Heart Rate Variability Variables Research Articles

Training-related Changes In Cardiac Autonomic Function Assessed Before And After Graded Exercise Testing

Aerobic training improves cardiac autonomic function, leading to increased heart rate variability (HRV) and decreased heart rate (HR) at rest. Intense exercise such as graded exercise testing (GXT) acutely increases HR and decreases HRV, which eventually return to resting levels post-exercise. Autonomic recovery after exercise may improve with training. PURPOSE: To examine the relationship between HRV and HR before and after GXT, and to assess changes resulting from 18 weeks of aerobic training. METHODS: Healthy young adults (n = 12, 7f; age 20.9 ± 0.6) completed physiological testing prior to enrollment in a marathon training course, and again after training. Testing included a 10-minute seated monitoring of HR/HRV (REST) with a Polar RS800cx watch and chest-strap, followed by GXT, and a 20-minute seated recovery period with HR/HRV monitoring. Recovery data were divided into two 10-minute segments (REC1 and REC2) for analysis. Mean HR and the following HRV measures were assessed using Kubios HRV Version 3.3: Standard deviation (SDNN), root mean square of the successive differences (RMSSD), high frequency power (HF), low frequency power (LF), low frequency to high frequency ratio (LF/HF), sample entropy (SE), and detrended fluctuation analysis α1 (DFAα1) and α2 (DFAα2). Repeated measures ANOVA was used to compare 10-minute segments (REST, REC1, and REC2) and to assess changes with training. RESULTS: All HRV measures and HR were different between segments (p ≤ 0.05), with HR lowest during REST and highest during REC1. Similarly, HRV measures reflected greatest variability during REST and lowest during REC1. Several measures of HRV, as well as HR changed with training. Heart rate decreased (p = 0.023) at REST (75.0 ± 17.3, 70.1 ± 14.2 bpm), during REC1 (106.3 ± 13.7, 100.1 ± 10.7) and REC2 (102.8 ± 11.9, 95.6 ± 10.3). With training, RMSSD increased (REST: 56.5 ± 29.3, 64.7 ± 32.4 ms; REC1: 6.8 ± 3.4, 8.5 ± 4.5; REC2: 9.4 ± 4.5, 11.1 ± 4.1; p = 0.048). Similarly, HF (p = 0.031) and DFAα1 (p = 0.017) exhibited greater variability across the three segments after training. CONCLUSIONS: Differences in cardiac autonomic function between timepoints before and after GXT were observed. Aerobic training reduced HR and increased selected HRV variables.

Heart Rate Variability Biofeedback to Treat Anxiety in Young People With Autism Spectrum Disorder: Findings From a Home-Based Pilot Study.

BackgroundPeople with autism spectrum disorder (ASD) frequently experience high levels of anxiety. Despite this, many clinical settings do not provide specialist ASD mental health services, and demand for professional support frequently outstrips supply. Across many sectors of health, investigators have explored digital health solutions to mitigate demand and extend the reach of professional practice beyond traditional clinical settings.ObjectiveThis critical appraisal and pilot feasibility study examines heart rate variability (HRV) biofeedback as an approach to help young people with ASD to manage anxiety symptoms outside of formal settings. The aim is to explore the use of portable biofeedback devices to manage anxiety, while also highlighting the risks and benefits of this approach with this population.MethodsWe assessed the feasibility of using home-based HRV biofeedback for self-management of anxiety in young people with ASD. We adopted coproduction, involving people with ASD, to facilitate development of the study design. Next, a separate pilot with 20 participants with ASD (n=16, 80% male participants and n=4, 20% female participants, aged 13-24 years; IQ>70) assessed adoption and acceptability of HRV biofeedback devices for home use over a 12-week period. Data were collected from both carers and participants through questionnaires and interviews; participants also provided single-lead electrocardiogram recordings as well as daily reports through smartphone on adoption and use of their device.ResultsPre-post participant questionnaires indicated a significant reduction in anxiety in children (t6=2.55; P=.04; Cohen d=0.99) as well as adults (t7=3.95; P=.006; Cohen d=0.54). Participant age was significantly negatively correlated with all HRV variables at baseline, namely high-frequency heart rate variability (HF-HRV: P=.02), the root mean square of successive differences in normal heartbeat contractions (RMSSD: P=.02) and the variability of normal-to-normal interbeat intervals (SDNN: P=.04). At follow-up, only SDNN was significantly negatively correlated with age (P=.05). Levels of ASD symptoms were positively correlated with heart rate both before (P=.04) and after the intervention (P=.01). The majority (311/474, 65.6%) of reports from participants indicated that the devices helped when used. Difficulties with the use of some devices and problems with home testing of HRV were noted. These initial findings are discussed within the context of the strengths and challenges of remotely delivering a biofeedback intervention for people with ASD.ConclusionsHRV biofeedback devices have shown promise in this pilot study. There is now a need for larger evaluation of biofeedback to determine which delivery methods achieve the greatest effect for people with ASD.Trial RegistrationClinicalTrials.gov NCT04955093; https://clinicaltrials.gov/ct2/show/NCT04955093

