Autonomic control of heart rate during exercise studied by heart rate variability spectral analysis

Autonomic regulation in athletic horses repetitively participating in two novice jumping classes on consecutive days

Introduction

Animal welfare is of great concern in equestrian sports and has been evaluated in athletic horses competing at different levels. However, the impact of consecutive days of jumping competition and the extent of resultant stress responses remains unclear. To address this point, the present study compared the changes in stress response via heart rate variability (HRV) in horses participating in two national jumping events on consecutive days.

Methods

The study involved six experienced horses equipped with heart rate monitoring devices. HRV variables were measured before, during, and after jumping at 10-min intervals for 60 min on each competition day.

Results

Multiple HRV variables decreased to varying degrees on both days from warm-up until 30 min post-jumping. Meanwhile, the mean heart rate increased during jumping and returned to normal levels at 50 min post-jumping on the first day (for all intervals, p < 0.05-0.001), while it remained elevated beyond 60 min post-jumping on the second day (for all intervals, p < 0.01-0.001). Additionally, maximum heart rate and respiratory rate were higher on the second day than in the first round during the warm-up phase (p < 0.05 for both variables). The proportion of the HRV low-frequency band was higher during riding on the second day (p < 0.05), while the proportion of the high-frequency band was reduced during warm-up on the first day (p < 0.05) and during course riding on the second (p < 0.01). Meanwhile, the sympathetic nervous system index took longer to return to baseline on the second day than on the first.

Discussion

These results suggest that autonomic regulation differed in horses between jumping rounds on two consecutive days, with horses experiencing higher sympathetic activity and potentially increased stress in the second round. This information is important for riders, highlighting the need to be mindful of potential stress that could, at least in part, impact the welfare of horses participating in the same jumping competition on consecutive days.

Characterizing Heart Rate Variability Response to Maximal Exercise Testing in People with Huntington's Disease

Background

Huntington's disease (HD) is an autosomal dominant, neurodegenerative disease that involves dysfunction in the autonomic nervous system (ANS). Heart rate variability (HRV) is a valid and noninvasive measure for ANS dysfunction, yet no study has characterized HRV response to exercise in people with HD.

Objective

Characterize HRV response to exercise in individuals with HD and explore its implications for exercise prescription and cardiac dysautonomia mechanisms.

Methods

19 participants with HD were recruited as part of a cohort of individuals enrolled in the Physical Activity and Exercise Outcomes in Huntington's Disease (PACE-HD) study at Teachers College, Columbia University (TC). 13 non-HD age- and gender-matched control participants were also recruited from TC. HRV was recorded with a Polar H10 heart rate (HR) monitor before, during, and after a ramp cycle-ergometer exercise test.

Results

Participants with HD showed reduced HR peak (p < 0.01) and HR reserve (p < 0.001) compared with controls. Participants with HD demonstrated reduced root mean square of successive differences between normal-to-normal intervals (RMSSD) and successive differences of normal-to-normal intervals (SDSD) at rest (p < 0.001). Participants with HD also showed differences for low frequency (LF) power (p < 0.01), high frequency (HF) normalized units (nu) (p < 0.05), LF (nu) (p < 0.001), and HF/LF ratio (p < 0.05) compared with controls.

Conclusions

We found reduced aerobic exercise capacity and sympathovagal dysautonomia both at rest and during post-exercise recovery in people with HD, suggesting modified exercise prescription may be required for people with HD. Further investigations focusing on cardiac dysautonomia and underlying mechanisms of sympathovagal dysautonomia in people with HD are warranted.

Heart Rate Variability-Derived Thresholds for Exercise Intensity Prescription in Endurance Sports: A Systematic Review of Interrelations and Agreement with Different Ventilatory and Blood Lactate Thresholds

BACKGROUND

Exercise intensities are prescribed using specific intensity zones (moderate, heavy, and severe) determined by a 'lower' and a 'higher' threshold. Typically, ventilatory (VT) or blood lactate thresholds (LT), and critical power/speed concepts (CP/CS) are used. Various heart rate variability-derived thresholds (HRVTs) using different HRV indices may constitute applicable alternatives, but a systematic review of the proximity of HRVTs to established threshold concepts is lacking.

OBJECTIVE

This systematic review aims to provide an overview of studies that determined HRVTs during endurance exercise in healthy adults in comparison with a reference VT and/or LT concept.

METHODS

A systematic literature search for studies determining HRVTs in healthy individuals during endurance exercise and comparing them with VTs or LTs was conducted in Scopus, PubMed and Web of Science (until January 2022). Studies claiming to describe similar physiological boundaries to delineate moderate from heavy (HRVTlow vs. VTlow and/or LTlow), and heavy from severe intensity zone (HRVThigh vs. VThigh and/or LThigh) were grouped and their results synthesized.

RESULTS

Twenty-seven included studies (461 participants) showed a mean difference in relative HR between HRVTlow and VTlow of - 0.6%bpm in weighted means and 0.02%bpm between HRVTlow and LTlow. Bias between HR at HRVTlow and VTlow was 1 bpm (limits of agreement (LoA): - 10.9 to 12.8 bpm) and 2.7 bpm (LoA: - 20.4 to 25.8 bpm) between HRVTlow and LTlow. Mean difference in HR between HRVThigh and VThigh was 0.3%bpm in weighted means and 2.9%bpm between HRVThigh and LThigh while bias between HR at HRVThigh and VThigh was - 4 bpm (LoA: - 17.9 to 9.9 bpm) and 2.5 bpm (LoA: - 12.1 to 17.1 bpm) between HRVThigh and LThigh.

CONCLUSION

HRVTlow seems to be a promising approach for the determination of a 'lower' threshold comparable to VTlow and potentially for HRVThigh compared to VThigh, although the latter needs further empirical evaluation. LoA for both intensity zone boundaries indicates bias of HRVTs on an individual level. Taken together, HRVTs can be a promising alternative for prescribing exercise intensity in healthy, male athletes undertaking endurance activities but due to the heterogeneity of study design, threshold concepts, standardization, and lack of female participants, further research is necessary to draw more robust and nuanced conclusions.

Rapid adjustments to autonomic control of cardiac rhythm at the onset of isometric exercise in healthy young adults

Sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) influences on cardiac rhythm at the onset of exercise, a time of rapid autonomic adjustments, are clinically important areas of investigation. Continuous wavelet transform (CWT) involves time-frequency-based heart rate variability (HRV) analysis allowing investigation of autonomic influences on cardiac rhythm during short durations of exercise. Therefore, the purpose of this study was to characterize SNS and PNS influences on cardiac rhythm at the onset of isometric exercise in healthy young adults. CWT analysis was retrospectively applied to R-R interval data (electrocardiogram) previously collected from 14 healthy young adults (26 ± 2 years) who performed 30-s, one-legged, isometric, calf exercise at 70% maximal voluntary contraction (MVC; 70% MVC trial) or rested (0% MVC trial). Absolute and normalized low-frequency (aLF, nLF; 0.04-0.15 Hz) and high-frequency (aHF, nHF; 0.15-0.4 Hz) bands and LF/HF were used to analyze one 30-s baseline period and six 5-s time windows during the 30-s exercise (70% MVC) or rest (0% MVC). Statistical analysis involved two-way analysis of variance with post-hoc analysis. aHF, aLF, LF/HF, nHF, and nLF displayed a trial-time interaction (all p ≤ 0.027). In the 70% compared to the 0% MVC trial, aHF and nHF were lower after 5-30 s (all p ≤ 0.040), aLF was lower after 20-30 s (all p ≤ 0.011) and LF/HF and nLF were higher after 5-20 s (all p ≤ 0.045). These results indicate the reduction of the PNS influence on cardiac rhythm begins sooner than the augmentation of the SNS influence at the onset of isometric exercise in healthy young adults.

Effects of physical training on functional, clinical, morphological, behavioural and psychosocial outcomes in post-COVID-19 infection: COVID-19 and REhabilitation study (CORE-study)-a study protocol for a randomised controlled clinical trial

BACKGROUND

The COVID-19 pandemic remains ongoing, with a significant number of survivors who have experienced moderate to severe clinical conditions and who have suffered losses of great magnitude, especially in functional capacity, triggering limitations to daily autonomy and quality of life. Among the possibilities of intervention for disease rehabilitation, physical exercise training stands out, which can benefit several health outcomes and favours the adoption of healthier behaviours. Therefore, the aim of the study will be to analyse the effects of physical training on the functional, clinical, morphological, behavioural and psychosocial status in adults and the elderly following COVID-19 infection.

METHODS

A randomised controlled clinical trial is to be conducted in parallel, with the experimental group undergoing an intervention involving a multicomponent physical rehabilitation programme, carried out at the Sports Center in partnership with the Academic Hospital of the Federal University of Santa Catarina, in Florianópolis, Brazil. Participants will be adults and the elderly, of both sexes, in a post-COVID-19-infection state, who were hospitalised during the infection. The intervention will have a total duration of 24 weeks and will include a multicomponent physical training programme, which will have gradual progression in frequency, duration and intensity over time. Regarding the outcomes, before, at the 12th and after 24 weeks of intervention, functional (primary outcome = functional index of aerobic capacity), clinical, morphological, behavioural and psychosocial outcomes will be assessed.

