Robust circadian rhythm in heart rate and its variability: influence of exogenous melatonin and photoperiod

Association between individual differences in interoception and cardiac coherence during heart rate variability biofeedback

Heart rate variability biofeedback (HRVBF) is the training to increase vagally-mediated heart rate variability (vmHRV), accompanied by slow-paced breathing and feedback of heart rhythm. It has been reported to be effective for emotion and cognition. In recent years, increased attention has turned toward participant characteristics as factors affecting HRVBF training effects. Focusing on neural basis commonalities between the mechanisms of HRVBF training effects and processing interoception, this study comprehensively measured interoception and examined the relationship between interoception and cardiac coherence reflecting HRVBF effects. Fifty-four healthy young participants were recruited, and subjective interoception was measured using the Japanese version of Multidimensional Assessment of Interoceptive Awareness (MAIA-J) and the Japanese version of the Body Perception Questionnaire-Body Awareness Very Short Form (BPQ-BAVSF-J), objective interoception using heartbeat counting task (HCT), heart rate variability (HRV), visual exteroception, and the coherence score achieved by HRVBF. We conducted a multiple regression analysis with interoception, HRV, and visual exteroception parameters as explanatory variables and the coherence score as the objective variable. Some subjective interoception and HRV parameters were found to be associated with the coherence score. Our results were consistent with previous studies, showing that higher vmHRV was related to high cardiac coherence. Interoception effects on cardiac coherence may be limited because of the low adjusted coefficient of determination and less selected explanatory variables in the multiple regression analysis. Our results may contribute toward predicting HRVBF training effects and the screening of those who are likely to benefit from the training from the perspective of interoception and vmHRV.

More variable circadian rhythms in epilepsy captured by long-term heart rate recordings from wearable sensors

OBJECTIVE

The circadian rhythm synchronizes physiological and behavioral patterns with the 24-h light-dark cycle. Disruption to the circadian rhythm is linked to various health conditions, although optimal methods to describe these disruptions remain unclear. An emerging approach is to examine the intraindividual variability in measurable properties of the circadian rhythm over extended periods. Epileptic seizures are modulated by circadian rhythms, but the relevance of circadian rhythm disruption in epilepsy remains unexplored. Our study investigates intraindividual circadian variability in epilepsy and its relationship with seizures.

METHODS

We retrospectively analyzed >70 000 h of wearable smartwatch data (Fitbit) from 143 people with epilepsy (PWE) and 31 healthy controls. Circadian oscillations in heart rate time series were extracted, daily estimates of circadian period, acrophase, and amplitude properties were produced, and estimates of the intraindividual variability of these properties over an entire recording were calculated.

RESULTS

PWE exhibited greater intraindividual variability in period (76 vs. 57 min, d = .66, p < .001) and acrophase (64 vs. 48 min, d = .49, p = .004) compared to controls, but not in amplitude (2 beats per minute, d = -.15, p = .49). Variability in circadian properties showed no correlation with seizure frequency nor any differences between weeks with and without seizures.

SIGNIFICANCE

For the first time, we show that heart rate circadian rhythms are more variable in PWE, detectable via consumer wearable devices. However, no association with seizure frequency or occurrence was found, suggesting that this variability might be underpinned by the epilepsy etiology rather than being a seizure-driven effect.

Sleep and cardiac autonomic modulation in older adults: Insights from an at-home study with auditory deep sleep stimulation

The autonomic nervous system regulates cardiovascular activity during sleep, likely impacting cardiovascular health. Aging, a primary cardiovascular risk factor, is associated with cardiac autonomic disbalance and diminished sleep slow waves. Therefore, slow waves may be linked to aging, autonomic activity and cardiovascular health. However, it is unclear how sleep and slow waves are linked to cardiac autonomic profiles across multiple nights in older adults. We conducted a randomized, crossover trial involving healthy adults aged 62-78 years. Across 2 weeks, we applied auditory stimulation to enhance slow waves and compared it with a SHAM period. We measured sleep parameters using polysomnography and derived heart rate, heart rate variability approximating parasympathetic activity, and blood pulse wave approximating sympathetic activity from a wearable. Here, we report the results of 14 out of 33 enrolled participants, and show that heart rate, heart rate variability and blood pulse wave within sleep stages differ between the first and second half of sleep. Furthermore, baseline slow-wave activity was related to cardiac autonomic activity profiles during sleep. Moreover, we found auditory stimulation to reduce heart rate variability, while heart rate and blood pulse wave remained unchanged. Lastly, within subjects, higher heart rate coincided with increased slow-wave activity, indicating enhanced autonomic activation when slow waves are pronounced. Our study shows the potential of cardiac autonomic markers to offer insights into participants' baseline slow-wave activity when recorded over multiple nights. Furthermore, we highlight that averaging cardiac autonomic parameters across a night may potentially mask dynamic effects of auditory stimulation, potentially playing a role in maintaining a healthy cardiovascular system.