Statistical Associations between Geomagnetic Activity, Solar Wind, Cosmic Ray Intensity, and Heart Rate Variability in Patients after Open-Heart Surgery

The aim of this study was to identify associations of the parameters of heart rate variability (HRV) with the variations in geomagnetic activity (GMA), solar wind, and cosmic ray intensity (CRI) in patients after coronary artery bypass grafting or valve surgery in Kaunas, Lithuania, during 2008–2012. The data from 5-minute electrocardiograms (ECGs) in 220 patients were used. ECGs were carried out at 1.5 months, 1 year, and 2 years after the surgery (N = 495). A lower (higher) very-low-frequency-band (VLF) and a higher (lower) high-frequency band (HF) in normalised units (n.u.) were associated with a low maximal daily 3-hourly ap (the DST index > 1). A lower mean standard deviation of beat-to-beat intervals (SDNN) and VLF, LF, and HF powers were lower in patients when Ap < 8 occurred two days after the surgery, and a low solar wind speed (SWS) occurred two days before the ECG. The effect of CRI was non-significant if the linear trend was included in the model. Low GMA and a low SWS may effect some HRV variables in patients after open-heart surgery. The GMA during the surgery may affect the SDNN in short-term ECG during the longer period.

Mediation Analysis in Manual Therapy Research

ObjectiveThe purpose of this study was to illustrate the applicability of mediation analysis in the manual therapy field by assessing whether pain intensity, duration of pain, or the change in systolic blood pressure mediated the heart rate variability (HRV) of patients with musculoskeletal pain who received manual therapy. MethodsA secondary data analysis from a 3-arm, parallel, randomized, placebo-controlled, assessor-blinded, superiority trial was performed. Participants were randomized into spinal manipulation, myofascial manipulation, or placebo groups. Cardiovascular autonomic control was inferred from resting HRV variables (low-high frequency power ratio; LF/HF) and blood pressure responsiveness to a sympathoexcitatory stimulus (cold pressor test). Pain intensity and duration were assessed. Mediation models analyzed whether pain intensity, duration, or blood pressure independently affected the improvement of the cardiovascular autonomic control of patients with musculoskeletal pain after intervention. ResultsThe first assumption of mediation was met for LF/HF with statistical evidence of a total effect of spinal manipulation, as compared with placebo on HRV outcomes (β = 0.77 [0.17-1.30]); second and third assumptions showed no statistical evidence of a relationship between the intervention and pain intensity (β = –5.30 [–39.48 to 28.87]), pain intensity, and LF/HF (β = 0.00 [–0.01 to 0.01]). ConclusionIn this study of causal mediation analysis, the baseline pain intensity, duration of pain, and responsiveness of the systolic blood pressure to a sympathoexcitatory stimulus did not mediate the effects of the spinal manipulation on the cardiovascular autonomic control of patients with musculoskeletal pain. Accordingly, the immediate effect of spinal manipulation on the cardiac vagal modulation of patients with musculoskeletal pain may more likely be related to the intervention rather than the mediators investigated.

