Metabolic syndrome and short-term heart rate variability in young adults. The cardiovascular risk in young Finns study

Neuropeptide Y polymorphism increases the risk for asthma in overweight subjects; protection from atherosclerosis in asthmatic subjects--the cardiovascular risk in young Finns study

AIMS

The role of neuropeptide Y (NPY) and its gene polymorphisms in the development of atherosclerosis has become increasingly evident. In asthma, NPY has been shown to be involved as immunomodulator. In this study, we investigated the role of two functional NPY polymorphisms, NPY-Leu7Pro (rs16139) and NPY-399C/T (rs16147) and obesity for the development of asthma as well as atherosclerosis in asthmatic and non-asthmatic subjects. Also, we measured heart rate variability (HRV) and NPY in serum since these might contribute through these polymorphisms to both diseases.

METHODS AND RESULTS

Thousand hundred and seventy six Finnish young adults were genotyped and three groups (G1-G3) were formed based on the observed diplotypes. The NPY-Pro7 allele always co-existed with the NPY-399T allele indicating complete linkage disequilibrium. Here we show that overweight (BMI≥25kg/m2) was associated with 2.5-fold increased risk for asthma in subjects with the NPY-399T allele without NPY-Pro7 allele (G2, n=716). Overweight was also associated with increased atherosclerosis determined by carotid intima media thickness (cIMT), but asthma seemed to be more significant determinant than overweight in determing cIMT having a decreasing effect. NPY concentration in serum was diplotype-driven (G1=792.2(29.5), G2=849.0(18.9), G3=873.9(45.2) pg/ml) and correlated positively with cIMT in the group having NPY-Pro7 allele (G3, n=142). However, the subjects with asthma had a negative NPY-cIMT relationship. Total HRV was increased in asthma and correlated negatively with cIMT irrespective of the NPY genotype.

CONCLUSIONS

Overweight together with the NPY-399T allele without NPY-Pro7 allele was associated with increased risk for asthma. Atherosclerosis was decreased in subjects with asthma depending on the NPY genotype. The results reveal novel insights into the genetics and biology of the relationship of atherosclerosis and asthma.

Hypothalamic-pituitary-adrenal axis function in survivors of childhood acute lymphoblastic leukemia and healthy controls

Of all malignancies in children, acute lymphoblastic leukemia (ALL) is the most common type. Since survival significantly improves over time, treatment-related side effects become increasingly important. Glucocorticoids play an important role in the treatment of ALL, but they may suppress the hypothalamic-pituitary-adrenal (HPA) axis. The duration of HPA axis suppression is not yet well defined. The present study aimed at assessing the function of the HPA axis by determining the cortisol awakening response (CAR) and the dexamethasone (DEX) suppression test in children that were treated for childhood ALL, compared to a healthy age and sex matched reference group. In addition, questionnaires regarding sleep, fatigue, depression and quality of life were completed by the children and their parents. Fourty-three survivors who finished their treatment for childhood ALL 37 (interquartile range 22-75) months before and 57 healthy controls were included. No differences in CAR were observed between ALL survivors and the reference group, but survivors of ALL had higher morning cortisol levels and an increased cortisol suppression in response to oral dexamethasone. Higher cortisol levels in childhood ALL survivors were associated with more fatigue and poorer quality of life. We conclude that the experience of a stressful life event in the past may have caused a long-term dysregulation of the HPA axis in childhood ALL survivors, as reflected in an increased cortisol production and an enhanced negative feedback mechanism.

Heart rate variability changes at 2400 m altitude predicts acute mountain sickness on further ascent at 3000-4300 m altitudes

OBJECTIVE

If the body fails to acclimatize at high altitude, acute mountain sickness (AMS) may result. For the early detection of AMS, changes in cardiac autonomic function measured by heart rate variability (HRV) may be more sensitive than clinical symptoms alone. The purpose of this study was to ascertain if the changes in HRV during ascent are related to AMS.

METHODS

We followed Lake Louise Score (LLS), arterial oxygen saturation at rest (R-SpO(2)) and exercise (Ex-SpO(2)) and HRV parameters daily in 36 different healthy climbers ascending from 2400 m to 6300 m altitudes during five different expeditions.

