Mapping Early Brain-Body Interactions: Associations of Fetal Heart Rate Variation with Newborn Brainstem, Hypothalamic, and Dorsal Anterior Cingulate Cortex Functional Connectivity.

The autonomic nervous system (ANS) regulates the body's physiology, including cardiovascular function. As the ANS develops during the second to third trimester, fetal heart rate variability (HRV) increases while fetal heart rate (HR) decreases. In this way, fetal HR and HRV provide an index of fetal ANS development and future neurobehavioral regulation. Fetal HR and HRV have been associated with child language ability and psychomotor development behavior in toddlerhood. However, their associations with postbirth autonomic brain systems, such as the brainstem, hypothalamus, and dorsal anterior cingulate cortex (dACC), have yet to be investigated even though brain pathways involved in autonomic regulation are well established in older individuals. We assessed whether fetal HR and HRV were associated with the brainstem, hypothalamic, and dACC functional connectivity in newborns. Data were obtained from 60 pregnant individuals (ages 14-42) at 24-27 and 34-37 weeks of gestation using a fetal actocardiograph to generate fetal HR and HRV. During natural sleep, their infants (38 males and 22 females) underwent a fMRI scan between 40 and 46 weeks of postmenstrual age. Our findings relate fetal heart indices to brainstem, hypothalamic, and dACC connectivity and reveal connections with widespread brain regions that may support behavioral and emotional regulation. We demonstrated the basic physiologic association between fetal HR indices and lower- and higher-order brain regions involved in regulatory processes. This work provides the foundation for future behavioral or physiological regulation research in fetuses and infants.

A Putative Apoplastic Effector of Clavibacter capsici, ChpGCc as Hypersensitive Response and Virulence (Hrv) Protein in Plants.

Clavibacter bacteria use secreted apoplastic effectors, such as putative serine proteases, for virulence in host plants and for hypersensitive response (HR) induction in nonhost plants. Previously, we have shown that Clavibacter capsici ChpGCc is important for the necrosis development in pepper (Capsicum annuum) leaves. Here, we determine the function of ChpGCc, along with three paralogous proteins, for HR induction in the apoplastic space of a nonhost plant, Nicotiana tabacum. The full-length and signal peptide-deleted (ΔSP) mature forms of all proteins fused with the tobacco PR1b signal sequence were generated. The full-length and ΔSP forms of ChpGCc and only the ΔSP forms of ChpECc and Pat-1Cc, but none of the ChpCCc, triggered HR. Based on the predicted protein structures, ChpGCc carries amino acids for a catalytic triad and a disulfide bridge in positions like Pat-1Cm. Substituting these amino acids of ChpGCc with alanine abolished or reduced HR-inducing activity. To determine whether these residues are important for necrosis development in pepper, alanine-substituted chpGCc genes were transformed into the C. capsici PF008ΔpCM1 strain, which lacks the intact chpGCc gene. The strain with any variants failed to restore the necrosis-causing ability. These results suggest that ChpGCc has a dual function as a virulence factor in host plants and an HR elicitor in nonhost plants. Based on our findings and previous results, we propose Clavibacter apoplastic effectors, such as ChpGCc, Pat-1Cm, Chp-7Cs, and ChpGCm, as hypersensitive response and virulence (Hrv) proteins that display phenotypic similarities to the hypersensitive response and pathogenicity (Hrp) proteins found in gram-negative bacteria. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The impact of virtual reality scenes on stress response characteristics of individuals with different personality traits.

Virtual reality based physical stress (VRPS) paradigms could eliminate the influence of social factors on participants, and it may be a desirable tool to explore the impact of personality traits on stress levels. In this study, we attempt to explore the effects of VRPS on stress response among individuals with different personality traits. Forty male participants with an average age of 22.79 ± 0.41 years were divided into two groups based on Harm Avoidance (HA) scores of Tridimensional Personality Questionnaire (TPQ), referred to as the Low-HA group and the High-HA group. The stress levels of the participants were assessed using salivary α-amylase (sAA) activity and heart rate variability (HRV) indices pre- and post-stress. The influence of personality traits on stress response among different groups was analyzed. VRPS significantly affected the sAA activity and HRV indicators of both groups. During and after stress, there were significant differences in sAA activity and HRV indicators between the two groups. The sAA levels and HRV indices of the Low-HA group were lower than those of the High-HA group. Furthermore, sAA levels and HRV indices were correlated with the scores of TPQ. VRPS scenarios elicit different stress responses on individuals with different harm avoidance personality traits. Stress evaluation based on VR scenarios presents potential in personality trait assessments, particularly for distinguishing between individuals with low and high HA tendencies.

