Symbolic Dynamics Analysis: a new methodology for foetal heart rate variability analysis

Cardiotocography (CTG) is a widespread foetal diagnostic methods. However, it lacks of objectivity and reproducibility since its dependence on observer's expertise. To overcome these limitations, more objective methods for CTG interpretation have been proposed. In particular, many developed techniques aim to assess the foetal heart rate variability (FHRV). Among them, some methodologies from nonlinear systems theory have been applied to the study of FHRV. All the techniques have proved to be helpful in specific cases. Nevertheless, none of them is more reliable than the others. Therefore, an in-depth study is necessary. The aim of this work is to deepen the FHRV analysis through the Symbolic Dynamics Analysis (SDA), a nonlinear technique already successfully employed for HRV analysis. Thanks to its simplicity of interpretation, it could be a useful tool for clinicians. We performed a literature study involving about 200 references on HRV and FHRV analysis; approximately 100 works were focused on non-linear techniques. Then, in order to compare linear and non-linear methods, we carried out a multiparametric study. 580 antepartum recordings of healthy fetuses were examined. Signals were processed using an updated software for CTG analysis and a new developed software for generating simulated CTG traces. Finally, statistical tests and regression analyses were carried out for estimating relationships among extracted indexes and other clinical information. Results confirm that none of the employed techniques is more reliable than the others. Moreover, in agreement with the literature, each analysis should take into account two relevant parameters, the foetal status and the week of gestation. Regarding the SDA, results show its promising capabilities in FHRV analysis. It allows recognizing foetal status, gestation week and global variability of FHR signals, even better than other methods. Nevertheless, further studies, which should involve even pathological cases, are necessary to establish its reliability.

Heart rate variability and biomarkers of systemic inflammation in patients with stable coronary heart disease: findings from the Heart and Soul Study

Chronic low-grade systemic inflammation is a key component in atherogenesis. Decreased heart rate variability (HRV), a strong predictor of cardiovascular events, has been associated with elevations in circulating levels of C-reactive protein (CRP), interleukin (IL)-6, and fibrinogen in apparently healthy individuals. We investigated whether decreased HRV is associated with inflammatory markers in patients with coronary heart disease (CHD).

Resting heart rate and incident heart failure and cardiovascular mortality in older adults: role of inflammation and endothelial dysfunction: the PROSPER study

Resting heart rate is a promising modifiable cardiovascular risk marker in older adults, but the mechanisms linking heart rate to cardiovascular disease are not fully understood. We aimed to assess the association between resting heart rate and incident heart failure (HF) and cardiovascular mortality, and to examine whether these associations might be attributable to systemic inflammation and endothelial dysfunction.

QTc interval and resting heart rate as long-term predictors of mortality in type 1 and type 2 diabetes mellitus: a 23-year follow-up

We evaluated the association of QT interval corrected for heart rate (QT(c)) and resting heart rate (rHR) with mortality (all-causes, cardiovascular, cardiac, and ischaemic heart disease) in subjects with type 1 and type 2 diabetes.

Heart rate variability does not discriminate between different levels of haemodynamic responsiveness during surgical anaesthesia

BACKGROUND: Hypnotic depth but not haemodynamic responsiveness is measured with EEG-based monitors. In this study we compared heart rate variability (HRV) in unstimulated patients and stimulation-induced HRV at different levels of anaesthesia. METHODS: A total of 95 ASA I or II patients were randomly assigned to five groups (Group 1: BIS 45(5), remifentanil 1 ng ml(-1); Group 2: BIS 45(5), remifentanil 2 ng ml(-1); Group 3: BIS 45(5), remifentanil 4 ng ml(-1); Group 4: BIS 30(5), remifentanil 2 ng ml(-1); Group 5: BIS 60(5), remifentanil 2 ng ml(-1)). A time- and frequency-domain analysis of the RR interval (RRI) from the electrocardiogram was performed. HRV before induction, before and after a 5 s tetanic stimulus of the ulnar nerve, and before and after tracheal intubation was compared between groups, between stimuli, and between responders to intubation [systolic arterial pressure (SAP) increase >20 mm Hg, a maximal heart rate (HR) after intubation >90 min(-1) or both] and non-responders (anova). RESULTS: Induction of anaesthesia significantly lowered HR and HRV. Mean RRI before stimulation was higher in G3 than in G1, G2, and G4 (P < 0.001), whereas the other HRV parameters were similar. Intubation induced a greater HRV response than tetanic stimulation. The mean RRI after intubation was lower in G3 compared with the other groups and the sd of the RRI after tetanic stimulation was lower in G3 compared with G5. Otherwise, unstimulated HRV and stimulation-induced HRV were similar in responders and non-responders. CONCLUSION: HRV parameters discriminate between awake and general anaesthesia, are different after tracheal intubation and a 5 s ulnar nerve stimulation, but do not discriminate between different levels of haemodynamic responsiveness during surgical anaesthesia.