Effects of sleep deprivation and 4‐7‐8 breathing control on heart rate variability, blood pressure, blood glucose, and endothelial function in healthy young adults

This study investigated the effects of sleep deprivation on heart rate variability (HRV), blood pressure (BP), fasting blood glucose (FBG), and endothelial function as well as the immediate effects of 4‐7‐8 breathing control on HRV and BP. In total, 43 healthy participants aged 19–25 years were classified into two groups: Twenty two in the with sleep deprivation group and 21 in the without sleep deprivation (control) group. Resting heart rate (HR), BP, HRV, FBG, and endothelial function were examined. Subsequently, participants practiced 4‐7‐8 breathing control for six cycles/set for three sets interspersed between each set by 1‐min normal breathing. Thereafter, the HR, BP, and HRV were immediately examined. The HRV, HR, and BP variables and FBG were not significantly different between the two groups. However, endothelial function was significantly lower in the sleep deprivation group than that in the control group (p < 0.05). In response to 4‐7‐8 breathing control, low‐ and very‐low‐frequency powers significantly decreased (p < 0.05), whereas high‐frequency power significantly increased (p < 0.05) in the control group. Moreover, time domain, total power, and very‐low‐frequency power significantly decreased (p < 0.05) in the sleep deprivation group. Both groups had significantly decreased HR and systolic BP (p < 0.05). HRV, HR, and BP variables showed no significant differences between the groups. Healthy young adults with and without sleep deprivation may have similar HRV, BP, and FBG values. However, sleep deprivation may cause decreased endothelial function. Furthermore, 4‐7‐8 breathing control can help participants improve their HRV and BP, particularly in those without sleep deprivation.

Impact of Basketball Match on the Pre-Competitive Anxiety and HRV of Youth Female Players.

The present study aimed to investigate the impact of a basketball competition on the pre-competitive anxiety and Heart Rate Variability (HRV) of young female basketball players. A total of 12 female basketball players participated in this cross-sectional study. Girls had a mean age of 14 (1.41) years old and a mean experience of 4 (0.85) years practicing basketball. The pre-competitive anxiety and the HRV was assessed the week before and immediately before and after the match. Results showed a significant reduction (p-value < 0.05) of the several HRV variables after the match compared to baseline and pre-competition measures. However, differences between baseline and pre-competition were not found. Furthermore, a significant increase in somatic anxiety after the competition was reported. Taking into account HRV, somatic anxiety, and cognitive anxiety results, young female basketball players did not exhibit an increase in pre-competition anxiety. HRV measurements before competition can help coaches and physical trainers to identify female players with higher pre-competitive anxiety and propose intervention to manage it. Future studies should investigate the impact of coaches and parents on the pre-competitive anxiety of female and male basketball players.

Heart rate markers for prediction of fetal acidosis in an experimental study on fetal sheep

To overcome the difficulties in interpreting fetal heart rate (FHR), several tools based on the autonomic nervous system and heart rate variability (HRV) have been developed. The objective of this study was to use FHR and HRV parameters for the prediction of fetal hypoxia. It was an experimental study in the instrumented fetal sheep. Repeated umbilical cord occlusions were performed to achieve severe acidosis. Hemodynamic parameters, ECG, and blood gases were analyzed. The variables used were heart rate baseline, HRV analysis (RMSSD, SDNN, LF, HF, HFnu, Fetal Stress Index (FSI), …), and morphological analysis of decelerations. The gold standard used to classify hypoxia was the fetal arterial pH (pH < 7.10). Different multivariable statistical methods (logistic regression and decision trees) were applied for the detection of acidosis. 21 lambs were instrumented. A total of 130 pairs of FHR/fetal pH analysis were obtained of which 29 in the acidosis group and 101 in the non-acidosis group. After logistic regression model with bootstrap resampling and stepwise backward selection, only one variable was selected, FSI. The AUC of FSI alone in this model was 0.81 with a sensitivity of 0.66, specificity of 0.88, PPV of 0.61, and NPV of 0.90 considering a threshold of 68. Decision trees with CHAID and CART algorithms showed a sensitivity of 0.48 and 0.59, respectively, and a specificity of 0.94 for both. All employed methods identified HRV variables as the most predictive of acidosis. The primary variables selected automatically were those from the HRV. Supporting the use of FHRV measures for the screening of fetal acidosis during labour is interesting.