Exploring the efficacy of sense of Okayness (SOK) as an antidote for stress in older adults: the role of SOK elevation intervention, heart rate variability (HRV), and cognitive performance in stressful and relaxing situations.

Sense of Okayness (SOK) is an emerging concept that describes a person's ability to remain stable and unshaken in the face of life transitions and hardships. This quality enables effective stress regulation and heightened tolerance to uncertainty. To investigate the possible role of the parasympathetic nervous system (PNS) in mediating the relationship between SOK and stress regulation among older individuals, an analytical sample of N = 69 participants (74% women) with a mean age of 78.75 years (SD age = 6.78) was recruited for a standardized cognitive assessment and stress induction. Baseline heart rate variability (HRV), measured via electrocardiogram (ECG), and SOK assessments were conducted prior to stress induction, along with a baseline cognitive evaluation. Subsequently, participants were subjected to a psychosocial stress paradigm, followed by either a 30-minute SOK elevation intervention (n = 40) or a control condition with nature sounds (n = 29). A second cognitive assessment was administered post-intervention, with continuous HRV measurement through ECG. The results revealed significant HRV changes due to the experimental intervention, though no significant differences were observed between the SOK intervention and control groups. Interestingly, individuals with high trait SOK displayed more stable HRV trajectories, exhibiting a smaller decline during the stress intervention and a milder increase during both the stressor and SOK intervention phases. Overall, these findings do suggest a significant association between SOK, parasympathetic activity, and stress reactivity. These results prompt further investigation into whether personality patterns, such as a strong SOK, may be linked to reduced vagal reactivity and better coping in old age.

Empathic stress is decreased by prior stressor experience and increased in a position of power.

The observation of a stressed individual can trigger a stress response in a passive observer. Little is known about the mechanisms of this so-termed empathic stress, including the observer's empathic involvement with the stressful situation. In 108 opposite-sex stranger dyads, we expected to increase the observer's empathic involvement with a stressed target performing a standardized laboratory stressor (Trier Social Stress Test, TSST; Kirschbaum et al., 1993) by exposing observers themselves to the TSST one week earlier. Conversely, we intended to decrease empathic involvement by granting observers a powerful position over the targets (by asking them to evaluate the targets' TSST performance and allegedly decide on their financial compensation). A control group without any manipulation was also included. In the preregistered data analysis, two types of empathic stress were investigated: vicarious stress, which evolves irrespective of the target's stress response, and stress resonance, which is proportional to the target's stress response. Irrespective of manipulation, observers exhibited vicarious stress in subjective and high-frequency heart rate variability (HF-HRV), and synchronized with the targets' stress reactivity in cortisol release. Prior TSST experience unexpectedly decreased observers' self-reported empathy and vicarious cortisol stress reactivity. The power manipulation, conversely, led to stronger observer vicarious stress in overall heart rate and HF-HRV reactivity. Based on Wondra and Ellsworth's (2015) appraisal theory, we propose that, due to their prior stressor exposure, observers habituated to said stressor, and consequently changed their evaluation of the target's stressful situation. In contrast, observers in the powerful position may have felt responsible for the targets, triggering a stronger vicarious stressful experience.

Single-step purification and characterization of Pseudomonas aeruginosa azurin.

Azurin is a small periplasmic blue copper protein found in bacterial strains such as Pseudomonas and Alcaligenes where it facilitates denitrification. Azurin is extensively studied for its ability to mediate electron-transfer processes, but it has also sparked interest of the pharmaceutical community as a potential antimicrobial or anticancer agent. Here we offer a novel approach for expression and single-step purification of azurin in Escherichia coli with high yields and optimal metalation. A fusion tag strategy using an N-terminal GST tag was employed to obtain pure protein without requiring any additional purification steps. After the on-column cleavage by HRV 3C Protease, azurin is collected and additionally incubated with copper sulphate to ensure sufficient metalation. UV-VIS absorption, mass spectroscopy, and circular dichroism analysis all validated the effective production of azurin, appropriate protein folding and the development of an active site with an associated cofactor. MD simulations verified that incorporation of the N-terminal GPLGS segment does not affect azurin structure. In addition, the biological activity of azurin was tested in HeLa cells.

