Heart Rate Variability and Cardiovascular Fitness: What We Know so Far

Women With Polycystic Ovary Syndrome and Excess Body Fat Exhibit Atypical Sympathetic Autonomic Modulation That is Partially Reversed by Aerobic Physical Training

OBJECTIVE

The aetiology of impairments in autonomic modulation of heart rate variability (HRV) in polycystic ovary syndrome (PCOS) remains unclear, as does the impact of aerobic physical training (APT) on controlling endocrine-metabolic disorders and HRV. This is because these women often present excess body fat. Therefore, we assessed whether the dysregulation in autonomic modulation of HRV in women with PCOS is due to endocrine-metabolic disorders and whether the combination of excess body fat with endocrine-metabolic disorders amplifies cardiovascular autonomic deficits. We also investigated whether APT positively influences autonomic modulation of HRV in PCOS.

DESIGN

Non-randomised clinical trial.

PARTICIPANTS

Women with and without PCOS with different percentages of body fat.

MEASUREMENTS

Participants were divided into four groups: women without PCOS with a body fat percentage between 22% and 29% (CONTROL group; 22%-29%); CONTROL (30%-37%) group; PCOS (22%-29%) group; and PCOS (30%-37%) group. Hemodynamic, metabolic, and hormonal characteristics and HRV parameters were obtained before and after 16 weeks of APT.

RESULTS

The PCOS (22%-29%) group exhibited lower vagal modulation than the CONTROL (22%-29%) group. In contrast, no significant differences were observed between the CONTROL (30%-37%) and PCOS (30%-37%) groups. Furthermore, the PCOS (30%-37%) group demonstrated lower sympathetic modulation than the PCOS (22%-29%) group. After APT, the PCOS (22%-29%) group increased in vagal modulation, while the PCOS (30%-37%) group increased in sympathetic modulation.

CONCLUSION

PCOS affects vagal modulation; however, this effect may be masked at elevated levels of body fat. Additionally, the combination of excess body fat with endocrine-metabolic dysregulation appears to reduce sympathetic modulation, possibly due to sympathetic drive hyperactivity. APT positively affected HRV in both PCOS groups.

Heart rate variability, a potential assessment tool for identifying anxiety, depression, and sleep disorders in elderly individuals

Introduction

This study investigates how anxiety, depression, and sleep disorders impact heart rate variability (HRV) in the elderly, exploring the clinical implications of HRV changes.

Methods

We examined 355 patients (163 men, 192 women) at Xijing Hospital from July 2021 to December 2022 during health check-ups. Demographics were recorded, and emotional status was assessed using the Hamilton Anxiety Scale (HAMA) and the Hamilton Depression Scale (HAMD). The Pittsburgh Sleep Quality Scale (PSQI) evaluated sleep quality. Patients were categorized into groups A-G based on the presence of emotional states and sleep disorders. HRV indices-SDNN, SDANN, RMSSD, PNN50, LF/HF, LF, and HF-were analyzed using ANOVA and multivariate logistic regression.

Results

No statistically significant differences were observed in demographic, clinical, and lifestyle factors across the eight groups. Variables assessed included age, sex, body mass index (BMI), fasting blood glucose, glycated hemoglobin (HbA1c), blood lipids, blood pressure, heart rate, and histories of smoking and alcohol consumption. Additionally, the presence of hypertension, diabetes, coronary heart disease, marital status, income, and education level were evaluated, with all showing equivalence (P > 0.05). Significant differences in HRV indices were observed across groups, particularly in group G (patients with anxiety, depression and sleep disorders), which showed decreased HRV parameters except LF/HF, and group H (control group), which showed increased parameters, also except LF/HF (P < 0.01). Anxiety was an independent risk factor for reduced SDNN, SDANN, and LF (P ≤ 0.01), and increased LF/HF ratio (P < 0.01). Depression was linked to decreased SDNN, RMSSD, PNN50, and HF (P < 0.05). Sleep disorders independently predicted reduced PNN50 and SDANN (P < 0.01).

Conclusion

HRV indices of individuals with varying emotional states and sleep disorders exhibited varying degrees of decrease. Anxiety, depression, and sleep disorders presented a superimposed effect on HRV. SDNN, SDANN, RMSSD, PNN50, HF and LF of HRV are of great reference value in the diagnosis of emotional and sleep disorders. For elderly patients experiencing cognitive impairment, HRV is anticipated to serve as a convenient and effective tool for assessing mood and sleep disorders.

Identification of Athleticism and Sports Profiles Throughout Machine Learning Applied to Heart Rate Variability

Heart rate variability (HRV) is a non-invasive health and fitness indicator, and machine learning (ML) has emerged as a powerful tool for analysing large HRV datasets. This study aims to identify athletic characteristics using the HRV test and ML algorithms. Two models were developed: Model 1 (M1) classified athletes and non-athletes using 856 observations from high-performance athletes and 494 from non-athletes. Model 2 (M2) identified an individual soccer player within a team based on 105 observations from the player and 514 from other team members. Three ML algorithms were applied -Random Forest (RF), Extreme Gradient Boosting (XGBoost), and Support Vector Machine (SVM)- and SHAP values were used to interpret the results. In M1, the SVM algorithm achieved the highest performance (accuracy = 0.84, ROC AUC = 0.91), while in M2 Random Forest performed best (accuracy = 0.92, ROC AUC = 0.94). Based on these results, we propose an athleticism index and a soccer identification index derived from HRV data. The findings suggest that ML algorithms, such as SVM and RF, can effectively generate indices based on HRV for identifying individuals with athletic characteristics or distinguishing athletes with specific sports profiles. These insights underscore the importance of integrating HRV assessments systematically into training regimens for enhanced athletic evaluation.

A consort-guided randomized, blinded, controlled clinical trial on the effects of 6 weeks training on heart rate variability in thoroughbred horses

BACKGROUND

Fitness assessment of horses remains challenging. Heart rate variability (HRV) can be used to monitor human athlete's training, but its value is unknown in horses.

HYPOTHESIS

The linear domain HRV variables are affected by fitness.

ANIMALS

Twelve healthy untrained thoroughbreds were randomly split into a training group (6 weeks of incremental racetrack training) and a control group (no training).

METHODS

Linear domain HRV variables were analyzed (high frequency [HF], low frequency [LF], their normalized units [Hfnu, Lfnu], root mean square of successive differences between beats [RMSSD], Poincaré plot features [SD1 and SD2]) while resting overnight before (baseline) and after 2, 4 and 6 weeks of training. V̇O2max and echocardiographic indexes were measured at baseline and after 6 weeks. Changes in HRV variables over time (ANOVA), and correlation with V̇O2max (Pearson's chi-squared test) were tested (P < .05 significance).

RESULTS

V̇O2max, LF/HF ratio, and LFnu increased while HFnu decreased in the training group (before and after training mean [SD] values: V̇O2max 134 [12.8]-146 [16.5] mL/[kg min]; P < .001; LF/HF ratio 0.51 [0.2]-0.91 [0.3] [P = .02]; LFnu 37.5 [10.1]-46.8 [7.8] [P = .02]; HFnu 76.2 [7.9]-53.2 [7.7] [P < .001]). Training did not affect RMSSD, SD1, SD2, resting HR, or echocardiographic indexes. Strong correlations were found between V̇O2max and HRV variables (V̇O2max and LFnu [r = -0.59, P = .04]; ΔV̇O2max and the corresponding ΔLF [r = -0.88, P = .02]).