The short-term effect of weather variables on heart rate variability in patients after open-heart surgery

ABSTRACT The aim of the study was to detect the associations between heart rate variability (HRV) and weather variables in patients who underwent coronary artery bypass grafting or valve surgery. The study was performed in Kaunas, Lithuania, during 2008–2012. We used data of 220 patients. HRV was assessed by a 5-minute electrocardiogram. The data were collected at 1.5 months, 1 year, and 2 years after the surgery (495 measurements). A negative association of standard deviation of beat-to-beat interval (SDNN), very low frequency (VLF), low frequency, and high frequency (HF) powers with a decrease in air temperature (T) during a 3-day period in the range of T < 1°C wind speed >2.75 knots 2 days before, and the daily North Atlantic Oscillation indices were observed. The effect of wind speed on SDNN and VLF power was stronger in males. Two days after relative humidity >89%, a lower mean VLF and higher HF in normalized units were found; in females, this effect was stronger 1.5 months after the surgery. Among patients after open-heart surgery, the HRV variables may be related to specific weather changes and the effect of weather was different for males and females and at different times after the surgery.

초보자 승마운동 시 완충고삐 사용을 통한 말의 스트레스 완화에 관한 연구

During equestrian exercise, communication between riders and horses is very important, and riders’ appropriate signals without any disturbance for the horses’ proper movements are required. Therefore, horses may get different stress depending on the rider’s riding balance, posture, and proficiency. This study was conducted to confirm the difference in the stress of horses between the beginner’s riding and the expert’s riding, additionally, to prove the effectiveness of buffer rein reducing stress even when beginners ride. Average heart rate (HR) was measured for five minutes in stages with a walk, and HR variability (HRV) were measured for three minutes in stages with both rising trot and sitting trot. HRV variables include root mean square of successive differences (RMSSD), standard deviation of normal to normal interval (SDNN), and ratio of low to high frequency components of a continuous series of heartbeats (low-frequency [LF]/high-frequency [HF]). The study involved 6 horses that underwent routine husbandry procedures. The average HR did not show a difference among groups in all exercise stages includes walk, rising trot, and sitting trot. RMSSDs showed lower values for the sitting trot when the beginner rides compared to the expert’s riding (p &lt; 0.05), which means the stress was more increased when beginners ride. On the other hand, when beginners ride using buffer reins, the RMSSD was increased in all exercise stages compared to the case of using regular reins. SDNN was increased when the beginners ride using buffer reins in the rising trot (p &lt; 0.05), which means the stress was more relieved. Ratio of low to high frequency components of a continuous series of heartbeats was not different among groups, but it showed decreased value when beginners use buffer reins rather than regular reins. In this study, it was confirmed that beginners induce more stress on horses than experts during riding exercise and that the use of the buffer reins by beginners more reduces the riding stress of horses compared to when they use regular reins.

