Heart Rate Dynamics Research Articles

Similarities and dissimilarities in response to specific submaximal aerobic exercise in newcomer and well-trained athletes

The study was aimed on evaluation the applicability of certain distinct characteristics of heart rate dynamics dependence upon physical training load as criteria of young athletes functional fitness. Nine elite adult canoe and kayak rowers and twenty five young skiers aged 11-13 took part in the research program. Canoe and kayak rowers performed incremental tests on a rowing simulator (4*1000 m). The following parameters were measured: heart rate, oxygen heart rate, breath frequency, respiratory exchange ratio, oxygen uptake, and minute ventilation. Young skiers performed moderate run on a stadium track maintaining constant speed to voluntary physical exhaustion. Comparison of the trends in young and elite athletes allows assuming that the response to the given load on the third segment of the test exceeded the current level of fitness and continuation of the exercise at this level can cause overstrain and overtraining. It has to be pointed out that this assumption requires further research with measurement of a broader range of parameters.

DYNAMICS OF PHYSIOLOGICAL STATUS IN LEVEL 1 DIFFICULTY HIKING TOURS

Aim. The paper aims to establish the features of physiological status in level 1 difficulty hiking tours. Materials and methods. 11 persons participated in the experiment. The experiment was conducted during a level 1 difficulty hiking tour along the Nurali ridge (Uchaly district, the republic of Bashkortostan). Physiological status of participants was assessed 16 times during the hiking tour (HR). Results. On the first day of the tour, the participants made camp, their heart rate was within reference values. On the second day, six crossings were made, two of which were to the Nurali ridge, four were the Nurali ridge traverse. During the crossings, the trained participants showed an insignificant increase in heart rate, while in untrained ones, heart rate values were within the first, second and third heart rate zones depending on the individual characteristics of the participants. On the third day, the participants made four crossings on the plain and one ascent to the Ashtau mountain; heart rate values were within the first and second heart rate zones. Conclusion. The participants of a level 1 difficulty hiking tour covered ≈ 37 km in 3 days. Heart rate dynamics suggests that untrained participants experienced more training effect since their heart rate values were within the zones of fat burning and endurance performance; trained parti­cipants could only maintain their physical fitness. The trail along the Nurali ridge can be recommended for unprepared tourists as a sports and recreation trail.

АВТОКОРРЕЛЯЦИОННЫЙ АНАЛИЗ КАРДИОИНТЕРВАЛОГРАММ В РАЗРЕЗЕ ТРЕХ ГРУПП ПАЦИЕНТОВ С РАСШИРЕННЫМ АНАЛИЗОМ ПЕРВИЧНОЙ ОБРАБОТКИ ДАННЫХ

Purpose of the study. To develop a method for analyzing the seasonal and cyclic components of R-R intervals by estimating the autocorrelation function (ACF). Material and methods. The study consists of conducting a practical analysis of ACF as an application to R-R intervals, divided into three groups: all patients are patients with atrial fibrillation. The first group had tachycardia; the second had bradycardia; the third group - are patients without specific features. It should be noted that the age of the patients, according to which the analysis was carried out, is from 40 years and older. Results. The module developed at VBA (Visual Basic for Applications) enables to apply the methods of primary processing of the studied data, to create the ACF with its graphic representation for rather large values of the lag variable τ=1,100 . Samples of 1000 values were examined. The most optimal data cleaning methods have been selected to get rid of excessive noise. A detailed analysis of ACF was carried out in the three groups of patients. Impressive research statistics have been compiled. Conclusions. In people with signs of tachycardia, all ACF ratios were not significant. In cases with severe tachycardia, ACF coefficients were positive, and had a decreasing trend. In the series with signs of bradycardia, almost all ACF coefficients were significant. ACF decreased with increasing lag τ. It can be concluded that in this group of time series there is a marked constant linear trend. In the group of patients with normal heart rate dynamics, insignificant ACF coefficients were obtained, which indicates the absence of any tendency. The coefficients were concentrated along the axis of the lag, had both positive and negative values. The oscillating process indicates only a strong stochastic component of the studied data.