CONCLUSIONS AND CLINICAL IMPORTANCE

Six weeks of training affected some frequency domain HRV variables. Further studies are necessary to validate the use of HRV for monitoring horses' responses to training.

Auxiliary identification of depression patients using interpretable machine learning models based on heart rate variability: a retrospective study

OBJECTIVE

Depression has emerged as a global public health concern with high incidence and disability rates, which are timely imperative to identify and intervene in clinical practice. The objective of this study was to explore the association between heart rate variability (HRV) and depression, with the aim of establishing and validating machine learning models for the auxiliary diagnosis of depression.

METHODS

The data of 465 outpatients from the Affiliated Hospital of Southwest Medical University were selected for the study. The study population was then randomly divided into training and test sets in a 7:3 ratio. Logistic regression (LR), support vector machine (SVM), random forest (RF) and eXtreme gradient boosting (XGBoost) algorithm models were used to construct risk prediction models in the training set, and the model performance was verified in the test set. The four models were evaluated by the area under the receiver operating characteristic curve (ROC), calibration curve and the decision curve analysis (DCA). Furthermore, we employed the SHapley Additive exPlanations (SHAP) method to illustrate the effects of the features attributed to the model.

RESULTS

There were 237 people in the depressed group and 228 in the non-depressed group. In the training set (n = 325) and test set (n = 140), the area under of the curve(AUC) values of the XGBoost model are 0.92 [95% confidence interval (CI) 0.888,0.95] and 0.82 (95% CI 0.754,0.892)] respectively, which are higher than the other three models. The XGBoost model has excellent predictive efficacy and clinical utility. The SHAP method was ranked according to the importance of the degree of influence on the model, with age, heart rate, Standard deviation of the NN intervals (SDNN), two nonlinear parameters of HRV and sex considered to be the top 6 predictors.

CONCLUSION

We provided a feasibility study of HRV as a potential biomarker for depression. The proposed model based on HRV provides clinicians with a quantitative auxiliary diagnostic tool, which is assist to improving the accuracy and efficiency of depression diagnosis, and can also be utilized for the monitoring and prevention of depression.

Cancer and Stress: Understanding the Connections and Interventions

Stress is ubiquitous in our modern society and contributes to many disease states. This narrative review describes the effect of stress/distress on cancer development and progression. Seminal randomized controlled trials, systematic reviews/meta-analyses, and distress management guidelines from the National Comprehensive Cancer Network (NCCN), the American Society of Clinical Oncology (ASCO), and the Society for Integrative LinearOncology (SIO) are highlighted. We describe the physiological effects of distress, distress assessment, and management. Psychological treatments are summarized. Evidence-based lifestyle modifications and integrative therapies are reviewed in detail, including mindfulness-based techniques, yoga, guided imagery, breathing techniques, hypnosis, exercise, music therapy, qigong/Tai Chi, eye movement desensitization and reprocessing, and improving sleep and heart rate variability. Recognition and treatment of distress can improve quality of life. More research is needed to determine the effects of managing distress on cancer outcomes, as well as the best type and duration of intervention, noting that the benefits of interventions may be specific for patients with different cancer types.

Low-Intensity Resistance Exercise in Cardiac Rehabilitation: A Narrative Review of Mechanistic Evidence and Clinical Implications

Cardiac rehabilitation, a multi-component intervention designed to mitigate the impact of cardiovascular disease, often underutilises low-intensity resistance exercise despite its potential benefits. This narrative review critically examines the mechanistic and clinical evidence supporting the incorporation of low-intensity resistance exercise into cardiac rehabilitation programmes. Research indicates that low-intensity resistance exercise induces hypertrophic adaptations by maximising muscle fibre activation through the size principle, effectively recruiting larger motor units as it approaches maximal effort. This activation promotes adaptation in both type I and II muscle fibres, resulting in comparable increases in myofibrillar protein synthesis and phosphorylation of key signalling proteins when compared to high-intensity resistance exercise. Low-intensity resistance exercise provides equivalent improvements in muscular strength and hypertrophy compared to high-intensity protocols while addressing barriers to participation, such as concerns about safety and logistical challenges. By facilitating engagement through a more accessible exercise modality, low-intensity resistance exercise might improve adherence rates and patient outcomes in cardiac rehabilitation. Additionally, the ability of low-intensity resistance exercise to address sarcopenia and frailty syndrome, significant determinants of cardiovascular disease progression, can enhance the recovery and overall quality of life for patients. This review establishes evidence-based recommendations for the inclusion of low-intensity resistance exercise in cardiac rehabilitation, offering a promising pathway to enhance the effectiveness of these programmes.

Association of heart rate variability with cardiorespiratory fitness and muscle strength in patients after hospitalization for COVID-19: An analytical cross-sectional study

INTRODUCTION

Patients with a moderate to severe clinical condition of COVID-19 who need hospitalization may have dysfunction in Cardiac Autonomic Control (CAC) and functional capacity.

OBJECTIVE

To assess the association of HRV with cardiorespiratory fitness and respiratory and peripheral muscle strength in patients after hospitalization for COVID-19.

METHOD

Cross-sectional study with individuals > 18-years old, post-hospitalization for COVID-19, with a positive RT-PCR test. Data on clinical condition and hospital admission were collected, and parameters of respiratory and peripheral muscle strength and functional capacity were evaluated with the 6-Minute Walk Test (6MWT). CAC was assessed by analyzing (Heart Rate Variability) HRV in the time (SDNN, RMSSD) and frequency domains (HF, LF, HF/LF ratio). Pearson correlation was performed between HRV measures and functional parameters.

RESULTS

The results showed low HRV in study participants, with positive correlations between 6MWT and RMSSD and between SDNN and HF power and negative correlations between Heart Rate and the LF/HF ratio. On the other hand, respiratory and peripheral muscle strength correlated positively with parameters that represent sympathetic nervous system expression (LF nu and LF power) and negatively with the LF/HF ratio. However, changes in HRV parameters were not associated with disease severity.

CONCLUSION

The dysautonomia of COVID-19 patients was correlated with functional sequelae, though not associated with disease severity parameters. There was low HRV, with low vagal expression, and imbalance in sympathetic/parasympathetic modulation in the study group.

Impact of spa therapy on physical activity, sleep and heart rate variability among individuals with fibromyalgia: Results of an ancillary study

Spa therapy is recommended to manage symptoms of fibromyalgia, but the physiological mechanisms underlying this improvement have been poorly studied. In an original study, we explored the effect of a 3-week rheumatology spa treatment for fibromyalgia patients on quality of life and with a symptom severity questionnaire. We present here the results of an ancillary study which explored three secondary criteria using objective measurement methods: diurnal actimetry for physical activity analysis, nocturnal actimetry for sleep analysis and heart rate variability. Eighty-three fibromyalgia patients were randomized to participate in an immediate 3-week rheumatological spa therapy, either a start within 6 weeks after inclusion (interventional group, n = 39) or a delayed, start 6 months after inclusion (control group, n = 44). Patients were asked to wear an actimeter (n = 56) to assess diurnal physical activity and sleep quality and a 24-h Holter ECG (n = 60) to assess nocturnal heart rate variability at baseline, 3 months and 6 months after inclusion. Time spent in sedentary and light physical activity was reduced to ∼30 min at 6 months in the interventional group (P = 0.027). Sleep quality and heart rate variability were not improved. Spa therapy made it possible to reduce sedentary activities in patients' daily life for up to 6 months afterwards, concomitant with the improvement in quality of life, pain and fatigue as highlighted in the original Thermalgi study.

