolic BP (SBP) and diastolic BP (DBP) heritabilities, respectively. Here, we determined whether these results could be confirmed in a much larger twin cohort of young adults with 24-hour ambulatory BP measurements.

METHODS

Ambulatory BP was available in 703 white twins (308 pairs and 87 singletons, aged 18-34 years, 50% males) from the Prenatal Programming Twin Study. A bivariate quantitative genetic twin model was used to analyze daytime and nighttime BP. We conducted a meta-analysis to compare and integrate results from the 2 twin cohorts.

RESULTS

Model fitting showed no sex differences for any of the measures. Heritabilities were 0.60 and 0.51 for SBP and 0.54 and 0.46 for DBP at daytime and nighttime. The specific heritability due to novel genetic effects emerging during the nighttime was 0.21 for SBP and 0.26 for DBP, which comprised 41% and 57% of the total nighttime heritability for SBP and DBP, respectively. Meta-analysis confirmed absence of cohort differences with very similar combined results.

CONCLUSIONS

In addition to genes that influence both daytime and nighttime BP, a large part of the heritability is explained by genes that specifically influence BP at night.

Heritability analyses show visit-to-visit blood pressure variability reflects different pathological phenotypes in younger and older adults: evidence from UK twins

BACKGROUND

Clinic and long-term average blood pressure (BP) are heritable traits with estimates of heritability ranging from 0.31 to 0.68. Long-term visit-to-visit BP variability (BPV) is emerging as a new cardiovascular risk predictor, though it is unclear if this is completely independent of BP. We hypothesize that BPV should demonstrate the same pattern of additive genetic, shared environmental and unique environmental variance as BP, if both are phenotypic surrogates.

METHOD

We studied 2889 twin pairs not on any BP-lowering therapy from the Twins UK cohort, and estimated the additive genetic variance for baseline BP, long-term average BP, BP trajectory (rate of change of BP in mmHg/year) and BPV (coefficient of variation and average real variability over an average of 3.2 visits). Heritability estimates were obtained by structural equation modelling adjusting for age, age, sex and BMI.

RESULTS

The heritabilities for baseline SBP and DBP were 0.51 (95% confidence interval 0.49, 0.53) and 0.56 (0.54, 0.58); long-term average SBP and DBP were 0.56 (0.53, 0.59) and 0.61 (0.58, 0.64); and systolic and diastolic trajectories over 10 years were 0.49 (0.46, 0.52) and 0.29 (0.27, 0.32), respectively. Both overall systolic and diastolic BPV showed no additive genetic variance contributing to the phenotypic variation, but after stratification by age, the younger subgroup (<51 years) showed heritability estimates of 0.44 (0.38, 0.50) for coefficient of variation and 0.35 (0.29, 0.41) for average real variability.

CONCLUSION

Age is a major factor that influences heritability estimation of BPV and it is likely that BPV in younger and older age groups may reflect different pathological phenotypes.

Arterial pressure and cerebral blood flow variability: friend or foe? A review

Variability in arterial pressure and cerebral blood flow has traditionally been interpreted as a marker of cardiovascular decompensation, and has been associated with negative clinical outcomes across varying time scales, from impending orthostatic syncope to an increased risk of stroke. Emerging evidence, however, suggests that increased hemodynamic variability may, in fact, be protective in the face of acute challenges to perfusion, including significant central hypovolemia and hypotension (including hemorrhage), and during cardiac bypass surgery. This review presents the dichotomous views on the role of hemodynamic variability on clinical outcome, including the physiological mechanisms underlying these patterns, and the potential impact of increased and decreased variability on cerebral perfusion and oxygenation. We suggest that reconciliation of these two apparently discrepant views may lie in the time scale of hemodynamic variability; short time scale variability appears to be cerebroprotective, while mid to longer term fluctuations are associated with primary and secondary end-organ dysfunction.