Triaxial accelerometers and subcutaneous biologgers as tools to record diurnal and nocturnal changes in locomotor activity, body temperature, heart rate, and heart rate variability in melatonin-treated lambs (Ovis aries)

The study of growth and development of lambs (Ovis aries) is essential in sheep farming, and melatonin plays an important role in the physiology of growing lambs. The effects of an exogenous melatonin treatment on several physiological characteristics in fattening lambs at weaning were studied. Eight lambs were assigned to one of two groups; those that did (melatonin group, n = 4) or did not (no-melatonin group, n = 4) receive two subcutaneous melatonin implants at weaning. At the end of the fattening period, to quantify locomotor activity (LA), each lamb was fitted with a triaxial accelerometer, for 7 days. Simultaneously, lambs received a surgically implanted subcutaneous temperature (T) and heart rate (HR) biologger, which was programmed to record data every 5 min. HR variability (HRV) variables (SDNN, the standard deviation of normal-to-normal R-R intervals, and RMSSD, the root mean square of consecutive deviations between normal heartbeats) were measured. All of the variables exhibited 24-h circadian rhythms. Time of day (daytime vs. nighttime) had a significant effect on LA, T, and HR, but considering both treatment with melatonin and time, differences between time for these variables were only observed in melatonin-treated lambs. Exogenous melatonin did not affect LA or T, but melatonin-treated lambs had lower HR, SDNN, and RMSSD than did non-treated lambs. In conclusion, the use of subcutaneous biologgers and triaxial accelerometers in growing lambs demonstrated circadian rhythms in LA, T, HR, and HRV, and melatonin treatment negatively affected HRV, but its effects on the other physiological variables differed between day and night.

Melatonin protect against pregabalin-induced gonadotoxicity via anti-oxidative, anti-inflammatory, anti-apoptotic, enzymatic and hormonal regulatory mechanisms in rats

BACKGROUND

The therapeutic value of pregabalin in managing various pathological states, such as sleep, anxiety, and bipolar disorders, fibromyalgia, epilepsy, and others, cannot be overstated. Nevertheless, the gonadotoxicity of this drug remains a concern. In contrast, melatonin, an endogenous hormone, is known for its beneficial effects on reproductive tissues following various insults. Thus, this study aimed to examine the impact of melatonin on male Wistar rats exposed to pregabalin.

METHODS

A total of sixty male Wistar rats, weighing between 120 and 140 g, were randomly assigned to six groups, with each group consisting of ten rats. The control group was given 0.5 ml of normal saline orally, whereas melatonin was administered alone at 10 mg/kg/BW, and pregabalin was delivered at low and high doses of 150 and 300 mg/kg/BW orally, respectively. At the specified dosages, rats were also treated simultaneously with low and high doses of pregabalin in combination with melatonin. All treatments lasted for 56 days. Biomarkers were assayed in the testicular and epididymal tissues, while hormones were assayed in the serum.

RESULTS

Pregabalin treatment resulted in notable decreases in the percentage body weight change, testicular weight, relative testicular weight, FSH, LH, testosterone, 3β-HSD, 17β-HSD, SOD, catalase, and GSH, as compared to the control group. However, these effects were mitigated in the groups administered melatonin in conjunction with pregabalin. Pregabalin treatment also caused significant elevations in lactate, pyruvate, LDH, GGT, MDA, caspase, IL-1β, NF-κB, and TNF-α, and distorted testicular histoarchitecture, but these effects were blunted in the group co-administered with pregabalin and melatonin. The histological findings paralleled the biochemical assays.

CONCLUSION

Conclusively, melatonin has a protective effect against pregabalin-induced gonadotoxicity through anti-oxidative, anti-inflammatory, anti-apoptotic, enzymatic, and hormonal regulatory mechanisms.

CLINICAL TRIAL NUMBER

Not applicable.