The height and LnLF power cover the most of sex differences during orthostasis

The sex differences in autonomic regulation of cardiovascular and respiratory system, as one of the key physiological mechanisms of disease, till now remain underexplored. We hypothesized that cardiovascular and respiratory systems share the same autonomic mechanisms, represented by heart rate variability (HRV) indexes, opposing the effect of orthostasis, which are partially different between sexes.The 147 participants, 78 men and 69 women were recruited from the student population of local University for the research study. The low and high frequency heart rate variability (LF and HF HRV) was computed from ECG recording in the sitting position for 5 minutes of resting and slow breathing (6 breaths per minute) stages. The sitting position was used according to requirement of spirometry system. The tidal volume (TV) and respiratory rate (RR) were recorded for one minute at the end of each stage. Systolic and diastolic blood pressure (SBP and DBP) were measured with automatic digital sphygmomanometer (OMRON EVOLV, Japan). Two‐way repeated measures MANOVA and MANCOVA (SPSS 22) were used to test for effects of orthostasis and sex on HR, SBP, DBP, HRV variables, TV, RR, and MV. Multiple stepwise regression analysis was used to determine predictors of cardiovascular and respiratory variables. Written informed consent was obtained from each participant.In the current study we found significant main effects of orthostasis on HR, DBP, LnLF, LnHF (P&lt;0.001 for each), and significant main effects of sex on HR, SBP, LnLF, TV, and MV (for HR P=0.004, for LnLF P=0.006, for the rest P&lt;0.001). Follow the significant sex by orthostasis interaction we found that RR increased only for men upon standing but not for women.Multiple stepwise linear regression analysis revealed that when adjusting for potentially confounding variables, the change of cardiovagal‐mediated LnHF power (Figure 1A) was an independent predictor of HR and RR response to orthostasis (Table 1, Models 1 and 2). Women was an independent predictor of dRR, while Women by dLnLF interaction determined dHR, showing that LnLF, indicating according to our hypothesis, baroreflex‐mediated sympathoinhibition, contribute to HR response in women (Fig. 1B).The BMI by LnLF power interaction was a negative predictor of resting RR (Table 1, Model 3). It is suggested that baroreflex‐mediated sympathoinhibition contribute to respiratory central pattern generator particularly in people with increased BMI. The same interaction was a positive predictor of TV (Table 1, Model 4) indicating that increased time of respiratory cycle accompines greater TV.The comparisons of the similar models with and without dummy variables indicating “Women”, revealed that the dummy variable replaced “Height” or “LnLF”, suggesting that differences in both independent variables relate to mechanisms controlling cardiorespiratory system specific to female gender.In conclusion, cardiovagal‐mediated LnHF HRV power controls both HR and RR and determines their response to orthostasis. The differences in height and LnLF power cover the most of the sex difference in mechanisms controlling cardiovascular and respiratory variables and their response to orthostasis.

P639. “Ask Your Heart What It Doth Know”: 100+ Heart Rate Variability-Based Biomarkers of Mental and Physical Health Identified in a Large Cohort of Trauma Survivors

Personal health monitors that include assessment of heart rate variability (HRV) are becoming ubiquitous. Short-term HRV variables highlight complex interactions, including between the autonomic nervous system, respiratory rate, and baroreceptors. There is increasing interest in determining whether caregivers and patients can leverage such monitors to help assess mental and physical health and response to treatment.

Heart rate variability in men with lower urinary tract symptoms: a case-control study.

Measurement of heart rate variability (HRV) allows evaluation of autonomic nervous system activity. Decreased HRV is associated with autonomic disbalance, poor health and higher mortality. Our objective is to evaluate the HRV in men with lower urinary tract symptoms (LUTS) through a case-control study. LUTS were considered as the outcome and HRV variables were considered as exposure. The protocol included anamnesis, LUTS assessment, anthropometry, blood pressure and HRV measurement by analyzing the variation in the time interval between consecutive heartbeats or RR intervals. The mathematical study of HRV indicators allowed the assessment of the cardiac autonomic modulation of the volunteers. Eighty nine patients were included in the study, with 34 allocated to the case group (with LUTS) and 55 to the control group (without LUTS). The patients were similar in terms of age and systolic and diastolic blood pressure. Among the HRV variables, the mean VLF index for the very low frequency of the spectrum associated with the frequency domain was significantly higher in volunteers without LUTS. Control group patients presented a mean of 113.18 ± 166.74 ms2, while patients with LUTS presented a mean of 69.21 ± 61.98 ms2 (p = 0.032). Men 50-59years of age without chronic diseases and with LUTS have an unfavorable cardiac autonomic profile indicated by significantly lower levels of the VLF component of HRV compared to men without LUTS.