DISCUSSION

This study will contribute to a greater understanding of the safety, adherence and benefits of physical training in the rehabilitation of post-COVID-19 patients. The results of this study will be disseminated through presentations at congresses, workshops, peer-reviewed publications and local and international conferences, especially with a view to proposing a post-COVID-19 rehabilitation care protocol.

TRIAL REGISTRATION

ReBEC, RBR-10y6jhrs . Registered on 22 February 2022. 2015.

Comparison of the Effects of Aerobic versus Resistance Exercise on the Autonomic Nervous System in Middle-Aged Women: A Randomized Controlled Study

This study was conducted to investigate the changes in the autonomic nervous system in middle-aged women induced by aerobic and resistance exercise. A randomized controlled design was adopted; 22 premenopausal middle-aged women were divided into the resistance training and aerobic exercise groups (n = 11 each). Each group followed a specific 60 min exercise program three times a week for 12 weeks. The participants’ heart rate variability (HRV) was measured to analyze the low(LF)- and high-frequency (HF) activity, and the LF/HF ratio was calculated to examine the autonomic nervous system’s activities. A repeated-measures analysis of variance was used to analyze the effects of resistance and aerobic exercise. LF activity significantly increased in both the resistance training (p < 0.001) and aerobic exercise (p < 0.5) groups, indicating a significant variation according to time effect. HF activity was significantly increased only in resistance training (p < 0.001) with a significant variation in time (p < 0.001) and an interaction effect (p < 0.01). The LF/HF ratio did not vary significantly in either group. The findings in this study suggest that both aerobic exercise and resistance training were effective for sympathetic nerve activities in middle-aged women and that the effects on the sympathetic and parasympathetic activities were greater for resistance training.

Kinetic changes in sweat lactate following fatigue during constant workload exercise

It is useful to investigate various physiological responses induced by fatigue in athletes. Moreover, wearable noninvasive sensors, including sweat sensors, are compatible with fatigue evaluation because of their ease of use, and ability to measure repeatedly and continual data. This cross-sectional study aimed to clarify how sweat lactate elimination curves obtained during constant workload exercise changed following fatigue. Seventeen recreationally trained males (average age, 20.6 ± 0.8 years) completed two consecutive constant workload exercise tests (at 25% peak power) with rest intervals; the participants were encouraged to perform Test 1 until exhaustion and Test 2 only for 10 min. Subjective fatigue (numerical rating scale with face rating scale), sweat lactate, and sweat rate were measured for 10 min in each test. Subjective fatigue was compared using the Wilcoxon signed-rank test and time to each constant value between Tests 1 and 2 was compared using paired t-test. Subjective fatigue significantly increased during Test 2 compared with that during Test 1. After Test 1, the sweat lactate elimination curve demonstrated a leftward shift, as proved by the significantly sooner observation of the peak and constant values of sweat lactate (2, 3, and 4 μA) (p < 0.01). Our preliminary results suggest that the sweat lactate elimination curve is different in the fatigue state. Further research may provide insight in the application of this curve to the evaluation for fatigue.

The ratio of heart rate to heart rate variability reflects sympathetic activity during incremental cycling exercise

A low-frequency to a high-frequency component ratio (LF/HF) in heart rate variability (HRV) may not accurately reflect sympathetic nervous activity during exercise. Thus, a valid HRV-based index of sympathetic nervous activity is needed. Therefore, the heart rate to LF ratio (Heart rate/LF) was evaluated as sympathetic nervous activity index which is reflected by catecholamine levels during incremental exercise. In this study, 15 healthy adults performed an incremental exercise test using a cycle ergometer. HRV was derived from electrocardiography and HRV components related to the autonomic nervous system were obtained using frequency analysis. Heart rate/LF was calculated using the heart rate and LF component produced by HRV analysis. Catecholamine, blood lactate levels and respiratory gas were also measured throughout the exercise test. While LF/HF did not increase with increasing exercise intensity, Heart rate/LF non-linearly increased during the incremental exercise test, as did noradrenaline and blood lactate. Interestingly, Heart rate/LF values were positively correlated with noradrenaline (ρ = 0.788, p < 0.05) and blood lactate (ρ = 0.802, p < 0.05) levels and carbon dioxide production (ρ = 0.903, p < 0.05) from at rest through the exercise stages. Heart rate/LF reflects sympathetic nervous activity and metabolic responses during incremental cycling exercise and has potential as an HRV index of sympathetic nervous activity during exercise.Trial registration: UMIN Japan identifier: UMIN000039639..

Aberrant autonomic pattern during the post-exercise recovery phase in long QT syndrome patients

OBJECTIVES

It is well-established that the autonomic nervous system (ANS) plays a central role in arrhythmogenesis. During and after exercise the ANS is particularly active, and since long QT syndrome (LQTS) patients have an increased risk of lethal arrhythmias during physical activity, it is important to investigate the autonomic function in these patients. In this study we investigate the ANS response during and after exercise in LQTS patients and healthy age and sex matched controls.

METHODS

Forty-four genotype-verified adult LQTS patients and forty-four healthy age- and sex-matched controls performed a submaximal bicycle exercise stress test. Heart rate recovery (HRR) and heart rate variability (HRV) were analyzed from registered electrocardiogram (ECG) and vector electrocardiogram (VCG) recordings collected throughout rest, exercise and in the post-exercise phase.

RESULTS

LQTS patients had a slower HRR than controls at 1- and 4-min post-exercise (p < 0.001). During the post-exercise phase, LQTS patients had a lower total power (p < 0.001), low frequency power (p < 0.001) and high frequency power (p < 0.001) than controls. In the same phase, LQTS patients off betablocker (BB) treatment showed a lower high frequency power (p = 0.01) and different low frequency/high frequency ratio (p = 0.003) when comparing with LQTS patients on BB treatment.

CONCLUSIONS

The parasympathetic effect on both HRR and HRV after exercise appears depressed in this LQTS patient cohort compared to healthy controls. This indicates an aberrant ANS response during the post-exercise phase which might be compensated by BB treatment. Our findings emphasize the importance of performing further investigations to identify the role of the ANS in LQTS arrhythmogenesis.

Enhanced detection of abnormalities in heart rate variability and dynamics by 7-day continuous ECG monitoring

Background

The analysis of heart rate variability (HRV) and heart rate (HR) dynamics by Holter ECG has been standardized to 24 hs, but longer‐term continuous ECG monitoring has become available in clinical practice. We investigated the effects of long‐term ECG on the assessment of HRV and HR dynamics.

Methods

Intraweek variations in HRV and HR dynamics were analyzed in 107 outpatients with sinus rhythm. ECG was recorded continuously for 7 days with a flexible, codeless, waterproof sensor attached on the upper chest wall. Data were divided into seven 24‐h segments, and standard time‐ and frequency‐domain HRV and nonlinear HR dynamics indices were computed for each segment.

Results

The intraweek coefficients of variance of HRV and HR dynamics indices ranged from 2.9% to 26.0% and were smaller for frequency‐domain than for time‐domain indices, and for indices reflecting slower HR fluctuations than faster fluctuations. The indices with large variance often showed transient abnormalities from day to day over 7 days, reducing the positive predictive accuracy of the 24‐h ECG for detecting persistent abnormalities over 7 days. Conversely, 7‐day ECG provided 2.3‐ to 6.5‐fold increase in sensitivity to detect persistent plus transient abnormalities compared with 24‐h ECG. It detected an average of 1.74 to 2.91 times as many abnormal indices as 24‐h ECG.

Conclusions

Long‐term ECG monitoring increases the accuracy and sensitivity of detecting persistent and transient abnormalities in HRV and HR dynamics and allows discrimination between the two types of abnormalities. Whether this discrimination improves risk stratification deserves further studies.

A method to quantify autonomic nervous system function in healthy, able-bodied individuals

BACKGROUND

The autonomic nervous system (ANS) maintains physiological homeostasis in various organ systems via parasympathetic and sympathetic branches. ANS function is altered in common diffuse and focal conditions and heralds the beginning of environmental and disease stresses. Reliable, sensitive, and quantitative biomarkers, first defined in healthy participants, could discriminate among clinically useful changes in ANS function. This framework combines controlled autonomic testing with feature extraction during physiological responses.

METHODS

Twenty-one individuals were assessed in two morning and two afternoon sessions over two weeks. Each session included five standard clinical tests probing autonomic function: squat test, cold pressor test, diving reflex test, deep breathing, and Valsalva maneuver. Noninvasive sensors captured continuous electrocardiography, blood pressure, breathing, electrodermal activity, and pupil diameter. Heart rate, heart rate variability, mean arterial pressure, electrodermal activity, and pupil diameter responses to the perturbations were extracted, and averages across participants were computed. A template matching algorithm calculated scaling and stretching features that optimally fit the average to an individual response. These features were grouped based on test and modality to derive sympathetic and parasympathetic indices for this healthy population.