Relevance of high glycaemic index breakfast for heart rate variability among collegiate students with early and late chronotypes

Plasma glucose spikes affect cardiac autonomic modulation resulting in a decrease of heart rate variability (HRV). We hypothesize that a later chronotype or a higher morning plasma melatonin level is associated with larger decreases of HRV following an early high glycaemic index (GI) breakfast. In persons with an early (n = 21) or a late (n = 15) chronotype who consumed a high GI breakfast at 7 a.m. glucose data were continuously monitored. Time domain HRV parameters were calculated from blood volume pulses derived by wireless wrist worn multisensor. HRV changes (values after minus values before breakfast) were associated with chronotype by multivariable linear regression adjusted for age, sex and baseline levels. Morning plasma melatonin levels were determined from samples drawn on the run-in day. Time domain parameters indicate a higher HRV before high GI breakfast in both chronotypes. A later chronotype tended to be associated with smaller decreases of mean interbeat intervals (p = 0.08) only; no associations were seen with morning melatonin levels. This exploratory analysis in a small sample provides a first indication that in young healthy adults later chronotype might be associated with reduced ANS activation following a high GI breakfast. Future studies should elucidate whether this indicates parasympathetic or sympathetic inhibition.

Melatonin's Impact on Wound Healing

Melatonin (5-methoxy-N-acetyltryptamine) is an indoleamine compound that plays a critical role in the regulation of circadian rhythms. While melatonin is primarily synthesized from the amino acid tryptophan in the pineal gland of the brain, it can also be produced locally in various tissues, such as the skin and intestines. Melatonin's effects in target tissues can be mediated through receptor-dependent mechanisms. Additionally, melatonin exerts various actions via receptor-independent pathways. In biological systems, melatonin and its endogenous metabolites often produce similar effects. While injuries are common in daily life, promoting optimal wound healing is essential for patient well-being and healthcare outcomes. Beyond regulating circadian rhythms as a neuroendocrine hormone, melatonin may enhance wound healing through (1) potent antioxidant properties, (2) anti-inflammatory actions, (3) infection control, (4) regulation of vascular reactivity and angiogenesis, (5) analgesic (pain-relieving) effects, and (6) anti-pruritic (anti-itch) effects. This review aims to provide a comprehensive overview of scientific studies that demonstrate melatonin's potential roles in supporting effective wound healing.

Influence of night shift work on circadian heart-rate rhythm in nurses: using a Holter electrocardiogram that can be continuously measured for two weeks

The influence of night shift work on circadian heart-rate rhythm was examined in nurses engaged in shift work using a Holter electrocardiogram, continuously measured for two weeks, and cosine periodic regression analysis. We enrolled 11 nurses who were engaged in a two-shift system. The R2 value in the cosine regression curve of heart-rate rhythm (concordance rate), indicating the concordance rate between the actual heart rate over 24 h and the cosine regression curve approximated by the least-squares procedure, was significantly lower in the night shift (0.40 ± 0.15) than in the day shift (0.66 ± 0.19; p<0.001). Moreover, the amplitude was significantly lower and the acrophase was significantly delayed in the night shift. Thus, the circadian heart-rate rhythm was disrupted by the night shift work. Although the heart-rate acrophase recovered during the day and two days after the night shift, the concordance rate and amplitude did not recover, indicating that the influence of night shift work on circadian heart-rate rhythm might persist even two days after the night shift. Based on these results, adequate clinical attention should be paid to how to spend the day and two days after the night shift to correct the circadian heart-rate rhythm disruption caused by night shift work.

Reliable Contactless Monitoring of Heart Rate, Breathing Rate, and Breathing Disturbance During Sleep in Aging: Digital Health Technology Evaluation Study

BACKGROUND

Longitudinal monitoring of vital signs provides a method for identifying changes to general health in an individual, particularly in older adults. The nocturnal sleep period provides a convenient opportunity to assess vital signs. Contactless technologies that can be embedded into the bedroom environment are unintrusive and burdenless and have the potential to enable seamless monitoring of vital signs. To realize this potential, these technologies need to be evaluated against gold standard measures and in relevant populations.

OBJECTIVE

We aimed to evaluate the accuracy of heart rate and breathing rate measurements of 3 contactless technologies (2 undermattress trackers, Withings Sleep Analyzer [WSA] and Emfit QS [Emfit]; and a bedside radar, Somnofy) in a sleep laboratory environment and assess their potential to capture vital signs in a real-world setting.

METHODS

Data were collected from 35 community-dwelling older adults aged between 65 and 83 (mean 70.8, SD 4.9) years (men: n=21, 60%) during a 1-night clinical polysomnography (PSG) test in a sleep laboratory, preceded by 7 to 14 days of data collection at home. Several of the participants (20/35, 57%) had health conditions, including type 2 diabetes, hypertension, obesity, and arthritis, and 49% (17) had moderate to severe sleep apnea, while 29% (n=10) had periodic leg movement disorder. The undermattress trackers provided estimates of both heart rate and breathing rate, while the bedside radar provided only the breathing rate. The accuracy of the heart rate and breathing rate estimated by the devices was compared with PSG electrocardiogram-derived heart rate (beats per minute) and respiratory inductance plethysmography thorax-derived breathing rate (cycles per minute), respectively. We also evaluated breathing disturbance indexes of snoring and the apnea-hypopnea index, available from the WSA.