FUNCTIONAL FEATURES OF THE MYOCARDIUM AMONG FIRST-YEAR STUDENTS OF DIFFERENT ETHNIC GROUPS WITH REGARD TO THE TYPE OF AUTONOMIC REGULATION OF THE CARDIAC RHYTHM

The analysis of the dynamics of heart rate and blood pressure components in students of five ethnic groups - Arabic, Indian, African, Latin American and Russian, taking into account the most characteristic types of autonomous regulation of heart rate (HR) with the third moderate predominance of autonomous regulation (MPAR) and the fourth - a pronounced predominance of autonomous regulation (PPAR) HR. A mediocre level of fitness of the cardiovascular system among students: Russian and Arab with MPAR HR at both stages; Indian and Latin American with MPAR and PPAR HR types of regulation of heart rhythm at the 1st stage; African with MPAR HR on the 2nd stage. The rest of the students - a good level of fitness. High vs. normal values of systolic pressure indicate a maladaptive state of groups of Arab and African students at both stages, Indian with the MPAR HR at the second stage. Increased pulse pressure (PP) in Russian students at the second stage with the PPAR HR, among Arabic, Latin American, African students at both stages, notes a decrease in their myocardial functionality against the background of diastolic fatigue and disadaptation to conditions of relative physiological rest. Under conditions of relative physiological rest, the high anti-normal values of systolic blood pressure (SBP) indicated the maladaptive state of groups of Arab and African students at both stages, Indian with MPAR at the 2nd stage. High PD in all subgroups of Arab, African and Latin American students at the 2nd stage with PPAR and at the rest of the groups with MPAR and PPAR HR are objective indicators of myocardial diastolic fatigue, reduction of its functional capabilities and manifestation of maladaptation in conditions of relative physiological rest.

Patterns of Heart Rate Dynamics in Healthy Aging Population: Insights from Machine Learning Methods

Costa et. al (Frontiers in Physiology (2017) 8255) proved that abnormal features of heart rate variability (HRV) can be discerned by the presence of particular patterns in a signal of time intervals between subsequent heart contractions, called RR intervals. In the following, the statistics of these patterns, quantified using entropic tools, are explored in order to uncover the specifics of the dynamics of heart contraction based on RR intervals. The 33 measures of HRV (standard and new ones) were estimated from four hour nocturnal recordings obtained from 181 healthy people of different ages and analyzed with the machine learning methods. The validation of the methods was based on the results obtained from shuffled data. The exploratory factor analysis provided five factors driving the HRV. We hypothesize that these factors could be related to the commonly assumed physiological sources of HRV: (i) activity of the vagal nervous system; (ii) dynamical balance in the autonomic nervous system; (iii) sympathetic activity; (iv) homeostatic stability; and (v) humoral effects. In particular, the indices describing patterns: their total volume, as well as their distribution, showed important aspects of the organization of the ANS control: the presence or absence of a strong correlation between the patterns’ indices, which distinguished the original rhythms of people from their shuffled representatives. Supposing that the dynamic organization of RR intervals is age dependent, classification with the support vector machines was performed. The classification results proved to be strongly dependent on the parameters of the methods used, therefore determining that the age group was not obvious.

Temporal dynamics of heart rate during sleep in people with depression

Temporal dynamics of heart rate during sleep in people with depression

Alterations in heart-brain interactions under mild stress during a cognitive task are reflected in entropy of heart rate dynamics

Many people experience mild stress in modern society which raises the need for an improved understanding of psychophysiological responses to stressors. Heart rate variability (HRV) may be associated with a flexible network of intricate neural structures which are dynamically organized to cope with diverse challenges. HRV was obtained in thirty-three healthy participants performing a cognitive task both with and without added stressors. Markers of neural autonomic control and neurovisceral complexity (entropy) were computed from HRV time series. Based on individual anxiety responses to the experimental stressors, two subgroups were identified: anxiety responders and non-responders. While both vagal and entropy markers rose during the cognitive task alone in both subgroups, only entropy decreased when stressors were added and exclusively in anxiety responders. We conclude that entropy may be a promising marker of cognitive tasks and acute mild stress. It brings out a new central question: why is entropy the only marker affected by mild stress? Based on the neurovisceral integration model, we hypothesized that neurophysiological complexity may be altered by mild stress, which is reflected in entropy of the cardiac output signal. The putative role of the amygdala during mild stress, in modulating the complexity of a coordinated neural network linking brain to heart, is discussed.