Association between obstructive sleep apnea and arrhythmia and heart rate variability among hypertensive patients.

BACKGROUND: The relationship between obstructive sleep apnea (OSA) and the occurrence of arrhythmias and heart rate variability (HRV) in hypertensive patients is not elucidated. Our study investigates the association between OSA, arrhythmias, and HRV in hypertensive patients. METHODS: We conducted a cross-sectional analysis involving hypertensive patients divided based on their apnea-hypopnea index (AHI) into two groups: the AHI ≤ 15 and the AHI > 15. All participants underwent polysomnography (PSG), 24-hour dynamic electrocardiography (DCG), cardiac Doppler ultrasound, and other relevant evaluations. RESULTS: The AHI > 15 group showed a significantly higher prevalence of frequent atrial premature beats and atrial tachycardia (P = 0.030 and P = 0.035, respectively) than the AHI ≤ 15 group. Time-domain analysis indicated that the standard deviation of normal-to-normal R-R intervals (SDNN) and the standard deviation of every 5-minute normal-to-normal R-R intervals (SDANN) were significantly higher in the AHI > 15 group (P = 0.020 and P = 0.033, respectively). Frequency domain analysis revealed that the low-frequency (LF), high-frequency (HF) components, and the LF/HF ratio were also significantly elevated in the AHI > 15 group (P < 0.001, P = 0.031, and P = 0.028, respectively). Furthermore, left atrial diameter (LAD) was significantly larger in the AHI > 15 group (P < 0.001). Both univariate and multivariable linear regression analyses confirmed a significant association between PSG-derived independent variables and the dependent HRV parameters SDNN, LF, and LF/HF ratio (F = 8.929, P < 0.001; F = 14.832, P < 0.001; F = 5.917, P = 0.016, respectively). CONCLUSIONS: Hypertensive patients with AHI > 15 are at an increased risk for atrial arrhythmias and left atrial dilation, with HRV significantly correlating with OSA severity.

Comprehensive linear and nonlinear heart rate variability normative data in children.

BACKGROUND: The autonomic nervous system (ANS) is critical in regulating involuntary bodily functions, including heart rate. Heart rate variability (HRV) reflects the complex interplay between the ANS and humoral factors, making it a valuable noninvasive tool for assessing autonomic function. While HRV has been extensively studied in adults, normative data for HRV in children, primarily based on long-term rhythm recordings, are limited. OBJECTIVE: This study aimed to establish comprehensive normative data for HRV in children. METHODS: In this retrospective study, we examined 24-h Holter monitors of children aged 1 day to 18 years, divided into six age groups, at Nemours Children's Health in Orlando, Florida, spanning the years 2013-2023. HRV analysis encompassed time-domain, frequency-domain, and nonlinear indices. RESULTS: Holter data for a total of 247 patients in six age groups were included. An age-related uptrend was observed in all time- and frequency-domain variables except the normalized unit of low-frequency power. Entropy analysis revealed contradictory results among different entropy techniques. Sample and approximate entropy analyses were consistent and showed less complexity and more predictability of HRV with decreasing heart rate, while Shannon entropy analysis showed the opposite. Fractal detrended fluctuation analysis exhibited significant decreases across the age groups, suggestive of diminishing self-similarity of HRV patterns. CONCLUSION: Control of heart rate and HRV is a highly complex process and requires further study for a better understanding. It seems that no single parameter can fully elucidate the entire process. A combination of time-domain, frequency-domain, and nonlinear indices may be necessary to explain HRV behavior in the growing body.

Intra- and Inter-Rater Reliability of Linear and Nonlinear Measures of Short-Term Heart Rate Variability Following Combat-Related Traumatic Injury.