RESULTS

A significant positive correlation (p = 0.000377) was found between sympathetic amplitude response and body mass index. Additionally, longer duration and larger amplitude sympathetic and longer duration parasympathetic responses occurred in afternoon testing sessions; larger amplitude parasympathetic responses occurred in morning sessions.

CONCLUSIONS

These results demonstrate the robustness and sensitivity of an algorithmic approach to extract multimodal responses from standard tests. This novel method of quantifying ANS function can be used for early diagnosis, measurement of disease progression, or treatment evaluation.

TRIAL REGISTRATION

This study registered with Clinicaltrials.gov , identifier NCT04100486 . Registered September 24, 2019, https://www.clinicaltrials.gov/ct2/show/NCT04100486 .

Monitoring training in women's volleyball: Supine or seated heart rate variability?

We aimed to examine changes in resting heart rate variability, submaximal exercising heart rate (HRex), countermovement-jump height (CMJ), perceptual wellbeing, and internal load throughout preparatory training in elite women's volleyball players. We also aimed to determine which HRV measurement position (supine vs. seated) provided greater associations with the various markers of training adaptation. Thirteen players (age = 25.8 ± 3.0 years, height = 178.1 ± 6.7 cm, weight = 69.7 ± 7.6 kg) were monitored throughout four successive training camps preceding the Asia Cup. Daily measures of the root-mean square of successive differences were used to calculate the mean (LnRMSSD_M) and coefficient of variation (LnRMSSD_CV) for each camp. Averages were also determined for Hooper's Index and session ratings of perceived exertion (sRPE). HRex and CMJ were tested at the start of each camp. RESULTS: Seated LnRMSSD_CV, HRex, CMJ, and sRPE increased at camp 3 (p < 0.05), then reverted to values similar to camp 2. Changes in seated LnRMSSD_M were associated with changes in HRex (r = -0.68 to -0.71, p < 0.05). Occasional associations (p < 0.05) were observed between LnRMSSD_CV and Hooper's Index (r = 0.59) and CMJ (r = -0.57), and changes in HRex (r = 0.69) and HRR (r = -0.62). CONCLUSIONS: A reduced cardiorespiratory response to a standardized submaximal workload was associated with increased seated LnRMSSD_M. Higher seated LnRMSSD_CV was observed in response to increased sRPE and was often associated with decrements in various status markers. Seated LnRMSSD provided more associations with indicators of training adaptation than supine measures.

Heart Rate Variability Reactivity to Food Image Stimuli is Associated with Body Mass Index

Appetitive control is driven by the hedonic response to food and affected by several factors. Heart rate variability (HRV) signals have been used to index autonomic activity and arousal levels towards visual stimuli. The current research aimed to examine the influence of body mass index (BMI), disordered eating behaviors, and sex on the HRV reactivity to food in a nonclinical sample. Thirty-eight healthy male and sixty-one healthy female participants completed questionnaires assessing disordered eating symptoms. HRV was recorded when the participants received visual stimuli of high-calorie food, neutral and negative emotional signals. Generalized estimating equation models were used to investigate the associations between HRV, BMI, disordered eating behaviors, and sex across the three stimulus types. Male participants demonstrated a higher ratio of low-frequency power to high-frequency power (LF/HF) than females across all the stimulus types. An increase in LF/HF reactivity to food signals was observed in all the study subjects. The moderation effect of BMI on LF/HF in response to food signals was also observed. Our study suggests that body weight may play a role in the interaction between sympathetic activity and food stimuli; however, how the interaction between sympathetic activity and food stimuli contributes to diet control warrants further investigation.

Changes in saliva biomarkers during a standardized increasing intensity field exercise test in endurance horses

Salivary biomarkers could be useful to evaluate stress, fitness level, and skeletal muscle damage associated to exercise in horses in an easy and non-painful way. Therefore, this study aims to evaluate if cortisol in saliva (sCor), salivary alpha-amylase (sAMY) and butyrylcholinesterase (sBChE) and lactate (sLA) and creatine kinase (sCK) in saliva of horses can show changes during a standardized exercise test, and if they are related to heart rate variability (HRV) parameters related to sympathetic and parasympathetic tone, fitness level or skeletal muscle damage. For this purpose, ten endurance horses were submitted to a standardized exercise test in field conditions. Saliva and blood were obtained at basal time (TB), after the seven bouts of velocity (T + 01 to T + 07), and 5, 15, 30, and 45 min later (T + 5, T + 15, T + 30, and T + 45). Five endurance horses in resting condition (control group) were also enrolled. HRV and fitness level parameters, and plasma CK as a marker of muscle damage were also evaluated. Salivaryalpha-amylase increased at T + 30 (P = 0.03), sBChE at T + 5 (P = 008), and sCK at T + 07 (P = 0.009) after the exercise test, with significant differences between the exercise and control groups' results. The sCor did not show significant changes during the exercise test in the exercise group but higher concentration compared to the control horses (P < 0.001) were observed. sCor, sAMY, sBChE, and sCK showed a positive correlation (r values between 0.47 and 0.64) with the sympathetic tone and a negative correlation (r values between -0.37 and -0.56) with the parasympathetic tone. In conclusion, sAMY, sBChE, and sCK showed significant increases in ten endurance horses after an increasing intensity velocity exercise. Values of sCor, sAMY, sBChE, and sCK were associated with HRV, which is used to evaluate stress, and therefore, they could be potentially used to assess the exercise-related stress after a physical effort.

Toward brain-heart computer interfaces: a study on the classification of upper limb movements using multisystem directional estimates

OBJECTIVE

Brain-computer interfaces (BCI) exploit computational features from brain signals to perform a given task. Despite recent neurophysiology and clinical findings indicating the crucial role of functional interplay between brain and cardiovascular dynamics in locomotion, heartbeat information remains to be included in common BCI systems. In this study, we exploit the multidimensional features of directional and functional interplay between electroencephalographic and heartbeat spectra to classify upper limb movements into three classes.

APPROACH

We gathered data from 26 healthy volunteers that performed 90 movements; the data were processed using a recently proposed framework for brain-heart interplay (BHI) assessment based on synthetic physiological data generation. Extracted BHI features were employed to classify, through sequential forward selection scheme and k-nearest neighbors algorithm, among resting state and three classes of movements according to the kind of interaction with objects.

MAIN RESULTS

The results demonstrated that the proposed brain-heart computer interface (BHCI) system could distinguish between rest and movement classes automatically with an average 90% of accuracy.

SIGNIFICANCE

Further, this study provides neurophysiology insights indicating the crucial role of functional interplay originating at the cortical level onto the heart in the upper limb neural control. The inclusion of functional BHI insights might substantially improve the neuroscientific knowledge about motor control, and this may lead to advanced BHCI systems performances.

Hemodynamics and cardiac autonomic modulation after an acute concurrent exercise circuit in older individuals with pre- to established hypertension

OBJECTIVES

Few studies have investigated whether post-exercise hypotension (PEH) after concurrent exercise (CEX) is related to changes in cardiac output (Q) and systemic vascular resistance (SVR) in older individuals. We tested whether PEH after a single bout of CEX circuits performed in open-access facilities at the Third Age Academies (TAA) in Rio de Janeiro City (Brazil) would be concomitant with decreased Q and SVR in individuals aged ≥60 years with prehypertension. Moreover, we assessed autonomic modulation as a potential mechanism underlying PEH.

METHODS

Fourteen individuals (age, 65.8±0.9 y; systolic/diastolic blood pressure [SBP/DBP], 132.4±12.1/72.8±10.8 mmHg; with half of the patients taking antihypertensive medications) had their blood pressure (BP), heart rate (HR), Q, SVR, HR variability (HRV), and spontaneous baroreflex sensitivity (BRS) recorded before and 50 min after CEX (40-min circuit, including seven stations of alternate aerobic/resistance exercises at 60-70% HR reserve) and non-exercise control (CONT) sessions. The study protocol was registered in a World Health Organization-accredited office (Trial registration RBR-7BWVPJ).

RESULTS

SBP (Δ=-14.2±13.1 mmHg, p=0.0001), DBP (Δ=-5.2±8.2 mmHg, p= 0.04), Q (Δ=-2.2±1.5 L/min, p=0.0001), and BRS (Δ=-3.5±2.6 ms/mmHg; p=0.05) decreased after CEX as compared with the CONT session. By contrast, the HR increased (Δ=9.4±7.2 bpm, p<0.0001), and SVR remained stable throughout the postexercise period as compared with the CONT session (Δ=0.10±0.22 AU, p=0.14). We found no significant difference between the CEX and CONT with respect to the HRV indexes reflecting autonomic modulation.

CONCLUSION

CEX induced PEH in the older individuals with prehypertension status. At least in the first 50 min, PEH occurred parallel to the decreased Q and increased HR, while SVR was not different. The changes in autonomic outflow appeared to be unrelated to the acute cardiac and hemodynamic responses.