RESULTS

All 3 contactless technologies provided acceptable accuracy in estimating heart rate (mean absolute error <2.12 beats per minute and mean absolute percentage error <5%) and breathing rate (mean absolute error ≤1.6 cycles per minute and mean absolute percentage error <12%) at 1-minute resolution. All 3 contactless technologies were able to capture changes in heart rate and breathing rate across the sleep period. The WSA snoring and breathing disturbance estimates were also accurate compared with PSG estimates (WSA snore: r2=0.76; P<.001; WSA apnea-hypopnea index: r2=0.59; P<.001).

CONCLUSIONS

Contactless technologies offer an unintrusive alternative to conventional wearable technologies for reliable monitoring of heart rate, breathing rate, and sleep apnea in community-dwelling older adults at scale. They enable the assessment of night-to-night variation in these vital signs, which may allow the identification of acute changes in health, and longitudinal monitoring, which may provide insight into health trajectories.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

RR2-10.3390/clockssleep6010010.

Symptomatic bradyarrhythmias in the athlete-Underlying mechanisms and treatments

Bradyarrhythmias including sinus bradycardia and atrioventricular (AV) block are frequently encountered in endurance athletes especially at night. While these are well tolerated by the young athlete, there is evidence that generally from the fifth decade of life onward, such arrhythmias can degenerate into pathological symptomatic bradycardia requiring pacemaker therapy. For many years, athletic bradycardia and AV block have been attributed to high vagal tone, but work from our group has questioned this widely held assumption and demonstrated a role for intrinsic electrophysiological remodeling of the sinus node and the AV node. In this article, we argue that bradyarrhythmias in the veteran athlete arise from the cumulative effects of exercise training, the circadian rhythm and aging on the electrical activity of the nodes. We consider contemporary strategies for the treatment of symptomatic bradyarrhythmias in athletes and highlight potential therapies resulting from our evolving mechanistic understanding of this phenomenon.

Measuring heart rate in captive chimpanzees without anesthesia

Heart rate measurements can be useful for the monitoring of both physical and mental condition in humans and nonhuman animals. Yet, information about heart rates in chimpanzees, who are phylogenetically the closest species to humans, is scarce. Existing data on chimpanzee heart rates have mainly been collected from chimpanzees under anesthesia. To address this issue, we conducted electrocardiogram recordings in captive chimpanzees under normal conditions without anesthesia based on positive reinforcement training. We obtained a total of 771 recordings from 35 individuals (22 males and 13 females, 14-53 years old) with no cardiac problems. The females had a higher heart rate than the male chimpanzees, and heart rate decreased as a function of age. In addition, heart rate was lower in the morning and increased during the day. Overall, the mean heart rate of adult males was 86.5 beats/min, and that of female chimpanzees 106.4 beats/min. Our data could serve as a reference point for future research and health-based monitoring of chimpanzee heart rates.

Diurnal variation of heart rate variability in individuals with spinal cord injury

BACKGROUND

Heart rate variability (HRV) may provide objective information about cardiogenic autonomic balance in individuals with spinal cord injury (SCI). The aim of this study was to characterize the diurnal variation of HRV in individuals with SCI at lesion level T6 and above and lesion level below T6.

METHODS

This was a retrospective analysis of a prior cross-sectional study. Individuals with chronic SCI underwent 24 h recording of the time between consecutive R waves (RR interval) to derive parameters of HRV as follows: standard deviation of all normal-to-normal R-R intervals (SDNN) and square root of the mean of the squared differences between successive R-R intervals (RMSSD) (time domain); and high frequency power (HF), low-frequency power (LF), very low frequency power (VLF), ultra-low frequency power (ULF) and total power (TP) (frequency domain). Changes in the magnitude of HRV outcomes over the 24 h period were investigated using a novel multi-component cosinor model constrained to the form of a three-harmonic Fourier series.

RESULTS

Participants were grouped as lesion level T6 and above (n = 22) or below T6 (n = 36). Most of them were male (n = 40, 69%) and the median age (interquartile range) was 50.5 (28) years. Both groups exhibited similar diurnal patterns in most HRV metrics. The lowest values occurred in the late afternoon (4-6 pm) and gradually increased, peaking around midnight to early morning (1-6 am). Exceptions included RMSSD, which peaked before midnight, and ULF, which showed a double peak pattern that peaked from 11 am to 1 pm and 4-6 am in participants with lesion level at T6 and above. The HRV values in participants with lesion level T6 and above were generally lower than participants with lesion level below T6, except for peak values of RMSSD, HF and LF.