Heart rate variability and autonomic nervous system imbalance: Potential biomarkers and detectable hallmarks of aging and inflammaging

The most cutting-edge issue in the research on aging is the quest for biomarkers that transcend molecular and cellular domains to encompass organismal-level implications. We recently hypothesized the role of Autonomic Nervous System (ANS) imbalance in this context. Studies on ANS functions during aging highlighted an imbalance towards heightened sympathetic nervous system (SNS) activity, instigating a proinflammatory milieu, and attenuated parasympathetic nervous system (PNS) function, which exerts anti-inflammatory effects via the cholinergic anti-inflammatory pathway (CAP) and suppression of the hypothalamic-pituitary-adrenal (HPA) axis. This scenario strongly suggests that ANS imbalance can fuel inflammaging, now recognized as one of the most relevant risk factors for age-related disease development. Recent recommendations have increasingly highlighted the need for actionable strategies to improve the quality of life for older adults by identifying biomarkers that can be easily measured, even in asymptomatic individuals. We advocate for considering ANS imbalance as a biomarker of aging and inflammaging. Measures of ANS imbalance, such as heart rate variability (HRV), are relatively affordable, non-invasive, and cost-effective, making this hallmark easily diagnosable. HRV gains renewed significance within the aging research landscape, offering a tangible link between pathophysiological perturbations and age-related health outcomes.

Association of CETP Gene Polymorphisms and Haplotypes with Acute Heart Rate Response to Exercise

Polymorphisms in the cholesteryl ester transfer protein (CETP) gene are known to be strongly associated with increased cardiovascular risk, primarily through their effects on the lipid profile and consequently on atherosclerotic risk. The acute heart rate response (AHRR) to physical activity is closely related to individual cardiovascular health. This study aimed to investigate the effect of CETP gene polymorphisms on AHRR. Our analysis examines the association of five single nucleotide polymorphisms (SNPs; rs1532624, rs5882, rs708272, rs7499892, and rs9989419) and their haplotypes (H) in the CETP gene with AHRR in 607 people from the Hungarian population. Individual AHRR in the present study was assessed using the YMCA 3-min step test and was estimated as the difference between resting and post-exercise heart rate, i.e., delta heart rate (ΔHR). To exclude the direct confounding effect of the CETP gene on the lipid profile, adjustments for TG and HDL-C levels, next to conventional risk factors, were applied in the statistical analyses. Among the examined five SNPs, two showed a significant association with lower ΔHR (rs1532624-Cdominant: B = -8.41, p < 0.001; rs708272-Gdominant: B = -8.33, p < 0.001) and reduced the risk of adverse AHRR (rs1532624-Cdominant: OR = 0.44, p = 0.004; rs708272-Gdominant: OR = 0.43, p = 0.003). Among the ten haplotypes, two showed significant association with lower ΔHR (H3-CAGCA: B = -6.81, p = 0.003; H9-CGGCG: B = -14.64, p = 0.015) and lower risk of adverse AHRR (H3-CAGCA: OR = 0.58, p = 0.040; H9-CGGCG: OR = 0.05, p = 0.009) compared to the reference haplotype (H1-AGACG). Our study is the first to report a significant association between CETP gene polymorphisms and AHRR. It also confirms that the association of the CETP gene with cardiovascular risk is mediated by changes in heart rate in response to physical activity, in addition to its effect on lipid profile.

The effect of exercise training on heart rate variability in patients with hypertension: A systematic review and meta-analysis

We aimed to assess the effect of exercise training on heart rate variability (HRV) in hypertensive patients and to provide practical recommendations. We systematically searched seven databases for randomized controlled trials (RCTs) comparing the efficacy of exercise interventions vs. non-exercise control for HRV in adults with hypertension. HRV parameters, blood pressure (BP), and heart rate (HR) from the experimental and control groups were extracted to carry out meta-analysis. To explore the heterogeneity, we performed sensitivity analysis, sub-analysis, and meta-regression. Twelve RCTs were included, and the main results demonstrated exercise produced improvement in root mean square of successive RR-intervals differences (RMSSD) and high frequency (HF), and reductions in LF/HF, resting systolic blood pressure (SBP), and HR. The sub-analysis and meta-regression showed that AE improved more HRV indices and was effective in reducing BP compared with RE. Follow-up duration was also an important factor. Data suggests exercise training has ameliorating effects on HRV parameters, resting SBP, and HR in hypertensive patients, showing enhanced autonomic nervous system function and vagal activity. This effect may be better realized with exercise interventions of 4 weeks or more. Considering our results and the hypertension practice guidelines, we tend to recommend patients choose supervised AE.

Heart rate and heart rate variability in horses undergoing hot and cold shoeing

Heart rate variability (HRV) is a frequently used indicator of autonomic responses to various stimuli in horses. This study aimed to investigate HRV variables in horses undergoing cold (n = 25) or hot (n = 26) shoeing. Multiple HRV variables were measured and compared between horses undergoing cold and hot shoeing, including the time domain, frequency domain, and nonlinear variables pre-shoeing, during shoeing, and at 30-minute intervals for 120 minutes post-shoeing. The shoeing method interacted with time to change the HRV variables standard deviation of RR intervals (SDNN), root mean square of successive RR interval differences (RMSSD), very-low-frequency band, low-frequency band (LF), the LF to high-frequency band ratio, respiratory rate, total power, standard deviation perpendicular to the line of identity (SD1), and standard deviation along the line of identity (SD2). SDNN, RMSSD, and total power only increased 30 minutes after hot shoeing (all p < 0.05). Triangular interpolation of normal-to-normal intervals (TINN) and the HRV triangular index increased during and up to 120 minutes after hot shoeing (p < 0.05-0.001). TINN increased only during cold shoeing (p < 0.05). LF increased 30 and 60 minutes after hot shoeing (both p < 0.05). SD1 and SD2 also increased 30 minutes after hot shoeing (both p < 0.05). SDNN, TINN, HRV triangular index, LF, total power, and SD2 were higher in hot-shoed than cold-shoed horses throughout the 120 minutes post-shoeing. Differences in HRV were found, indicating increased sympathovagal activity in hot shoed horses compared to cold shoed horses.

Validity of a Heart Rate Monitor for Heart Rate Variability Analysis During an Orthostatic Challenge

Heart rate variability (HRV) is used as a measure of autonomic nervous system (ANS) function and is based on heart rate (HR) beat-to-beat time interval variance analysis. Various techniques are used for recording HR, however, few studies have compared Holter-type recordings vs HR monitors (HRM) during an orthostatic challenge.

OBJECTIVES

Compare HRV measures from an electrocardiogram (ECG) Holter and a HRM as a tool for investigating ANS response for post-concussion rehabilitation follow-up.

METHODS

Twenty-seven participants (n = 27; 15 females, 12 males), 18 to 35 years old, non-smoking, no history of cardiac illness and physically active (3 times per week, 60 mins, moderate intensity exercise) participated in the study. ECG signals and HRM were recorded beat-to-beat (R-R) simultaneously. A motorized tilt table was set at 0 degree for supine and 85 degrees for standing position. Participants were instructed to remain for 7 minutes in each position. R-R signals from both Holter and Polar HRM recording starting points were matched before further analysis. Bland-Altman plots were used to compare recordings from the Holter (gold standard) and the Polar HRM in both positions. Unpaired t-test was used to compare measurements obtained with both systems. Significance was set at p < 0.05.

