Zuzana Visnovcova

Complexity and time asymmetry of heart rate variability are altered in acute mental stress.

We aimed to study the complexity and time asymmetry of short-term heart rate variability (HRV) as an index of complex neurocardiac control in response to stress using symbolic dynamics and time irreversibility methods. ECG was recorded at rest and during and after two stressors (Stroop, arithmetic test) in 70 healthy students. Symbolic dynamics parameters (NUPI, NCI, 0V%, 1V%, 2LV%, 2UV%), and time irreversibility indices (P%, G%, E) were evaluated. Additionally, HRV magnitude was quantified by linear parameters: spectral powers in low (LF) and high frequency (HF) bands. Our results showed a reduction of HRV complexity in stress (lower NUPI with both stressors, lower NCI with Stroop). Pattern classification analysis revealed significantly higher 0V% and lower 2LV% with both stressors, indicating a shift in sympathovagal balance, and significantly higher 1V% and lower 2UV% with Stroop. An unexpected result was found in time irreversibility: significantly lower G% and E with both stressors, P% index significantly declined only with arithmetic test. Linear HRV analysis confirmed vagal withdrawal (lower HF) with both stressors; LF significantly increased with Stroop and decreased with arithmetic test. Correlation analysis revealed no significant associations between symbolic dynamics and time irreversibility. Concluding, symbolic dynamics and time irreversibility could provide independent information related to alterations of neurocardiac control integrity in stress-related disease.

Vagal function indexed by respiratory sinus arrhythmia and cholinergic anti-inflammatory pathway

The autonomic nervous system, in particular vagal function, plays an important role in a wide range of somatic and mental disorders. Cardiac vagal function can be indexed by the respiratory sinus arrhythmia (RSA) - oscillations in heart rate linked to respiration mediated predominantly by fluctuations of vagus nerve efferent traffic originating in the nucleus ambiguus. Moreover, the neurocardiac vagal modulation has been shown to be related to physiological adaptability/flexibity and emotional regulation. Thus, greater vagal withdrawal during stressors and subsequent recovery should be indicative of a more flexible physiological response system. Importantly, the vagal inhibitory function plays a key role in the regulation of allostatic processes including the immune response (cholinergic anti-inflammatory pathway). Decreased cardiovagal function (lower RSA) was shown to be associated with increased proinflammatory markers and acute-phase proteins indicating increased allostatic load and poor health. Thus, the study of the vagal-immune interactions could help illuminate the pathway via which psychosocial factors may influence health and disease.

Heart rate time irreversibility is impaired in adolescent major depression

UNLABELLEDnWe aimed to study heart rate time irreversibility--a nonlinear qualitative characteristics of heart rate variability indicating complexity of cardiac autonomic control at rest and in response to physiological stress (orthostasis) in never-treated major depressive disorder (MDD) adolescent female patients.nnnMETHODSnWe studied 20 MDD girls and 20 healthy age-matched girls at the age of 15 to 18 years. The ECG was recorded in supine position and in response to position change from lying to standing (orthostasis). Time irreversibility analysis was performed using Portas (P%), Guziks (G%) and Ehlers (E) index. The depressive disorder severity was evaluated using Montgomery-Asberg Depression Rating Scale (MADRS) and Childrens Depression Inventory (CDI).nnnRESULTSnResting heart rate time irreversibility indices (logG%, logP%, Ehlers index) were significantly reduced in MDD female patients without significant differences in response to orthostasis in MDD girls compared to controls. No significant correlations between time irreversibility and MDD severity were observed.nnnCONCLUSIONnThis study revealed the impaired heart rate asymmetry pattern indicating an altered complexity of cardiac autonomic regulation in adolescent female patients suffering from MDD.

HEART RATE VARIABILITY AND ELECTRODERMAL ACTIVITY AS NONINVASIVE INDICES OF SYMPATHOVAGAL BALANCE IN RESPONSE TO STRESS

Abstract The autonomic nervous system (ANS) is a principal regulatory system for maintaining homeostasis, adaptability and physiological flexibility of the organism at rest as well as in response to stress. In the aspect of autonomic regulatory inputs on the cardiovascular system, recent research is focused on the study of exaggerated/diminished cardiovascular reactivity in response to mental stress as a risk factor for health complications, e.g. hypertension. Thus, the analysis of biological signals reflecting a physiological shift in sympathovagal balance during stress in the manner of vagal withdrawal associated with sympathetic overactivity is important. The heart rate variability, i.e. “beat-to-beat” oscillations of heart rate around its mean value, reflects mainly complex neurocardiac parasympathetic control. The electrodermal activity could represent “antagonistic” sympathetic activity, the so-called “sympathetic arousal” in response to stress. The detailed study of the physiological parameters under various stressful stimuli and in recovery phase using traditional and novel mathematical analyses could reveal discrete alterations in sympathovagal balance. This article summarizes the importance of heart rate variability and electrodermal activity assessment as the potential noninvasive indices indicating autonomic nervous system activity in response to mental stress.