Extreme bradycardia and tachycardia in the world’s largest animal

The biology of the blue whale has long fascinated physiologists because of the animal's extreme size. Despite high energetic demands from a large body, low mass-specific metabolic rates are likely powered by low heart rates. Diving bradycardia should slow blood oxygen depletion and enhance dive time available for foraging at depth. However, blue whales exhibit a high-cost feeding mechanism, lunge feeding, whereby large volumes of prey-laden water are intermittently engulfed and filtered during dives. This paradox of such a large, slowly beating heart and the high cost of lunge feeding represents a unique test of our understanding of cardiac function, hemodynamics, and physiological limits to body size. Here, we used an electrocardiogram (ECG)-depth recorder tag to measure blue whale heart rates during foraging dives as deep as 184 m and as long as 16.5 min. Heart rates during dives were typically 4 to 8 beats min-1 (bpm) and as low as 2 bpm, while after-dive surface heart rates were 25 to 37 bpm, near the estimated maximum heart rate possible. Despite extreme bradycardia, we recorded a 2.5-fold increase above diving heart rate minima during the powered ascent phase of feeding lunges followed by a gradual decrease of heart rate during the prolonged glide as engulfed water is filtered. These heart rate dynamics explain the unique hemodynamic design in rorqual whales consisting of a large-diameter, highly compliant, elastic aortic arch that allows the aorta to accommodate blood ejected by the heart and maintain blood flow during the long and variable pauses between heartbeats.

Consecutive non-training days over a weekend for assessing cardiac parasympathetic variation in response to accumulated exercise stress

ABSTRACT Purpose: To examine the association between day-to-day resting cardiac parasympathetic variability over consecutive non-training days (i.e. weekend) and accumulated exercise stress when quantified using indices of cardiovascular strain. Methods: Twelve international calibre female field hockey players training as part of a national team were participants over a four-week mesocycle prior to a 2016 Olympic qualifying tournament. On-field exercise stress was examined using heart rate (HR) dynamics and quantified as; (1) training load and (2) time (min) spent above anaerobic threshold. The square root of the mean squared differences of successive cardiac cycles (R–R intervals) recorded on Saturday and Sunday were individually calculated and log-transformed prior to being averaged (Ln rMSSDweekend). Day-to-day variation in Ln rMSSD over the weekend was expressed using the coefficient of variation (Ln rMSSDCV). Non-linear regression analysis examined the association between accumulated exercise stress and Ln rMSSDCV. Results: A quadratic association between each index of exercise stress and Ln rMSSDCV was identified. After converting the coefficient of determination into a correlation coefficient (90% CL), the respective association between Ln rMSSDCV and training load (AU); r = 0.40 (0.16:0.59) and time above threshold; r = 0.35 (0.06:0.59) were observed. Conclusion: Ln rMSSDCV derived over consecutive non-training days displayed a moderate, yet significant association between accumulated exercise stress when expressed as global or high-intensity indices of cardiovascular strain. Weekend assessments may offer a practical and appropriate juncture between microcycles to assess the magnitude of perturbation in cardiac autonomic homeostasis prior to entering subsequent training periods.

Multiscale Entropy of Cardiac and Postural Control Reflects a Flexible Adaptation to a Cognitive Task

In humans, physiological systems involved in maintaining stable conditions for health and well-being are complex, encompassing multiple interactions within and between system components. This complexity is mirrored in the temporal structure of the variability of output signals. Entropy has been recognized as a good marker of systems complexity, notably when calculated from heart rate and postural dynamics. A degraded entropy is generally associated with frailty, aging, impairments or diseases. In contrast, high entropy has been associated with the elevated capacity to adjust to an ever-changing environment, but the link is unknown between entropy and the capacity to cope with cognitive tasks in a healthy young to middle-aged population. Here, we addressed classic markers (time and frequency domains) and refined composite multiscale entropy (MSE) markers (after pre-processing) of heart rate and postural sway time series in 34 participants during quiet versus cognitive task conditions. Recordings lasted 10 min for heart rate and 51.2 s for upright standing, providing time series lengths of 500–600 and 2048 samples, respectively. The main finding was that entropy increased during cognitive tasks. This highlights the possible links between our entropy measures and the systems complexity that probably facilitates a control remodeling and a flexible adaptability in our healthy participants. We conclude that entropy is a reliable marker of neurophysiological complexity and adaptability in autonomic and somatic systems.

Exponential model for analysis of heart rate responses and autonomic cardiac modulation during different intensities of physical exercise.

