Assessment of autonomic function in cardiovascular disease: physiological basis and prognostic implications

Heart rate variability and mortality in critically ill COVID-19 pneumonia patients

Background

Heart rate variability (HRV) has prognostic value for predicting mortality in both cardiovascular and sepsis patients. Decreased HRV has been associated with increased mortality and morbidity. However, the prognostic significance of HRV in critically ill patients COVID-19 pneumonia still remains unknown. The current study aimed to (1) evaluate prognostic utility of HRV parameters on outcomes in patients with severe COVID-19 pneumonia and (2) assess the correlation between HRV parameters and inflammatory markers.

Methods

Consecutive critically ill patients with COVID-19 pneumonia admitted to a tertiary referral intensive care unit from October 2021 to June 2022 in Bangkok, Thailand were enrolled. HRV parameters over the 24 h following intensive care unit admission were recorded using telemetry and analyzed using the Holter program (Philips Holter 2010 Plus/1810 Series). Receiver-operating characteristic (ROC) curve analysis was used to determine optimum threshold cutoffs of various HRV parameters. Formal comparisons of in-hospital mortality between patients with and without a decrease in HRV were performed using Cox regression after adjusting for potential confounders.

Results

A total of 65 patients were enrolled in the study. Patients were classified into two groups: survivors (n = 44, 68 %) and non-survivors (n = 21, 32 %). The standard deviation of normal-to-normal intervals (SDNN) was significantly lower in non-survivors than in survivors (70.30 vs. 105.95; p = 0.03). The SDNN predicted in-hospital mortality with an area under the ROC curve of 0.67 (95 % CI 0.55-0.79). At a cutoff of 70 ms, the SDNN showed a sensitivity and specificity of 0.48 and 0.86. The low SDNN group (<70 ms) demonstrated higher median ferritin, IL-6, and hs-C-reactive protein levels than did the normal SDNN group, although such differences did not reach statistical significance (1139.0 vs. 508.4; p = 0.137 and 91.2 vs. 64.4; p = 0.352, respectively). After adjusting for potential confounders in the multivariable model, the adjusted hazard ratio for in-hospital mortality in those with SDNN <70 ms was 3.70 (95 % CI 1.34-10.24).

Conclusion

A decrease in SDNN, a commonly used HRV parameter, was associated with mortality and inflammatory biomarkers in critically ill patients with COVID-19 pneumonia.

Exploring heart rate variability in polycystic ovary syndrome: implications for cardiovascular health: a systematic review and meta-analysis

OBJECTIVES

Polycystic ovary syndrome (PCOS) is a prevalent and complex endocrine disorder that affects women of reproductive age. It has significant implications for female endocrine function, reproductive health, and metabolic disturbances, including insulin resistance, impaired glucose tolerance, and dyslipidemia. Studies have shown that decreased heart rate variability (HRV), a marker of autonomic dysfunction, is associated with adverse cardiovascular events. Recent research has focused on investigating autonomic function in PCOS, and some studies have suggested altered autonomic drive in these patients. The aim of this systematic review and meta-analysis was to evaluate cardiac autonomic function by analyzing HRV in women with PCOS.

METHODS

This systematic review was prepared using PRISMA reporting guidelines. The databases searched were PubMed, Scopus, Web of Science, and Cochrane. Risk of Bias was assessed using ROBINS-I for non-RCTs. The GRADE approach was employed to evaluate the level of certainty in the evidence for each outcome. In order to identify the underlying cause of high heterogeneity, a subgroup analysis was conducted. Sensitivity analysis was checked. A random effect model was used and calculated a pooled standardized mean difference (SMD) with a 95% confidence interval (CI).

RESULTS

Seventeen articles were included in the final analysis, varied in quality, ranging from a "low" to a "high risk of bias". Combined analyses indicated a notable decrease in HRV among individuals with PCOS compared to the control group. Significant changes were observed in SDNN (SMD: -0.763, 95%CI [-1.289 to -0.237], p=0.004), PNN50 (SMD: -1.245, 95%CI [-2.07, -0.419], p=0.003), LF/HF ratio (SMD: 0.670, 95%CI [0.248, 1.091], p=0.002), HFnu (SMD: -0.873, 95%CI [-1.257, -0.489], p=0.000), LFnu (SMD: 0.840, 95%CI [0.428, 1.251], p=0.000) and TP (SMD: -1.997, 95%CI [-3.306, -0.687], p=0.003). The heterogeneity was partially explained by types of study design. Subgroup analysis revealed significant alterations of HRV in normal-weighted and overweight PCOS cases. Conversely, no significant changes in HRV were observed in obese PCOS cases.

CONCLUSION

The findings of this meta-analysis provide evidence suggesting diminished HRV in individuals with PCOS compared to non-PCOS control group.

Joint association of sedentary time and physical activity with abnormal heart rate recovery in young and middle-aged adults

BACKGROUND

Abnormal heart rate recovery (HRR), representing cardiac autonomic dysfunction, is an important predictor of cardiovascular disease. Prolonged sedentary time (ST) is associated with a slower HRR. However, it is not clear how much moderate-to-vigorous physical activity (MVPA) is required to mitigate the adverse effects of sedentary behavior on HRR in young and middle-aged adults. This study aimed to examine the joint association of ST and MVPA with abnormal HRR in this population.

METHODS

A cross-sectional analysis was conducted on 1253 participants (aged 20-50 years, 67.8% male) from an observational study assessing cardiopulmonary fitness in Fujian Province, China. HRR measured via cardiopulmonary exercise tests on a treadmill was calculated as the difference between heart rate at peak exercise and 2 min after exercise. When the HRR was ≤ 42 beats·minute-1 within this time, it was considered abnormal. ST and MVPA were assessed by the IPAQ-LF. Individuals were classified as having a low sedentary time (LST [< 6 h·day-1]) or high sedentary time (HST [≥ 6 h·day-1]) and according to their MVPA level (low MVPA [0-149 min·week-1], medium MVPA [150-299 min·week-1], high MVPA [≥ 300 min·week-1]). Finally, six ST-MVPA groups were derived. Associations between ST-MVPA groups with abnormal HRR incidence were examined using logistic regression models.

RESULTS

53.1% of the young and middle-aged adults had less than 300 min of MVPA per week. In model 2, adjusted for possible confounders (e.g. age, sex, current smoking status, current alcohol consumption, sleep status, body mass index), HST was associated with higher odds of an abnormal HRR compared to LST (odds ratio (OR) = 1.473, 95% confidence interval (CI) = 1.172-1.852). Compared with the reference group (HST and low MVPA), the HST and high MVPA groups have a lower chance of abnormal HRR (OR, 95% CI = 0.553, 0.385-0.795). Compared with individuals with HST and low MVPA, regardless of whether MVPA is low, medium, or high, the odds of abnormal HRR in individuals with LST is significantly reduced (OR, 95% CI = 0.515, 0.308-0.857 for LST and low MVPA; OR, 95% CI = 0.558, 0.345-0.902 for LST and medium MVPA; OR, 95% CI = 0.476, 0.326-0.668 for LST and high MVPA).

CONCLUSION

Higher amounts of MVPA appears to mitigate the increased odds of an abnormal HRR associated with HST for healthy young and middle-aged adults.

Effect of Piracetam and Iron Treatment on Heart Rate Variability in Patients With Breath-Holding Spell

BACKGROUND

Breath-holding spells are a benign condition primarily seen in 3% to 5% of healthy children aged between six months and five years. Although no specific treatment is recommended due to its benign nature, iron and piracetam are used in severe or recurrent cases. We planned to compare the heart rate variability (HRV) before and after treatment with 24-hour Holter monitoring in patients receiving iron and piracetam treatment and investigate the treatment's effectiveness.

METHODS

Twenty-five patients who applied to the outpatient clinic between 2013 and 2015 due to breath-holding spells were included in the study. The patients who received piracetam and iron therapy and underwent 24-hour rhythm Holter monitoring were evaluated retrospectively.

RESULTS

Fourteen (56%) of these patients were evaluated as having cyanotic-type and 11 (44%) patients were assessed as having pale-type breath-holding spells. A significant difference was found only between hourly peak heart rate and total power in the group receiving iron treatment. Significant differences were also found among the minimum heart rate, mean heart rate, the standard deviation of RR intervals, the mean square root of the sum of the squares of their difference between adjacent RR intervals, spectpow, and low frequency before and after the treatment in the patients who started piracetam treatment (P < 0.05).

CONCLUSIONS

Our study is critical as it is the first to investigate the effects of treatment options on various HRV in patients with breath-holding spells. There were statistically significant changes in HRV parameters in patients receiving piracetam, and the number of attacks decreased significantly. Piracetam treatment contributes positively to the breath-holding spell with regard to efficacy and HRV, therefore it can be used to treat breath-holding spells.

Occurrence of Dysrhythmias During Ventilatory Weaning and Its Association With Length of Mechanical Ventilation and In-hospital Complications

BACKGROUND

The occurrence of cardiac dysrhythmias during ventilatory weaning and its impact on the length of ventilation and occurrence of complications have not been systematically investigated.

OBJECTIVES

The aim of this study was to evaluate the association between cardiac dysrhythmias during weaning and the duration of ventilation and complications during ventilator weaning.

METHOD

Data on the length of ventilation and complications were collected from the medical records of 30 mechanically ventilated patients. Continuous electrocardiographic recordings were collected at baseline and during the initial weaning trial. Multiple regression analysis was used to evaluate the association between dysrhythmias and length of ventilation. The relationship between prolonged ventilation and complications was assessed using the χ2 analysis.

RESULTS

Supraventricular ectopic beats during weaning positively predicted the length of ventilation (P < .01). Prolonged ventilation (>7 days) is associated with the occurrence of renal insufficiency and septicemia.

CONCLUSION

The association between the occurrence of supraventricular ectopic beats during ventilator weaning and the length of ventilation requires further evaluation and tailored management to improve patient outcomes.