CONCLUSION

This study demonstrated substantial diurnal variation of HRV in participants with SCI in both groups of participants. In clinical and research settings, diurnal variations in HRV must be taken into consideration.

Autonomic biosignals, seizure detection, and forecasting

Wearable devices have attracted significant attention in epilepsy research in recent years for their potential to enhance patient care through improved seizure monitoring and forecasting. This narrative review presents a detailed overview of the current clinical state of the art while addressing how devices that assess autonomic nervous system (ANS) function reflect seizures and central nervous system (CNS) state changes. This includes a description of the interactions between the CNS and the ANS, including physiological and epilepsy-related changes affecting their dynamics. We first discuss technical aspects of measuring autonomic biosignals and considerations for using ANS sensors in clinical practice. We then review recent seizure detection and seizure forecasting studies, highlighting their performance and capability for seizure detection and forecasting using devices measuring ANS biomarkers. Finally, we address the field's challenges and provide an outlook for future developments.

Prediction of the efficacy of group cognitive behavioral therapy using heart rate variability based smart wearable devices: a randomized controlled study

BACKGROUND

Depression and anxiety are common and disabling mental health problems in children and young adults. Group cognitive behavioral therapy (GCBT) is considered that an efficient and effective treatment for these significant public health concerns, but not all participants respond equally well. The aim of this study was to examine the predictive ability of heart rate variability (HRV), based on sensor data from consumer-grade wearable devices to detect GCBT effectiveness in early intervention.

METHODS

In a study of 33 college students with depression and anxiety, participants were randomly assigned to either GCBT group or a wait-list control (WLC) group. They wore smart wearable devices to measure their physiological activities and signals in daily life. The HRV parameters were calculated and compared between the groups. The study also assessed correlations between participants' symptoms, HRV, and GCBT outcomes.

RESULTS

The study showed that participants in GCBT had significant improvement in depression and anxiety symptoms after four weeks. Higher HRV was associated with greater improvement in depressive and anxious symptoms following GCBT. Additionally, HRV played a noteworthy role in determining how effective GCBT was in improve anxiety(P = 0.002) and depression(P = 0.020), and its predictive power remained significant even when considering other factors.

CONCLUSION

HRV may be a useful predictor of GCBT treatment efficacy. Identifying predictors of treatment response can help personalize treatment and improve outcomes for individuals with depression and anxiety.

TRIAL REGISTRATION

The trial has been retrospectively registered on [22/06/2023] with the registration number [NCT05913349] in the ClinicalTrials.gov. Variations in heart rate variability (HRV) have been associated with depression and anxiety, but the relationship of baseline HRV to treatment outcome in depression and anxiety is unclear. This study predicted GCBT effectiveness using HRV measured by wearable devices. 33 students with depression and anxiety participated in a trial comparing GCBT and wait-list control. HRV parameters from wearables correlated with symptoms (PHQ, PSS) and GCBT effectiveness. Baseline HRV levels are strongly associated with GCBT treatment outcomes. HRV may serve as a useful predictor of efficacy of GCBT treatment,facilitating personalized treatment approaches for individuals with depression and anxiety.

Unraveling the interplay of circadian rhythm and sleep deprivation on mood: A Real-World Study on first-year physicians

The interplay between circadian rhythms, time awake, and mood remains poorly understood in the real-world. Individuals in high-stress occupations with irregular schedules or nighttime shifts are particularly vulnerable to depression and other mood disorders. Advances in wearable technology have provided the opportunity to study these interactions outside of a controlled laboratory environment. Here, we examine the effects of circadian rhythms and time awake on mood in first-year physicians using wearables. Continuous heart rate, step count, sleep data, and daily mood scores were collected from 2,602 medical interns across 168,311 days of Fitbit data. Circadian time and time awake were extracted from minute-by-minute wearable heart rate and motion measurements. Linear mixed modeling determined the relationship between mood, circadian rhythm, and time awake. In this cohort, mood was modulated by circadian timekeeping (p<0.001). Furthermore, we show that increasing time awake both deteriorates mood (p<0.001) and amplifies mood's circadian rhythm nonlinearly. These findings demonstrate the contributions of both circadian rhythms and sleep deprivation to underlying mood and show how these factors can be studied in real-world settings using Fitbits. They underscore the promising opportunity to harness wearables in deploying chronotherapies for psychiatric illness.