Day-to-night time differences in the relationship between cardiorespiratory coordination and heart rate variability

Heart rate variability (HRV) and cardiorespiratory coordination, i.e. the temporal interplay between oscillations of heartbeat and respiration, reflect information related to the cardiovascular and autonomic nervous system. The purpose of this study was to investigate the relationship between spectral measures of HRV and measures of cardiorespiratory coordination. In 127 subjects from a normal population a 24 h Holter ECG was recorded. Average heart rate (HR) and the following HRV parameters were calculated: very low (VLF), low (LF) and high frequency (HF) oscillations and LF/HF. Cardiorespiratory coordination was quantified using average respiratory rate (RespR), the ratio of heart rate and respiratory rate (HRR), the phase coordination ratio (PCR) and the extent of cardiorespiratory coordination (PP). Pearson's correlation coefficient r was used to quantify the relationship between each pair of the variables across all subjects. HR and HRR correlated strongest during daytime (r = 0.89). LF/HF and PP showed a negative correlation to a reasonable degree (r = -0.69). During nighttime sleep these correlations decreased whereas the correlation between HRR and RespR (r = -0.47) as well as between HRR and PCR (r = 0.73) increased substantially. In conclusion, HRR and PCR deliver considerably different information compared to HRV measures whereas PP is partially linked reciprocally to LF/HF.

[Is resting heart rate a cardiovascular risk factor?]

During recent years, resting heart rate was not considered as a cardiovascular risk factor. However, new evidences have showed that resting heart rate is an important prognostic factor for sudden cardiac death and heart failure in the general population, and especially among patients with known cardiac disease. Interestingly, resting heart rate not only predicts cardiac mortality but also all-cause mortality. The most common pathophysiological explanation is related to the fact that increased heart rate increases myocardial oxygen consumption and in parallel reduces coronary blood flow (reduction in the diastolic duration).

Effects of pediatric adiposity on heart rate variability

The relationship between obesity and heart rate variability (HRV) has been studied in adults and adolescents, but is not determined in young pediatrics. The purpose of this study was to assess autonomic activity using HRV in a pediatric population. We hypothesized that obese children would have reduced parasympathetic and increased sympathetic activity compared to age-matched subjects. 42 pediatric subjects (ages 3-5) were classified into 3 groups based on body mass index-for-age; normal, overweight and obese. HRV and respiratory rate were recorded during 3 minute baseline, 2 minute isometric handgrip and 3 minute recovery. HRV was analyzed in the time domain [heart rate (HR), RR interval (RRI) and RRI standard deviation (RRISD)] and frequency domain [low frequency (LF), high frequency (HF) and LF/HF ratio] using repeated measures ANOVA. Spearman’s correlations were used to examine the relations between BMI and HRV at rest. Significant condition effects were found between baseline, exercise and recovery, but these responses were not significantly different between the normal, overweight and obese children. BMI was negatively correlated with LF/HF, while BMI was positively correlated with RRISD, LF, HF and nHF. Our data demonstrate that higher BMI in the pediatric population is correlated with higher parasympathetic and lower sympathetic activity. These findings are contrary to HRV responses observed in adults and adolescents, suggesting complex relationships between age, obesity and autonomic control of the heart. The data supports the concept of an age reliance of HRV and a novel relationship between adiposity and body mass index in 3-5 year olds.