Heart Rate Recovery: Up to Date in Heart Failure-A Literature Review

The rising prevalence of cardiovascular disease underscores the growing significance of heart failure (HF). Pathophysiological insights into HF highlight the dysregulation of the autonomic nervous system (ANS), characterized by sympathetic overactivity and diminished vagal tone, impacting cardiovascular function. Heart rate recovery (HRR), a metric measuring the heart's ability to return to its baseline rate post-exertion, plays a crucial role in assessing cardiovascular health. Widely applied across various cardiovascular conditions including HF, coronary artery disease (CAD), and arterial hypertension (HTN), HRR quantifies the difference between peak and recovery heart rates. Given its association with elevated sympathetic tone and exercise, HRR provides valuable insights into the perspective of HF, beyond effort tolerance, reaching toward prognostic and mortality indicators. Incorporating HRR into cardiovascular evaluations enhances our understanding of autonomic regulation in HF, offering potential implications for prognostication and patient management. This review addresses the significance of HRR in HF assessment, analyzing recently conducted studies, and providing a foundation for further research and clinical application.

Abnormal heart rate responses to exercise in non-severe COPD: relationship with pulmonary vascular volume and ventilatory efficiency

BACKGROUND

Despite being a prognostic predictor, cardiac autonomic dysfunction (AD) has not been well investigated in chronic obstructive pulmonary disease (COPD). We aimed to characterise computed tomography (CT), spirometry, and cardiopulmonary exercise test (CPET) features of COPD patients with cardiac AD and the association of AD with CT-derived vascular and CPET-derived ventilatory efficiency metrics.

METHODS

This observational cohort study included stable, non-severe COPD patients. They underwent clinical evaluation, spirometry, CPET, and CT. Cardiac AD was determined based on abnormal heart rate responses to exercise, including chronotropic incompetence (CI) or delayed heart rate recovery (HRR) during CPET.

RESULTS

We included 49 patients with FEV1 of 1.2-5.0 L (51.1-129.7%), 24 (49%) had CI, and 15 (31%) had delayed HRR. According to multivariate analyses, CI was independently related to reduced vascular volume (VV; VV ≤ median; OR [95% CI], 7.26 [1.56-33.91]) and low ventilatory efficiency (nadir VE/VCO2 ≥ median; OR [95% CI], 10.67 [2.23-51.05]). Similar results were observed for delayed HRR (VV ≤ median; OR [95% CI], 11.46 [2.03-64.89], nadir VE/VCO2 ≥ median; OR [95% CI], 6.36 [1.18-34.42]).

CONCLUSIONS

Cardiac AD is associated with impaired pulmonary vascular volume and ventilatory efficiency. This suggests that lung blood perfusion abnormalities may occur in these patients. Further confirmation is required in a large population-based cohort.

Differences in heart rate responses to upright posture are associated with variations in the high-frequency power of heart rate variability

High resting heart rate is a cardiovascular risk factor, but limited data exist on the underlying hemodynamics and reproducibility of supine-to-upright increase in heart rate. We recorded noninvasive hemodynamics in 574 volunteers [age, 44.9 yr; body mass index (BMI), 26.4 kg/m2; 49% male] during passive head-up tilt (HUT) using whole body impedance cardiography and radial artery tonometry. Heart rate regulation was evaluated using heart rate variability (HRV) analyses. Comparisons were made between quartiles of supine-to-upright heart rate changes, in which heart rate at rest ranged 62.6-64.8 beats/min (P = 0.285). The average upright increases in heart rate in the quartiles 1-4 were 4.7, 9.9, 13.5, and 21.0 beats/min, respectively (P < 0.0001). No differences were observed in the low-frequency power of HRV, whether in the supine or upright position, or in the high-frequency power of HRV in the supine position. Upright high-frequency power of HRV was highest in quartile 1 with lowest upright heart rate and lowest in quartile 4 with highest upright heart rate. Mean systolic blood pressure before and during HUT (126 vs. 108 mmHg) and the increase in systemic vascular resistance during HUT (650 vs. 173 dyn·s/cm5/m2) were highest in quartile 1 and lowest in quartile 4. The increases in heart rate during HUT on three separate occasions several weeks apart were highly reproducible (r = 0.682) among 215 participants. To conclude, supine-to-upright increase in heart rate is a reproducible phenotype with underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. As heart rate at rest influences prognosis, future research should elucidate the prognostic significance of these phenotypic differences.NEW & NOTEWORTHY Subjects with similar supine heart rates are characterized by variable increases in heart rate during upright posture. Individual heart rate increases in response to upright posture are highly reproducible as hemodynamic phenotypes and present underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. These results indicate that resting heart rate obtained in the supine position alone is not an optimal means of classifying people into groups with differences in cardiovascular function.

The role of the autonomic nervous system in polycystic ovary syndrome

This article reviewed the relationship between the autonomic nervous system and the development of polycystic ovary syndrome (PCOS). PCOS is the most common reproductive endocrine disorder among women of reproductive age. Its primary characteristics include persistent anovulation, hyperandrogenism, and polycystic ovarian morphology, often accompanied by disturbances in glucose and lipid metabolism. The body's functions are regulated by the autonomic nervous system, which consists mainly of the sympathetic and parasympathetic nervous systems. The autonomic nervous system helps maintain homeostasis in the body. Research indicates that ovarian function in mammals is under autonomic neural control. The ovaries receive central nervous system information through the ovarian plexus nerves and the superior ovarian nerves. Neurotransmitters mediate neural function, with acetylcholine and norepinephrine being the predominant autonomic neurotransmitters. They influence the secretion of ovarian steroids and follicular development. In animal experiments, estrogen, androgens, and stress-induced rat models have been used to explore the relationship between PCOS and the autonomic nervous system. Results have shown that the activation of the autonomic nervous system contributes to the development of PCOS in rat. In clinical practice, assessments of autonomic nervous system function in PCOS patients have been gradually employed. These assessments include heart rate variability testing, measurement of muscle sympathetic nerve activity, skin sympathetic response testing, and post-exercise heart rate recovery evaluation. PCOS patients exhibit autonomic nervous system dysfunction, characterized by increased sympathetic nervous system activity and decreased vagal nerve activity. Abnormal metabolic indicators in PCOS women can also impact autonomic nervous system activity. Clinical studies have shown that various effective methods for managing PCOS regulate patients' autonomic nervous system activity during the treatment process. This suggests that improving autonomic nervous system activity may be an effective approach in treating PCOS.

The Heart's Function as a Pump Assessed via Impedance Cardiography and the Autonomic System Balance in Patients with Early-Stage Acromegaly

BACKGROUND

Acromegaly is a rare, chronic disease that involves structural and functional abnormalities of the cardiovascular system. Acromegaly likely affects interactions between the cardiovascular system and the autonomic nervous system (ANS). Therefore, assessing the relationship between sympathetic-parasympathetic balance by analyzing heart rate variability (HRV) and the hemodynamic profile via impedance cardiography (ICG) may be useful in learning the exact nature of interactions between the ANS and the cardiovascular system. The purpose of this study was to assess a possible association between HRV and ICG-based parameters of cardiac function in patients newly diagnosed with acromegaly.

METHODS

This observational cohort study was conducted on 33 patients (18 men, mean age of 47 years) newly diagnosed with acromegaly and no significant comorbidities. A correlation analysis (Spearman's rank coefficient R) of the parameters assessed via ICG and the HRV assessed via 24 h ambulatory electrocardiography was performed. ICG assessments included the following parameters: stroke volume index (SI), cardiac index (CI), acceleration index (ACI), velocity index (VI), and Heather index (HI). The analysis of HRV included both time-domain parameters (pNN50, SDNN, SDSD, rMSSD) and frequency-domain parameters (total power (TP) and its individual frequency bands: low-frequency (LF day/night), high-frequency (HF day/night), and the LF/HF ratio (day/night)).

RESULTS

Frequency-domain HRV analysis showed the following correlations: (1) lower nighttime LF values with higher ACI (R = -0.38; p = 0.027) and HI (R = -0.46; p = 0.007) values; (2) higher nighttime HF values with higher ACI (R = 0.39; p = 0.027) and HI (R = 0.43; p = 0.014) values; (3) lower nighttime LF/HF values with higher ACI (R = -0.36; p = 0.037) and HI (R = -0.42; p = 0.014) values; (4) higher nighttime TP values with higher SI values (R = 0.35; p = 0.049). Time-domain parameters of HRV showed a significant correlation only between the nighttime values of SDSD and SI (R = 0.35; p = 0.049) and between the daytime and nighttime values of SDNN and HR (R = -0.50; p = 0.003 and R = -0.35; p = 0.046). In multivariate regression, only ACI was revealed to be independently related to HRV.

CONCLUSIONS

In patients newly diagnosed with acromegaly, the relationship between the sympathetic-parasympathetic balance assessed via HRV and the hemodynamic profile assessed via ICG was revealed. Better function of the left ventricle was associated with a parasympathetic shift in the autonomic balance.