RESULTS

No significant differences were observed between R-R measurements taken with both systems under equal conditions (supine and standing). Same variables under similar conditions were significantly correlated (p = 0.0001).

CONCLUSION

Both recording and analysis systems (Holter vs HRM) yielded comparable results. Thus, both systems appear valid and interchangeable for HRV analysis for measuring orthostatic challenge HRV responses.

Comparison of Heart Rate Variability in Thai Older Adults with Hypertension, Pre-Hypertension, and Normotension

Objectives

This study aims to compare HRV variables across three cohorts: normotensive (NT), prehypertensive (pre-HT), and hypertensive (HT) and to assess the relationship between the blood pressure (BP) and HRV parameters.

Methods

Employing a cross-sectional design, 64 older participants were categorized based on the Joint National Committee's criteria into NT (n = 10), pre-HT (n = 33), and HT (n = 21) groups. Anthropometric data, lipid profiles, and HRV indices were evaluated. HRV data were obtained from the Polar V800 chest strap device using HRV Kubios software for data analysis of short-term recordings lasting 10 minutes. This analysis encompasses both time and frequency domain assessments. The time domain includes the standard deviation of NN intervals (SDNN), the root mean square of successive RR interval differences (RMSSD), and the percentage of successive RR intervals differing by over 50 ms (pNN50). The frequency domain includes low frequency (LF), high frequency (HF), and the ratio of LF-to-HF power (LF/HF). Data were statistically analyzed via one-way analysis of variance (ANOVA) and Pearson correlation.

Results

The HT group exhibited significantly lower values in SDNN, pNN50, LF power, and HF power in comparison to the NT group (P < 0.05). Moreover, the HT group had a significantly lower SDNN value compared to the pre-HT group (P < 0.05). Inverse associations were uncovered between systolic and diastolic blood pressure and SDNN, pNN50, and HF power (P < 0.05). Multiple regression further highlighted the significance of systolic and pulse pressure concerning HF power (P < 0.05).

Conclusions

HRV indices are reduced in Thai older adults with HT compared with those with NT. Monitoring HRV in older adults can provide valuable insights into autonomic function and cardiovascular disease risk.

What do we know about the role of menopause in cardiovascular autonomic regulation in hypertensive women?

OBJECTIVE

We investigated the systemic arterial hypertension effects on cardiovascular autonomic modulation and baroreflex sensitivity (BRS) in women with or without preserved ovarian function.

METHODS

A total of 120 women were allocated into two groups: middle-aged premenopausal women (42 ± 3 y old; n = 60) and postmenopausal women (57 ± 4 y old; n = 60). Each group was also divided into two smaller groups (n = 30): normotensive and hypertensive. We evaluated hemodynamic and anthropometric parameters, cardiorespiratory fitness, BRS, heart rate variability (HRV), and blood pressure variability. The effects of hypertension and menopause were assessed using a two-way analysis of variance. Post hoc comparisons were performed using the Student-Newman-Keuls test.

RESULTS

Comparing premenopausal groups, women with systemic arterial hypertension showed lower BRS (9.1 ± 4.4 vs 13.4 ± 4.2 ms/mm Hg, P < 0.001 ) and HRV total variance (1,451 ± 955 vs 2,483 ± 1,959 ms 2 , P = 0.005) values than normotensive; however, the vagal predominance still remained. On the other hand, both postmenopausal groups showed an expressive reduction in BRS (8.3 ± 4.2 vs 11.3 ± 4.8 ms/mm Hg, P < 0.001) and HRV characterized by sympathetic modulation predominance (low-frequency oscillations; 56% ± 17 vs 44% ± 17, P < 0.001), in addition to a significant increase in blood pressure variability variance (28.4 ± 14.9 vs 22.4 ± 12.5 mm Hg 2 , P = 0.015) compared with premenopausal groups. Comparing both postmenopausal groups, the hypertensive group had significantly lower values ​​of HRV total variance (635 ± 449 vs 2,053 ± 1,720 ms 2 , P < 0.001) and BRS (5.3 ± 2.8 vs 11.3 ± 3.2 ms/mm Hg) than the normotensive.

CONCLUSIONS

Hypertensive middle-aged premenopausal women present HRV autonomic modulation impairment, but they still maintain a vagal predominance. After menopause, even normotensive women show sympathetic autonomic predominance, which may also be associated with aging. Furthermore, postmenopausal women with hypertension present even worse cardiac autonomic modulation.

Regulation of exercise on heart rate variability in perimenopausal and postmenopausal women

Heart rate variability (HRV) is a non-invasive quantitative measure of cardiac autonomic nervous activity. Due to the increase of age and the decrease of estrogen level in perimenopausal and postmenopausal women, the cardiac autonomic nervous function is abnormal, increasing the risk of cardiovascular disease. Proper exercise can increase estrogen levels, improve cardiovascular health, regulate cardiac autonomic nervous activity, and reduce the risk of cardiovascular disease. Low-moderate intensity aerobic exercise, resistance exercise, aerobic combined resistance exercise and mind-body exercise have positive effects on HRV in perimenopausal and postmenopausal women. Therefore, summarizing the effects of different exercise modes on HRV in perimenopausal and postmenopausal women, as well as the mechanism of exercise training improvement on HRV, so as to adopt better exercise strategies to improve HRV of perimenopausal and postmenopausal women, and thus reduce the risk of cardiovascular diseases and improve the health level and quality of life of perimenopausal and postmenopausal women.

Heart Rate Variability as a Predictor of +Gz Tolerance During the High-G Selective Test

INTRODUCTION: Preselection of pilot candidates in the military is critical and determines the quality of subsequent selection. The Aero Medical Institute in Belgrade uses the following centrifuge endpoints: peripheral vision loss, heart rate above 180 bpm, cardiac arrhythmias, and G-induced loss of consciousness to assess relaxed +Gz tolerance. The aim of this study was to evaluate heart rate variability (HRV) associated with cardiovascular adaptability to different types of stress as a predictor of +Gz tolerance.METHODS: Thirty-six candidates were exposed to centrifuge runs, consisting of the following +Gz-acceleration phases: a 2-G plateau followed by an increase to 5.5 G, a decrease to 2 G, and ending with a plateau. Time-domain HRV indices were calculated for candidates, for a 60-s 2-G plateau, and for the entire test. The correlation was made between the groups that did (Group 1) and did not meet the criteria (Group 2).RESULTS: The results show significantly lower values in all time domain HRV indices, namely standard deviation of the normal-to-normal interval (SDNN) and root mean square of successive differences, in Group 2. Mean SDNN values were 45.98 ± 24.80 ms (2-G plateau) and 109.99 ± 39.64 ms (entire test) in Group 1, while the SDNN were 22.99 ± 12.04 ms and 69.70 ± 33.45 ms in Group 2. Root mean square of successive differences was higher in Group 1 for the 2-G plateau and for the entire test.DISCUSSION: The results suggest that HRV is positively correlated with +Gz-tolerance and can be used as an additional selection tool for military aircrew.Bacevic N, Ninkovic M, Drvendzija M, Vidakovic J, Bacevic M, Stepanic P. Heart rate variability as a predictor of +Gz tolerance during the high-G selective test. Aerosp Med Hum Perform. 2024; 95(2):93-100.