Vagal Flexibility during Exercise: Impact of Training, Stress, Anthropometric Measures, and Gender

We evaluated the effect of physical training, stress, anthropometric measures, and gender upon the reactivity and recovery of the heart rate variability (HRV) during a cardiorespiratory test. Professors (N = 54) were evaluated using the following: physical training: time, frequency, and length of physical exercise; resting heart rate (HR); maximum HR; and recovery HR; stress: stress symptoms, work stress, vital events, and perceived stress; anthropometric measures: body mass index, waist circumference (WC), waist-hip ratio (WHR), and fat percentage (FP); and HRV before, during, and after the test. The HRV decreased during and increased after the test. Increased recovery HR was associated with the decreased vagal output during the test, and decreased recovery HR was associated with the increased posttest vagal input. The higher the work control and stress symptoms of men and the higher the perceived stress for both genders, the lower the vagal output during the test. The lower stress symptom and work control of men and the lower work demand of women were associated with the posttest vagal increase. The increased WC and decreased WHR of men were associated with the lower vagal output during the test and the lower posttest vagal increase. The lower FP also was associated with the greater recovery.

Dynamical heart beat correlations during running

Fluctuations of the human heart beat constitute a complex system that has been studied mostly under resting conditions using conventional time series analysis methods. During physical exercise, the variability of the fluctuations is reduced, and the time series of beat-to-beat RR intervals (RRIs) become highly non-stationary. Here we develop a dynamical approach to analyze the time evolution of RRI correlations in running across various training and racing events under real-world conditions. In particular, we introduce dynamical detrended fluctuation analysis and dynamical partial autocorrelation functions, which are able to detect real-time changes in the scaling and correlations of the RRIs as functions of the scale and the lag. We relate these changes to the exercise intensity quantified by the heart rate (HR). Beyond subject-specific HR thresholds the RRIs show multiscale anticorrelations with both universal and individual scale-dependent structure that is potentially affected by the stride frequency. These preliminary results are encouraging for future applications of the dynamical statistical analysis in exercise physiology and cardiology, and the presented methodology is also applicable across various disciplines.

Context-aware experience sampling reveals the scale of variation in affective experience

Emotion research typically searches for consistency and specificity in physiological activity across instances of an emotion category, such as anger or fear, yet studies to date have observed more variation than expected. In the present study, we adopt an alternative approach, searching inductively for structure within variation, both within and across participants. Following a novel, physiologically-triggered experience sampling procedure, participants' self-reports and peripheral physiological activity were recorded when substantial changes in cardiac activity occurred in the absence of movement. Unsupervised clustering analyses revealed variability in the number and nature of patterns of physiological activity that recurred within individuals, as well as in the affect ratings and emotion labels associated with each pattern. There were also broad patterns that recurred across individuals. These findings support a constructionist account of emotion which, drawing on Darwin, proposes that emotion categories are populations of variable instances tied to situation-specific needs.

The effect of green walking on heart rate variability: A pilot crossover study

We investigated the effects of regular walking in green and suburban environments on heart rate variability (HRV) and blood pressure (BP) in middle-aged adults. Twenty-three adults participated in a non-randomized crossover experiment comprised of once-weekly 50-min moderate-intensity walking sessions. Separated by a two-week washout period, participants walked for three weeks in each of two treatment conditions (green and suburban) in a local arboretum and suburban sidewalks of Chaska, MN. Eleven participants completed green walking first and 12 suburban walking first. Walks were split into 15-min intra-walk phases, with phases representing each walk's beginning, middle, and final 15-min. Repeated measures linear mixed models evaluated (1) HRV phase differences between treatments and HRV change within treatments, and (2) pre- and post-walk BP differences between treatments and pre-to post-walk BP changes. Intra-walk phase analyses revealed higher HRV during green walking vs. suburban walking during phase 2 (p < 0.0001) and phase 3 (p = 0.02). Less HRV reduction was seen between intra-walk phases 1 and 2 during green vs. suburban walking (p = 0.02). Pre-to post-walk changes revealed decreased mean systolic BP for both green (p = 0.0002) and suburban (p = 0.003) walking conditions, but not for diastolic BP. Post-walk BP results were similar after both green walking and suburban walking. In summary, walking sessions in a green environment elicited greater beneficial HRV responses compared to a suburban environment. Additionally, walking in either environment, green or suburban, promoted reductions in systolic BP.

Effects of a Single Power Strength Training Session on Heart Rate Variability When Performed at Different Simulated Altitudes

Álvarez-Herms, Jesús, Sonia Julià-Sánchez, Hannes Gatterer, Francisco Corbi, Gines Viscor, and Martin Burtscher. Effects of a single power strength training session on heart rate variability when performed at different simulated altitudes. High Alt Med Biol. 21:292-296, 2020. Background: This study assessed heart rate variability (HRV) after a single power strength training session performed at different hypoxic levels. Materials and Methods: Eight physically active subjects (31.1 ± 4.3 years; 177.6 ± 3.0 cm; 70.1 ± 5.2 kg) performed 6 bouts of 15-second continuous maximal jump exercises interspersed by 3 minutes of rest at different altitude levels (total volume of each session: 20 minutes). The normoxic hypoxia levels were FiO₂ low altitude: 20.9%; moderate altitude: 16.5%; and high altitude: 13.5%. Results: Average power output during the jumps was similar for all conditions (≅3150 W). Twenty-four hours before (PRE) and 24 hours after (POST) each training session, HRV parameters (R-R, square root of the mean of the sum of differences between intervals [RMSSD], pNN50, and very low frequency, low frequency, and high frequency) were determined without resulting in significant statistical differences, neither from PRE to POST nor between conditions (p > 0.05). Conclusions: This study showed a negligible perturbation of HRV parameters 24 hours after a single power strength session up to a hypoxic level equivalent to 4000 m. Further studies are needed to determine the hypoxia-dependent threshold and intensities of training loads affecting HRV.

Post-exertional increase in first-phase ejection fraction in recreational marathon runners

OBJECTIVES

Running a marathon has been equivocally associated with acute changes in cardiac performance. First-phase ejection fraction is a novel integrated echocardiographic measure of left ventricular contractility and systo-diastolic coupling which has never been studied in the context of physical activity. The aim of this study was to assess first-phase ejection fraction following recreational marathon running along with standard echocardiographic indices of systolic and diastolic function.Design and participants: Runners (n = 25, 17 males), age (mean ± standard deviation) 39 ± 9 years, were assessed before and immediately after a marathon race which was completed in 4 h, 10 min ± 47 min.

MAIN OUTCOME MEASURES

Central hemodynamics were estimated with applanation tonometry; cardiac performance was assessed using standard M-mode two-dimensional Doppler, tissue-doppler imaging and speckle-tracking echocardiography. First-phase ejection fraction was calculated as the percentage change in left ventricular volume from end-diastole to the time of peak aortic blood flow.

RESULTS

Conventional indices of systolic function and cardiac performance were similar pre- and post-race while aortic systolic blood pressure decreased by 9 ± 8 mmHg (P < 0.001) and first-phase ejection fraction increased by approximately 48% from 16.3 ± 3.9% to 22.9 ± 2.5% (P < 0.001). The ratio of left ventricular transmitral Doppler early velocity (E) to tissue-doppler imaging early annular velocity (e') increased from 5.1 ± 1.8 to 6.2 ± 1.3 (P < 0.01).

CONCLUSION

In recreational marathon runners, there is a marked increase in first-phase ejection fraction after the race despite no other significant change in cardiac performance or conventional measure of systolic function. More detailed physiological studies are required to elucidate the mechanism of this increase.

Four-second dynamic exercise testing (T4S) for the assessment of cardiac vagal modulation in obese adolescents

BACKGROUND

Reduced vagal activity is often present in obese adolescents. Simple and practical strategies for the assessment of isolate parasympathetic outflow in this population are therefore useful.

OBJECTIVES

To compare the methods derived from heart rate variability (HRV) analysis at rest and 4 s exercise testing (T4S) for the assessment of cardiac parasympathetic modulation in adolescents classified as obese (OB) or with normal weight (NW). Additionally, associations between total and trunk fat versus autonomic modulation determined by the two methods were calculated.

APPROACH

A cross-sectional study was conducted with 50 adolescents (26 OB and 24 NW, 14.7  ±  1.5 years), comparing autonomic indices provided by HRV and T4S. Body fractioning was determined employing dual-energy x-ray absorptiometry (DXA).

MAIN RESULTS

The cardiac vagal index (CVI) obtained from T4S and standard time- and frequency-domain HRV measures were lower in OB versus NW (P  ⩽  0.05). Correlations between CVI and HRV indices of cardiac vagal modulation were as follows: CVI versus RMSSD (r  =  0.44; P  =  0.003); CVI versus pNN50 (r  =  0.32; P  =  0.04); CVI versus HF (r  =  0.35; P  =  0.02). Associations between body fat, android/gynoid ratio, and percent trunk fat versus CVI were of similar magnitude and direction than versus HRV indices.