Assessment of Autonomic Nervous System Activity Using Spectral Analysis of Heart Rate Variability After Continuous Positive Airway Pressure (CPAP) Therapy in Patients With Sleep Apnea

Heart rate variability (HRV) measurements have emerged as a valuable tool for understanding the functioning of the autonomic nervous system (ANS) and assessing the health outcomes of obstructive sleep apnea (OSA) in patients. Sleep and the ANS exert a mutual influence on each other. Sleep promotes relaxation and recovery of the ANS. Conversely, ANS activity plays a role in regulating the onset and maintenance of sleep. The impact of continuous positive airway pressure (CPAP) therapy on patient recovery levels was investigated by assessing the restoration of ANS activity using HRV indicators. The study included patients with OSA who had been on CPAP for at least eight weeks. The patients were divided into two groups, namely the experimental group (CPAP-compliant) and the control group (CPAP-non-compliant). The study included a total of 38 patients, with 20 in the CPAP-compliant group and 18 in the CPAP-non-compliant group. The HRV analysis included time- and frequency-domain measures. Data was collected in various resting conditions, including lying down, standing, regular breathing, and under physiological stress induced by deep breathing and the Valsalva maneuver. After CPAP treatment, there was an increase in the average values for SDNN for deep breathing and Valsalva maneuvers. The mean changes in SDNN for CPAP-non-compliant versus CPAP-compliant groups for normal breathing increased from 32.50±5.33 to 42.40±8.03, while the values for Valsalva increased from 20.16±2.47 to 25.45±3.03. Despite the observed variations in SDNN, there was no significant change in the average change in heart rate (∆ HR), except during the Valsalva maneuver. Post-CPAP values for the Valsalva ratio were significantly decreased in deep breathing. The E:I ratio for the CPAP-compliant group during normal breathing was 1.08±.16 compared to 1.55±.09; t (36) =-11.15, p <0.001 in the CPAP-non-compliant group. During deep breathing, the ratio was 1.36±.15 versus 1.59±.24; t (36) =-3.578, p <0.001. The high frequency (HF)nu mean values for deep breathing were 34.06±5.546 compared to 35.00±6.358; t (36) = -.485, p=.630. For the Valsalva maneuver, the values were 29.94±4.721 versus 26.95±6.621; t (36) =1.589, p=.060. The HF/low frequency (LF) ratio was found to be significant only in supine, standing, and normal breathing. The utilization of CPAP therapy was found to be effective in achieving and sustaining autonomic balance during tasks like standing and engaging in regular breathing patterns. During activities that involve intense physical effort, like the Valsalva maneuver, the HRV metrics did not indicate any significant balance between sympathetic and parasympathetic activity. However, using CPAP therapy for a prolonged period can be beneficial in consistently improving the sympathovagal balance in these patients.

Unveiling the Multifaceted Problems Associated with Dysrhythmia

Dysrhythmia is a term referring to the occurrence of spontaneous and repetitive changes in potentials with parameters deviating from those considered normal. The term refers to heart anomalies but has a broader meaning. Dysrhythmias may concern the heart, neurological system, digestive system, and sensory organs. Ion currents conducted through ion channels are a universal phenomenon. The occurrence of channel abnormalities will therefore result in disorders with clinical manifestations depending on the affected tissue, but phenomena from other tissues and organs may also manifest themselves. A similar problem concerns the implementation of pharmacotherapy, the mechanism of which is related to the impact on various ion currents. Treatment in this case may cause unfavorable effects on other tissues and organs. Drugs acting through the modulation of ion currents are characterized by relatively low tissue specificity. To assess a therapy's efficacy and safety, the risk of occurrences in other tissues with similar mechanisms of action must be considered. In the present review, the focus is shifted prominently onto a comparison of abnormal electrical activity within different tissues and organs. This review includes an overview of the types of dysrhythmias and the basic techniques of clinical examination of electrophysiological disorders. It also presents a concise overview of the available pharmacotherapy in particular diseases. In addition, the authors review the relevant ion channels and their research technique based on patch clumping.

Association between nighttime heart rate and cardiovascular mortality in patients with implantable cardioverter-defibrillator: A cohort study

BACKGROUND

Although studies have shown that an increased resting heart rate measured randomly at a single point of the day has been associated with adverse cardiovascular outcomes, the utility of continuous monitoring of nighttime heart rate (NTHR) has remained largely uninvestigated.

OBJECTIVE

This study aimed to explore the association between NTHR and cardiovascular mortality.

METHODS

The Study of Home Monitoring System Safety and Efficacy in Cardiac Implantable Electronic Device-implanted Patients, which is a prospective cohort study, enrolled patients with implantable cardioverter-defibrillator (ICD) or cardiac resynchronization therapy defibrillator between 2010 and 2015. Baseline NTHR was measured during the programmed sleep period from 30 to 60 days after implantation. The primary outcome was cardiovascular mortality, fitted by a restricted cubic spline function.

RESULTS

A total of 534 implantable cardioverter-defibrillator recipients with sinus rhythm during the detection window were included in the study. The mean baseline NTHR was 59.6 ± 8.0 beats/min. During the follow-up period of 60.4 ± 21.8 months, 88 (16.5%) patients experienced cardiovascular mortality. After considering potential confounders, a linear association was observed. Each 1 beat/min increase in NTHR was associated with a 7.8%, 10.1%, and 5.7% increase in the risk of cardiovascular mortality in the total population, patients with heart failure, and patients without heart failure, respectively.

CONCLUSION

Continuous monitoring of NTHR may identify patients at high risk of cardiovascular mortality in a timely manner, with the potential for "preemptive" action.

TRIAL REGISTRATION

No. ChiCTR-ONRC-13003695.

Post-exercise heart rate variability recovery after 800-m endurance run load among Cameroonian adolescent's males

The 800-m (m) run is part of Physical Education classes in Cameroon, after which arrhythmias may occur during recovery. Hence, this study aimed at determining relationship between 800-m run loads on cardiac autonomic recovery among school adolescents. Forty-two male adolescents (aged [17 ​± ​1] years) performed 800-m. Post-exercise heart rate variability (HRV) was recorded during 5-min (min) (HRV5-min) and 15-min (HRV15-min) in time: Standard deviation of normal to normal (SDNN); Root mean square of successive differences (RMSSD) and frequency domain (LH: Low frequency, HF: High frequency, TP: Total power). Rating of Perceived Exertion (RPE) and blood lactate concentration (BLa) were measured after exercise. In HRV5-min, RPE was associated with SDNN (r ​= ​-0.44, p ​< ​0.01) and RMSSD (r ​= ​-0.38, p ​< ​0.05). BLa was correlated with SDNN (r ​= ​-0.38, p ​< ​0.05) and RMSSD (r ​= ​-0.56, p ​< ​0.001) in the time-domain, LF (r ​= ​-0.64, p ​< ​0.001), HF (r ​= ​-0.58, p ​< ​0.001) and TP (r ​= ​-0.61, p ​< ​0.001) in frequency-domain. Moreover, RPE was correlated with LF (r ​= ​-0.44, p ​< ​0.01), TP (r ​= ​-0.49, p ​< ​0.01) while exercise duration with HF (r ​= ​-0.38, p ​< ​0.05). In HRV15-min, BLa was correlated with RMSSD (r ​= ​-0.53, p ​< ​0.001) and SDNN (r ​= ​-0.68, p ​< ​0.001). RPE was negatively correlated SDNN (r ​= ​-0.53, p ​< ​0.01) and RMSSD (r ​= ​-0.44, p ​< ​0.01). BLa was associated with HF (r ​= ​-0.55, p ​< ​0.001), TP (r ​= ​-0.50, p ​< ​0.01) and RPE with LF (r ​= ​-0.51, p ​< ​0.01), HF (r ​= ​-0.50, p ​< ​0.01), TP (r ​= ​-0.49, p ​< ​0.01). In addition, exercise duration was negatively linked to HF (r ​= ​-0.36, p ​< ​0.05). This study outlined that in untrained adolescents an increase of 800-m loads is associated with a slow vagal indexes of HRV during the recovery.

Association between admission heart rate and major adverse cardiovascular events in acute myocardial infarction participants with different left ventricular ejection fraction

BACKGROUND

This study intended to investigate the independent effect of admission heart rate (HR) on the risk of major adverse cardiovascular events (MACEs) in acute myocardial infarction (AMI) patients with different left ventricular ejection fraction (LVEF) levels.

METHODS

The study was a secondary analysis of the Acute Coronary Syndrome Quality Improvement in Kerela Trial. The relationship between admission HR and 30-day adverse outcomes in AMI patients with different LVEF levels was detected using a Logistic regression model. Interaction tests were used to compare the effects of different subgroups on HR and MACEs.

RESULTS

Our study enrolled 18,819 patients. In both partially and fully adjusted models (Model1 and Model2), the risk of MACEs was highest in patients with HR ≥ 120 (OR: 1.62, 95%CI: (1.16, 2.26), P = 0.004, Model1; OR: 1.46, 95%CI: (1.00, 2.12), P = 0.047, Model2). There was a significant interaction between LVEF and HR (P for interaction = 0.003). Meanwhile, the trend test for this association showed that HR was positively and significantly associated with the MACEs in LVEF≥40% group (OR (95%CI): 1.27 (1.12, 1.45), P < 0.001). However, in LVEF<40% group, the trend test was not statistically significant (OR (95%CI): 1.09 (0.93, 1.29), P = 0.269).

CONCLUSION

This study found that elevated admission HR was associated with a significantly higher risk for MACEs in patients admitted with AMI. Elevated admission HR was significantly associated with the risk of MACEs in AMI patients without low LVEF but not those with low LVEF (<40%). LVEF levels should be considered when evaluating the association between admission HR and the prognosis of AMI patients in the future.

Assessment of short-term effects of thoracic radiotherapy on the cardiovascular parasympathetic and sympathetic nervous systems

Background

Prior research suggests that cardiovascular autonomic dysfunction might be an early marker of cardiotoxicity induced by antitumor treatment and act as an early predictor of cardiovascular disease-related morbidity and mortality. The impact of thoracic radiotherapy on the parasympathetic and sympathetic nervous systems, however, remains unclear. Therefore, this study aimed to evaluate the short-term effects of thoracic radiotherapy on the autonomic nervous system, using deceleration capacity (DC), acceleration capacity (AC) of heart rate, and heart rate variability (HRV) as assessment tools.

Methods

A 5 min electrocardiogram was collected from 58 thoracic cancer patients before and after thoracic radiotherapy for DC, AC, and HRV analysis. HRV parameters employed included the standard deviation of the normal-normal interval (SDNN), root mean square of successive interval differences (RMSSD), low frequency power (LF), high frequency power (HF), total power (TP), and the LF to HF ratio. Some patients also received systemic therapies alongside radiotherapy; thus, patients were subdivided into a radiotherapy-only group (28 cases) and a combined radiotherapy and systemic therapies group (30 cases) for additional subgroup analysis.