Effects of exercise training on heart rate variability in individuals with lower extremity arterial disease and claudication: A systematic review

PURPOSE

To perform a systematic review of studies assessing the effects of regular exercise on heart rate variability (HRV) in individuals with lower extremity arterial disease (LEAD) and symptoms of claudication.

METHODS

A systematic search in the electronic databases MEDLINE, Embase, and Scielo, was conducted and updated on January 21, 2023. Randomized clinical trials investigating patients with LEAD and IC, assessing ≥ 4 wk of exercise interventions, and reporting at least one HRV measure (e.g., time or frequency domains) at baseline and follow-up were included. Two reviewers independently screened studies for inclusion, performed data extraction, and quality assessment of included studies.

RESULTS

Data from 7 trials were included (i.e., 5 walking, 1 resistance, and 1 isometric handgrip training), totaling 327 patients (66% males; range: 61 - 68 yr; ankle brachial index: 0.4 - 0.7). Following exercise training, three studies investigating walking training reported an increase in parasympathetic modulation indices and/or a decrease in sympathetic modulation indices (n = 2) as well as an increase in non-linear indices (n = 1).

CONCLUSION

The current evidence is weak, and larger randomized controlled trials are needed to confirm the efficacy of exercise training in improving HRV. Additionally, the high divergence in the methodology of studies indicated the need for standard tools to improve the quality of HRV measurements in exercise trials. It is recommended to use standard procedures in future trials investigating HRV.

Autonomic nervous system dysfunction in pediatric sport-related concussion: a systematic review

Objective

To identify, appraise and synthesize the evidence of autonomic nervous system (ANS) dysfunction following sport-related concussion in pediatric populations.

Methods

A literature search was conducted using MEDLINE (Ovid), SportDiscus (EBSCO), CINAHL (EBSCO), EMBASE (Ovid) and PsycINFO (Ovid). Studies were selected and appraised using the Joanna Briggs Institute (JBI) critical appraisal tools. Data was extracted from the included studies and qualitatively synthesized.

Results

Eleven studies were included in the synthesis. There was variability in the methods used to measure ANS function between studies, and sample populations and time to assessment following concussion varied considerably. There was also variability in the direction of change of ANS function between some studies.

Conclusion

This systematic review identifies that concussion is associated with dysregulation of ANS function in pediatric athletes. We identified some weaknesses in the extant literature which may be due to existing logistical and financial barriers to implementing valid ANS measurements in clinical and sports settings.

Impact of a combination of pimobendan, furosemide, and enalapril on heart rate variability in naturally occurring, symptomatic, myxomatous mitral valve degeneration dogs

BACKGROUND

Pimobendan, diuretics, and an angiotensin-converting enzyme inhibitor (ACEi) are widely used for the management of chronic valvular heart disease in dogs; however, the effects of that combination on heart rate variability (HRV) are unknown. The purpose of this study was to assess the HRV of symptomatic myxomatous mitral valve degeneration (MMVD) dogs in response to therapy with a combination of pimobendan, diuretics, and ACEi.

RESULTS

MMVD stage C (n = 17) dogs were enrolled and a 1-hour Holter recording together with echocardiography, blood pressure measurement, and blood chemistry profiles were obtained before and 1, 3, and 6 months after oral treatment with pimobendan (0.25 mg/kg), enalapril (0.5 mg/kg), and furosemide (2 mg/kg) twice daily. The results revealed that MMVD stage C dogs at the baseline had lower values of time-domain indices, low frequency (LF), high frequency (HF), and total power, as well as higher value of LF/HF. Triple therapy significantly increases these parameters in MMVD stage C dogs (P < 0.05). A positive moderate correlation was observed between time domain parameters and a left ventricular internal diastole diameter normalized to body weight (P < 0.05).

CONCLUSIONS

It can be concluded that MMVD stage C dogs possess low HRV due to either the withdrawal of parasympathetic tone or enhanced sympathetic activation, and a combination therapy was shown to enhance cardiac autonomic modulation inferred from the increased heart rate variability. Therefore, a combination therapy may be useful for restoring normal autonomic nervous system activity in dogs with MMVD stage C.

Flexibility: A Hidden But Trainable Morbidity in Pediatric Patients with Congenital Heart Disease

Flexibility is important for range of motion, muscular performance, and injury prevention with exercise. Promoting exercise is important for patients with congenital and pediatric acquired heart disease (CHD), yet there are a paucity of data addressing flexibility in this population. We hypothesized that flexibility was worse in pediatric patients with CHD than the general population but could be improved with directed training. Patients at Boston Children's Hospital who participated in the pediatric Cardiac Fitness Program between 09/2016 and 11/2022 were retrospectively analyzed. Flexibility was assessed via sit-and-reach (SaR) box. Data from baseline and 60 days into the fitness program intervention were compared to age-matched population norms, and changes over time were assessed. Analyses were also stratified by sex and history of sternotomy. Patients with paired baseline and 60-day data were analyzed (n = 46, age 8-23 years old, 52% male). The mean SaR at baseline for CHD patients was 24.3 cm, significantly lower than the population norm (p = 0.002). The mean for male (n = 24, 21.2 cm) and female (n = 22, 27.2 cm) CHD patients was significantly lower than their respective population norms (p = 0.017 and p = 0.026, respectively). After the fitness intervention, flexibility in CHD patients significantly improved to normal, including patients with a history of sternotomy. Flexibility was significantly lower in CHD patients than the general population, but normalized with training. Further research is warranted to investigate associations of flexibility with other measures of fitness, cardiovascular status, and quality of life, as well as benefits gained with training.

Assessing aerobic physical efficiency through temple surface temperature measurements during light, heavy exercise, and recovery

The study was conducted to determine thecorrelation between the selected measures of aerobic physical efficiency and changes in the temple surface temperature in response to light and heavy exercise. 25 physically active men aged 19-25 were recruited for the study. They performed a graded exercise test on a cycle ergometer to measure maximum power (Pmax) and a test verifying the value of maximum oxygen uptake (VO2max). Then, two 3-min submaximal efforts with constant-intensity of 2.2 W·kgLBM-1 and 5 W·kgLBM-1, respectively were performed. During the constant-intensity efforts, the temperature of the temple surface was measured. Then, the difference between the temperature of the temple measured at the end of the exercise and the temperature measured at the beginning of the exercise was calculated (ΔT1-2.2, ΔT1-5, respectively). It was shown that ΔT1-2.2 correlated statistically significantly with VO2max (ml·min-1·kg-1) (r = 0.49; p = 0.01) and Pmax (W·kg-1) (r = 0.41, p = 0.04). Moreover, ΔT1-5 correlated statistically significantly with VO2max (l·min-1) (r = - 0.41; p = 0.04). Changes in body surface temperature in response to light exercise positively correlate with measurements of aerobic physical efficiency, such as VO2max and Pmax. When the exercise intensity is high (5 W·kgLBM-1), the correlation between exercise body temperature changes and VO2max becomes negative.

A Serious Game to Self-Regulate Heart Rate Variability as a Technique to Manage Arousal Level Through Cardiorespiratory Biofeedback: Development and Pilot Evaluation Study

BACKGROUND

Heart rate variability biofeedback (HRVB) is an established intervention for increasing heart rate variability (HRV) in the clinical context. Using this technique, participants become aware of their HRV through real-time feedback and can self-regulate it.