RESULTS

After an ascent to 2400 m, root mean square successive differences, high-frequency power (HF(2 min)) of HRV were 17-51% and Ex-SpO(2) was 3% lower in those climbers who suffered from AMS at 3000 to 4300 m than in those only developing AMS later (≥5000 m) or not at all (all p < 0.01). At the altitude of 2400 m RMSSD(2 min) ≤ 30 ms and Ex-SpO(2) ≤ 91% both had 92% sensitivity for AMS if ascent continued without extra acclimatization days.

CONCLUSIONS

Changes in supine HRV parameters at 2400 m were related to AMS at 3000-4300 m Thus, analyses of HRV could offer potential markers for identifying the climbers at risk for AMS.

Metabolic syndrome, physical activity and cardiac autonomic function

BACKGROUND

Our primary aim was to investigate the associations that components of metabolic syndrome and physical activity have with cardiac autonomic nervous system activity as estimated by heart rate variability (HRV) in young adults free of metabolic abnormalities. We also aimed to identify predictors of 3-year changes in HRV.

METHODS

Physical activity was assessed annually in 163 healthy participants over 3 years (2008-2010). Components of metabolic syndrome measured annually were; waist circumference, systolic blood pressure, high-density lipoprotein, triglycerides, glucose, and C-reactive protein. A linear mixed regression model was used to assess associations between HRV, metabolic syndrome components and physical activity. Linear regression was used to identify predictors of changes in HRV.

RESULTS

 Metabolic syndrome components were negatively associated with HRV indices and higher heart rate, while physical activity was associated with higher HRV and lower heart rate. Physical activity and inflammation were predictors of positive and negative changes in HRV indices, respectively.

CONCLUSIONS

 In participants without significant metabolic abnormalities, metabolic syndrome components were still associated with less favourable HRV profiles. Physical activity and inflammation were both able to predict changes in HRV, albeit in different directions. It appears that the process of autonomic dysfunction starts at a young age and may be mediated in part by inflammation. Metabolic syndrome prevalence is increasing in younger populations; promoting the metabolic and autonomic benefits of exercise remains imperative.

Heart rate variability is independently associated with C-reactive protein but not with Serum amyloid A. The Cardiovascular Risk in Young Finns Study

BACKGROUND

Increased levels of C-reactive protein (CRP) and serum amyloid A (SAA) are associated with an increased risk of cardiovascular disease. It is hypothesized that dysregulation of the autonomic nervous system (ANS) leads to increased inflammation via the cholinergic anti-inflammatory pathway. Heart rate variability (HRV) is a marker of ANS function. HRV has been shown to be associated with CRP levels. Currently, there are no studies addressing the relationship between HRV and SAA.

DESIGN

The purpose of this study was to compare the associations between HRV, CRP and SAA in healthy young adults. CRP and SAA concentrations and short-term HRV indices [high frequency (HF), low frequency (LF), total spectral component of HRV, root mean square differences of successive R-R intervals, the standard deviation of all R-R intervals and ratio between LF and HF) were measured in 1601 men and women aged 24-39 taking part in the Cardiovascular Risk in Young Finns study.

RESULTS

A significant inverse correlation (P < 0·05) between HRV indices and inflammatory markers was observed. However, in linear regression analyses, only inverse association between HRV indices and CRP levels remained significant (P < 0·05), while association between HRV indices and SAA levels was attenuated to the null (P > 0·05) after adjusting for age, sex, body mass index, cholesterol levels, leptin and other common traditional cardiovascular risk factors.

CONCLUSIONS

Reduced HRV indices are independently associated with increased CRP levels, but not with SAA levels. This association supports the hypothesis that dysregulation of the ANS may lead to increased inflammation early in adulthood.

The metabolically healthy but obese postmenopausal woman presents a favourable heart rate variability profile

OBJECTIVE

The purpose of this study was to investigate the heart rate variability (HRV) profile in obese women displaying the metabolically healthy but obese (MHO) phenotype.