Results

Thoracic radiotherapy resulted in a significant reduction in DC (8.5 [5.0, 14.2] vs. 5.3 [3.5, 9.4], p = 0.002) and HRV parameters SDNN (9.9 [7.03, 16.0] vs. 8.2 [6.0, 12.4], p = 0.003), RMSSD (9.9 [6.9, 17.5] vs. 7.7 [4.8, 14.3], p = 0.009), LF (29 [10, 135] vs. 24 [15, 50], p = 0.005), HF (35 [12, 101] vs. 16 [9, 46], p = 0.002), TP (74 [41, 273] vs. 50 [33, 118], p < 0.001), and a significant increase in AC (-8.2 [-14.8, -4.9] vs. -5.8 [-10.1, -3.3], p = 0.003) and mean heart rate (79.8 ± 12.6 vs. 83.9 ± 13.6, p = 0.010). Subgroup analysis indicated similar trends in mean heart rate, DC, AC, and HRV parameters (SDNN, RMSSD, LF, HF, TP) in both the radiotherapy group and the combined treatment group post-radiotherapy. No statistically significant difference was noted in the changes observed in DC, AC, and HRV between the two groups pre- and post-radiotherapy.

Conclusion

Thoracic radiotherapy may induce cardiovascular autonomic dysfunction by reducing parasympathetic activity and enhancing sympathetic activity. Importantly, the study found that the concurrent use of systemic therapies did not significantly amplify or contribute to the alterations in autonomic function in the short-term following thoracic radiotherapy. DC, AC and HRV are promising and feasible biomarkers for evaluating autonomic dysfunction caused by thoracic radiotherapy.

A multiscale predictive digital twin for neurocardiac modulation

Cardiac function is tightly regulated by the autonomic nervous system (ANS). Activation of the sympathetic nervous system increases cardiac output by increasing heart rate and stroke volume, while parasympathetic nerve stimulation instantly slows heart rate. Importantly, imbalance in autonomic control of the heart has been implicated in the development of arrhythmias and heart failure. Understanding of the mechanisms and effects of autonomic stimulation is a major challenge because synapses in different regions of the heart result in multiple changes to heart function. For example, nerve synapses on the sinoatrial node (SAN) impact pacemaking, while synapses on contractile cells alter contraction and arrhythmia vulnerability. Here, we present a multiscale neurocardiac modelling and simulator tool that predicts the effect of efferent stimulation of the sympathetic and parasympathetic branches of the ANS on the cardiac SAN and ventricular myocardium. The model includes a layered representation of the ANS and reproduces firing properties measured experimentally. Model parameters are derived from experiments and atomistic simulations. The model is a first prototype of a digital twin that is applied to make predictions across all system scales, from subcellular signalling to pacemaker frequency to tissue level responses. We predict conditions under which autonomic imbalance induces proarrhythmia and can be modified to prevent or inhibit arrhythmia. In summary, the multiscale model constitutes a predictive digital twin framework to test and guide high-throughput prediction of novel neuromodulatory therapy. KEY POINTS: A multi-layered model representation of the autonomic nervous system that includes sympathetic and parasympathetic branches, each with sparse random intralayer connectivity, synaptic dynamics and conductance based integrate-and-fire neurons generates firing patterns in close agreement with experiment. A key feature of the neurocardiac computational model is the connection between the autonomic nervous system and both pacemaker and contractile cells, where modification to pacemaker frequency drives initiation of electrical signals in the contractile cells. We utilized atomic-scale molecular dynamics simulations to predict the association and dissociation rates of noradrenaline with the β-adrenergic receptor. Multiscale predictions demonstrate how autonomic imbalance may increase proclivity to arrhythmias or be used to terminate arrhythmias. The model serves as a first step towards a digital twin for predicting neuromodulation to prevent or reduce disease.

The Cardiac Comeback-Beating Stronger: Exploring the Remarkable Resilience of the Heart in COVID-19 Recovery through Cardiac Autonomic Analysis

Background and Objectives: Analyzing the cardiac autonomic function in COVID-19 patients can provide insights into the impact of the virus on the heart's regulatory mechanisms and its recovery. The autonomic nervous system plays a crucial role in regulating the heart's functions, such as heart rate, blood pressure, and cardiac output. This study aimed to investigate the impact of COVID-19 on heart rate variability (HRV) during a 6-min walk test (6MWT). Materials and Methods: The study included 74 participants, consisting of 37 individuals who had recovered from mild to moderate COVID-19 and 37 healthy controls. The study assessed heart rate variability (HRV) and blood pressure both before and after a 6-min walk test (6MWT). Results: The study found significant differences in a few time domains (SDNN and pNN50) and all frequency domain measures, whereas there were no significant differences in demographic characteristics or blood pressure between COVID-19-recovered individuals and healthy controls at rest. There were significant 6MWT effects on average HR, time-domain (SDNN and pNN50) measures of HRV, and all frequency domain measures of HRV. A significant group × 6MWT interaction was found for SDNN, pNN50, total power, Ln total power, LF, HF, Ln LF, Ln HF, and LF nu. Conclusions: Cardiac Autonomic analysis through HRV is essential to ensure the continued health and well-being of COVID-19 survivors and to minimize the potential long-term impacts of the disease on their cardiovascular system. This suggests that HRV analysis during the recovery phase following exercise could serve as a valuable tool for evaluating the physiological effects of COVID-19 and monitoring the recovery process.

Chronic vagus nerve stimulation in patients with heart failure: challenge or failed translation?

Autonomic imbalance between the sympathetic and parasympathetic nervous systems contributes to the progression of chronic heart failure (HF). Preclinical studies have demonstrated that various neuromodulation strategies may exert beneficial cardioprotective effects in preclinical models of HF. Based on these encouraging experimental data, vagus nerve stimulation (VNS) has been assessed in patients with HF with a reduced ejection fraction. Nevertheless, the main trials conducted thus far have yielded conflicting findings, questioning the clinical efficacy of VNS in this context. This review will therefore focus on the role of the autonomic nervous system in HF pathophysiology and VNS therapy, highlighting the potential reasons behind the discrepancy between preclinical and clinical studies.

Evaluation of a new treadmill exercise protocol to unmask type 1 Brugada electrocardiographic pattern: can we improve diagnostic yield?

AIMS

High precordial leads (HPL) on the resting electrocardiogram (ECG) are widely used to improve diagnostic detection of type 1 Brugada ECG pattern (Br1ECGp). A parasympathetic activation marks the initial recovery phase of treadmill stress testing (TET), and this can be useful for detecting the typical ECG pattern. Our study aimed to evaluate the role of a new HPL-treadmill exercise testing (TET) protocol in detecting Br1ECGp fluctuation compared to resting HPL-ECG.

METHODS AND RESULTS

74 out of 163 patients of a Brugada syndrome (BrS) Brazilian cohort (GenBra Registry) underwent exercise testing with HPL-TET protocol. Precordial leads were displayed in strategic positions in the right and left parasternal spaces. The step-by-step analysis included ECG classification (as presence or absence of Br1ECGp) in standard vs. HPL leads placement in the following sequences: resting phase, maximal exercise, and the passive recovery phase (including 'quick lay down'). For heart rate recovery (HRR) measurements and comparisons, a Student's t-test was applied. McNemar tests compared the detection of Br1ECGp. The significance level was defined as P < 0.05. Fifty-seven patients (57/74; 77%) were male, the mean age was 49.0 ± 14, 78.4% had spontaneous BrS, and the mean Shanghai score was 4.5. The HPL-TET protocol increased Br1ECGp detection by 32.4% against resting HPL-ECG (52.7% vs. 20.3%, P = 0.001) alone.

CONCLUSION

Stress testing using HPL with the passive recovery phase in the supine position offers an opportunity to unmask the type 1 Br1ECGp, which could increase the diagnostic yield in this population.

Biomarkers of oxidative stress and reproductive complications

Oxidative stress is the result of an imbalance between the formation of reactive oxygen species (ROS) and the levels of enzymatic and non-enzymatic antioxidants. The assessment of biological redox status is performed by the use of oxidative stress biomarkers. An oxidative stress biomarker is defined as any physical structure or process or chemical compound that can be assessed in a living being (in vivo) or in solid or fluid parts thereof (in vitro), the determination of which is a reproducible and reliable indicator of oxidative stress. The use of oxidative stress biomarkers allows early identification of the risk of developing diseases associated with this process and also opens up possibilities for new treatments. At the end of the last century, interest in oxidative stress biomarkers began to grow, due to evidence of the association between the generation of free radicals and various pathologies. Up to now, a significant number of studies have been carried out to identify and apply different oxidative stress biomarkers in clinical practice. Among the most important oxidative stress biomarkers, it can be mentioned the products of oxidative modifications of lipids, proteins, nucleic acids, and uric acid as well as the measurement of the total antioxidant capacity of fluids in the human body. In this review, we aim to present recent advances and current knowledge on the main biomarkers of oxidative stress, including the discovery of new biomarkers, with emphasis on the various reproductive complications associated with variations in oxidative stress levels.

Autonomic heart rate modulation in patients with coronavirus disease 2019 in mechanical ventilation

BACKGROUND

Patients with coronavirus disease 2019 on automatic mechanical ventilation have greater heart rate modulation with greater parasympathetic modulation.

OBJECTIVE

To analyze the autonomic modulation of heart rate in critically ill patients with coronavirus disease 2019 on invasive mechanical ventilation.

METHODS

A cross-section study was carried out with 36 individuals divided into two groups. The control group included patients of both genders, in orotracheal intubation with invasive mechanical ventilation under controlled assisted mode, hospitalized in the intensive care unit for another 24 h. In the non-COVID group, patients diagnosed with coronavirus disease 2019 in the same condition mentioned in the control group.

RESULTS

There was a significant increase in heart rate variability (standard deviation of all normal RR intervals recorded at an interval of time; p=0.001; triangular interpolation histogram of RR intervals; p=0.048; and SD2; p=0.014) in the coronavirus disease group compared to the non-COVID group. Successively, the parameters that demonstrate parasympathetic modulation are shown to be higher in the group of patients with coronavirus disease 2019 (root mean square of the square of differences between adjacent normal RR intervals in an interval of time; p<0.001; pNN50; p<0.001; SD1; p=0.002; and high frequency; p=0.022).

CONCLUSIONS

There was a greater autonomic modulation of heart rate with a greater parasympathetic modulation in patients with coronavirus disease 2019 on mechanical ventilation.