BACKGROUND: Heart rate variability (HRV) is a marker of autonomic function. However, the reliability of short-term HRV measurement in individuals with combat-related traumatic injury (CRTI) remains undetermined. METHODS: An intra- and inter-rater reliability study was conducted using a subsample (n = 35) of British servicemen with CRTI enrolled in the ongoing ADVANCE study. A five-minute epoch of single-lead electrocardiogram data collected during spontaneous breathing was used to measure HRV. HRV analyses were independently performed by two examiners using Kubios. Intraclass correlation coefficient (ICC), standard error of measurement (SEM), minimum detectable change (MDC), and coefficient of variance were calculated for linear [root mean square of successive difference (RMSSD), standard deviation of NN interval, low-frequency, high-frequency, total power] and nonlinear (SD1-2, acceleration and deceleration capacities, sample entropy) measures. Bland-Altman %plots were used to assess bias in intra- and inter-rater HRV data. RESULTS: The mean age of participants was 39.3 ± 6.3 years. An excellent ICC score of 0.9998 (95% CI 0.9997, 0.9999) was observed for intra-rater analyses of RMSSD, and similar excellent ICC scores were seen for all other HRV measures. The inter-rater reliability analyses produced an excellent ICC score (range 0.97-1.00). Comparatively, frequency-domain measures produced higher MDC% and SEM% scores than time-domain and nonlinear measures in both inter- and intra-rater analyses. The Bland-Altman plots revealed relatively higher bias for frequency-domain and nonlinear measures than time-domain measures. CONCLUSION: ECG-related short-term HRV measures were reliable in injured servicemen under spontaneous breathing. However, the reliability appeared better with the time-domain measure than frequency-domain and nonlinear measures in this sample.

Effects of 3-month Qigong exercise on heart rate variability and respiration in anxious college students.

OBJECTIVE: This longitudinal study aimed to investigate the effects of Qigong on the anxiety state, heart rate variability (HRV), and breathing of anxious college students. METHODS: A total of 37 individuals (18-25 years old) were randomly allocated to the control (n = 19) and intervention (n = 18) groups. Qigong interventions were conducted five times weekly for 12 weeks, with each session lasting 60 min. Hamilton Anxiety Scale, Fatigue Scale 14, Pittsburgh Sleep Quality Index, and 36-item Short Form Survey, HRV, and respiration data were collected before and after the 3-month intervention. RESULTS: Individuals who participated in the three-month Qigong exercise intervention showed a significant reduction in anxiety, particularly mental anxiety (p < 0.05). Subjects in the intervention group presented a decrease in skin temperature (p < 0.05) and an increase in blood volume pulsation (p < 0.05). Meanwhile, HRV exhibited a significant increase in the standard deviation of interbeat interval before and after comparisons (p < 0.05) and between the two groups (p = 0.039) and a reduction in the normalized low-frequency power after the intervention. Moreover, the intervention group experienced increased abdominal breathing depth and abdominal breathing per minute (p < 0.05). CONCLUSION: These findings indicate that Qigong is an effective mind-body exercise strategy for relieving anxiety. HRV and breathing were improved accordingly among college students after the completion of the 3-month Qigong program.

Negative mood induction in children: An examination across mood, physiological, and cognitive variables.

Experimental mood induction procedures are commonly used in studies of children's emotions, although research on their effectiveness is lacking. Studies that support their effectiveness report sample-level changes in self-reported affect from pre- to post-induction, and a subset of children who do not self-report expected changes in affect (i.e., "nonresponders"). Given children's limited abilities to self-report their emotions, it is critical to know whether these paradigms also shift physiological and social-cognitive indices of emotion. We hypothesized increases in physiological reactivity and accuracy for discerning facial expressions of negative emotions from pre- to post-induction and smaller increases for nonresponders, Children (N = 80; 7- to 12-year-olds) completed a facial emotion recognition task and had an electrocardiogram recorded to index high-frequency heart rate variability (HF-HRV) before and after a mood induction procedure. The mood induction involved watching a 3-min sad film clip while attending to their feelings. In the sample overall, from pre- to post-mood induction, children self-reported significantly sadder affect, displayed significant increases in HF-HRV, and displayed significant increases in accuracy of recognizing facial emotion expressions congruent with the mood induced. One quarter (25%) of the sample did not self-report expected increases in sad affect. Contrary to expectations, responders and nonresponders did not differ in mood-induced changes in physiological reactivity or emotion recognition accuracy. These findings support that mood inductions are efficacious in shifting not only children's self-reported affect but also underlying physiological and social-cognitive processes. Furthermore, they are an effective methodology for research questions related to underlying processes even in self-reported nonresponders.

Impact of supra-maximal interval training vs. high-intensity interval training on cardiac auto-regulation response in physically active adults.