DESIGN

We studied 47 obese, sedentary postmenopausal women. Subjects were classified as MHO or at risk based on insulin resistance as assessed with the homeostatic model assessment (HOMA) index. Subjects were divided into tertiles according to HOMA values. Subjects in the lower tertile were categorised as MHO while subjects in the upper 2 tertiles represented at risk subjects. Outcome measures were heart rate variability factors (RR intervals, SDNN, LF, HF, pNN50, RMSSD), body temperature, body composition (DEXA) and a lipid profile as well as glucose and insulin.

RESULTS

MHO individuals had significantly lower resting heart rate, body temperature, lean body mass as well as fasting insulin and HOMA levels compared to at risk subjects (p < 0.05). In addition, RR intervals, SDNN and LF were significantly higher in MHO individuals (p < 0.05). Moreover, stepwise regression analysis showed that SDNN was an independent predictor of the variation in HOMA in our cohort.

CONCLUSION

Results of the present study indicate that postmenopausal women displaying the MHO phenotype present a favourable HRV profile. Therefore, higher HRV could be associated, at least in part, in the protective profile of MHO individuals.

Systemic hemodynamics in young adults with the metabolic syndrome: the Cardiovascular Risk in Young Finns Study

OBJECTIVE

We conducted the present study to examine associations of three different metabolic syndrome (MetS) definitions and their components to arterial stiffness, systemic vascular resistance, and left ventricular function at population level. In addition, the objective of the study was to examine associations of spontaneous recovery from MetS over 6 years' follow-up to systemic hemodynamics.

METHODS

The study population consisted of 1,741 Finnish young adults (aged 30-45 years) who had complete MetS risk factor and hemodynamic data available at 2007. Associations of spontaneous recovery from MetS to systemic hemodynamics was studied on a subpopulation of 1,391 subjects who had also complete MetS risk factor data available at 2001. Hemodynamic measurements were performed using a whole-body impedance cardiography device.

RESULTS

MetS and increasing number of MetS components were associated with lower stroke index (P < 0.001) and higher systemic vascular resistance index (P < 0.005) and arterial pulse wave velocity (P < 0.005). In MetS persistent group, stroke index was lower (P = 0.024), and pulse wave velocity was higher (P = 0.003) compared to MetS recovery group.

CONCLUSION

All current MetS definitions identify young adults with altered systemic hemodynamics, and recovery from MetS is associated with a favorable hemodynamic profile.

Particulate air pollution, metabolic syndrome, and heart rate variability: the multi-ethnic study of atherosclerosis (MESA)

BACKGROUND

Cardiac autonomic dysfunction has been suggested as a possible biologic pathway for the association between fine particulate matter ≤ 2.5 µm in diameter (PM2.5) and cardiovascular disease (CVD). We examined the associations of PM2.5 with heart rate variability, a marker of autonomic function, and whether metabolic syndrome (MetS) modified these associations.

METHODS

We used data from the Multi-Ethnic Study of Atherosclerosis to measure the standard deviation of normal-to-normal intervals (SDNN) and the root mean square of successive differences (rMSSD) of 5,465 participants 45-84 years old who were free of CVD at the baseline examination (2000-2002). Data from the U.S. regulatory monitor network were used to estimate ambient PM2.5 concentrations at the participants' residences. MetS was defined as having three or more of the following criteria: abdominal obesity, hypertriglyceridemia, low high-density lipoprotein cholesterol, high blood pressure, and high fasting glucose.

RESULTS

After controlling for confounders, we found that an interquartile range (IQR) increase in 2-day average PM2.5 (10.2 µg/m3) was associated with a 2.1% decrease in rMSSD [95% confidence interval (CI), -4.2 to 0.0] and nonsignificantly associated with a 1.8% decrease in SDNN (95% CI, -3.7 to 0.1). Associations were stronger among individuals with MetS than among those without MetS: an IQR elevation in 2-day PM2.5 was associated with a 6.2% decrease in rMSSD (95% CI, -9.4 to -2.9) among participants with MetS, whereas almost no change was found among participants without MetS (p-interaction = 0.005). Similar effect modification was observed in SDNN (p-interaction = 0.011).

CONCLUSION

These findings suggest that autonomic dysfunction may be a mechanism through which PM exposure affects cardiovascular risk, especially among persons with MetS.