The association between cardiac autonomic system function at the entrance to rehabilitation and walking-endurance two months later among children following-ABI

BACKGROUND

The cardiac autonomic control system function is frequently impaired after brain injury. An association exists between the cardiac autonomic control system and endurance performance.

AIM

To evaluate the association between cardiac autonomic control system indices at the beginning of the inpatient rehabilitation and walking endurance two months later among children and adolescents following acquired brain injury.

METHODS

A prospective study included 28 children and adolescents following acquired brain injury in the sub-acute phase. A Polar device (RS800CX) records heart rate as a proxy measure of autonomic function at sitting and lying supine on admission and two months later. The 6-minute walk test was assessed at the second assessment in 25 participants. Non-parametric tests were used with statistical significance defined as p < 0.05.

RESULTS

There were statistically significant differences in heart rate variability between lying and sitting positions, which were positively correlated with the 6-minutes walk test results two months later, mainly in the parasympathetic components (r_s = 0.51 p-value <0.01).

CONCLUSIONS

At the beginning of the rehabilitation of children and adolescents following acquired brain injury, a simple manipulation - position change from sitting to lying, activates cardiac autonomic control system responses. These responses are positively associated with walking endurance two months later.

A System Based on Photoplethysmography and Photobiomodulation for Autonomic Nervous System Measurement and Adjustment

(1) Background: The imbalance of the autonomic nervous system (ANS) is common worldwide. Many people have high tension when the sympathetic nervous system is hyperactive or low attention when the parasympathetic nervous system is hyperactive. To improve autonomic imbalance, a feasible and integrated system was proposed to measure and affect the ANS status. (2) Methods: The proposed system consists of a signal-processing module, an LED stimulation module, a photoplethysmography (PPG) sensor and an LCD display. The heart rate variability (HRV) and ANS status can be analyzed from PPG data. To confirm HRV analysis from PPG data, an electrocardiogram (ECG) device was also used to measure HRV. Additionally, photobiomodulation (PBM) was used to affect the ANS status, and two acupuncture points (Neiguan (PC6) and Shenmen (HT7)) were stimulated with different frequencies (10 Hz and 40 Hz) of PBM. (3) Results: Two subjects were tested with the developed system. HRV metrics were discussed in the time domain and frequency domain. HRV metrics have a similar change trend on PPG and ECG signals. In addition, the SDNN was increased, and the parasympathetic nervous system (PNS: HF (%)) was enhanced with a 10 Hz pulse rate stimulation at the Neiguan acupoint (PC6). Furthermore, the SDNN was increased, and the sympathetic nervous system (SNS: LF (%)) was enhanced with a 40 Hz pulse rate stimulation at the Shenmen (HT7) acupoint. (4) Conclusion: A prototype to measure and affect the ANS was proposed, and the functions were feasible. The test results show that stimulating the Neiguan (PC6) acupoint can inhibit the SNS. In contrast, stimulating the Shenmen (HT7) acupoint can activate the SNS. However, more experiments must be conducted to confirm the effect by choosing different pulse rates, dosages and acupoints.

Implication of heart rate variability on cerebral small vessel disease: A potential therapeutic target

OBJECTIVE

This study aimed to investigate the relationships of heart rate variability (HRV) with the presence, severity, and individual neuroimaging markers of cerebral small vessel disease (CSVD).

METHOD

A total of 4676 participants from the Third China National Stroke Registry (CNSR-III) study were included in this cross-sectional analysis. CSVD and its markers, including white matter hyperintensity (WMH), lacunes, enlarged perivascular spaces (EPVS), cerebral microbleeds (CMBs), and brain atrophy (BA), were evaluated. Two common HRV parameters, including the square root of the mean of the sum of the squares of differences between adjacent N-N intervals (RMSSD) and the standard deviation of all N-N intervals (SDNN), were used to evaluate the function of the autonomic nervous system (ANS). Binary or ordinal logistic regression analyses were performed to investigate the association between HRV and CSVD. In addition, two-sample mendelian randomization (MR) analyses were performed to investigate the causality of HRV with CSVD.

RESULTS

RMSSD was significantly associated with total burden of CSVD (Wardlaw's scale, common odds ratio [cOR] 0.80, 95% confidence interval [CI] 0.67-0.96, p = 0.02; Rothwell's scale, cOR 0.75, 95% CI 0.60-0.93, p = 0.008) and the presence of CSVD (Rothwell, OR 0.75, 95% CI 0.60-0.93, p = 0.008). However, no significant associations between SDNN and the presence or total burden of CSVD were observed. Moreover, RMSSD was related to WMH burden (OR 0.80, 95% CI 0.66-0.96, p = 0.02), modified WMH burden (cOR 0.82, 95% CI 0.69-0.97, p = 0.02), and Deep-WMH (OR 0.75, 95% CI 0.62-0.91, p = 0.003), while SDNN was related to Deep-WMH (OR 0.80, 95% CI 0.66-0.96, p = 0.02) and BA (cOR 0.80, 95% CI 0.68-0.95, p = 0.009). Furthermore, adding HRV to the conventional model based on vascualr risk factors enhanced the predictive performance for CSVD, as validated by the integrated discrimination index (p < 0.05). In addition, no causality between HRV and CSVD was observed in two-sample MR analyses.

CONCLUSION

Decreased HRV may be a potential risk factor of CSVD, implying the possible role of the ANS in the pathogenesis of CSVD.

Complement activation mainly mediates the association of heart rate variability and cognitive impairment in adults with obstructive sleep apnea without dementia

STUDY OBJECTIVES

The relationship between autonomic nervous system dysfunction measured by heart rate variability (HRV) and cognitive impairment in obstructive sleep apnea (OSA) patients is complex and still not well understood. We aimed to analyze the role of complement activation, Alzheimer's disease (AD) biomarkers, and white matter hyperintensity (WMH) in modulating the association of HRV with cognitive performance.

METHODS

There were 199 subjects without dementia, including 42 healthy controls, 80 OSA patients with mild cognitive impairment (MCI), and 77 OSA patients without cognitive impairment. All participants who completed polysomnography, cognition, WMH volume, and 5-min HRV analysis were recorded during wakefulness and sleep periods. Neuron-derived exosome and astrocyte-derived exosome proteins were measured by ELISA kits.

RESULTS

The OSA with MCI group were associated with a lower mean of standard deviations of R-R intervals for 5-min intervals (SDANN index) during wakefulness, standard deviation of the R-R interval (SDNN) during sleep stage and percentage of adjacent R-R intervals differing by more than 50 ms (PNN50) in each stage compared with OSA without MCI. The influence of HRV on cognition was partially mediated by complement activation (C5b-9 mediated a maximum of 51.21%), AD biomarkers, and WMH.

CONCLUSIONS

Lower SDANN index and PNN50 during wakefulness and SDNN and PNN50 during sleep periods were found in OSA patients with MCI, suggesting potential vulnerability to autonomic and parasympathetic dysfunction. Complement activation, AD biomarkers, and WMH might partially mediate and interact with the influence of HRV on cognitive impairment in OSA patients.

CLINICAL TRIAL REGISTRATION

ChiCTR1900021544.

Device-evaluated autonomic nervous function for predicting ventricular arrhythmias and all-cause mortality in patients who underwent cardiac resynchronization therapy-defibrillator

Introduction: Autonomic nervous system (ANS) function quantified by heart rate variability (HRV) was associated with long-term prognosis, but it was rarely used in the evaluation of patients with heart failure, especially those with cardiac resynchronization therapy-defibrillator (CRT-D) implantation. This study aimed to describe the changes in ANS function among patients who underwent CRT-D with remote home monitoring function, and explore predictive value of HRV for ventricular tachyarrhythmias (VTAs) and all-cause mortality. Method: Patients who underwent CRT-D implantation were included. Device-measured all-day HR, night-time HR, and HRV (measured by the standard deviation of the atrial-atrial sensed intervals) were used to quantify ANS function. Multivariate Cox proportional hazards models were fitted to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) of VTAs or all-cause mortality in relation to ANS function at baseline and 6 months post-implantation. The cutoff value was determined using restrictive cubic splines. Multivariable logistic regression was further established to determine factors influencing postoperative HRV. Results: A total of 170 patients treated with CRT-D were eligible for analysis. During a median follow-up period of 50.8 months, 61 patients died and 69 patients experienced at least one spontaneous episode of VTAs. At 6 months after CRT implantation, 114 patients showed improvement in HRV, increasing from 66.4 ± 19.4 ms to 76.7 ± 21.2 ms. The postoperative HRV was associated with both all-cause mortality (HRs: 0.983; 95% CI: 0.968 to 0.998, p = 0.012) and VTAs (HRs: 0.973; 95% CI: 0.954 to 0.993, p = 0.008), and the relative risk would significantly increase when the postoperative HRV lower than 75 ms. After adjusting for basic ANS function and possible influencing factors, patients without diabetes (p = 0.018) and with higher daily physical activity (p = 0.041) could maintain higher postoperative HRV after CRT implantation. Conclusion: More than two-thirds of heart failure patients showed improvement in ANS function following CRT treatment. However, patients with diabetes and low daily physical activity levels have difficulty maintaining a higher postoperative HRV, which is associated with a worse clinical outcome.

Evaluation of autonomic nervous system functions by using tilt table test and heart rate variability in epileptic children

Objective: The value of head-up tilt test (HUTT) for differential diagnosis of epilepsy and the autonomic nervous system functions in epileptic children using heart rate variability (HRV) are studied. Patients and Methods: The study group consisted of 16 children with idiopatic/criptogenic epilepsy and 12 controls. Heart rate, PR interval, corrected QT (QTc) interval, QT and QTc dispersion were calculated using 12-lead electrocardiogram (ECG), HRV analysis was performed using the Holter recordings obtained both during HUTT and throughout the day. Time domain parameters, standard deviation of all RR intervals (SDNN), the standard deviation of mean NN intervals in five-minutes recording (SDANN), mean standard deviation of NN intervals in five-minutes recordings (SDNNi), root mean square of successive differences (RMSSD), count divided by the total number of all NN intervals (pNN50) and frequency domain parameters low frequency (LF), high frequency (HF), lowfrequency/ high-frequency ratio (LF/HF) were calculated in both and compared between the two groups. Results: Head-up tilt test was positive in 4 epileptic children (25%), none of controls were positive. The heart rate of the patients were higher than the controls (p=0.015). LF/HF ratio in 24-hour Holter recordings, were significantly lower (1.13±0.6, 1.83±0.7 respectively, p=0.002); the SDANN during HUTT (28.7±20.2, 18.2 ± 19.9 respectively, p=0.024) were significantly higher in the patients than the controls. Conclusion: Head-up tilt test positivity is frequent in epileptic children, and cannot be used in differential diagnosis. HRV calculated both from 24 hour Holter recordings and Holter recordings under orthostatic stress were impaired in favour of parasympathetic system in epileptic children.