The modifying effect of trait anxiety on the association of fine particulate matter with heart rate variability variables.

Previous studies have shown that exposures to ambient particulate matter with aerodynamic diameter <2.5μm (PM2.5) and stress are associated with adverse cardiovascular health effects. To investigate the potential modifying effect of trait anxiety on the association between short-term exposures to PM2.5 and HRV variables. A panel of 92 middle-aged and elderly adults in Tianjin and Shanghai were recruited for repeated follow-ups with measurements of 24-h personal exposures to air pollutants and Holter ECG monitoring. Heart rate variability (HRV) variables calculated over 5-minute segments during the 24 h, including low frequency power (LF), high frequency power (HF), standard deviation of normal-to-normal intervals (SDNN) and root mean square of successive differences (rMSSD), were included in the analysis. The Trait Anxiety Inventory was used to investigate the long-term general anxiety level of the participants. Generalized linear mixed-effects model was used to analyze the association between exposure factors and HRV variables, and potential effect modification by trait anxiety. Data on 87 participants were included in final analysis after exclusions. Higher exposure to PM2.5 was associated with lower levels of LF, HF, SDNN and rMSSD, and the largest decreases in LF, HF, SDNN and rMSSD were found at 3-h moving average. Trait anxiety significantly modified the associations of PM2.5 with LF, HF, SDNN and rMSSD, with stronger inverse associations found in high trait anxiety group than in low trait anxiety group. For an IQR (27.3μg/m³) increase in PM2.5 at 3-h moving average, there were decreases of 3.50% (95% CI: -4.46%, -2.54%) and 3.50% (95% CI: -4.49%, -2.50%) in the high trait anxiety group, and decreases of 0.81% (95% CI: -1.22%, -0.40%) and 0.65% (95% CI: -1.07%, -0.23%) in the low trait anxiety group in HF and rMSSD, respectively (both p for interaction<0.01). Our study suggests that trait anxiety could modify the association of short-term exposure to PM2.5 with HRV variables, indicating that higher trait anxiety may increase the cardiac susceptibility to air pollution in the study participants.

Does the Heart Fall Asleep?-Diurnal Variations in Heart Rate Variability in Patients with Disorders of Consciousness.

The current study investigated heart rate (HR) and heart rate variability (HRV) across day and night in patients with disorders of consciousness (DOC). We recorded 24-h electrocardiography in 26 patients with DOC (i.e., unresponsive wakefulness syndrome (UWS; n = 16) and (exit) minimally conscious state ((E)MCS; n = 10)). To examine diurnal variations, HR and HRV indices in the time, frequency, and entropy domains were computed for periods of clear day- (forenoon: 8 a.m.–2 p.m.; afternoon: 2 p.m.–8 p.m.) and nighttime (11 p.m.–5 a.m.). The results indicate that patients’ interbeat intervals (IBIs) were larger during the night than during the day, indicating HR slowing. The patients in UWS showed larger IBIs compared to the patients in (E)MCS, and the patients with non-traumatic brain injury showed lower HRV entropy than the patients with traumatic brain injury. Additionally, higher HRV entropy was associated with higher EEG entropy during the night. Thus, cardiac activity varies with a diurnal pattern in patients with DOC and can differentiate between patients’ diagnoses and etiologies. Moreover, the interaction of heart and brain appears to follow a diurnal rhythm. Thus, HR and HRV seem to mirror the integrity of brain functioning and, consequently, might serve as supplementary measures for improving the validity of assessments in patients with DOC.