PURPOSE: This study aimed to examine the impact of supra-maximal interval training (SMIT) and high-intensity interval training (HIIT) on cardiac auto-regulation response. METHODS: Physically active young adults volunteered to participate in the study with a randomized cross-over counterbalanced design (N = 12). HIIT sessions consisted of 20 bouts of 10 s of exercise followed by 50 s of recovery, totaling 20 min at two different intensities; "all-out (SMIT)" vs. "115-130% Wmax (HIIT)". The cardiac auto-regulation included heart rate variability (HRV) and vascular function. HRV and vascular function were measured at baseline and five different time points after acute exercise. RESULTS: The SMIT was higher in workload (31%), peak heart rate (28%), and rate of perceived exertion (40%) compared with HIIT (all p < 0.001). The R-R interval, NN50, and pNN50 measured until 60 min after acute exercise was higher in the HIIT compared with SMIT (all p < 0.05). The SMIT elicited a greater shift in ln LF/HF ratio immediately after acute exercise (3802%, p < 0.01) and induced a decrease in bilateral ba-PWV at the time point 5 min after acute exercise, persisting until 65 min after (p < 0.05). Yet, HIIT showed no change over time in the frequency domain of HRV and blood vascular tone after cessation of acute exercise. CONCLUSION: Our findings confirmed that SMIT is a more potent modulator of the autonomic nervous system compared with HIIT. Further study is needed to monitor through complete recovery to baseline, to understand acute cardiac auto-regulation response after cessation of various exercise intensities identical interval training protocol.

Predicting daily recovery during long-term endurance training using machine learning analysis.

PURPOSE: The aim of this study was to determine if machine learning models could predict the perceived morning recovery status (AM PRS) and daily change in heart rate variability (HRV change) of endurance athletes based on training, dietary intake, sleep, HRV, and subjective well-being measures. METHODS: Self-selected nutrition intake, exercise training, sleep habits, HRV, and subjective well-being of 43 endurance athletes ranging from professional to recreationally trained were monitored daily for 12 weeks (3572 days of tracking). Global and individualized models were constructed using machine learning techniques, with the single best algorithm chosen for each model. The model performance was compared with a baseline intercept-only model. RESULTS: Prediction error (root mean square error [RMSE]) was lower than baseline for the group models (11.8 vs. 14.1 and 0.22 vs. 0.29 for AM PRS and HRV change, respectively). At the individual level, prediction accuracy outperformed the baseline model but varied greatly across participants (RMSE range 5.5-23.6 and 0.05-0.44 for AM PRS and HRV change, respectively). CONCLUSION: At the group level, daily recovery measures can be predicted based on commonly measured variables, with a small subset of variables providing most of the predictive power. However, at the individual level, the key variables may vary, and additional data may be needed to improve the prediction accuracy.

Orthostatic testing for heart rate and heart rate variability monitoring in exercise science and practice.

Orthostatic testing, involving the transition from different body positions (e.g., from lying or sitting position to an upright or standing position), offers valuable insights into the autonomic nervous system (ANS) functioning and cardiovascular regulation reflected through complex adjustments in, e.g., measures of heart rate (HR) and heart rate variability (HRV). This narrative review explores the intricate physiological mechanisms underlying orthostatic stress responses and evaluates its significance for exercise science and sports practice. Into this matter, active orthostatic testing (e.g., active standing up) challenges the cardiovascular autonomic function in a different way than a passive tilt test. It is well documented that there is a transient reduction in blood pressure while standing up, leading to a reflex increase in HR and peripheral vasoconstriction. After that acute response systolic and diastolic blood pressures are usually slightly increased compared to supine lying body position. The ANS response to standing is initiated by instantaneous cardiac vagal withdrawal, followed by sympathetic activation and vagal reactivation over the first 25-30 heartbeats. Thus, HR increases immediately upon standing, peaking after 15-20 beats, and is less marked during passive tilting due to the lack of muscular activity. Standing also decreases vagally related HRV indices compared to the supine position. In overtrained endurance athletes, both parasympathetic and sympathetic activity are attenuated in supine and standing positions. Their response to standing is lower than in non-overtrained athletes, with a tendency for further decreased HRV as a sign of pronounced vagal withdrawal and, in some cases, decreased sympathetic excitability, indicating a potential overtraining state. However, as a significant main characteristic, it could be noted that additional pathophysiological conditions consist in a reduced responsiveness or counter-regulation of neural drive in ANS according to an excitatory stimulus, such as an orthostatic challenge. Hence, especially active orthostatic testing could provide additional information about HR(V) reactivity and recovery giving valuable insights into athletes' training status, fatigue levels, and adaptability to workload. Measuring while standing might also counteract the issue of parasympathetic saturation as a common phenomenon especially in well-trained endurance athletes. Data interpretation should be made within intra-individual data history in trend analysis accounting for inter-individual variations in acute responses during testing due to life and physical training stressors. Therefore, additional measures (e.g., psychometrical scales) are required to provide context for HR and HRV analysis interpretation. However, incidence of orthostatic intolerance should be evaluated on an individual level and must be taken into account when considering to implement orthostatic testing in specific subpopulations. Recommendations for standardized testing procedures and interpretation guidelines are developed with the overall aim of enhancing training and recovery strategies. Despite promising study findings in the above-mentioned applied fields, further research, thorough method comparison studies, and systematic reviews are needed to assess the overall perspective of orthostatic testing for training monitoring and fine-tuning of different populations in exercise science and training.