Normative values of resting heart rate variability in young male contact sport athletes: Reference values for the assessment and treatment of concussion

Objective

The objective of this study was to identify the main determinants of heart rate variability (HRV) in male athletes aged 14 to 21 years who practice competitive contact sports and to integrate these determinants with the aim of defining normative values of short-term HRV in the time and frequency domains.

Methods

Participants (n = 369) were aged 14 to 21 years and included 221 football players and 148 ice hockey players. HRV was measured for 5 min at rest, and standard HRV parameters in the time and frequency domains were calculated. Heart rate (HR), age, body mass index (BMI), number of sports weekly practices (WSP) and concussion history (mTBI) were considered determinants potentially able to influence HRV.

Results

Multiple regression analysis revealed that HR was the primary determinant of standard HRV parameters. The models accounted for 13% to 55% of the total variance of HRV and the contribution of HR to this model was the strongest (β ranged from -0.34 to -0.75). HR was the only determinant that significantly contributes to all HRV parameters. To counteract this dependence, we calculated HRV corrected by the mean RR interval (RRm). Such corrections do not remove any physiological differences in HRV; they simply remove the mathematical bias. HRV parameters were therefore normalized, and their normative limits were developed relative to the mean heart rate. After correction, the correlation coefficients between HR and all corrected HRV parameters were not statistically significant and ranged from -0.001 to 0.045 (p > 0.40 for all). The automatically corrected HRV calculator, which recalculates standard HRV parameters and converts them into corrected parameters in addition to determining whether a given value is within normal limits, facilitates clinical interpretation.

Conclusion

This study provides for the first time corrected normative values of short-term and resting state HRV parameters in competitive contact sport athletes aged 14 to 21 years. These values were developed independently of the major determinants of HRV. The baseline values for HRV parameters given here could be used in clinical practice when assessing and monitoring cerebral concussions. They may assist in decision making for a safe return to play.

Predictive Value of Exercise Blood Pressure Changes for Orthostatic Hypotension in Patients With Parkinson's Disease

BACKGROUND AND PURPOSE

Orthostatic hypotension (OH) is common in patients with Parkinson's disease (PD). Early recognition OH is required with sensitive assessments. The purpose of this study was to determine whether blood pressure (BP) changes during exercise can predict the occurrence of OH in PD.

METHODS

This prospective cohort study included 80 consecutive patients with PD. All patients agreed to participate in a baseline evaluation and cardiopulmonary exercise test (CPET). According to the initial active standing test (AST), those without OH (PD-nonOH) at baseline had their AST results followed up for 6 months. The main outcome was defined as whether patients without OH at baseline would develop OH after 6 months. Logistic regression analysis was applied to identify the relevant variables. A nomogram was constructed based on clinical features and identified variables. The concordance index (C-index) and area under the receiver operating characteristic curve (AUC) were used to evaluate the accuracy and predictive ability of the nomogram, respectively.

RESULTS

CPET results indicated that peak load, peak heart rate, heart rate recovery at 1 min, and systolic BP change (ΔSBP) were lower in those with OH than in the PD-nonOH group (p<0.05) at baseline. Logistic regression analysis indicated that peak load and ΔSBP during CPET had significant effects on OH (p<0.05). Age, sex, peak load, and ΔSBP were used to construct the nomogram model (C-index=0.761). The prediction model had an AUC of 0.782 (95% confidence interval=0.649-0.889) and a specificity and sensitivity of 70.0% and 81.8%, respectively.

CONCLUSIONS

This study has identified predictive factors for OH development in patients with PD. CPET could be used as a complementary examination to identify patients at a high risk of OH.

High-Intensity Interval Training Combined with Different Types of Exercises on Cardiac Autonomic Function. An Analytical Cross-Sectional Study in CrossFit® Athletes

It is well established that endurance exercise has positive effects on cardiac autonomic function (CAF). However, there is still a dearth of information about the effects of regular high-intensity interval training combined with different types of exercises (HIITCE) on CAF.

OBJECTIVE

The aim of this study is to compare CAF at rest, its reactivity, and reactivation following maximal exercise testing in HIITCE and endurance athletes.

METHODS

An observational study was conducted with 34 male athletes of HIITCE (i.e., CrossFit^®) [HG: n = 18; 30.6 ± 4.8 years] and endurance athletes (i.e., triathlon) [TG.: n = 16; 32.8 ± 3.6 years]. We analyzed 5 min of frequency-domain indices (TP, LF, HF, LFn, HFn, and LF/HF ratio) of heart rate variability (HRV) in both supine and orthostatic positions and its reactivity after the active orthostatic test. Post-exercise heart rate recovery (HRR) was assessed at 60, 180, and 300 s. Statistical analysis employed a non-parametric test with a p-value set at 5%.

RESULTS

The HG showed reduced HFn and increased LFn modulations at rest (supine). Overall cardiac autonomic modulation (TP) at supine and all indices of HRV at the orthostatic position were similar between groups. Following the orthostatic test, the HG showed low reactivity for all HRV indices compared to TG. After the exercise, HRR does not show a difference between groups at 60 s. However, at 180 and 300 s, an impairment of HRR was observed in HG than in TG.

CONCLUSION

At rest (supine), the HG showed reduced parasympathetic and increased sympathetic modulation, low reactivity after postural change, and impaired HRR compared to TG.

A flexible adhesive surface electrode array capable of cervical electroneurography during a sequential autonomic stress challenge

This study introduces a flexible, adhesive-integrated electrode array that was developed to enable non-invasive monitoring of cervical nerve activity. The device uses silver-silver chloride as the electrode material of choice and combines it with an electrode array consisting of a customized biopotential data acquisition unit and integrated graphical user interface (GUI) for visualization of real-time monitoring. Preliminary testing demonstrated this electrode design can achieve a high signal to noise ratio during cervical neural recordings. To demonstrate the capability of the surface electrodes to detect changes in cervical neuronal activity, the cold-pressor test (CPT) and a timed respiratory challenge were employed as stressors to the autonomic nervous system. This sensor system recording, a new technique, was termed Cervical Electroneurography (CEN). By applying a custom spike sorting algorithm to the electrode measurements, neural activity was classified in two ways: (1) pre-to-post CPT, and (2) during a timed respiratory challenge. Unique to this work: (1) rostral to caudal channel position-specific (cephalad to caudal) firing patterns and (2) cross challenge biotype-specific change in average CEN firing, were observed with both CPT and the timed respiratory challenge. Future work is planned to develop an ambulatory CEN recording device that could provide immediate notification of autonomic nervous system activity changes that might indicate autonomic dysregulation in healthy subjects and clinical disease states.

Role of insulin resistance in the association between resting heart rate and type 2 diabetes: A prospective study

BACKGROUND

Elevated resting heart rate (RHR) is a predictor of incident type 2 diabetes (T2D). Insulin resistance is thought to play a role in this association; however, the extent to which insulin resistance mediates this association is unclear.

METHODS

1309 Japanese individuals without diabetes were recruited during 2009-2012 and followed for 5 years, of whom 78 developed T2D, as diagnosed by the 75 g oral glucose tolerance test. Supine RHR was measured by electrocardiography. Using logistic regression analysis, we examined the association between RHR and incident T2D, and interaction with the homeostasis model assessment of insulin resistance (HOMA-IR) index. Causal mediation analysis was applied to decompose the effect of RHR on the outcome and estimate the proportion mediated by the HOMA-IR index.

RESULTS

The sex- and age-adjusted cumulative incidence rate of T2D increased with increasing RHR. After adjustment for sex, age, waist circumference, current smoking status, alcohol use, habitual exercise, and cardiovascular disease medications, individuals with a RHR ≥80 bpm, compared with <60 bpm, showed an increased risk of incident T2D [odds ratio (OR), 2.89; 95 % confidence interval (CI), 1.07 to 7.80]. Multivariate adjusted OR for the total effect per 1 SD increase in RHR on incident T2D was 1.37 (95 % CI, 1.01 to 1.74) in the mediation analysis, and the proportion of the total indirect effect mediated by the HOMA-IR index was 27.5 % (95 % CI, 1.5 to 53.5).

CONCLUSIONS

Approximately 30 % of the effect of RHR on incident T2D was explained by the indirect effect of insulin resistance.

Does Exercise Training Improve Cardiac-Parasympathetic Nervous System Activity in Sedentary People? A Systematic Review with Meta-Analysis

The aim of this study was to investigate the training-induced effect on cardiac parasympathetic nervous system (PNS) activity, assessed by resting heart rate variability (HRV) and post-exercise heart rate recovery (HRR), in sedentary healthy people. Electronic searches were carried out in PubMed, Embase, and Web of Science. Random-effects models of between-group standardised mean difference (SMD) were estimated. Heterogeneity analyses were performed by means of the chi-square test and I2 index. Subgroup analyses and meta-regressions were performed to investigate the influence of potential moderator variables on the training-induced effect. The results showed a small increase in RMSSD (SMD+ = 0.57 [95% confidence interval (CI) = 0.23, 0.91]) and high frequency (HF) (SMD+ = 0.21 [95% CI = 0.01, 0.42]) in favour of the intervention group. Heterogeneity tests reached statistical significance for RMSSD and HF (p ≤ 0.001), and the inconsistency was moderate (I2 = 68% and 60%, respectively). We found higher training-induced effects on HF in studies that performed a shorter intervention or lower number of exercise sessions (p ≤ 0.001). Data were insufficient to investigate the effect of exercise training on HRR. Exercise training increases cardiac PNS modulation in sedentary people, while its effect on PNS tone requires future study.