OBJECTIVE

The aim of this study was 2-fold: first, to develop a serious game that applies the HRVB technique to teach participants to self-regulate HRV and, second, to test the app with participants in a pilot study.

METHODS

An HRVB app called the FitLab Game was developed for this study. To play the game, users must move the main character up and down the screen, avoiding collisions with obstacles. The wavelength that users must follow to avoid these obstacles is based on the user's basal heart rate and changes in instantaneous heart rate. To test the FitLab Game, a total of 16 participants (mean age 23, SD 0.69 years) were divided into a control group (n=8) and an experimental group (n=8). A 2 × 2 factorial design was used in each session. Participants in the experimental condition were trained in breathing techniques.

RESULTS

Changes in the frequency and time domain parameters of HRV and the game's performance features were evaluated. Significant changes in the average RR intervals and root mean square of differences between adjacent RR intervals (RMSSD) were found between the groups (P=.02 and P=.04, respectively). Regarding performance, both groups showed a tendency to increase the evaluated outcomes from baseline to the test condition.

CONCLUSIONS

The results may indicate that playing different levels leads to an improvement in the game's final score by repeated training. The tendency of changes in HRV may reflect a higher activation of the mental system of attention and control in the experimental group versus the control group. In this context, learning simple, voluntary strategies through a serious game can aid the improvement of self-control and arousal management. The FitLab Game appears to be a promising serious game owing to its ease of use, high engagement, and enjoyability provided by the instantaneous feedback.

Pathological Heart Rate Regulation in Apparently Healthy Individuals

Cardiovascular diseases are the leading cause of morbidity and mortality in adults worldwide. There is one common pathophysiological aspect present in all cardiovascular diseases-dysfunctional heart rhythm regulation. Taking this aspect into consideration for cardiovascular risk predictions opens important research perspectives, allowing for the development of preventive treatment techniques. The aim of this study was to find out whether certain pathologically appearing signs in the heart rate variability (HRV) of an apparently healthy person, even with high HRV, can be defined as biomarkers for a disturbed cardiac regulation and whether this can be treated preventively by a drug-free method. This multi-phase study included 218 healthy subjects of either sex, who consecutively visited the physician at Gesundheit clinic because of arterial hypertension, depression, headache, psycho-emotional stress, extreme weakness, disturbed night sleep, heart palpitations, or chest pain. In study phase A, baseline measurement to identify individuals with cardiovascular risks was done. Therefore, standard HRV, as well as the new cardiorhythmogram (CRG) method, were applied to all subjects. The new CRG analysis used here is based on the recently introduced LF drops and HF counter-regulation. Regarding the mechanisms of why these appear in a steady-state cardiorhythmmogram, they represent non-linear event-based dynamical HRV biomarkers. The next phase of the study, phase B, tested whether the pathologically appearing signs identified via CRG in phase A could be clinically influenced by drug-free treatment. In order to validate the new CRG method, it was supported by non-linear HRV analysis in both phase A and in phase B. Out of 218 subjects, the pathologically appearing signs could be detected in 130 cases (60%), p < 0.01, by the new CRG method, and by the standard HRV analysis in 40 cases (18%), p < 0.05. Thus, the CRG method was able to detect 42% more cases with pathologically appearing cardiac regulation. In addition, the comparative CRG analysis before and after treatment showed that the pathologically appearing signs could be clinically influenced without the use of medication. After treatment, the risk group decreased eight-fold-from 130 people to 16 (p < 0.01). Therefore, progression of the detected pathological signs to structural cardiac pathology or arrhythmia could be prevented in most of the cases. However, in the remaining risk group of 16 apparently healthy subjects, 8 people died due to all-cause mortality. In contrast, no other subject in this study has died so far. The non-linear parameter which is able to quantify the changes in CRGs before versus after treatment is FWRENYI4 (symbolic dynamic feature); it decreased from 2.85 to 2.53 (p < 0.001). In summary, signs of pathological cardiac regulation can be identified by the CRG analysis of apparently healthy subjects in the early stages of development of cardiac pathology. Thus, our method offers a sensitive biomarker for cardiovascular risks. The latter can be influenced by non-drug treatments (acupuncture) to stop the progression into structural cardiac pathologies or arrhythmias in most but not all of the patients. Therefore, this could be a real and easy-to-use supplemental method, contributing to primary prevention in cardiology.

Physiological and Biomechanical Monitoring in American Football Players: A Scoping Review

American football is the sport with the highest rates of concussion injuries. Biomedical engineering applications may support athletes in monitoring their injuries, evaluating the effectiveness of their equipment, and leading industrial research in this sport. This literature review aims to report on the applications of biomedical engineering research in American football, highlighting the main trends and gaps. The review followed the PRISMA guidelines and gathered a total of 1629 records from PubMed (n = 368), Web of Science (n = 665), and Scopus (n = 596). The records were analyzed, tabulated, and clustered in topics. In total, 112 studies were selected and divided by topic in the biomechanics of concussion (n = 55), biomechanics of footwear (n = 6), biomechanics of sport-related movements (n = 6), the aerodynamics of football and catch (n = 3), injury prediction (n = 8), heat monitoring of physiological parameters (n = 8), and monitoring of the training load (n = 25). The safety of players has fueled most of the research that has led to innovations in helmet and footwear design, as well as improvements in the understanding and prevention of injuries and heat monitoring. The other important motivator for research is the improvement of performance, which has led to the monitoring of training loads and catches, and studies on the aerodynamics of football. The main gaps found in the literature were regarding the monitoring of internal loads and the innovation of shoulder pads.

Hourly personal temperature exposure and heart rate variability: A multi-center panel study in populations at intermediate to high-risk of cardiovascular disease

BACKGROUND

Several studies reported temperature exposure was associated with altered cardiac automatic function, while this effect of temperature on hourly heart rate variability (HRV) among populations with cardiovascular risks was seldom addressed.

METHODS

We conducted this panel study in four Chinese cities with three repeated visits among 296 participants at intermediate to high-risk of cardiovascular disease (CVD). Real-time temperature level and 24-h ambulatory electrocardiogram were monitored during each seasonal visit. Linear mixed-effects models were used to investigate associations between individual temperature and HRV parameters, and the seasonal effects and circadian effect were also evaluated.

RESULTS

We found the overall downward trend of hourly HRV associated with acute exposure to higher temperature. For each 1 °C increment in temperature of 1-3 h prior to HRV measurements (lag 1-3 h), hourly standard deviation of normal-to-normal intervals (SDNN) decreased by 0.38% (95% confidence interval [CI]: 0.22, 0.54), 0.28% (95% CI: 0.12, 0.44), and 0.20% (95% CI: 0.04, 0.36), respectively. Similar inverse associations between temperature and HRV were observed in stratified analyses by temperature level. Inverse associations for cold and warm seasons were also observed, despite some effects gradually decreased and reversed in the warm season as lag times extended. Moreover, HRV showed a more significant reduction with increased temperature during daytime than nighttime. Percent change of hourly SDNN was -0.41% (95% CI: -0.62, -0.21) with 1 °C increment of lag 1 h during daytime, while few obvious changes were revealed during nighttime.