Recovery Sleep After Sleep Restriction Is Insufficient to Return Elevated Daytime Heart Rate and Systolic Blood Pressure to Baseline Levels

OBJECTIVE

Sleep restriction alters daytime cardiac activity, including elevating heart rate (HR) and blood pressure (BP). There is minimal research on the cumulative effects of sleep loss and the response after subsequent recovery sleep on HR and BP. This study examined patterns of HR and BP across baseline, sleep restriction, and recovery conditions using multiple daytime cardiac measurements.

METHODS

Participants (15 healthy men, mean [standard deviation] = 22.3 [2.8] years) completed an 11-day inpatient protocol with three nights of 10 hours/night baseline sleep opportunity, five sleep restriction nights (5-hour/night sleep opportunity), and two recovery nights (10-hour/night sleep opportunity). Resting HR and BP were measured every 2 hours during wake. Multilevel models with random effects for individuals examined daytime HR and BP across study conditions and days into the study.

RESULTS

Mean daytime HR was 1.2 (0.5) beats/min lower during sleep restriction compared with baseline ( p < .001). During recovery, HR was 5.5 (1.0) beats/min higher ( p < .001), and systolic BP (SBP) was 2.9 (1.1) mm Hg higher ( p = .009). When accounting for days into the study (irrespective of condition) and measurement timing across the day, HR increased by 7.6 beats/min and SBP increased by 3.4 mm Hg across the study period ( p < .001).

CONCLUSIONS

Our findings suggest that daytime HR and SBP increase after successive nights of sleep restriction, even after accounting for measurement time of day. HR and SBP did not recover to baseline levels after two recovery nights of sleep, suggesting that longer recovery sleep may be necessary to recover from multiple, consecutive nights of moderate sleep restriction.

Time-of-Day Effects of Exercise on Cardiorespiratory Responses and Endurance Performance-A Systematic Review and Meta-Analysis

ABSTRACT

Kang, J, Ratamess, NA, Faigenbaum, AD, Bush, JA, Finnerty, C, DiFiore, M, Garcia, A, and Beller, N. Time-of-day effects of exercise on cardiorespiratory responses and endurance performance-A systematic review and meta-analysis. J Strength Cond Res 37(10): 2080-2090, 2023-The time-of-day effect of exercise on human function remains largely equivocal. Hence, this study aimed to further analyze the existing evidence concerning diurnal variations in cardiorespiratory responses and endurance performance using a meta-analytic approach. Literature search was conducted through databases, including PubMed, CINAHL, and Google Scholar. Article selection was made based on inclusion criteria concerning subjects' characteristics, exercise protocols, times of testing, and targeted dependent variables. Results on oxygen uptake (V̇ o2 ), heart rate (HR), respiratory exchange ratio, and endurance performance in the morning (AM) and late afternoon or evening (PM) were extracted from the chosen studies. Meta-analysis was conducted with the random-effects model. Thirty-one original research studies that met the inclusion criteria were selected. Meta-analysis revealed higher resting V̇ o2 (Hedges' g = -0.574; p = 0.040) and resting HR (Hedges' g = -1.058; p = 0.002) in PM than in AM. During exercise, although V̇ o2 remained indifferent between AM and PM, HR was higher in PM at submaximal (Hedges' g = -0.199; p = 0.046) and maximal (Hedges' g = -0.298; p = 0.001) levels. Endurance performance as measured by time-to-exhaustion or the total work accomplished was higher in PM than in AM (Hedges' g = -0.654; p = 0.001). Diurnal variations in V̇ o2 appear less detectable during aerobic exercise. The finding that exercising HR and endurance performance were greater in PM than in AM emphasizes the need to consider the effect of circadian rhythm when evaluating athletic performance or using HR as a criterion to assess fitness or monitor training.

The Role of the Circadian Rhythm in Dyslipidaemia and Vascular Inflammation Leading to Atherosclerosis

Cardiovascular diseases (CVD) are among the leading causes of death worldwide. Many lines of evidence suggest that the disturbances in circadian rhythm are responsible for the development of CVDs; however, circadian misalignment is not yet a treatable trait in clinical practice. The circadian rhythm is controlled by the central clock located in the suprachiasmatic nucleus and clock genes (molecular clock) located in all cells. Dyslipidaemia and vascular inflammation are two hallmarks of atherosclerosis and numerous experimental studies conclude that they are under direct influence by both central and molecular clocks. This review will summarise the results of experimental studies on lipid metabolism, vascular inflammation and circadian rhythm, and translate them into the pathophysiology of atherosclerosis and cardiovascular disease. We discuss the effect of time-respected administration of medications in cardiovascular medicine. We review the evidence on the effect of bright light and melatonin on cardiovascular health, lipid metabolism and vascular inflammation. Finally, we suggest an agenda for future research and recommend on clinical practice.