Reliability of recovery heart rate variability measurements as part of the Lamberts Submaximal Cycle Test and the relationship with training status in trained to elite cyclists.

PURPOSE: To determine if post-exercise heart rate variability, in the form of logged transformed root mean square of successive differences of the R-R intervals (LnRMSSD) can be measured reliably during the recovery from a submaximal cycle test and what the relationship of LnRMSSD is with training status of the cyclists. METHODS: Fourteen male cyclists participated in the reliability part for the study, which included performing six Lamberts Submaximal Cycle Test (LSCT), during which recovery LnRMSSD was measured over 30 s (LnRMSSD30 s), 60 s LnRMSSD60 s)and 90 s LnRMSSD90 s). In addition, fifty male and twenty female cyclists completed a peak power output (PPO) test (including VO2peak) and 40 km time trial (40 km TT) before which they performed the LSCT as a standardized warm-up. Relationships between the LnRMSSD and PPO, VO2peak and 40 km TT time were studied. RESULTS: Due to the design of the LSCT, submaximal heart and breathing rate were similar at the end of stage 3 of the LSCT, as well as during the recovery periods. The highest reliability was found in LnRMSSD60 s (ICC: 0.97) with a typical error of the measurement (TEM: 5.8%). In line with this the strongest correlations were found between LnRMSSD60 s and PPO (r = 0.93[male]; 0.85[female]), VO2peak (r = 0.71[male]; 0.63[female];) and 40 km TT (r = - 0.83[male]; - 0.63[female]). CONCLUSIONS: LnRMSSD60 s can be measured reliably after the LSCT and can predict PPO, VO2peak and 40 km TT performance well in trained-to-elite cyclists. These findings suggest that recovery LnRMSSD can potentially play an important role in monitoring and fine-tuning training prescriptions in trained-to-elite cyclists.

An in-depth analysis of the polyvagal theory in light of current findings in neuroscience and clinical research.

The polyvagal theory has led to the understanding of the functions of the autonomic nervous system in biological development in humans, since the vagal system, a key structure within the polyvagal theory, plays a significant role in addressing challenges of the mother-child dyad. This article aims to summarize the neurobiological aspects of the polyvagal theory, highlighting some of its strengths and limitations through the lens of new evidence emerging in several research fields-including comparative anatomy, embryology, epigenetics, psychology, and neuroscience-in the 25 years since the theory's inception. Rereading and incorporating the polyvagal idea in light of modern scientific findings helps to interpret the role of the vagus nerve through the temporal dimension (beginning with intrauterine life) and spatial dimension (due to the numerous connections of the vagus with various structures and systems) in the achievement and maintenance of biopsychosocial well-being, from the uterus to adulthood.

Exercise intensity measurement using fractal analysis of heart rate variability: Reliability, agreement and influence of sex and cardiorespiratory fitness.