Cardiovascular control during orthostatic and mental stress: Conditional entropy based analysis

The aim of this study was to characterize the changes in cardiovascular dynamics as a result of orthostatic and mental stress and their combination by linear and information domain analysis of heart rate and blood pressure oscillations. We recorded beat-to-beat RR intervals and systolic blood pressure values in 16 volunteers during mental arithmetics task and head-up tilt test and their simultaneous administration. The analysis included spectral measures and quantification of cardiovascular signals complexity and their mutual causal coupling. Our results demonstrated that orthostatic and mental stress challenges - despite similar heart rate and blood pressure changes - evoked different effects on cardiovascular control system. The novel conditional entropy based measures were sensitive to detect differences in heart rate and blood pressure dynamics responses evoked by mental stress in different body positions.

Alterations in vagal-immune pathway in long-lasting mental stress.

We studied a potential impact of chronic psychosocial load on the allostatic biomarkers--cardiac vagal activity, inflammation, and oxidative stress in healthy undergraduate students. Continuous resting ECG signals were monitored in a group of 16 female healthy students (age: 23.2±0.2 years, BMI: 20.9±0.5 kg/m2) at two time periods: right after holiday (rest period) and a day before final exams (stress period). Vagal activity was quantified by spectral analysis of heart rate variability at high frequency band (HF-HRV). The immune response was assessed from the level of tumor necrosis factor-alpha (TNF-α) in plasma. In addition, mean RR intervals were evaluated. We found that HF-HRV was significantly reduced and the TNF-α was increased in the stress period compared with the rest period. No significant changes were found in the RR interval. In conclusion, allostatic load induced by stress and the accompanying greater immune response decreased cardiovagal regulation in healthy young subjects. These findings may help understand the pathway by which stress can influence health and disease.

The complexity of electrodermal activity is altered in mental cognitive stressors

The aim of this study was to evaluate potential changes in the electrodermal activity (EDA) to enable the detection of variations in the sympathetic nervous system during mental load and recovery period. Several EDA parameters were used: SCA (skin conductance amplitude), frequency of NS-EDR (nonspecific electrodermal responses), SIE (symbolic information entropy), and ApEn (approximate entropy). The cohort consisted of 50 healthy students (average age: 23.33±0.24yr., 25 women). The stress profile consisted of five phases: baseline (P1), Stroop test (P2), recovery (P3), mental arithmetic test (P4), and recovery (P5). All phases of the stress profile lasted six minutes. The results indicate that the three EDA indices have sufficient sensitivity to detect changes in the sympathetic nervous system. The SCA, SIE and ApEn were significantly increased during mental loads and decreased during recovery periods. However, SCA remained significantly elevated during recovery periods versus baseline, and SIE and ApEn decreased significantly during recovery versus baseline. The frequency of NS-EDR had no significant changes during stress. The EDA is a sensitive marker for evaluation of changes during the activation of sympathetic nervous system under the influence of a load. Detailed knowledge of EDA regulatory mechanisms associated with stress could provide important information associated with autonomic dysregulation.

Symbolic dynamics of heart rate variability — a promising tool to investigate cardiac sympathovagal control in attention deficit/hyperactivity disorder (ADHD)?

We aimed to evaluate complex cardiac sympathovagal control in attention deficit/hyperactivity disorder (ADHD) by using heart rate variability (HRV) nonlinear analysis - symbolic dynamics. We examined 29 boys with untreated ADHD and 25 healthy boys (age 8-13 years). ADHD symptoms were evaluated by ADHD-RS-IV scale. ECG was recorded in 3 positions: baseline supine position, orthostasis, and clinostasis. Symbolic dynamics indices were used for the assessment of complex cardiac sympathovagal regulation: normalised complexity index (NCI), normalised unpredictability index (NUPI), and pattern classification measures (0V%, 1V%, 2LV%, 2UV%). The results showed that HRV complexity was significantly reduced at rest (NUPI) and during standing position (NCI, NUPI) in ADHD group compared to controls. Cardiac-linked sympathetic index 0V% was significantly higher during all posture positions and cardiovagal index 2LV% was significantly lower to standing in boys suffering from ADHD. Importantly, ADHD symptom inattention positively correlated with 0V%, and negatively correlated with NCI, NUPI. Concluding, symbolic dynamics revealed impaired complex neurocardiac control characterised by potential cardiac beta-adrenergic overactivity and vagal deficiency at rest and to posture changes in boys suffering from ADHD that is correlated with inattention. We suggest that symbolic dynamics indices could represent promising cardiac biomarkers in ADHD.