Wearable derived cardiovascular responses to stressors in free-living conditions

Stress contributes to the progression of many diseases. Despite stress' contribution towards disease, few methods for continuously measuring stress exist. We investigated if continuously measured cardiovascular signals from a wearable device can be used as markers of stress. Using wearable technology (WHOOP Inc, Boston, MA) that continuously measures and calculates heart rate (HR) and heart rate variability (root-mean-square of successive differences; HRV), we assessed duration and magnitude of deviations in HR and HRV around the time of a run (from 23665 runs) or high-stress work (from 8928 high-stress work events) in free-living conditions. HR and HRV were assessed only when participants were motionless (HRmotionless). Runs were grouped into light, moderate, and vigorous runs to determine dose response relationships. When examining HRmotionless and HRV throughout the day, we found that these metrics display circadian rhythms; therefore, we normalized HRmotionless and HRV measures for each participant relative to the time of day. Relative to the period within 30 minutes leading up to a run, HRmotionless is elevated for up to 180-210 minutes following a moderate or vigorous run (P<0.05) and is unchanged or reduced following a light run. HRV is reduced for at least 300 minutes following a moderate or vigorous run (P<0.05) and is unchanged during a light run. Relative to the period within 30 minutes leading up to high-stress work, HRmotionless is elevated during and for up to 30 minutes following high-stress work. HRV tends to be lower during high-stress work (P = 0.06) and is significantly lower 90-300 minutes after the end of the activity (P<0.05). These results demonstrate that wearables can quantify stressful events, which may be used to provide feedback to help individuals manage stress.

Day-night patterns in heart rate variability and complexity: differences with age and cardiopulmonary disease

STUDY OBJECTIVES

Heart rate variability (HRV) measures provide valuable insights into physiology; however, gaps remain in understanding circadian patterns in heart rate dynamics. We aimed to explore day-night differences in heart rate dynamics in patients with chronic cardiopulmonary disease compared with healthy controls.

METHODS

Using 24-hour heart rate data from patients with chronic obstructive pulmonary disease (COPD) and/or heart failure (n = 16) and healthy adult controls (older group: ≥50 years, n = 42; younger group: 20-49 years, n = 136), we compared day-night differences in conventional time and frequency domain HRV indices and a multiscale-entropy-based complexity index (CI1-20) of HRV among the 3 groups.

RESULTS

Twenty-four-hour HRV showed significant day-night differences (marked with "△") among younger healthy (mean age: 34.5 years), older healthy (mean age: 61.6 years), and cardiopulmonary patients (mean age: 68.4 years), including change in percentage of adjacent intervals that differ > 50 ms (△pNN50), high frequency (△HF), normalized low frequency (△nLF), ratio (△LF/HF), and △CI1-20. Among these, △LF/HF (2.13 ± 2.35 vs 1.1 ± 2.47 vs -0.35 ± 1.25; P < .001) and △CI1-20 (0.15 ± 0.24 vs 0.02 ± 0.28 vs -0.21 ± 0.27; P < .001) were significant in each pairwise comparison following analysis of variance tests. Average CI1-20 was highest in younger healthy individuals and lowest in cardiopulmonary patients (1.37 ± 0.12 vs 1.01 ± 0.27; P < .001). Younger healthy patients showed a heart rate complexity dipping pattern (night < day), older healthy patients showed nondipping, and cardiopulmonary patients showed reverse dipping (night > day).

CONCLUSIONS

As measures of 24-hour variability, traditional and complexity-based metrics of HRV exhibit large day-night differences in healthy individuals; these differences are blunted, or even reversed, in individuals with cardiopulmonary pathology. Measures of diurnal dynamics may be useful indices of reduced adaptive capacity in patients with cardiopulmonary conditions.

CITATION

Ma Y, Chang M-C, Litrownik D, Wayne PM, Yeh GY. Day-night patterns in heart rate variability and complexity: differences with age and cardiopulmonary disease. J Clin Sleep Med. 2023;19(5):873-882.

Integrating the pattern of negative emotion processing and acute stress response with childhood stress among healthy young adults