SIGNIFICANCE

The T4S proved to be adequate to detect cardiac parasympathetic impairment in obese adolescents. Moreover, vagal modulation assessed by HRV and T4S inversely correlated with visceral adipose tissue. These findings along with the simplicity and safety of the T4S should encourage its use in the assessment of cardiac parasympathetic modulation in obese pediatric populations.

Increased Heart Rate during Walk Test Predicts Chronic-Phase Worsening of Renal Function in Patients with Acute Myocardial Infarction and Normal Kidney Function

Chronic-phase worsening renal function (WRF) in patients with acute myocardial infarction (AMI) has been associated with poor prognosis. However, there is no consensus on either the method of prevention or the cause. The aim of this study was to determine factors predictive of chronic-phase WRF from the viewpoint of circulatory dynamics response to exercise during hospitalization of AMI patients without renal dysfunction on admission. We studied 186 consecutively AMI patients who underwent the 200-m walk test. Chronic-phase WRF was defined as a 20% decrease in estimated glomerular filtration rate (eGFR) from baseline to 8–10 months after AMI onset. Heart rate (HR) and systolic blood pressure recorded during the 200-m walk test were evaluated as circulatory dynamics responses. In total, 94 patients were enrolled. Multiple linear regression analysis showed that ΔHR (peak-rest) associated significantly with ΔeGFR (β = 0.427, p = 0.018). The receiver operating characteristic curve of ΔHR to predict chronic-phase WRF showed an area under the curve of 0.77, with a cut-off value of 22.0 bpm having a 95% sensitivity and 55% specificity. Among circulatory dynamics responses during exercise in the acute phase after AMI, ΔHR was an independent predictor of chronic-phase WRF.

Low-Intensity Exercise Training Increases Heart Rate Variability in Patients With Peripheral Artery Disease

Patients with peripheral artery disease (PAD), consistent with others with atherosclerotic occlusive disorders, have autonomic dysfunction (as measured by low heart rate variability [HRV]) that predisposes them to sympathetically mediated cardiac arrhythmias and sudden death. Exercise therapy has been shown to increase HRV in patients with coronary artery disease by increasing parasympathetic modulation of heart rate. This study quantified the circulatory and autonomic effects of a progressive, 12-week home-based, low-intensity (pain-free walking) exercise program in PAD and intermittent claudication. Participants (N = 33, mean age 67.8 8.1 years) were randomly assigned to either a walking group (n = 18), whose members performed a structured, 12-week, progressive walking program 5 days/week for 12 weeks, or a comparison group (n = 15), whose members performed usual activities. Circulatory measures (heart rate, blood pressure, and rate pressure product) and autonomic measures (HRV) were obtained at the beginning (Week 1) and end (Week 12) of the study. Minimal change in circulatory measures occurred. However, spectral analysis of HRV revealed that autonomic function improved significantly in members of the walking group; specifically, there was an increase in parasympathetic and a decrease in sympathetic modulation. Members of the walking group also significantly increased maximal walking distance. These findings suggest that a structured, low-intensity, high-frequency walking program improves autonomic function by increasing HRV in patients with PAD.

Impaired heart rate variability, Valsalva and 30:15 ratio indexes are associated with reduced submaximal exercise capacity in subjects with diabetes mellitus

AIMS

To assess cardiac autonomic control and its association with submaximal exercise measured using the 6-minute walk test (6MWT) in subjects with type-2 diabetes mellitus (DM2).

METHODS

Cardiac autonomic control was assessed using Ewing's tests and heart rate variability (HRV) in DM2 volunteers (DG, n = 22) and sex-, age- and body mass index-matched non-diabetic controls (CG, n = 22) before, during and after 6MWT.

RESULTS

Before the 6MWT, DG presented lower HRV represented by reduced SDNN [median 28.9 ms² (IQR:18.6-35.4) vs. 45.1 (IQR:39.2-62.67), p < 0.001] and Total Power [median 785 ms² (IQR:256-1264) vs. 1757 ms² (IQR:1006-2912), p = 0.004]. Exercise capacity was reduced in DG [maximal predicted distance (%) = 88.4 ± 6.4 vs. 95.2 ± 11.0%, p = 0.018]. DG demonstrated lower global HRV during recovery and lower parasympathetic drive, represented by reduced RMSSD, during all phases of the 6MWT. Moreover, supine HR (r = -0.32), HR orthostatism (ρ = -0.40), SDNN pre-6MWT (ρ = 0.39), TP pre-6MWT (ρ = 0.38), Valsalva ratio (ρ = 0.39) and 30:15 ratio (ρ = 0.38) were all correlated with maximal walked distance.

CONCLUSIONS

DM2 subjects presented abnormal HRV during and after submaximal exercise. Furthermore, autonomic control impairment in orthostatism, represented by lower global HRV (SDNN, Total power) and lower Ewing's indexes (Valsalva and 30:15 ratios), was associated with lower exercise capacity.

Recovery of Heart Rate Variability After Exercise Under Hot Conditions: The Effect of Relative Humidity

INTRODUCTION

The aim of this study was to analyze changes in heart rate variability (HRV) during exercise in hot environments and recovery to baseline values depending on relative humidity.

METHODS

Ten recreational runners participated in this study. Each participant performed 2 trials consisting of 30 min of continuous running under hot and dry (HD) (38°C and 28% relative humidity) and hot and humid (HH) conditions (38°C and 64% relative humidity) at their common 10 km race-running rhythm. HRV and body mass were assessed pre- and post-trial; the rating of perceived exertion and HRV were assessed during the trial; and HRV measurements were repeated 2, 4, 8, and 24 h postexercise. Primary HRV outcomes were root mean square of the successive differences, high frequency power, stress score, and sympathetic/parasympathetic ratio. One-way analysis of variance testing was used to analyze differences.

RESULTS

No significant difference in body mass occurred across the different conditions or distances covered (P>0.05). Rating of perceived exertion presented the highest correlation values with stress score (r=0.729 for HD; r=0.568 for HH) and sympathetic/parasympathetic ratio (r=0.621 for HD; r=0.519 for HH) during exercise. HRV recovered to baseline values more quickly after exercising under dry conditions (4 h) than under humid conditions (between 8 and 24 h).

CONCLUSIONS

Stress score and sympathetic/parasympathetic ratio seem to be the best HRV predictors of internal load. Although there are no differences in HRV during recovery at the same time points in both conditions, the recovery is slower after exercise in HH than in HD.

The acute effects of aerobic exercise on sleep in patients with depression: study protocol for a randomized controlled trial

BACKGROUND

Unipolar depression is one of the most important mental disorders. Insomnia is a symptom of cardinal importance in depression. It increases the risk to develop depression, negatively affects disease trajectory, is the most common symptom after remission, increases the risk of relapse, and is associated with higher suicide rates. Existing therapies for insomnia in depression have limitations. Further adjuvant therapies are therefore needed. Acute aerobic exercise has been shown to have beneficial effects on sleep in healthy individuals and patients with insomnia. We therefore hypothesize that a single session of aerobic exercise has a positive impact on sleep in patients with unipolar depression. This trial aims to investigate the effects of a single bout of aerobic exercise on the subsequent night's sleep in patients with depression.

METHODS/DESIGN

This is a two-arm parallel group, randomized, outcome assessor blinded, controlled, superiority trial. Patients between 18 and 65 years of age with a primary diagnosis of unipolar depression (without a psychotic episode) are included. Exclusion criteria are regular use of hypnotic agents, opioids, and certain beta-blockers, as well as the presence of factors precluding exercise, history of epilepsy, restless legs syndrome, moderate obstructive sleep apnea, and a BMI > 40. The intervention is a single bout of aerobic exercise, performed for 30 min on a bicycle ergometer at 80% individual anaerobic threshold. The control group sits and reads for 30 min. The primary outcome is sleep efficiency measured by polysomnography. Secondary outcomes include further polysomnographic variables, subjective pre-sleep arousal, nocturnal cardiovascular autonomic modulation, subjective sleep quality, daytime sleepiness, and adverse events. According to the sample size calculation, a total of 92 patients will be randomized using minimization.

DISCUSSION

This trial will add new information to the body of knowledge concerning the treatment of insomnia in patients with depression. Thereby, the results will inform decision makers on the utility of acute aerobic exercise.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03673397 . Protocol version 1 registered on 17 September 2018.

Pitfalls of assessment of autonomic function by heart rate variability

Although analysis of heart rate variability is widely used for the assessment of autonomic function, its fundamental framework linking low-frequency and high-frequency components of heart rate variability with sympathetic and parasympathetic autonomic divisions has developed in the 1980s. This simplified framework is no longer able to deal with much evidence about heart rate variability accumulated over the past half-century. This review addresses the pitfalls caused by the old framework and discusses the points that need attention in autonomic assessment by heart rate variability.