The aim of this study was to compare the heart rate (HR) dynamics and variability before and after high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) protocols with workloads based on treadmill workload at which maximal oxygen uptake was achieved . Ten participants performed cardiopulmonary exercise testing (CPET) to obtain oxygen uptake . All training protocols were performed on a treadmill, with 0% grade, and had similar total distance. The MICT was composed by 21 min at 70% of . The first HIIT protocol (HIIT-30 : 30) was composed by 29 repetitions of 30 s at 100% of and the second HIIT protocol (HIIT-4 : 3) was composed by three repetitions of 4 min at 90% of . Before, during and after each training protocol, HR dynamics and variability (HRV) were analysed by standard kinetics and linear (time and frequency domains). The repeated measures analysis of variance indicated that the HR dynamics, which characterizes the speed of HR during the rest to exercise transition, was statistically (p < 0.05) slower during MICT in comparison to both HIIT protocols. The HRV analysis, which characterizes the cardiac autonomic modulation during the exercise recovery, was statistically higher in HIIT-4 : 3 in comparison to MICT and HIIT-30 : 30 protocols (p < 0.005 and p = 0.012, respectively), suggesting that the HIIT-4 : 3 induced higher sympathetic and lower parasympathetic modulation during exercise in comparison to the other training protocols. In conclusion, HIIT-4 : 3 demonstrated post-exercise sympathetic hyperactivity and a higher HRpeak, while the HIIT-30 : 30 and MICT resulted in better HRV and HR in the exercise-recovery transition. The cardiac autonomic balance increased in HIIT-30 : 30 while HIIT-4 : 3 induced sympathetic hyperactivity and cardiac overload.

P3522Vagus nerve stimulation for chronic heart failure: differences in therapy delivery and clinical efficacy in ANTHEM-HF, INOVATE-HF, and NECTAR-HF

Abstract Background Vagus Nerve Stimulation (VNS) is meant to deliver Autonomic Regulation Therapy (ART) to neurological targets with sufficient neuromodulation (NM) to ameliorate chronic heart failure (CHF). VNS delivery consists of its intensity (a combination of pulse amplitude, pulse frequency, and pulse duration), polarity, duty cycle (DC; stimulation “on” time and “off” time), and mode (continuous, or intermittent and periodic). In the ANTHEM-HF Pilot Study patients with CHF and reduced ejection fraction (HFrEF), VNS intensity was up-titrated until a change in heart rate (HR) dynamics was objectively confirmed. This did not require any change in GDMT and was associated with significant improvements in LVEF, 6-minute walk distance (6MWD), Minnesota Living with HF (MLWHF) score, and HR variability. Methods Qualitative and quantitative analyses used data from peer-reviewed publications and other sources in the public domain to compare VNS delivery in ANTHEM-HF, INOVATE-HF, and NECTAR-HF. Results (Table): Up-titration of VNS intensity was attempted in all 3 studies. In contrast to ANTHEM-HF, INOVATE-HF aimed only at peripheral neural targets. VNS intensity was delivered at a lower pulse frequency, and had a variable DC as a consequence of R-wave synchronization and only intermittent, periodic stimulation. In NECTAR-HF VNS intensity was delivered at a higher pulse frequency, and this was associated with intolerable adverse off-target effects which restricted VNS up-titration. Significant improvements in EF, 6MWD, MLWHF, and SDNN occurred in ANTHEM-HF relative to the other studies. ANTHEM-HF (n=60) INOVATE-HF (n=436) NECTAR-HF (n=63) Neural Target Central/Peripheral Peripheral Central/Peripheral Delivery Site Left or right CVN Right CVN Right CVN Delivery Intensity: Amplitude (milliamperes) 2.0±0.6 3.9±1.0 1.4±0.8 Frequency (Hertz) 10 1–2 20 Duration (microseconds) 250 500 300 Electrode Polarity (Cathode) Caudal Cephalad Caudal Duty Cycle 23% 25% 17% On Time/Off Time (seconds) 18/62 Variable 10/50 Mode of Delivery Cyclic/Continuous Intermittent/Periodic Cyclic/Continuous Clinical Efficacy at 6 Months: EF 32.4±7.2 to 37.2±10.4 Not available 30.5±6.0 to 32.7±6.4 6MWD 287±66 to 346±78 317±109 to 347±123 Not available MLWHFS 40±14 to 21±10 Not available 44.2±22.2 to 35.8±20.8 SDNN 94±26 to 111±50 Not available 146±48 to 130±52 Values reported as mean ± standard deviation; CVN = Cervical vagus nerve. *p&lt;0.05 versus NECTAR-HF; **p&lt;0.05 versus INOVATE-HF; ***p&lt;0.025 versus NECTAR-HF; ****p&lt;0.001 versus NECTAR-HF (Analysis using two-sample t-test of the means). Conclusion VNS differed in ANTHEM-HF when compared to INOVATE-HF and NECTAR-HF. The neural targets, pulse frequencies for titration, and the DC for NM were different. VNS in ANTHEM-HF was clinically efficacious. The ongoing ANTHEM-HFrEF Pivotal Study uses a similar paradigm. Acknowledgement/Funding LivaNova PLC