Heart rate variability and the risk of heart failure and its subtypes in post-menopausal women: The Women's Health Initiative study

Background

Low heart rate variability (HRV), a measure of autonomic imbalance, is associated with increased risk of coronary heart disease (CHD) and heart failure (HF). However, its relationship with HF subtypes; heart failure with preserved ejection fraction (HFpEF) and heart failure with reduced ejection fraction (HFrEF) has not been studied prior.

Methods and findings

We conducted a longitudinal study in Women’s Health Initiative study cohort to investigate the association of baseline quartiles of resting heart rate (rHR) and HRV measures; SDNN (SD of normal-to-normal RR interval) and RMSSD (root mean square of successive difference of RR interval) measured by twelve-lead electrocardiogram (ECG) on enrollment, with the risk of hospitalized HF and its subtypes. Total of 28,603 post-menopausal women, predominantly non-Hispanic whites (69%), with a mean (SD) age of 62.6 (7.1) years, free of baseline CHD and HF were included. In a fully adjusted cox-proportional hazards regression model which adjusted for age, race, BMI, alcohol intake, education, physical activity, hyperlipidemia, hypertension, left ventricular hypertrophy, use of beta-blocker, calcium-channel blocker, hormone therapy, and time-varying incident CHD, the hazard ratios of lowest quartile of HRV (Q1) with HF risk were significant (Q1 SDNN compared to Q4 SDNN: 1.22, 95% CI 1.07, 1.39; Q1 RMSSD compared to Q4 RMSSD: 1.17, 95% CI 1.02, 1.33). On subgroup analysis of HF subtypes, low HRV was associated with elevated HFpEF risk (Q1 vs Q4 SDNN: 1.22, 95% CI 1.02, 1.47) but not with HFrEF (Q1 vs Q4 SDNN: 1.19, 95% CI 0.95, 1.50; Q1 RMSSD: 1.13, 95% CI 0.90, 1.43).

Conclusion

Low HRV is associated with elevated overall hospitalized HF risk and HFpEF risk in post-menopausal women. Whether interventions to increase HRV through healthy lifestyle changes will decrease HF risk warrants further investigation.

Associations between heart rate variability and maximal fat oxidation in two different cohorts of healthy sedentary adults

BACKGROUND AND AIMS

Resting heart rate variability (HRV) and maximal fat oxidation (MFO) during exercise are both considered as a noninvasive biomarkers for early detection of cardiovascular risk factors. Thus, this study aimed to analyze the relationship between resting HRV parameters and MFO during exercise, and the intensity of exercise that elicit MFO (Fat_max) in healthy sedentary adults.

METHODS AND RESULTS

A total of 103 healthy young adults (22.2 ± 2.3 years old, 67% female; from the ACTIBATE cohort) and 67 healthy middle-aged adults (53.1 ± 5.0 years old, 52% female; from the FIT-AGEING cohort) were included in this cross-sectional study. HRV was assessed using a Polar RS800CX heart rate monitor, while MFO and Fat_max were determined during a graded exercise treadmill test using indirect calorimetry. No significant associations were observed for healthy young adults (standardized β coefficients ranged from -0.063 to 0.094, and all P ≥ 0.347) and for middle-aged adults (standardized β coefficients ranged from -0.234 to 0.090, and all P ≥ 0.056). Nevertheless, only a weak association was observed between one HRV parameter in time-domain (the percentage of R-R intervals that shows a difference higher than 50 ms [pNN50]) and MFO in the cohort of middle-aged adults (β coefficient = -0.279, and P = 0.033).

CONCLUSION

The results of this study suggest that resting HRV parameters are not associated with MFO and Fat_max during exercise in two independent cohorts of healthy sedentary young and middle-aged adults, respectively.

Association of resting heart rate with cognitive decline and dementia in older adults: A population-based cohort study

INTRODUCTION

Resting heart rate (RHR) predicts future risk for cardiovascular disease (CVD). However, longitudinal studies investigating the relationship of RHR with cognitive decline are scarce.

METHODS

This population-based cohort study included 2147 participants (age≥60) in SNAC-K who were free of dementia and regularly followed from 2001-2004 to 2013-2016. RHR was assessed with electrocardiogram. Dementia was diagnosed following the Diagnostic and Statistical Manual of Mental Disorders 4th Revision criteria. Global cognitive function was assessed using Mini-Mental State Examination (MMSE). Data were analyzed using Cox and linear mixed-effects models.

RESULTS

RHR≥80 (vs. 60-69) bpm was associated with a multi-adjusted hazard ratio of 1.55 (95% confidence interval 1.06-2.27) for dementia. The association remained significant after excluding participants with prevalent and incident CVDs. Similarly, RHR≥80 bpm was associated with a multi-adjusted β-coefficient of -0.13 (-0.21 to -0.04) for MMSE score.

DISCUSSION

Higher RHR is associated with increased risk for dementia and faster cognitive decline independent of CVDs in a general population of elderly people.

The mediation function of resting heart rate in how physical activity improves all-cause mortality: Continuous and automatic measurement via cardiac implantable electronic devices

Background

Physical activity (PA) and resting heart rate (RHR) are connected with all-cause mortality. Moreover, there was an inverse correlation between PA and RHR. However, the causal relationship between PA, RHR, and long-term mortality has been rarely evaluated and quantified, particularly the mediation effect of RHR in the association between PA and all-cause mortality.

Objective

To describe the relationship between PA and RHR when consistently measured via cardiac implantable electronic devices (CIED) and further explore the mediation effect of PA on all-cause mortality through RHR.

Materials and methods

Patients who underwent CIED implantation and received remote home monitoring services were included. During the first 30–60 days after CIED implantation, daily PA and RHR were continuously measured and automatically transmitted by CIED. The primary endpoint was all-cause mortality. The multiple linear regression model was used to confirm the relationship between PA and RHR. The predictive values of both PA and RHR for all-cause mortality were assessed by multivariable Cox proportional hazards models. The causal mediation model was further established to verify and quantify the mediation effect of RHR in the association between PA and all-cause mortality.

Results

A total of 730 patients with CIED were included. The mean daily PA and RHR were 10.7 ± 5.7% and 61.3 ± 9.1 bpm, respectively. During a mean follow-up period of 55.8 months, 187 (26.5%) death was observed. A negative linear relationship between PA and RHR was demonstrated in the multiple regression model (β = −0.260; 95% CI: −0.377 to −0.143, p < 0.001). Multivariable Cox proportional hazards analysis showed that both lower levels of PA (HR = 0.907; 95% CI: 0.878–0.936, p < 0.001) and higher RHR (HR = 1.016; 95% CI: 1.001–1.032, P = 0.031) were independent risk factors of all-cause mortality. Causal mediation analysis further confirmed and quantified the mediation function of RHR in the process of PA improving all-cause mortality (mediation proportion = 3.9%; 95% CI: 0.2–10.0%, p = 0.036).

Conclusion

The effects of the higher level of PA on improving life prognosis may be partially mediated through RHR among patients with CIED. It indicates that changes in the autonomic nervous function during postoperative rehabilitation exercises should get more attention.

Cardiovascular Dysautonomia in Patients with Breast Cancer

Breast cancer is the most frequent malignant disease among women, being responsible for a considerable percentage of fatalities and comorbidities every year. Despite advances in early detection and therapy, evidence shows that breast cancer survivors are at increased risk of developing other chronic conditions, such as cardiovascular diseases.

Autonomic dysfunction is an emerging, but poorly understood topic that has been suggested as a risk factor for cardiovascular disease in breast cancer patients. It clinically manifests through persistently elevated heart rates and abnormal heart rate variability, even before any signs of cardiovascular dysfunction appear. Since changes in the left ventricular ejection fraction only manifest when myocardial injury has already occurred, it has been hypothesized that autonomic dysfunction can constitute an early biomarker of cardiovascular impairment in breast cancer patients.

This review focuses on the direct and indirect effects of cancer and its treatment on the autonomic nervous system in breast cancer patients. We highlight the mechanisms potentially involved in cancer and antineoplastic therapy-related autonomic imbalance and review the potential strategies to prevent and/or attenuate autonomic dysfunction.

There are gaps in the current knowledge; more research in this area is needed to identify the relevance of autonomic dysfunction and define beneficial interventions to prevent cardiovascular disease in breast cancer patients.

The Diabetic Cardiorenal Nexus

The end-stage of the clinical combination of heart failure and kidney disease has become known as cardiorenal syndrome. Adverse consequences related to diabetes, hyperlipidemia, obesity, hypertension and renal impairment on cardiovascular function, morbidity and mortality are well known. Guidelines for the treatment of these risk factors have led to the improved prognosis of patients with coronary artery disease and reduced ejection fraction. Heart failure hospital admissions and readmission often occur, however, in the presence of metabolic, renal dysfunction and relatively preserved systolic function. In this domain, few advances have been described. Diabetes, kidney and cardiac dysfunction act synergistically to magnify healthcare costs. Current therapy relies on improving hemodynamic factors destructive to both the heart and kidney. We consider that additional hemodynamic solutions may be limited without the use of animal models focusing on the cardiomyocyte, nephron and extracellular matrices. We review herein potential common pathophysiologic targets for treatment to prevent and ameliorate this syndrome.