Heart rate variability: are you using it properly? Standardisation checklist of procedures

BACKGROUND

Heart rate variability is used as an assessment method for cardiac autonomic modulation. Since the Task Force's publication on heart rate variability in 1996, the European Heart Rhythm Association Position Paper in 2015 and a recent publication in 2017, attention has been paid to recommendations on using heart rate variability analysis methods, as well as their applications in different physiological conditions and clinical studies. This analysis has proved to be useful as a complementary tool for clinical evaluation and to assess the effect of non-pharmacological therapeutic interventions, such as physical exercise programmes, on cardiac autonomic modulation.

OBJECTIVE

The aim of this article is to make recommendations and to develop a checklist of normalisation procedures regarding the use of heart rate variability data collection and analysis methodology, focusing on the cardiology area and cardiac rehabilitation.

METHODS

Based on previous heart rate variability publications, this paper provides a description of the most common shortcomings of using the analysis methods and considers recommendations and suggestions on how to minimise these occurrences by using a specific checklist.

CONCLUSIONS

This article includes recommendations and a checklist regarding the use of heart rate variability collection and analysis methods. This work could help improve reporting on clinical evaluation and therapeutic intervention results and consequently, disseminate heart rate variability knowledge.

The pulmonary and autonomic effects of high-intensity and low-intensity exercise in diesel exhaust

BACKGROUND

Exposure to air pollution impairs aspects of pulmonary and autonomic function and causes pulmonary inflammation. However, how exercising in air pollution affects these indices is poorly understood. Therefore, the purpose of this study was to determine the effects of low-intensity and high-intensity cycling with diesel exhaust (DE) exposure on pulmonary function, heart rate variability (HRV), fraction of exhaled nitric oxide (FeNO), norepinephrine and symptoms.

METHODS

Eighteen males performed 30-min trials of low-intensity or high-intensity cycling (30 and 60% of power at VO_2peak) or a resting control condition. For each subject, each trial was performed once breathing filtered air (FA) and once breathing DE (300μg/m³ of PM_2.5, six trials in total). Pulmonary function, FeNO, HRV, norepinephrine and symptoms were measured prior to, immediately post, 1 h and 2 h post-exposure. Data were analyzed using repeated-measures ANOVA.

RESULTS

Throat and chest symptoms were significantly greater immediately following DE exposure than following FA (p < 0.05). FeNO significantly increased 1 h following high-intensity exercise in DE (21.9 (2.4) vs. 19.3 (2.2) ppb) and FA (22.7 (1.7) vs. 19.9 (1.4)); however, there were no differences between the exposure conditions. All HRV indices significantly decreased following high-intensity exercise (p < 0.05) in DE and FA. The exception to this pattern was LF (nu) and LF/HF ratio, which significantly increased following high-intensity exercise (p < 0.05). Plasma norepinephrine (NE) significantly increased following high-intensity exercise in DE and FA, and this increase was greater than following rest and low-intensity exercise (p < 0.05). DE exposure did not modify any effects of exercise intensity on HRV or norepinephrine.

CONCLUSIONS

Healthy individuals may not experience greater acute pulmonary and autonomic effects from exercising in DE compared to FA; therefore, it is unclear if such individuals will benefit from reducing vigorous activity on days with high concentrations on particulate matter.

Influence of Age on Cardiorespiratory Kinetics During Sinusoidal Walking in Humans

We sought to determine the influence of age on cardiorespiratory kinetics during sinusoidal walking in two groups: 13 healthy young subjects (YG; 7 men and 6 women, age 21 ± 2 years) and 15 healthy elderly subjects (ELD; 9 men and 6 women, age 67 ± 5 years). A treadmill’s speed was sinusoidally changed between 3 and 6 km h^-1 in the YG and between 3 and 5 km h^-1 in the ELD during periods of 1, 2, 5, and 10 min, and in a stepwise manner. We compared the groups’ heart rate (HR), ventilation (V˙_E), and gas exchange (CO₂ output (V˙CO₂) and O₂ uptake (V˙O₂)) responses. We determined the phase shift (PS) and the normalized amplitude (Amp) ratio of these kinetics in relation to the sinusoidal change in walking speed in response to the magnitude from the maximum to minimum speeds as revealed by a Fourier analysis in all cardiorespiratory variables. Both the Amp ratio and PS in the V˙_E, V˙CO₂, and V˙O₂ responses were very similar between the ELD and YG, and being independent of the periods of sinusoidal oscillations. In marked contrast, the PS of the HR kinetics was significantly slowed in the ELD compared to the YG. The Amp ratio of HR was not related to the covariance variation of HR (CVHR) at standing rest in the ELD. The HR kinetics during sinusoidal walking may not be attributable to parasympathetic nerve activity into the heart in the ELD. The slope of the Amp of V˙_E related to the Amp of V˙CO₂ (V˙_E/V˙CO₂ slope) was steeper in the ELD (0.0258) compared to the YG (0.0132), suggesting that exercise hyperpnea could be greatly induced during walking in the ELD. These findings suggest that aging influences the alterations of autonomic nervous system-dependent slower HR kinetics and exercise hyperpnea during walking in the ELD.

Differential kinetics of the cardiac, ventilatory, and gas exchange variables during walking under moderate hypoxia

We investigated the effects of moderate hypoxia (FiO₂ = 15%) on different kinetics between pulmonary ventilation (V˙E) and heart rate (HR) during treadmill walking. Breath-by-breathV˙E, oxygen uptake (V˙O2), carbon dioxide output (V˙CO2), and HR were measured in 13 healthy young adults. The treadmill speed was sinusoidally changed from 3 to 6 km·h^-1 with four oscillation periods of 1, 2, 5, and 10 min. The amplitude (Amp), phase shift (PS) and mean values of these kinetics were obtained by harmonic analysis. The mean values of all of these responses during walking at a sinusoidally changing speed became greater under hypoxia compared to normoxia (FiO₂ = 21%), indicating that moderate hypoxia could achieve an increased energy expenditure (increased V˙O2 and V˙CO2) and hyperventilation. The Amp values of the V˙E, V˙O2, and V˙CO2 kinetics were not significantly different between normoxia and hypoxia at most periods, although a significantly smaller Amp of the HR was observed at faster oscillation periods (1 or 2 min).The PS of the HR was significantly greater under hypoxia than normoxia at the 2, 5, and 10 min periods, whereas the PS of the V˙E, V˙O2, and V˙CO2 responses was not significantly different between normoxia and hypoxia at any period. These findings suggest that the lesser changes in Amp and PS in ventilatory and gas exchange kinetics during walking at a sinusoidally changing speed were remarkably different from a deceleration in HR kinetics under moderate hypoxia.

Time-varying analysis of electrodermal activity during exercise

The electrodermal activity (EDA) is a useful tool for assessing skin sympathetic nervous activity. Using spectral analysis of EDA data at rest, we have previously found that the spectral band which is the most sensitive to central sympathetic control is largely confined to 0.045 to 0.25 Hz. However, the frequency band associated with sympathetic control in EDA has not been studied for exercise conditions. Establishing the band limits more precisely is important to ensure the accuracy and sensitivity of the technique. As exercise intensity increases, it is intuitive that the frequencies associated with the autonomic dynamics should also increase accordingly. Hence, the aim of this study was to examine the appropriate frequency band associated with the sympathetic nervous system in the EDA signal during exercise. Eighteen healthy subjects underwent a sub-maximal exercise test, including a resting period, walking, and running, until achieving 85% of maximum heart rate. Both EDA and ECG data were measured simultaneously for all subjects. The ECG was used to monitor subjects' instantaneous heart rate, which was used to set the experiment's end point. We found that the upper bound of the frequency band (Fmax) containing the EDA spectral power significantly shifted to higher frequencies when subjects underwent prolonged low-intensity (Fmax ~ 0.28) and vigorous-intensity exercise (Fmax ~ 0.37 Hz) when compared to the resting condition. In summary, we have found shifting of the sympathetic dynamics to higher frequencies in the EDA signal when subjects undergo physical activity.

Influence of exercise modality on cardiac parasympathetic and sympathetic indices during post-exercise recovery

OBJECTIVES

This study investigated indirect measures of post-exercise parasympathetic reactivation (using heart-rate-variability, HRV) and sympathetic withdrawal (using systolic-time-intervals, STI) following upper- and lower-body exercise.

DESIGN

Randomized, counter-balanced, crossover.

METHODS

13 males (age 26.4±4.7years) performed maximal arm-cranking (MAX-ARM) and leg-cycling (MAX-LEG). Subsequently, participants undertook separate 8-min bouts of submaximal HR-matched exercise of each mode (ARM and LEG). HRV (including natural-logarithm of root-mean-square-of-successive-differences, Ln-RMSSD) and STI (including pre-ejection-period, PEP) were assessed throughout 10-min seated recovery.