Endothelial function in children with white-coat hypertension

Several studies have demonstrated endothelial dysfunction in patients with essential hypertension. However, the presence of endothelial dysfunction in children with white-coat hypertension has not been studied. We evaluated the endothelial function in children with white-coat hypertension and essential hypertension using axa0novel method based on the assessment of flow-mediated dilation (FMD). Study involved 106 children: 30 white-coat hypertensives (age 16.3xa0±xa01.3xa0years, meanxa0±xa0SD), 30 essential hypertensives (age 16.4xa0±xa01.3xa0years), and 46 healthy controls (age 16.2xa0±xa01.4xa0years). Ultrasound scans of the right brachial artery were performed using Prosound F75 Aloka system during protocol: baseline (1xa0min), forearm ischemia (5xa0min), and post-occlusion phase (3xa0min). FMD (%) was expressed as a change of the arterial diameter from baseline to maximum post-occlusion value and the valuesxa0<xa05% were considered as deficient FMD. We found significantly lower FMD in both essential and white-coat hypertension compared to control group (pxa0<xa00.05 for both) with no significant difference between the hypertensive groups. Deficient FMD was found in both hypertensive groups, but not in the control group. The occurence of deficient FMD was significantly higher in both essential and white-coat hypertensives compared to controls (pxa0<xa00.01 for both) with no significant difference between the hypertensive groups. Our findings of endothelial dysfunction indicated by impaired FMD in pediatric patients with white-coat hypertension could help to elucidate the mechanisms of the increased cardiovascular risk that could be similar as found in essential hypertension; therefore, white-coat hypertension should not be considered axa0benign phenomenon.

Improved assessment of arterial stiffness using corrected cardio-ankle vascular index (CAVI0) in overweight adolescents with white-coat and essential hypertension

Abstract Arterial stiffness is a marker of vascular damage. Although adiposity increases cardiovascular risk, the relationship between paediatric overweight and arterial stiffness is unclear. The study aimed to evaluate the simultaneous effect of hypertension and overweight on arterial stiffness using cardio-ankle vascular index (CAVI) and related novel, theoretically blood pressure (BP)-independent, index CAVI0. CAVI and CAVI0 were measured in 140 adolescent boys (16.0u2009±u20091.9u2009years) divided into age-matched groups: normal-weight normotensives, overweight normotensives, overweight white-coat hypertensives, and overweight essential hypertensives. Overweight normotensives had significantly lower CAVI and CAVI0 compared to normal-weight normotensives (4.81u2009±u20090.64 vs. 5.33u2009±u20090.66, pu2009<u2009.01; 7.10u2009±u20090.99 vs. 7.81u2009±u20091.00, pu2009<u2009.01, respectively). CAVI and CAVI0 in overweight essential hypertensives showed no significant difference compared to normal-weight normotensives and were significantly higher compared to overweight normotensives (5.32u2009±u20090.77 vs. 4.81u2009±u20090.64, pu2009<u2009.01; 7.77u2009±u20091.19 vs. 7.10u2009±u20090.99, pu2009<u2009.01, respectively). CAVI, but not CAVI0, was associated positively with diastolic pressure (0.022u2009mmHg−1, pu2009=u2009.002) and negatively with pulse pressure (−0.022u2009mmHg−1, pu2009=u2009.001), and it was significantly higher in overweight white-coat hypertensives compared to overweight normotensives (5.20u2009±u20090.63 vs. 4.81u2009±u20090.64, pu2009<u2009.05). The lowering effect of overweight on arterial stiffness indexed by CAVI and CAVI0 in hypertensive adolescents seems to counterbalance the early arteriosclerotic effect of essential hypertension. The increase in CAVI, but not CAVI0, in overweight white-coat hypertensives could be attributable to residual BP dependence of CAVI, which is not present in CAVI0. Under certain conditions, CAVI0 may offer a clinically relevant improved assessment of arterial stiffness superior to CAVI.