The study aimed to establish the test-retest reliability of detrended fluctuation analysis of heart rate variability (DFA-α1) based exercise intensity thresholds, assess its agreement with ventilatory- and lactate-derived thresholds and the moderating effect of sex and cardiorespiratory fitness (CRF) on the agreement. Intensity thresholds for thirty-seven participants (17 females) based on blood lactate (LT1/LT2), gas-exchange (VT1/VT2) and DFA-α1 (αTh1/αTh2) were assessed. Heart rate (HR) at αTh1 and αTh2 showed good test-retest reliability (coefficient of variation [CV] < 6%), and moderate to high agreement with LTs (r = 0.40 - 0.57) and VTs (r = 0.61 - 0.66) respectively. Mixed effects models indicated bias magnitude depended on CRF, with DFA-α1 overestimating thresholds versus VTs for lower fitness levels (speed at VT1 <8.5 km⋅hr-1), while underestimating for higher fitness levels (speed at VT2 >15 km⋅hr-1; VO2max >55 mL·kg-1·min-1). Controlling for CRF, sex significantly affected bias magnitude only at first threshold, with males having higher mean bias (+2.41 bpm) than females (-1.26 bpm). DFA-α1 thresholds are practical and reliable intensity measures, however it is unclear if they accurately represent LTs/VTs from the observed limits of agreement and unexplained variance. To optimise DFA-α1 threshold estimation across different populations, bias should be corrected based on sex and CRF.

Heart Rate Variability Monitoring Based on Doppler Radar Using Deep Learning.

The potential of microwave Doppler radar in non-contact vital sign detection is significant; however, prevailing radar-based heart rate (HR) and heart rate variability (HRV) monitoring technologies often necessitate data lengths surpassing 10 s, leading to increased detection latency and inaccurate HRV estimates. To address this problem, this paper introduces a novel network integrating a frequency representation module and a residual in residual module for the precise estimation and tracking of HR from concise time series, followed by HRV monitoring. The network adeptly transforms radar signals from the time domain to the frequency domain, yielding high-resolution spectrum representation within specified frequency intervals. This significantly reduces latency and improves HRV estimation accuracy by using data that are only 4 s in length. This study uses simulation data, Frequency-Modulated Continuous-Wave radar-measured data, and Continuous-Wave radar data to validate the model. Experimental results show that despite the shortened data length, the average heart rate measurement accuracy of the algorithm remains above 95% with no loss of estimation accuracy. This study contributes an efficient heart rate variability estimation algorithm to the domain of non-contact vital sign detection, offering significant practical application value.

Developing a Five-Minute Normative Database of Heart Rate Variability for Diagnosing Cardiac Autonomic Dysregulation for Patients with Major Depressive Disorder.

Heart rate variability (HRV) is related to cardiac vagal control and emotional regulation and an index for cardiac vagal control and cardiac autonomic activity. This study aimed to develop the Taiwan HRV normative database covering individuals aged 20 to 70 years and to assess its diagnosing validity in patients with major depressive disorder (MDD). A total of 311 healthy participants were in the HRV normative database and divided into five groups in 10-year age groups, and then the means and standard deviations of the HRV indices were calculated. We recruited 272 patients with MDD for cross-validation, compared their HRV indices with the normative database, and then converted them to Z-scores to explore the deviation of HRV in MDD patients from healthy groups. The results found a gradual decline in HRV indices with advancing age in the HC group, and females in the HC group exhibit higher cardiac vagal control and parasympathetic activity than males. Conversely, patients in the MDD group demonstrate lower HRV indices than those in the HC group, with their symptoms of depression and anxiety showing a negative correlation with HRV indices. The Taiwan HRV normative database has good psychometric characteristics of cross-validation.

Relationship of Cycling Power and Non-Linear Heart Rate Variability from Everyday Workout Data: Potential for Intensity Zone Estimation and Monitoring.

The short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA-a1) of heart rate variability (HRV) has been shown to be a sensitive marker for assessing global organismic demands. The wide dynamic range within the exercise intensity spectrum and the relationship to established physiologic threshold boundaries potentially allow in-field use and also open opportunities to provide real-time feedback. The present study expands the idea of using everyday workout data from the AI Endurance app to obtain the relationship between cycling power and DFA-a1. Collected data were imported between September 2021 and August 2023 with an initial pool of 3123 workouts across 21 male users. The aim of this analysis was to further apply a new method of implementing workout group data considering representative values of DFA-a1 segmentation compared to single workout data and including all data points to enhance the validity of the internal-to-external load relationship. The present data demonstrate a universal relationship between cycling power and DFA-a1 from everyday workout data that potentially allows accessible and regular tracking of intensity zone demarcation information. The analysis highlights the superior efficacy of the representative-based approach of included data in most cases. Validation data of the performance level and the up-to-date relationship are still pending.