Hypothesis: Intensive insulin therapy-induced mortality is due to excessive serotonin autoinhibition and autonomic dysregulation

Action to Control Cardiovascular Risk in Diabetes (ACCORD), The Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation and the Veterans Affairs Diabetes Trial were designed to study whether older patients with type 2 diabetes mellitus could reduce the risk of heart attacks and stroke and thereby prolong their lives by maintaining their blood glucose levels at near-healthy levels but failed to demonstrate the hoped-for benefit. Why the trials failed, though, and why ACCORD saw significantly more deaths due to increased rates of cardiovascular events in the intensive therapy arm of the study are not clear. These data have now been confirmed by the results of the recently concluded NICE-SUGAR Study which again revealed that intensive glucose control increased mortality among adults in intensive care units. I propose that the negative results noted in these trials are due to altered brain serotonin concentrations and autonomic dysregulation in addition to the low-grade systemic inflammation, decreased endothelial nitric oxide and enhanced free radical generation, diminished anti-oxidant defenses and altered metabolism of essential fatty acids present in patients with type 2 diabetes.

Increased sympathetic and decreased parasympathetic activity rather than changes in hypothalamic-pituitary-adrenal axis activity is associated with metabolic abnormalities

CONTEXT

Stress is suggested to lead to metabolic dysregulations as clustered in the metabolic syndrome, but the underlying biological mechanisms are not yet well understood.

OBJECTIVE

We examined the relationship between two main str systems, the autonomic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis, with the metabolic syndrome and its components.

DESIGN

The design was baseline data (yr 2004-2007) of a prospective cohort: the Netherlands Study of Depression and Anxiety (NESDA).

SETTING

The study comprised general community, primary care, and specialized mental health care.

PARTICIPANTS

This study included 1883 participants aged 18-65 yr.

MAIN OUTCOME MEASURES

Autonomic nervous system measures included heart rate, respiratory sinus arrhythmia (RSA; high RSA reflecting high parasympathetic activity), and preejection period (PEP; high PEP reflecting low sympathetic activity). HPA axis measures included the cortisol awakening response, evening cortisol, and a 0.5 mg dexamethasone suppression test as measured in saliva. Metabolic syndrome was based on the updated Adult Treatment Panel III criteria and included high waist circumference, serum triglycerides, blood pressure, serum glucose, and low high-density lipoprotein cholesterol.

RESULTS

RSA and PEP were both independently negatively associated with the presence of the metabolic syndrome, the number of metabolic dysregulations as well as all individual components except high-density lipoprotein cholesterol (all P < 0.02). Heart rate was positively related to the metabolic syndrome, the number of metabolic dysregulations, and all individual components (all P < 0.001). HPA axis measures were not related to metabolic syndrome or its components.

CONCLUSION

Our findings suggest that increased sympathetic and decreased parasympathetic nervous system activity is associated with metabolic syndrome, whereas HPA axis activity is not.

Neuroadrenergic dysfunction in obesity: an overview of the effects of weight loss

PURPOSE OF REVIEW

The prevalence of obesity is rising to epidemic proportions worldwide, and in tandem so is that of type 2 diabetes. Neuroadrenergic abnormalities, comprising increased resting sympathetic nervous system activity and blunted sympathetic neural responsiveness are recognized features of metabolic syndrome obesity, which contribute importantly to both the pathophysiology and adverse clinical prognosis of this high-risk population. Weight loss is recommended as first-line treatment for obesity. This review examines the effects of nonpharmacological weight loss on sympathetic nervous system function under basal and stimulated conditions.

RECENT FINDINGS

Human weight loss trials show that even moderate weight reduction is accompanied by significant attenuation in resting whole-body norepinephrine spillover rate and muscle sympathetic nerve activity, an improvement in cardiac autonomic modulation, and a reversal of blunted sympathetic responsiveness at both peripheral and central nervous system levels. Recent findings underscore the relevance of insulin resistance in mediating blunted sympathetic responsiveness to endogenous hyperinsulinemia induced by glucose ingestion. Impaired insulin transport across the blood-brain barrier may be one mechanism mediating these effects. Weight loss reverses blunted sympathetic responsiveness to glucose, which has implications for postprandial energy expenditure and body weight homeostasis.

SUMMARY

The autonomic dysfunction of obesity is reversible with weight loss, highlighting the importance of lifestyle intervention as a key therapeutic modality.