RESULTS

Peak-HR was higher (p=0.001) during MAX-LEG (182±7beatsmin^-1) compared with MAX-ARM (171±12beatsmin^-1), while HR (p<0.001) and Ln-RMSSD (p=0.010) recovered more rapidly following MAX-ARM. PEP recovery was similar between maximal bouts (p=0.106). HR during submaximal exercise was 146±7 (LEG) and 144±8beatsmin^-1 (LEG) (p=0.139). Recovery of HR and Ln-RMSSD was also similar between submaximal modalities, remaining below baseline throughout recovery (p<0.001). PEP was similar during submaximal exercise (LEG 70±6ms; ARM 72±9ms; p=0.471) although recovery was slower following ARM (p=0.021), with differences apparent from 1- to 10-min recovery (p≤0.036). By 10-min post-exercise, PEP recovered to baseline (132±21ms) following LEG (130±21ms; p=0.143), but not ARM (121±17ms; p=0.001).

CONCLUSIONS

Compared with submaximal lower-body exercise, HR-matched upper-body exercise elicited a similar recovery of HR and HRV indices of parasympathetic reactivation, but delayed recovery of PEP (reflecting sympathetic withdrawal). Exercise modality appears to influence post-exercise parasympathetic reactivation and sympathetic withdrawal in an intensity-dependent manner. These results highlight the need for test standardization and may be relevant to multi-discipline athletes and in clinical applications with varying modes of exercise testing.

Real-Time Analysis of the Heart Rate Variability During Incremental Exercise for the Detection of the Ventilatory Threshold

Background

It has never been possible to immediately evaluate heart rate variability (HRV) during exercise. We aimed to visualize the real‐time changes in the power spectrum of HRV during exercise and to investigate its relationship to the ventilatory threshold (VT).

Methods and Results

Thirty healthy subjects (29.1±5.7 years of age) and 35 consecutive patients (59.0±13.2 years of age) with myocardial infarctions underwent cardiopulmonary exercise tests with an RAMP protocol ergometer. The HRV was continuously assessed with power spectral analyses using the maximum entropy method and projected on a screen without delay. During exercise, a significant decrease in the high frequency (HF) was followed by a drastic shift in the power spectrum of the HRV with a periodic augmentation in the low frequency/HF (L/H) and steady low HF. When the HRV threshold (HRVT) was defined as conversion from a predominant high frequency (HF) to a predominant low frequency/HF (L/H), the VO₂ at the HRVT (HRVT‐VO₂) was substantially correlated with the VO₂ at the lactate threshold and VT) in the healthy subjects (r=0.853 and 0.921, respectively). The mean difference between each threshold (0.65 mL/kg per minute for lactate threshold and HRVT, 0.53 mL/kg per minute for VT and HRVT) was nonsignificant (P>0.05). Furthermore, the HRVT‐VO₂ was also correlated with the VT‐VO₂ in these myocardial infarction patients (r=0.867), and the mean difference was −0.72 mL/kg per minute and was nonsignificant (P>0.05).

Conclusions

A HRV analysis with our method enabled real‐time visualization of the changes in the power spectrum during exercise. This can provide additional information for detecting the VT.

A "Wearable" Test for Maximum Aerobic Power: Real-Time Analysis of a 60-m Sprint Performance and Heart Rate Off-Kinetics

Maximum aerobic power (V˙O2peak) as an indicator of body fitness is today a very well-known concept not just for athletes but also for the layman. Unfortunately, the accurate measurement of that variable has remained a complex and exhaustive laboratory procedure, which makes it inaccessible to many active people. In this paper we propose a quick estimate of it, mainly based on the heart rate off-kinetics immediately after an all-out 60-m sprint run. The design of this test took into account the recent availability of wrist wearable, heart band free, multi-sensor smart devices, which could also inertially detect the different phases of the sprint and check the distance run. 25 subjects undertook the 60-m test outdoor and a V˙O2peak test on the laboratory treadmill. Running average speed, HR excursion during the sprint and the time constant (τ) of HR exponential decay in the off-kinetics were fed into a multiple regression, with measured V˙O2peak as the dependent variable. Statistics revealed that within the investigated range (25–55 ml O₂/(kg min)), despite a tendency to overestimate low values and underestimate high values, the three predictors confidently estimate individual V˙O2peak (R² = 0.65, p < 0.001). The same analysis has been performed on a 5-s averaged time course of the same measured HR off-kinetics, as these are the most time resolved data for HR provided by many modern smart watches. Results indicate that despite of the substantial reduction in sample size, predicted V˙O2peak still explain 59% of the variability of the measured V˙O2peak.

Modulation of Cardiac Autonomic Function by Fingolimod Initiation and Predictors for Fingolimod Induced Bradycardia in Patients with Multiple Sclerosis

Objective: It is well-known that initiation of fingolimod induces a transient decrease of heart rate. However, the underlying cardiac autonomic regulation is poorly understood. We aimed to investigate the changes of autonomic activity caused by the first dose of fingolimod using a long-term multiple trigonometric spectral analysis for the first time. In addition, we sought to use the continuous Holter ECG recording to find predictors for fingolimod induced bradycardia.

Methods: Seventy-eight patients with relapsing-remitting multiple sclerosis (RRMS) were included. As a part of the START study (NCT01585298), continuous electrocardiogram was recorded before fingolimod initiation, and until no <6 h post medication. Time domain and frequency domain heart rate variability (HRV) parameters were computed hourly to assess cardiac autonomic regulation. A long-term multiple trigonometric regressive spectral (MTRS) analysis was applied on successive 1-h-length electrocardiogram recordings. Decision tree analysis was used to find predictors for bradycardia following fingolimod initiation.

Results: Most of the HRV parameters representing parasympathetic activities began to increase since the second hour after fingolimod administration. These changes of autonomic regulations were in accordance with the decline of heart rate. Baseline heart rate was highly correlated with nadir heart rate, and was the only significant predicting factor for fingolimod induced bradycardia among various demographic, clinical and cardiovascular variables in the decision tree analysis.

Conclusions: The first dose application of fingolimod enhances the cardiac parasympathetic activity during the first 6 h post medication, which might be the underlying autonomic mechanism of reduced heart rate. Baseline heart rate is a powerful predictor for bradycardia caused by fingolimod.

Higher exercise intensity delays postexercise recovery of impedance-derived cardiac sympathetic activity

Systolic time intervals (STIs) provide noninvasive insights into cardiac sympathetic neural activity (cSNA). As the effect of exercise intensity on postexercise STI recovery is unclear, this study investigated the STI recovery profile after different exercise intensities. Eleven healthy males cycled for 8 min at 3 separate intensities: LOW (40%-45%), MOD (75%-80%), and HIGH (90%-95%) of heart-rate (HR) reserve. Bio-impedance cardiography was used to assess STIs - primarily pre-ejection period (PEP; inversely correlated with cSNA), as well as left ventricular ejection time (LVET) and PEP:LVET - during 10 min seated recovery immediately postexercise. Heart-rate variability (HRV), i.e., natural-logarithm of root mean square of successive differences (Ln-RMSSD), was calculated as an index of cardiac parasympathetic neural activity (cPNA). Higher preceding exercise intensity elicited a slower recovery of HR and Ln-RMSSD (p < 0.001), and these measures did not return to baseline by 10 min following any intensity (p ≤ 0.009). Recovery of STIs was also slower following higher intensity exercise (p ≤ 0.002). By 30 s postexercise, higher preceding intensity resulted in a lower PEP (98 ± 14 ms, 75 ± 6 ms, 66 ± 5 ms for LOW, MOD, and HIGH, respectively, p < 0.001). PEP recovered to baseline (143 ± 11 ms) by 5 min following LOW (139 ± 13 ms, p = 0.590) and by 10 min following MOD (145 ± 17 ms, p = 0.602), but was still suppressed at 10 min following HIGH (123 ± 21 ms, p = 0.012). Higher preceding exercise intensity attenuated the recovery of indices for cSNA (from STIs) and cPNA (from HRV) in a graded dose-response fashion. While exercise intensity must be considered, acute recovery may be a valuable period during which to concurrently monitor these noninvasive indices, to identify potentially abnormal cardiac autonomic responses.

Cardiac Autonomic Responses during Exercise and Post-exercise Recovery Using Heart Rate Variability and Systolic Time Intervals-A Review

Cardiac parasympathetic activity may be non-invasively investigated using heart rate variability (HRV), although HRV is not widely accepted to reflect sympathetic activity. Instead, cardiac sympathetic activity may be investigated using systolic time intervals (STI), such as the pre-ejection period. Although these autonomic indices are typically measured during rest, the “reactivity hypothesis” suggests that investigating responses to a stressor (e.g., exercise) may be a valuable monitoring approach in clinical and high-performance settings. However, when interpreting these indices it is important to consider how the exercise dose itself (i.e., intensity, duration, and modality) may influence the response. Therefore, the purpose of this investigation was to review the literature regarding how the exercise dosage influences these autonomic indices during exercise and acute post-exercise recovery. There are substantial methodological variations throughout the literature regarding HRV responses to exercise, in terms of exercise protocols and HRV analysis techniques. Exercise intensity is the primary factor influencing HRV, with a greater intensity eliciting a lower HRV during exercise up to moderate-high intensity, with minimal change observed as intensity is increased further. Post-exercise, a greater preceding intensity is associated with a slower HRV recovery, although the dose-response remains unclear. A longer exercise duration has been reported to elicit a lower HRV only during low-moderate intensity and when accompanied by cardiovascular drift, while a small number of studies have reported conflicting results regarding whether a longer duration delays HRV recovery. “Modality” has been defined multiple ways, with limited evidence suggesting exercise of a greater muscle mass and/or energy expenditure may delay HRV recovery. STI responses during exercise and recovery have seldom been reported, although limited data suggests that intensity is a key determining factor. Concurrent monitoring of HRV and STI may be a valuable non-invasive approach to investigate autonomic stress reactivity; however, this integrative approach has not yet been applied with regards to exercise stressors.