Heart Rate Dynamics in Patients with Obstructive Sleep Apnea: Heart Rate Variability and Entropy

Background: Obstructive sleep apnea (OSA), a highly prevalent sleep disorder, is closely related to cardiovascular disease (CVD). Our previous work demonstrated that Shannon entropy of the degree distribution (EDD), obtained from the network domain of heart rate variability (HRV), might be a potential indicator for CVD. Method: To investigate the potential association between OSA and EDD, OSA patients and healthy controls (HCs) were identified from a sleep study database. Then EDD was calculated from electrocardiogram (ECG) signals during sleep, followed by cross-sectional comparisons between OSA patients and HCs, and longitudinal comparisons from baseline to follow-up visits. Furthermore, for OSA patients, the association between EDD and OSA severity, measured by apnea-hypopnea index (AHI), was also analyzed. Results: Compared with HCs, OSA patients had significantly increased EDD during sleep. A positive correlation between EDD and the severity of OSA was also observed. Although the value of EDD became larger with aging, it was not OSA-specified. Conclusion: Increased EDD derived from ECG signals during sleep might be a potential dynamic biomarker to identify OSA patients from HCs, which may be used in screening OSA with high risk before polysomnography is considered.

Increased markers of cardiac vagal activity in leucine-rich repeat kinase 2-associated Parkinson's disease.

Cardiac autonomic dysfunction manifests as reduced heart rate variability (HRV) in idiopathic Parkinson's disease (PD), but no significant reduction has been found in PD patients who carry the LRRK2 mutation. Novel HRV features have not been investigated in these individuals. We aimed to assess cardiac autonomic modulation through standard and novel approaches to HRV analysis in individuals who carry the LRRK2 G2019S mutation. Short-term electrocardiograms were recorded in 14 LRRK2-associated PD patients, 25 LRRK2-non-manifesting carriers, 32 related non-carriers, 20 idiopathic PD patients, and 27 healthy controls. HRV measures were compared using regression modeling, controlling for age, sex, mean heart rate, and disease duration. Discriminant analysis highlighted the feature combination that best distinguished LRRK2-associated PD from controls. Beat-to-beat and global HRV measures were significantly increased in LRRK2-associated PD patients compared with controls (e.g., deceleration capacity of heart rate: p = 0.006) and idiopathic PD patients (e.g., 8th standardized moment of the interbeat interval distribution: p = 0.0003), respectively. LRRK2-associated PD patients also showed significantly increased irregularity of heart rate dynamics, as quantified by Rényi entropy, when compared with controls (p = 0.002) and idiopathic PD patients (p = 0.0004). Ordinal pattern statistics permitted the identification of LRRK2-associated PD individuals with 93% sensitivity and 93% specificity. Consistent results were found in a subgroup of LRRK2-non-manifesting carriers when compared with controls. Increased beat-to-beat HRV in LRRK2 G2019S mutation carriers compared with controls and idiopathic PD patients may indicate augmented cardiac autonomic cholinergic activity, suggesting early impairment of central vagal feedback loops in LRRK2-associated PD.

Identification and comparison of heart-rate dynamics during cycle ergometer and treadmill exercise.