Relationship between heart rate variability, interleukin-6, and soluble tissue factor in healthy subjects

Decreased heart rate variability (HRV) has been associated with an increased risk of atherosclerosis. We hypothesized that a decrease in frequency domains of resting HRV would be associated with elevated plasma levels of interleukin (IL)-6 and soluble tissue factor (sTF) both previously shown to prospectively predict atherothrombotic events in healthy subjects. Subjects were 102 healthy and unmedicated black and white middle-aged men and women. We determined IL-6 and sTF antigen in plasma and HRV measures from surface electrocardiogram data using spectral analysis. All statistical analyses controlled for age, gender, ethnicity, smoking status, blood pressure, and body mass index. Low amounts of low frequency (LF) power (beta=-0.31, p=0.007) and high frequency (HF) power (beta=-0.36, p=0.002) were associated with increased amounts of IL-6, explaining 7% and 9% of the variance, respectively. Interactions between LF power and IL-6 (p=0.002) and between HF power and IL-6 (p=0.012) explained 8% and 5%, respectively, of the variance in sTF. Post hoc analyses showed associations between IL-6 and sTF when LF power (beta=0.51, p<0.001) and HF power (beta=0.48, p<0.001) were low but not when LF power and high HF power were high. The findings suggest that systemic low-grade inflammatory activity is associated with a decrease in HRV. Furthermore, there was a positive relationship between plasma levels of IL-6 and sTF antigen when HRV was low. Inflammation and related hypercoagulability might particularly contribute to atherothrombotic events in a setting of decreased HRV.

Effects of a Beginning Judo Class on Heart Rate

We evaluated the heart rate responses of 15 adult and six child subjects to beginning judo class sessions. Heart rate responses were compared to cardiovascular intensity ranges recommended by the American College of Sports Medicine (ACSM). Heart rate responses of adults (n=15) averaged 70 percent of age-predicted maximum heart rate with a range of 96 beats/minute to 154 beats/minute. The heart rate responses of the children (n=6) averaged 68 percent of age-predicted maximum heart rate with a range of 133-161 beats/min. Our results show that judo is effective in elevating heart rate to levels recommended by the ACSM for appropriate periods of time to improve cardiovascular fitness.

Relation of heart rate recovery to psychological distress and quality of life in patients with chronic heart failure

BACKGROUND: Psychological distress, poor disease-specific quality of life (QoL), and reduction in vagally mediated early heart rate recovery (HRR) after exercise, all previously predicted morbidity and mortality in patients with chronic heart failure (CHF). We hypothesized lower HRR with greater psychological distress and poorer QoL in CHF. DESIGN: All assessments were made at the beginning of a comprehensive cardiac outpatient rehabilitation intervention program. METHODS: Fifty-six CHF patients (mean 58+/-12 years, 84% men) completed the Hospital Anxiety and Depression Scale and the Minnesota Living With Heart Failure Questionnaire. HRR was determined as the difference between HR at the end of exercise and 1 min after exercise termination (HRR-1). RESULTS: Elevated levels of anxiety symptoms (P=0.005) as well as decreased levels of the Minnesota Living With Heart Failure Questionnaire total (P = 0.025), physical (P=0.026), and emotional (P=0.017) QoL were independently associated with blunted HRR-1. Anxiety, total, physical, and emotional QoL explained 11.4, 8, 7.8, and 9.0%, respectively, of the variance after controlling for covariates. Depressed mood was not associated with HRR-1 (P=0.20). CONCLUSION: Increased psychological distress with regard to elevated anxiety symptoms and impaired QoL were independent correlates of reduced HRR-1 in patients with CHF. Reduced vagal tone might explain part of the adverse clinical outcome previously observed in CHF patients in relation to psychological distress and poor disease-specific QoL.

Heart rate recovery after exercise in chronic heart failure: Role of vital exhaustion and type D personality

OBJECTIVE: Vital exhaustion and type D personality previously predicted mortality and cardiac events in patients with chronic heart failure (CHF). Reduced heart rate recovery (HRR) also predicts morbidity and mortality in CHF. We hypothesized that elevated levels of vital exhaustion and type D personality are both associated with decreased HRR. METHODS: Fifty-one patients with CHF (mean age 58+/-12 years, 82% men) and left ventricular ejection fraction (LVEF)