CONCLUSIONS

Generally, increasing temperature was significantly associated with reduced HRV. Inverse relationships for cold and warm seasons were also observed. Associations during daytime were much more prominent than nighttime. Our findings clarified the relationship of temperature with HRV and provided evidence for prevention approaches to alleviate cardiac automatic dysfunction among populations at intermediate to high-risk of CVD.

Validity and Reliability of Short-Term Heart Rate Variability Parameters in Older People in Response to Physical Exercise

BACKGROUND

Currently, and to the best of our knowledge, there is no standardized protocol to measure the effect of low- to moderate-intensity physical exercise on autonomic modulation focused in older people.

AIM

Validate a test-retest short-term exercise protocol for measuring the autonomic response through HRV in older people.

METHODS

A test-retest study design was used. The participants were selected through intentional non-probabilistic sampling. A total of 105 older people (male: 21.9%; female: 78.1%) were recruited from a local community. The assessment protocol evaluated HRV before and immediately after the 2-min step test. It was performed twice on the same day, considering a time of three chronological hours between the two measurements.

RESULTS

The posterior distribution of estimated responses in the Bayesian framework suggests moderate to strong evidence favoring a null effect between measurements. In addition, there was moderate to robust agreement between heart rate variability (HRV) indices and assessments, except for low frequency and very low frequency, which showed weak agreement.

CONCLUSIONS

Our results provide moderate to strong evidence for using HRV to measure cardiac autonomic response to moderate exercise, suggesting that it is sufficiently reliable to show similar results to those shown in this test-retest protocol.

Influence of sleep duration and sex on age-related differences in heart rate variability: Findings from program 4 of the HAIE study

Heart rate variability (HRV) is an important marker of cardiac autonomic regulation and health. We examined the influence of sleep duration and sex on HRV in younger and middle-aged adults. Cross-sectional data (888 participants, 44% women) were analyzed from Program 4 of the Healthy Aging in Industrial Environment study (HAIE). Sleep duration was measured across 14 days using Fitbit Charge monitors. Short-term EKG recordings were used to evaluate HRV in the time (RMSSD) and frequency domains (low frequency (LF) and high frequency (HF) power). Regression analysis showed age was associated with lower HRV across all HRV variables (all P < 0.001). Sex was a significant predictor for LF (β = 0.52) and HF (β = 0.54; both P < 0.001) in normalized units. Similarly, sleep duration was only associated with HF in normalized units (β = 0.06, P = 0.04). To explore this finding further, participants within each sex were separated into groups based on age (<40 and ≥ 40y) and adequate sleep duration (<7 and ≥7 h). Middle-aged women with sleep durations <7 h, but not ≥7 h, had lower HRV than younger women after adjusting for medications, respiratory frequency, and cardiorespiratory fitness (peak VO₂). Middle-aged women with sleep durations <7 h also had lower RMSSD (33 ± 2 vs. 41±4 ms, P = 0.04), HF power (5.6 ± 0.1 vs. 6.0 ± 0.1 log ms², P = 0.04), and HF in normalized units (39 ± 1 vs. 48 ± 2, P = 0.01) than middle-aged women with sleep durations ≥7 h. In contrast, middle-aged men irrespective of sleep duration had lower HRV than younger men. These results suggest that adequate sleep duration may positively influence HRV in middle-aged women but not men.

Physical Exercise Effects on Cardiovascular Autonomic Modulation in Postmenopausal Women-A Systematic Review and Meta-Analysis

BACKGROUND

The cardioprotective effect of physical exercise has been demonstrated in several studies. However, no systematic or updated analysis has described the effects of physical exercise on cardiovascular autonomic modulation in postmenopausal women.

AIM

to describe the effects of physical exercise on cardiovascular autonomic modulation in postmenopausal women.

METHODS

The Scopus, PubMed, and Embase databases were searched for randomized clinical trials published between January 2011 and December 2021, and regarding the effects of physical exercise on cardiovascular autonomic modulation in postmenopausal women. Two independent authors processed the citations. The methodological quality was evaluated using the PEDRo scale.

RESULTS

Of the 91 studies identified, only 8 met the inclusion criteria, of which 7 had fair or poor methodological quality. The analyzed studies investigated the effects of functional training, whole-body vibration, muscular resistance, stretching, and aerobic exercises performed at home or at the gym. The majority of these exercise modalities showed improvements in heart-rate variability (HRV) indices and in the low-frequency band of blood pressure variability. The meta-analysis shows that exercise increased the standard deviation of instantaneous beat-to-beat variability (SD1) (mean difference (MD) = 3.99; 95% confidence interval (CI) = 1.22 to 6.77, n = 46; I²: 0%) and the standard deviation of long-term variability (SD2) (MD = 11.37; 95% CI = 2.99 to 19.75; n = 46; I²: 0%).

CONCLUSIONS

Aerobic exercise and some nonconventional training modalities may have beneficial effects on cardiovascular autonomic modulation in postmenopausal women. More high-quality studies are still needed to further confirm their efficacy and safety.

Does Wearable-Measured Heart Rate Variability During Sleep Predict Perceived Morning Mental and Physical Fitness?

The emergence of wearable sensor technology may provide opportunities for automated measurement of psychophysiological markers of mental and physical fitness, which can be used for personalized feedback. This study explores to what extent within-subject changes in resting heart rate variability (HRV) during sleep predict the perceived mental and physical fitness of military personnel on the subsequent morning. Participants wore a Garmin wrist-worn wearable and filled in a short morning questionnaire on their perceived mental and physical fitness during a period of up to 46 days. A custom-built smartphone app was used to directly retrieve heart rate and accelerometer data from the wearable, on which open-source algorithms for sleep detection and artefact filtering were applied. A sample of 571 complete observations in 63 participants were analyzed using linear mixed models. Resting HRV during sleep was a small predictor of perceived physical fitness (marginal R² = .031), but not of mental fitness. The items on perceived mental and physical fitness were strongly correlated (r = .77). Based on the current findings, resting HRV during sleep appears to be more related to the physical component of perceived fitness than its mental component. Recommendations for future studies include improvements in the measurement of sleep and resting HRV, as well as further investigation of the potential impact of resting HRV as a buffer on stress-related outcomes.

The effect of heart rate variability biofeedback in patients with acute coronary syndrome: A protocol for systematic review and meta-analysis

BACKGROUND

Acute coronary syndrome (ACS), the acute manifestation of ischemic heart disease, remains a major cause of morbidity and mortality worldwide. Soon after ACS, autonomic imbalance acts to preserve the proper functioning of the cardiovascular system and consequently of the whole body. In this study, we perform a protocol for systematic review and meta-analysis to evaluate the efficacy of heart rate variability biofeedback in improving the prognosis in patients with ACS.

METHODS

The protocol of this review was registered in PROSPERO (CRD42022379184). Meanwhile, it will be reported follow the guidelines of the preferred reporting items for systematic reviews and meta-analyses protocol. We will search 3 foreign electronic databases (Cochrane Library, Embase, Pubmed) and 4 Chinese electronic databases (China National Knowledge Infrastructure, WangFang Database, Chinese Biomedical Literature Database and Chinese Scientific Journal Database) to collect potential studies from their inceptions to December 2022. Risk of bias will be assessed according to the Cochrane Risk of Bias Tool. Data synthesis and statistical analysis will be performed using the RevMan 5.3 (The Nordic Cochrane Centre, The Cochrane Collaboration, Denmark) software.

RESULTS

The results of this systematic review will be published in a peer-reviewed journal.