Aim and methodsThe aim of this study was to compare the dynamics of heart rate (HR) response to exercise using a cycle ergometer (CE) and a treadmill (TM). Using a sample of 25 healthy male participants, the time constant of HR dynamics was estimated for both modalities in response to square-wave excitation.ResultsThe principal finding was that the time constant of heart-rate dynamics around somewhat-hard exercise intensity (Borg rating of perceived exertion = 13) does not differ significantly between the CE and TM (68.7 s ± 21.5 s vs. 62.5 s ± 18.5 s [mean ± standard deviation]; CE vs. TM; p = 0.20). An observed moderate level of evidence that root-mean-square model error was higher for the CE than for the TM (2.5 bpm ± 0.5 bpm vs. 2.2 bpm ± 0.5 bpm, p = 0.059) may reflect a decrease in heart rate variability with increasing HR intensity because, in order to achieve similar levels of perceived intensity, mean heart rate for the CE was ∼25 bpm lower than for the TM.Conclusion and significanceThese results have important implications for model-based design of automatic HR controllers, because, in principle, the same dynamic controller, merely scaled according to the differing steady-state gains, should be able to be applied to the CE and TM exercise modalities.

Failure to de-arouse during sleep-onset transitions in the heart rates of individuals with sleep-onset insomnia

ObjectiveIncreased cardiovascular risk associated with sleep-onset insomnia has been reported, but the patterns of heart rate (HR) transitions during sleep onset in individuals with sleep-onset insomnia remain uncertain. This study explored the HR dynamics during objective and subjective sleep onset transitions among sleep-onset insomnia. MethodsSeventeen good sleepers and 17 individuals with sleep-onset insomnia had their night-time HR measured. HR and heart rate variability (HRV) were analyzed within 8-min periods of pre- and post-transition of stage N1, stage N2 and subjective sleep onset. ResultsA significantly higher low-frequency percentage of HRV was observed in pre-N1 period among insomnia group, compared with good sleepers. Decline in HR begins in 160 s prior to N1 onset among good sleepers, whereas the HRs of insomnia group were reduced only after N1 onset in comparison to their HRs at the time of N1 onset. The good sleepers and insomnia group both had their HRs dropped to a level comparable to their HRs at respective stage N2 onset at 220 s and 80 s prior to N2 onset. No differences in HR was found during subjective sleep onset transition in both groups. ConclusionDuring the wake-to-sleep transition, a low and stable HR was observed before cortical alternations in good sleepers; however, a consistently high HR until N1 onset was shown among sleep-onset insomnia. This finding suggests a state-dependent and failure to de-arouse from the high arousal level of wakefulness into light sleep is associated with sleep initiation difficulty.

Impact of Oxidative Stress on Long-Term Heart Rate Variability: Linear Versus Non-Linear Heart Rate Dynamics

Heart rate variability (HRV) is a widely used non-invasive and quantitative marker of cardiac autonomic control. Elevated oxidative stress (OS) and reduced HRV have been proven in specific disease subsets. However, the impact of OS on the long-term heart rate dynamics of both conventional linear and non-linear origin in the general population is not known. The 24-hour ambulatory electrocardiogram recordings and plasma 8-iso-prostaglandin F2α (8-iso-PGF2α) levels as an OS marker were acquired simultaneously in 71 consecutive patients. The conventional time and frequency domain HRV parameters and non-linear parameters were measured. The 8-iso-PGF2α is a significant determinant of most long-term conventional time and frequency domain HRV parameters and standard deviation (SD1, perpendicular to the line of identity; SD2, along the line of identity) descriptors from Poincaré plot analysis, but not of non-linear complexity and fractal parameters. Patients with a high OS burden had lower absolute low-frequency and high-frequency powers during both the night and morning periods, with a significant decrease in high-frequency power in the morning. Oxidative stress is one of the significant determinants of the HRV. The severity of OS is reflected in the conventional time and frequency domain HRV parameters, but not in the non-linear measurements.

Effects of Acute Normobaric Hypoxia on Non-linear Dynamics of Cardiac Autonomic Activity During Constant Workload Cycling Exercise.