Preprocessing Methods for Ambulatory HRV Analysis Based on HRV Distribution, Variability and Characteristics (DVC).

Thanks to wearable devices joint with AI algorithms, it is possible to record and analyse physiological parameters such as heart rate variability (HRV) in ambulatory environments. The main downside to such setups is the bad quality of recorded data due to movement, noises, and data losses. These errors may considerably alter HRV analysis and should therefore be addressed beforehand, especially if used for medical diagnosis. One widely used method to handle such problems is interpolation, but this approach does not preserve the time dependence of the signal. In this study, we propose a new method for HRV processing including filtering and iterative data imputation using a Gaussian distribution. The particularity of the method is that many physiological aspects are taken into consideration, such as HRV distribution, RR variability, and normal boundaries, as well as time series characteristics. We study the effect of this method on classification using a random forest classifier (RF) and compare it to other data imputation methods including linear, shape-preserving piecewise cubic Hermite (pchip), and spline interpolation in a case study on stress. Features from reconstructed HRV signals of 67 healthy subjects using all four methods were analysed and separately classified by a random forest algorithm to detect stress against relaxation. The proposed method reached a stable F1 score of 61% even with a high percentage of missing data, whereas other interpolation methods reached approximately 54% F1 score for a low percentage of missing data, and the performance drops to about 44% when the percentage is increased. This suggests that our method gives better results for stress classification, especially on signals with a high percentage of missing data.

Assessment of Combination of Automated Pupillometry and Heart Rate Variability to Detect Driving Fatigue.

ObjectivesApproximately 20~30% of all traffic accidents are caused by fatigue driving. However, limited practicability remains a barrier for the real application of available techniques to detect driving fatigue. Use of pupillary light reflex (PLR) may be potentially effective for driving fatigue detection.MethodsA 90 min monotonous simulated driving task was utilized to induce driving fatigue. During the task, PLR measurements were performed at baseline and at an interval of 30 min. Subjective rating scales, heart rate variability (HRV) were monitored simultaneously.ResultsThirty-two healthy volunteers in China participated in our study. Based on the results of subjective evaluation and behavioral performances, driving fatigue was verified to be successfully induced by a simulated driving task. Significant variations of PLR and HRV parameters were observed, which also showed significant relevance with the change in Karolinska Sleepiness Scale at several timepoints (|r| = 0.55 ~ 0.72, P < 0.001). Furthermore, PLR variations had excellent ability to detect driving fatigue with high sensitivity and specificity, of which maximum constriction velocity variations achieved a sensitivity of 85.00% and specificity of 72.34% for driving fatigue detection, vs. 82.50 and 78.72% with a combination of HRV variations, a nonsignificant difference (AUC = 0.835, 0.872, P > 0.05).ConclusionsPupillary light reflex variation may be a potential indicator in the detection of driving fatigue, achieving a comparative performance compared with the combination with heart rate variability. Further work may be involved in developing a commercialized driving fatigue detection system based on pupillary parameters.

The Influence of an Acute Bout of High-Intensity Interval Exercise on Heart Rate Variability Indices and Stress Index in the Absence of Cardiometabolic Diseases

Introduction: The maximal rate of oxygen consumption is the gold standard when determining cardiorespiratory fitness (CF) in healthy and diseased populations. CF has been shown to influence the improvement of cardiac autonomic modulation (CAM) and lower the risk of morbidity and mortality rates. High-intensity interval exercise (HIIE) has been shown to influence CAM post-exercise in various populations. Heart rate variability (HRV) is a non-invasive way to assess CAM during, before, and after exercise. The purpose was to determine if a single acute bout of HIIE is influenced by age and CF when correlated to HRV variables to determine CAM in healthy and fit individuals. Methods: Thirty-four healthy individuals (n= 21 male; n = 13 female) completed a single acute bout of HIIE session to quantify CAM via HRV. HRV was assessed pre, 1-hour, and 24-hours post-exercise using time and frequency domains, and stress index (SI). Results: HRV time and frequency domains were not significantly changed. The SI was significantly different between pre, 1-hour, and 24-hours post-exercise (p = 0.001). The SI was also significantly different between age groups (p = 0.025). Conclusion: The lack of significant difference in CAM can be attributed to the participants high CF, which helps maintain their HRV as they age. Additionally, the SI appears to be a good metric to assess CF as individuals age.