CONCLUSION

This systematic review will provide high quality evidence to assess the efficacy of heart rate variability biofeedback in patients with ACS.

Combined effect of physical exercise and hormone replacement therapy on cardiovascular and metabolic health in postmenopausal women: A systematic review and meta-analysis

The cardioprotective effect of postmenopausal hormone replacement therapy (HRT) has been demonstrated in several studies. Similarly, physical exercise has yielded positive results. However, the effects of their combination remain inconclusive. This review describes the combined effects of physical exercise and hormone therapy on cardiovascular and metabolic health in postmenopausal women. We searched the Scopus, Web of Science, PubMed, and Embase databases and included randomized controlled trials published up to December 2021 on the combined effects of physical exercise and hormone therapy on cardiovascular and metabolic health in postmenopausal women. We identified 148 articles, of which only seven met the inclusion criteria (386 participants; 91 [23%] HRT + exercise; 104 [27%] HRT; 103 [27%] exercise; 88 [23%] placebo). The combined treatment further decreased systolic blood pressure (SBP) compared to the isolated effect of aerobic training (AT) (mean difference [MD]=-1.69; 95% confidence interval [CI]=-2.65 to -0.72, n=73). Nevertheless, it attenuated the decrease in diastolic blood pressure (DBP) (MD=0.78; 95%CI: 0.22-1.35, n=73), and the increase in peak oxygen consumption (VO2 peak) promoted by exercise (AT + HRT=2.8±1.4 vs AT + placebo=5.8±3.4, P=0.02). The combination of AT and oral HRT improved SBP. However, AT alone seemed to have a better effect on physical fitness and DBP in postmenopausal women.

Impact of COVID-19 Vaccination on Heart Rate Variability: A Systematic Review

Establishing and disseminating evidence-based safety information could potentially facilitate beneficial choices in coronavirus disease (COVID-19) vaccinations. This systematic review investigated the potential impact of COVID-19 vaccinations on human heart rate variability (HRV) parameters through comprehensive searches of four electronic medical databases. Five observational studies reporting HRV parameters of individuals vaccinated against COVID-19 and published up to 29 July 2022 were included in this review. Among them, four studies reported the square root of the mean squared differences of successive NN intervals (RMSSD) as their outcome, and the remaining study reported an HRV-based stress indicator. These studies reported short-term changes and rapid recovery in HRV parameters within up to 3 days after COVID-19 vaccination. Some studies showed that the impact of COVID-19 vaccinations on RMSSD was greater in women than men, and in the younger group than in the older group. The methodological quality of the included studies was not optimal; the review revealed short-term changes in HRV parameters, particularly RMSSD, following COVID-19 vaccination. However, as the included studies did not report important parameters besides RMSSD, the limitation exists that the postvaccination long-term HRV stability was not reported.

Neuro-vascular coupling and heart rate variability in patients with type II diabetes at different stages of diabetic retinopathy

Aims/Hypothesis

There is evidence that diabetes is accompanied by a break-down of functional hyperemia, an intrinsic mechanism of neural tissues to adapt blood flow to changing metabolic demands. However, to what extent functional hyperemia is altered in different stages of diabetic retinopathy (DR) in patients with type II diabetes is largely unknown. The current study set out to investigate flicker-induced retinal blood flow changes in patients with type II diabetes at different stages of DR.

Materials and methods

A total of 76 subjects were included in the present parallel-group study, of which 56 had diabetes with either no DR or different stages of non-proliferative DR (n = 29 no DR, 12 mild DR, 15 moderate to severe DR). In addition, 20 healthy subjects were included as controls. Retinal blood flow was assessed before and during visual stimulation using a combined measurement of retinal vessel calibers and blood velocity by the means of Doppler optical coherence tomography (OCT). To measure systemic autonomic nervous system function, heart rate variability (HRV) was assessed using a short-term orthostatic challenge test.

Results

In healthy controls, retinal blood flow increased by 40.4 ± 27.2% during flicker stimulation. Flicker responses in patients with DR were significantly decreased depending on the stage of the disease (no DR 37.7 ± 26.0%, mild DR 26.2 ± 28.2%, moderate to severe DR 22.3 ± 13.9%; p = 0.035, ANOVA). When assessing systemic autonomous neural function using HRV, normalized low frequency (LF) spectral power showed a significantly different response to the orthostatic maneuver in diabetic patients compared to healthy controls (p < 0.001).

Conclusion/Interpretation

Our study indicates that flicker induced hyperemia is reduced in patients with DR compared to healthy subjects. Further, this impairment is more pronounced with increasing severity of DR. Further studies are needed to elucidate mechanisms behind the reduced hyperemic response in patients with type II diabetes.

Clinical trial registration

[https://clinicaltrials.gov/], identifier [NCT03 552562].

Pulmonary Capacity, Blood Composition and Metabolism among Coal Mine Workers in High- and Low-Altitude Aboveground and Underground Workplaces

(1) Background: While previous studies revealed how underground mining might adversely affect the cardiopulmonary functions of workers, this study further investigated the differences between under- and aboveground mining at both high and low altitudes, which has received little attention in the literature. (2) Methods: Seventy-one healthy male coal mine workers were recruited, who had worked at least 5 years at the mining sites located above the ground at high (>3900 m; n = 19) and low (<120 m; n = 16) altitudes as well as under the ground at high (n = 20) and low (n = 16) altitudes. Participants’ heart rates, pulmonary functions, total energy expenditure and metabolism were measured over a 5-consecutive-day session at health clinics. (3) Results: Combining the results for both above- and underground locations, workers at high-altitude mining sites had significantly higher peak heart rate (HR), minimum average HR and training impulse as well as energy expenditure due to all substances and due to fat than those at low-altitude sites. They also had significantly higher uric acid, total cholesterol, creatine kinase and N-osteocalcin in their blood samples than the workers at low-altitude mining sites. At underground worksites, the participants working at high-altitude had a significantly higher average respiratory rate than those at low-altitude regions. (4) Conclusion: In addition to underground mining, attention should be paid to high-altitude mining as working under a hypoxia condition at such altitude likely presents physiological challenges.

Menstrual cycle-associated symptoms and workplace productivity in US employees: A cross-sectional survey of users of the Flo mobile phone app

Objective

Mood and physical symptoms related to the menstrual cycle affect women's productivity at work, often leading to absenteeism. However, employer-led initiatives to tackle these issues are lacking. Digital health interventions focused on women's health (such as the Flo app) could help fill this gap.

Methods

1867 users of the Flo app participated in a survey exploring the impact of their menstrual cycle on their workplace productivity and the role of Flo in mitigating some of the identified issues.

Results

The majority reported a moderate to severe impact of their cycle on workplace productivity, with 45.2% reporting absenteeism (5.8 days on average in the previous 12 months). 48.4% reported not receiving any support from their manager and 94.6% said they were not provided with any specific benefit for issues related to their menstrual cycle, with 75.6% declaring wanting them. Users stated that the Flo app helped them with the management of menstrual cycle symptoms (68.7%), preparedness and bodily awareness (88.7%), openness with others (52.5%), and feeling supported (77.6%). Users who reported the most positive impact of the Flo app were 18-25% less likely to report an impact of their menstrual cycle on their productivity and 12-18% less likely to take days off work for issues related to their cycle.

Conclusions

Apps such as Flo could equip individuals with tools to better cope with issues related to their menstrual cycle and facilitate discussions around menstrual health in the workplace.