AimMeasurements of Non-linear dynamics of heart rate variability (HRV) provide new possibilities to monitor cardiac autonomic activity during exercise under different environmental conditions. Using detrended fluctuation analysis (DFA) technique to assess correlation properties of heart rate (HR) dynamics, the present study examines the influence of normobaric hypoxic conditions (HC) in comparison to normoxic conditions (NC) during a constant workload exercise.Materials and MethodsNine well trained cyclists performed a continuous workload exercise on a cycle ergometer with an intensity corresponding to the individual anaerobic threshold until voluntary exhaustion under both NC and HC (15% O2). The individual exercise duration was normalized to 10% sections (10–100%). During exercise HR and RR-intervals were continuously-recorded. Besides HRV time-domain measurements (meanRR, SDNN), fractal correlation properties using short-term scaling exponent alpha1 of DFA were calculated. Additionally, blood lactate (La), oxygen saturation of the blood (SpO2), and rating of perceived exertion (RPE) were recorded in regular time intervals.ResultsWe observed significant changes under NC and HC for all parameters from the beginning to the end of the exercise (10% vs. 100%) except for SpO2 and SDNN during NC: increases for HR, La, and RPE in both conditions; decreases for SpO2 and SDNN during HC, meanRR and DFA-alpha1 during both conditions. Under HC HR (40–70%), La (10–90%), and RPE (50–90%) were significantly-higher, SpO2 (10–100%), meanRR (40–70%), and DFA-alpha1 (20–60%) were significantly-lower than under NC.ConclusionUnder both conditions, prolonged exercise until voluntary exhaustion provokes a lower total variability combined with a reduction in the amplitude and correlation properties of RR fluctuations which may be attributed to increased organismic demands. Additionally, HC provoked higher demands and loss of correlation properties at an earlier stage during the exercise regime, implying an accelerated alteration of cardiac autonomic regulation.

Vagus Nerve Stimulation for Chronic Heart Failure: Differences in Therapy Delivery and Clinical Efficacy in ANTHEM-HF, INOVATE-HF, and NECTAR-HF

Background Vagus Nerve Stimulation (VNS) is meant to deliver Autonomic Regulation Therapy (ART) to neurological targets with sufficient neuromodulation (NM) to ameliorate chronic heart failure (CHF). VNS delivery consists of its intensity (a combination of pulse amplitude, pulse frequency, and pulse duration), polarity, duty cycle (DC; stimulation “on” time and “off” time), and mode (continuous, or intermittent and periodic). In the ANTHEM-HF Pilot Study patients with CHF and reduced ejection fraction (HFrEF), VNS intensity was up-titrated until a change in heart rate (HR) dynamics was objectively confirmed. This did not require any change in GDMT and was associated with significant improvements in LVEF, 6-minute walk distance (6MWD), Minnesota Living with HF (MLWHF) score, and HR variability. Methods Qualitative and quantitative analyses used data from peer-reviewed publications and other sources in the public domain to compare VNS delivery in ANTHEM-HF, INOVATE-HF, and NECTAR-HF. Results (Table): Up-titration of VNS intensity was attempted in all 3 studies. In contrast to ANTHEM-HF, INOVATE-HF aimed only at peripheral neural targets. VNS intensity was delivered at a lower pulse frequency, and had a variable DC as a consequence of R-wave synchronization and only intermittent, periodic stimulation. In NECTAR-HF VNS intensity was delivered at a higher pulse frequency, and this was associated with intolerable adverse off-target effects which restricted VNS up-titration. Significant improvements in EF, 6MWD, MLWHF, and SDNN occurred in ANTHEM-HF relative to the other studies. Conclusion VNS differed in ANTHEM-HF when compared to INOVATE-HF and NECTAR-HF. The neural targets, pulse frequencies for titration, and the DC for NM were different. VNS in ANTHEM-HF was clinically efficacious. The ongoing ANTHEM-HFrEF Pivotal Study uses a similar paradigm.

Multiscale entropy profiling to estimate complexity of heart rate dynamics.

In the analysis of signal regularity from a physiological system such as the human heart, Approximate entropy (H_{A}) and Sample entropy (H_{S}) have been the most popular statistical tools used so far. While studying heart rate dynamics, it nevertheless becomes more important to extract information about complexities associated with the heart, rather than the regularity of signal patterns produced by it. A complex physiological system does not necessarily produce irregular signals and vice versa. In order to equip a regularity statistic to see through the respective system's level of complexity, the idea of multiscaling was introduced in H_{S} estimation. Multiscaling ideally requires an input signal to be (a) long and (b) stationary. However, the longer the data is the less stationary it is. The requirement multiscaling places on its data length largely limits its accuracy. We propose a novel method of entropy profiling that makes multiscaling require very short signal segments, granting better prospects of signal stationarity and estimation accuracy. With entropy profiling, an efficient multiscale H_{S} based analysis requires only 500-beat signals of atrial fibrillated data, as opposed to the earlier case that required at least 20 000 beats.