Temporal Variation Measure Analysis: An Improved Second‐Order Difference Plot

In this study, an improved second‐order difference plot is proposed to analyze the variability of heart rate variability. Although the variation of the physiological status of the cardiovascular system can be shown graphically by the second‐order difference plot, the descriptive ability of existing indicators for this plot is insufficient. As a result, the physiological information contained in the second‐order difference plot cannot be extracted adequately. Addressing the problem, the temporal variation measure analysis is presented to describe distribution patterns of scatter points in the second‐order difference plot quantitatively and extract the acceleration information for a variation of heart rate variability. Experiment results demonstrate the effectiveness of the temporal variation measure analysis. As a quantitative indicator, the temporal variation entropy is properly designed and successfully applied in the recognition and classification of the physiological statuses of the heart.

Effect of Stress on Heart Rate Variability in Medical Students: A Cross-sectional Study

Introduction: Medical education can impose significant psychological stress on undergraduate students. A considerable degree of psychological morbidity has been reported among medical students ranging from stress, interpersonal problems, and suicidal ideation to psychiatric disorders and they tend to have greater psychological distress than the general population. Stress is one of the factors known to cause variation in heart rate variability. Heart Rate Variability (HRV) is a proven reliable non invasive marker of cardiovascular health and has been used in cardiovascular risk stratification. Aim: To study the effect of stress on heart rate variability in medical students. Materials and Methods: The cross-sectional study was conducted in the Department of Physiology at JSS Medical College, Mysuru, Karnataka, India, from December 2017 to February 2018. Total 58 healthy first-year MBBS medical students aged between 18-25 years with normal Body Mass Index (BMI) were included in the study. The Medical Student Stressor Questionnaire (MSSQ), a validated instrument to identify sources of stress in medical students was used to assess the level of stress. AD Instruments PowerLab (Data Acquisition System) was used to record the frequency and time domain analysis of HRV from the limb leads. Kruskal-Wallis test was applied to assess the association between stress domains and HRV domains, using Statistical Package for Social Sciences (SPSS) version 23.0. Results: Most of the medical students had mild to moderate degrees of stress in all the domains of the MSSQ. There was no statistically significant (p-value&gt;0.05) association found between domains of stress with the time and frequency domains of the HRV. Conclusion: Though it was found that medical students were exposed to significant stressors during their medical training, the stress was of mild to a moderate degree which had no significant effect on HRV.

Assessment of meditation effects using heart rate variability analysis

Meditation is claimed to regularise the autonomic nervous system (ANS) and causes reduced metabolic movement, inciting physical and mental relaxation. It is being looked upon as the future integrative means of improving quality of life. The most accessible organ for the assessment of ANS activities is the heart and its oscillations. The heart rate variability (HRV) analysis has emerged as a successful non-invasive method that elucidates changes of sympathetic and vagal activity. The alternations of a heart are complex and constantly changing, which allows the cardiovascular system to rapidly adjust to sudden physical and psychological changes. In this paper, the exhaustive overview of HRV analysis attempts for evaluating meditation effects is presented. Moreover, HRV metrics, their clinical significance, applications and reported usefulness in meditation assessment are presented. The variations in HRV have been analysed using both linear and nonlinear parameters for both meditators and non-meditators. The effects of two meditation techniques namely, Chi and Kundalini yoga meditation on HRV have been investigated extensively, and significance of these techniques have been evaluated using statistical analysis.