Cardiac 123I-mIBG Imaging in Heart Failure

Cardiac sympathetic upregulation is one of the neurohormonal compensation mechanisms that play an important role in the pathogenesis of chronic heart failure (CHF). In the past decades, cardiac 123I-mIBG scintigraphy has been established as a feasible technique to evaluate the global and regional cardiac sympathetic innervation. Although cardiac 123I-mIBG imaging has been studied in many cardiac and neurological diseases, it has extensively been studied in ischemic and non-ischemic CHF. Therefore, this review will focus on the role of 123I-mIBG imaging in CHF. This non-invasive, widely available technique has been established to evaluate the prognosis in CHF. Standardization, especially among various combinations of gamma camera and collimator, is important for identifying appropriate thresholds for adequate risk stratification. Interestingly, in contrast to the linear relationship between 123I-mIBG-derived parameters and overall prognosis, there seems to be a "bell-shape" curve for 123I-mIBG-derived parameters in relation to ventricular arrhythmia or appropriate implantable cardioverter defibrillator (ICD) therapy in patients with ischemic CHF. In addition, there is a potential clinical role for cardiac 123I-mIBG imaging in optimizing patient selection for implantation of expensive devices such as ICD and cardiac resynchronization therapy (CRT). Based on cardiac 123I-mIBG data risk models and machine learning, models have been developed for appropriate risk assessment in CHF.

Different exercise training modalities similarly improve heart rate variability in sedentary middle-aged adults: the FIT-AGEING randomized controlled trial

PURPOSE

This study aimed to investigate the influence of different exercise training modalities on heart rate variability (HRV) in sedentary middle-aged adults; and to study whether changes in health-related outcomes (i.e., body composition and cardiometabolic risk) are associated with those hypothetical HRV changes in sedentary middle-aged adults.

METHODS

A total of 66 middle-aged adults (53.6 ± 4.4 years old; 50% women) were enrolled in the FIT-AGEING study. We conducted a 12-week randomized controlled trial. The participants were randomly assigned to 4 groups: (a) a control group (no exercise); (b) a physical activity recommendation from the World Health Organization group (PAR); (c) a high-intensity interval training group (HIIT); and (d) a high-intensity interval training group adding whole-body electromyostimulation (HIIT + EMS).

RESULTS

All exercise training modalities induced changes in HRV parameters (all P ≤ 0.001) without statistical differences between them (all P > 0.05). We found associations between changes in body composition and cardiometabolic risk and exercise-related changes in HRV.

CONCLUSION

Our results suggest that different exercise interventions (i.e., PAR, HIIT and HIIT + EMS) induced an enhancement of HRV in sedentary middle-aged adults. Our findings support the notion that exercise-related changes in HRV are associated with changes in body composition and cardiometabolic risk after the intervention program CLINICAL TRIAL REGISTRY: NCT03334357 (ClinicalTrials.gov). November 7, 2017 retrospectively registered.

B lymphocyte-derived acetylcholine limits steady-state and emergency hematopoiesis

Autonomic nerves control organ function through the sympathetic and parasympathetic branches, which have opposite effects. In the bone marrow, sympathetic (adrenergic) nerves promote hematopoiesis; however, how parasympathetic (cholinergic) signals modulate hematopoiesis is unclear. Here, we show that B lymphocytes are an important source of acetylcholine, a neurotransmitter of the parasympathetic nervous system, which reduced hematopoiesis. Single-cell RNA sequencing identified nine clusters of cells that expressed the cholinergic α7 nicotinic receptor (Chrna7) in the bone marrow stem cell niche, including endothelial and mesenchymal stromal cells (MSCs). Deletion of B cell-derived acetylcholine resulted in the differential expression of various genes, including Cxcl12 in leptin receptor+ (LepR+) stromal cells. Pharmacologic inhibition of acetylcholine signaling increased the systemic supply of inflammatory myeloid cells in mice and humans with cardiovascular disease.

Rapid Weight Loss Coupled with Sport-Specific Training Impairs Heart Rate Recovery in Greco-Roman Wrestlers

Wrestling is a sport that can be classified with the use of alternating aerobic–anaerobic metabolism with moderate but high-impact energy expenditure. Heart rate recovery (HRR) is the difference between heart rate during exercise and a certain amount of time after the start of recovery. The goal of this study was to determine the difference in HRR between two phases: high-intensity sport-specific training (HISST) combined with rapid weight loss (RWL)—phase 1 (P1) and HISST only—phase 2 (P2). Ten national-level wrestlers were included in this study. All participants underwent HISST along with RWL procedures for P1. Seven days later, during P2, an identical training session was performed with no RWL included. We found a statistically significant difference in the values obtained after the first and second minutes of recovery in the second set for both cases (p = 0.034 and p = 0.037, respectively), with higher HR values recorded in P1. It can be concluded that there is undoubtedly a difference in HRR during training and RWL compared to HISST alone. Additionally, HISST along with RWL could compromise the aerobic component of recovery.

The Evaluation of Biomarkers of Physical Activity on Stress Resistance and Wellness

Physical activity can improve health as well as reduce stress and the risk of developing several widespread diseases. However, there exists no accepted standard biomedical examination-method for stress evaluation. The purpose of this study was to investigate the effect of regular physical activity on stress and wellness as well as the evaluation of potential biomarkers in this field. This study included 105 people (mean age = 36.57 ± 1.4 years) who were randomly assigned into the exercise group 1 (EG-1) (n = 41), the exercise group 2 (EG-2) (n = 30), and the control group (CG) (n = 34). Measurements of stress and wellness were obtained by Multiscan BC-OXI before and after experimental period. This device presents a multifrequency segmental body composition 3D analyser with digital pulse oximeter. The key indicators of stress as well as for wellness were significantly improved in the EG-1. Parasympathetic activity showed significant changes as potential stress biomarker. Statistically significant gender differences were not observed in the comparable groups. The results suggest that the stress resistance and well-being significantly improved in the EG-1 due to regular physical activity. However, further research is necessary to determine effects of physical activity on integral health indicators.

Influence of Spontaneous and Mechanical Ventilation on Frequency-Based Measures of Heart Rate Variability

Frequency-based measures of heart rate variability have been shown to be a useful physiological marker in both clinical and research settings providing insight into the functioning of the autonomic nervous system. Ongoing interactions between the autonomic nervous system control of the heart and lung occurs during each ventilation cycle because of their anatomical position within the closed thoracic cavity. Mechanical ventilation and subsequent removal change the normal ventilator mechanics producing alterations in the tidal volume, intrathoracic pressure, and oxygen delivery. A noninvasive method called heart rate variability (HRV) can be used to evaluate this interaction during ventilation and can be quantified by applying frequency-based measures of the variability between heartbeats. Although HRV is a reliable method to measure alteration of the autonomic nervous system (ANS) function and cardiopulmonary interaction, there have been limited reports concerning the changes in the frequency-based measure of HRV during both spontaneous and mechanical ventilation. The purpose of this methodological study is therefore to describe the physiological influence of both spontaneous and mechanical ventilation on frequency-based measures of HRV.

Different acquisition systems for heart rate variability analysis may lead to diverse outcomes

Heart rate variability (HRV) is a relevant physiological variable for the estimation of cardiac autonomic function. Although the gold standard for HRV registration is the electrocardiogram (ECG), several applications (APPs) have been increasingly developed. The evaluation carried out by these devices must be compatible with ECG standards. The aim of this study was to compare the data obtained simultaneously with ECG and APP with chest heart rate transmitters. Fifty-six healthy individuals (28 men and 28 women) were evaluated at rest through a short simultaneous HRV measurement with both devices. Data from both acquisition systems were analyzed separately using their own analysis software and exported and analyzed using a validated software. Signal recordings were compatible between the two acquisition systems (Pearson r=0.99; P<0.0001). Although a high correlation was found for the HRV variables obtained in the time domain (Spearman r=0.99; P<0.0001), the correlation decreased in the frequency domain (Pearson r=0.85; P<0.0001) when two software programs were used. Comparison of the averages of spectral analysis parameters also showed differences when HRV data were analyzed separately in each device for low-frequency (LF) and high-frequency (HF) bands. Although the portability of these mobile devices allows for optimal HRV evaluation, the direct analysis obtained from these devices must be carefully evaluated with respect to frequency domain parameters.

The Predictive Value of Serum Calcium on Heart Rate Variability and Cardiac Function in Type 2 Diabetes Patients

BACKGROUND

Cardiovascular autonomic neuropathy (CAN) is common in patients with type 2 diabetes mellitus (T2DM), mainly presented as decreased heart rate variability (HRV) which often leads to cardiac death. However, HRV measurement is not convenient in most clinics. Therefore, identifying high-risk patients for CAN in diabetes with easier measurements is crucial for the early intervention and prevention of catastrophic consequences.

METHODS

In this cross-sectional study, 675 T2DM patients with normocalcemia were selected. Of these, they were divided into two groups: normal HRV group (n = 425, 100 ms≤ SDNN ≤180 ms) vs. declined HRV group (n = 250, SDNN <100 ms). All patients' clinical data were collected and the correlation of clinical variables with HRV were analyzed by correlation and logistic regression analysis. The area below the ROC curve was used to evaluate the predictive performance of serum calcium on HRV.

RESULTS

In this study, declines in HRV were present in 37.0% of T2DM patients. Significant differences in albumin-adjusted serum calcium levels (CaA) (8.86 ± 0.27 vs. 9.13 ± 0.39 mg/dl, p <0.001) and E/A (0.78 ± 0.22 vs. 0.83 ± 0.26, p = 0.029) were observed between declined HRV and normal HRV groups. Bivariate linear correlation analysis showed that CaA and E/A were positively correlated with HRV parameters including SDNN (p < 0.001), SDNN index (p < 0.001), and Triangle index (p < 0.05). The AUC in the ROC curve for the prediction of CaA on HRV was 0.730 (95% CI (0.750-0.815), p < 0.001). The cutoff value of CaA was 8.87 mg/dl (sensitivity 0.644, specificity 0.814). The T2DM patients with CaA <8.87 mg/dl had significantly lower HRV parameters (SDNN, SDNN index, rMSSD, and triangle index) than those with CaA ≥8.87 mg/dl (p < 0.01, respectively). Multivariate logistic regression analysis showed a significantly increased risk of declined HRV in subjects with CaA level <8.87 mg/dl [OR (95% CI), 0.049 (0.024-0.099), p < 0.001].

CONCLUSIONS

Declined HRV is associated with a lower CaA level and worse cardiac function. The serum calcium level can be used for risk evaluation of declined HRV in T2DM patients even within the normocalcemic range.