Effectiveness of Moderate Intensity Interval Training as an Index of Autonomic Nervous Activity

The purpose of this study was to examine the effects of moderate intensity interval training from the change of the autonomic nervous activity. Ten male volunteers aged 21-22 years were studied. After 10-minute rest in a seated position, the subjects were asked to perform the strength of moderate cycling exercise in ergometer. Cycling rate was done in 50 times/min. Load resistance of the ergometer was set to 2.0 kgm. Subjects paused the exercise when the heart rate becomes 120 beats/min. Subjects have resumed the exercise when the heart rate returns to the value at rest. This trial was repeated twice. The experiment was ended when the heart rate of the subjects has returned to resting level. When the heart rate during exercise is maintained to less than 120 beats/min, sympathetic nerve activity during exercise did not work actively compared to the baseline. Vagus nerve activity after exercise cessation exceeds the baseline. It is clarified that the exercise as well as activating the vagus nerve activity stimulates the total autonomic nervous activity. It has revealed that at the time of interval training at moderate load the vagus nerve activity can be carried out.

The Effects of Direct Current Stimulation on Exercise Performance, Pacing and Perception in Temperate and Hot Environments

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulatory technique and has previously been shown to enhance submaximal exercise by reducing rating of perceived exertion (RPE). The present study examined the effects of tDCS on high-intensity self-paced exercise in temperate conditions and fixed followed by maximal exercise in the heat; it was hypothesised that performance and RPE would be altered.

METHODS

Two separate studies were undertaken in which exercise was preceded by 20-minutes of sham tDCS (SHAM), or anodal tDCS (TDCS). In study 1, six males completed a 20-km cycling time trial, on two occasions. Power output (PO), RPE, O₂ pulse_, and heart rate (HR) were measured throughout. In study 2, eight males completed fixed intensity cycling exercise at 55% of a pre-determined maximal power output (P_Max) for 25-minutes before undertaking a time to exhaustion test (TTE; 75% P_Max) in hot conditions (33 °C), on two occasions. Test duration, heart rate, thermal and perceptual responses were measured. Study specific and combined statistical analyses were undertaken and effect sizes established.

RESULTS

In study 1, mean PO was not improved with the tDCS (197 ± 20 W) compared to SHAM (197 ± 12 W) and there were no differences in pacing profile HR, O₂ pulse or RPE (p > .05). In study 2, TTE duration (SHAM 314 ± 334 s cf 237 ± 362 s tDCS), thermal, heart rate and perceptual responses were unchanged by tDCS compared to SHAM (p > .05). When combined, performance in the SHAM trial tended to better than the tDCS.

CONCLUSION

tDCS did not influence cycling performance (study 1) exercise tolerance (study 2) or perception (studies 1 and 2). tDCS does not appear to facilitate high intensity exercise performance or exercise performance in the heat.

Interaction of Biological Stress Recovery and Cognitive Vulnerability for Depression in Adolescence

Major Depressive Disorder is a common mental illness with rates increasing during adolescence. This has led researchers to examine developmental antecedents of depression. This study examined the association between depressive symptoms and the interaction between two empirically supported risk factors for depression: poor recovery of the biological stress system as measured through heart rate and cortisol, and cognitive vulnerabilities as indexed by rumination and a negative cognitive style. Adolescents (n = 127; 49 % female) completed questionnaires and a social stress task to elicit a stress response measured with neuroendocrine (cortisol) and autonomic nervous system (heart rate) endpoints. The findings indicated that higher depressive symptoms were associated with the combination of higher cognitive vulnerabilities and lower cortisol and heart rate recovery. These findings can enhance our understanding of stress responses, lead to personalized treatment, and provide a nuanced understanding of depression in adolescence.

Cardiac parasympathetic outflow during dynamic exercise in humans estimated from power spectral analysis of P-P interval variability

NEW FINDINGS

What is the central question of this study? Should we use the high-frequency (HF) component of P-P interval as an index of cardiac parasympathetic nerve activity during moderate exercise? What is the main finding and its importance? The HF component of P-P interval variability remained even at a heart rate of 120-140 beats min(-1) and was further reduced by atropine, indicating incomplete cardiac vagal withdrawal during moderate exercise. The HF component of R-R interval is invalid as an estimate of cardiac parasympathetic outflow during moderate exercise; instead, the HF component of P-P interval variability should be used. The high-frequency (HF) component of R-R interval variability has been widely used as an indirect estimate of cardiac parasympathetic (vagal) outflow to the sino-atrial node of the heart. However, we have recently found that the variability of the R-R interval becomes much smaller during dynamic exercise than that of the P-P interval above a heart rate (HR) of ∼100 beats min(-1). We hypothesized that cardiac parasympathetic outflow during dynamic exercise with a higher intensity may be better estimated using the HF component of P-P interval variability. To test this hypothesis, the HF components of both P-P and R-R interval variability were analysed using a Wavelet transform during dynamic exercise. Twelve subjects performed ergometer exercise to increase HR from the baseline of 69 ± 3 beats min(-1) to three different levels of 100, 120 and 140 beats min(-1). We also examined the effect of atropine sulfate on the HF components in eight of the 12 subjects during exercise at an HR of 140 beats min(-1) . The HF component of P-P interval variability was significantly greater than that of R-R interval variability during exercise, especially at the HRs of 120 and 140 beats min(-1). The HF component of P-P interval variability was more reduced by atropine than that of R-R interval variability. We conclude that cardiac parasympathetic outflow to the sino-atrial node can be estimated better by the HF component of P-P interval variability during exercise and that cardiac parasympathetic nerve activity exists during moderate dynamic exercise.

Postexercise heart rate variability following treadmill and cycle exercise: a comparison study

The purpose of this study was to compare postexercise heart rate variability (HRV) immediately following acute bouts of treadmill (T) and cycle (C) exercise at 65% of mode-specific maximal oxygen consumption reserve (65% VO₂ R). Fourteen apparently healthy men participated in this study. On two separate and randomized days, each participant performed 30 min of exercise at 65% VO₂ R on T and C. Supine HRV was evaluated as normalized and log-transformed (ln) high-frequency (HF) and low-frequency (LF) spectral power, as well as the LF:HF ratio in 5-min segments immediately before (PRE) and at 10-15 min (POST1) and 25-30 min (POST2) following each exercise bout. There were no significant differences in the HRV values at PRE between the modalities. Following each exercise bout, lnHF was significantly lower at POST2 following C compared to T. In addition, lnLF and LF:HF were significantly higher at POST1 and POST2 following C compared to T. All HRV metrics returned towards baseline 30 min following T but remained significantly different than PRE values after C. These results suggest that following exercise at 65% of mode-specific VO₂ R, C is associated with a greater delay of postexercise HRV recovery than T in apparently healthy men.

Errata Corrige. Orthostatic Reactivity in Patients with Ischemic Stroke in the Chronic Period. http://dx.doi.org/10.3889/oamjms.2015.090

AIM:

This study aims to trace the influence of specialized kinesitherapeutic methodology (SKTM) on orthostatic reactivity in patients with ischemic stroke in the chronic period (ISChP).

MATERIAL AND METHODS:

An active orthostatic test is used for the evaluation of the orthostatic reactions. The arterial blood pressure and heart rate were defined in the 10 minutes of supine position, before and after 1, 5 and 10 minutes of active upright position. The orthostatic autoregulation is evaluated four times - at the beginning of the study, on the 10th day, on the 1st month and three months after the start of the KT. The classification by Thulesius was used to separate the patients into two groups depending on the type of their orthostatic reactivity.

RESULTS:

At the beginning of the study of infringements symptomatic type orthostatic reactivity (SOR) was observed in 24 patients and hypertensive type orthostatic reactivity (HOR) was observed in the remaining 32 patients. Once applied SKTM establish improvement of orthostatic autoregulation for the groups SOR and HOR at the 10th day and the 1st month with a level of significance p <0.05.

CONCLUSION:

The applied specialized kinesitherapeutic methodology continued later as an adapted exercise program at home, has significantly improved the orthostatic reactivity in patients with orthostatic dysregulation due to the ISChP.