Background: Childhood adversity might impair corticolimbic brain regions, which play a crucial role in emotion processing and the acute stress response. The dimensional model of childhood adversity proposed that deprivation and threat dimensions might associated with individuals' development through different mechanisms. However, few studies have explored the relationship between different dimensions of childhood stress, emotion processing, and acute stress reactivity despite the overlapping brain regions of the last two. With the aid of event-related potentials technique, we explore whether negative emotion processing, which might be particularly relevant for adaptive stress responding among individuals with adverse childhood experience, mediates the relationship between dimensional childhood stress and acute stress response. Method: Fifty-one young adults completed a free-viewing task to evaluate neural response to negative stimuli measured by late positive potential (LPP) of ERPs (Event-related potentials). On a separate day, heart rate and salivary cortisol were collected during a social-evaluative stress challenge (i.e., TSST, Trier Social Stress Test). After the TSST, childhood trauma questionnaire was measured to indicate the level of abuse (as a proxy of threat) and neglect (as a proxy of deprivation) dimensions. Multiple linear regression and mediation analysis were used to explore the relationship among the childhood stress, emotion processing and acute stress response. Results: Higher level of childhood abuse (but not neglect) was distinctly related to smaller LPP amplitudes to negative stimuli, as well as smaller heart rate reactivity to acute stress. For these participants, smaller LPP amplitudes were linked with smaller heart rate reactivity to acute stress. Furthermore, decreased LPP amplitudes to negative stimuli mediated the relationship between higher level of childhood abuse and blunted heart rate reactivity to stress. Conclusions: Consistent with the dimensional model of childhood stress, our study showed that childhood abuse is distinctly associated with neural as well as physiological response to threat. Furthermore, the blunted neural response to negative stimuli might be the underlying mechanism in which childhood abuse leads to the blunted acute stress response. Considering that all the participants are healthy in the present study, the blunted processing of negative stimuli might rather reflect adaptation instead of vulnerability, in order to prevent stress overshooting in the face of early-life threatening experiences.

Circadian Rhythms Disrupted by Light at Night and Mistimed Food Intake Alter Hormonal Rhythms and Metabolism

Availability of artificial light and light-emitting devices have altered human temporal life, allowing 24-hour healthcare, commerce and production, and expanding social life around the clock. However, physiology and behavior that evolved in the context of 24 h solar days are frequently perturbed by exposure to artificial light at night. This is particularly salient in the context of circadian rhythms, the result of endogenous biological clocks with a rhythm of ~24 h. Circadian rhythms govern the temporal features of physiology and behavior, and are set to precisely 24 h primarily by exposure to light during the solar day, though other factors, such as the timing of meals, can also affect circadian rhythms. Circadian rhythms are significantly affected by night shift work because of exposure to nocturnal light, electronic devices, and shifts in the timing of meals. Night shift workers are at increased risk for metabolic disorder, as well as several types of cancer. Others who are exposed to artificial light at night or late mealtimes also show disrupted circadian rhythms and increased metabolic and cardiac disorders. It is imperative to understand how disrupted circadian rhythms alter metabolic function to develop strategies to mitigate their negative effects. In this review, we provide an introduction to circadian rhythms, physiological regulation of homeostasis by the suprachiasmatic nucleus (SCN), and SCN-mediated hormones that display circadian rhythms, including melatonin and glucocorticoids. Next, we discuss circadian-gated physiological processes including sleep and food intake, followed by types of disrupted circadian rhythms and how modern lighting disrupts molecular clock rhythms. Lastly, we identify how disruptions to hormones and metabolism can increase susceptibility to metabolic syndrome and risk for cardiovascular diseases, and discuss various strategies to mitigate the harmful consequences associated with disrupted circadian rhythms on human health.

CovidRhythm: A Deep Learning Model for Passive Prediction of Covid-19 Using Biobehavioral Rhythms Derived From Wearable Physiological Data

Goal: To investigate whether a deep learning model can detect Covid-19 from disruptions in the human body's physiological (heart rate) and rest-activity rhythms (rhythmic dysregulation) caused by the SARS-CoV-2 virus. Methods: We propose CovidRhythm, a novel Gated Recurrent Unit (GRU) Network with Multi-Head Self-Attention (MHSA) that combines sensor and rhythmic features extracted from heart rate and activity (steps) data gathered passively using consumer-grade smart wearable to predict Covid-19. A total of 39 features were extracted (standard deviation, mean, min/max/avg length of sedentary and active bouts) from wearable sensor data. Biobehavioral rhythms were modeled using nine parameters (mesor, amplitude, acrophase, and intra-daily variability). These features were then input to CovidRhythm for predicting Covid-19 in the incubation phase (one day before biological symptoms manifest). Results: A combination of sensor and biobehavioral rhythm features achieved the highest AUC-ROC of 0.79 [Sensitivity = 0.69, Specificity = 0.89, F[Formula: see text] = 0.76], outperforming prior approaches in discriminating Covid-positive patients from healthy controls using 24 hours of historical wearable physiological. Rhythmic features were the most predictive of Covid-19 infection when utilized either alone or in conjunction with sensor features. Sensor features predicted healthy subjects best. Circadian rest-activity rhythms that combine 24 h activity and sleep information were the most disrupted. Conclusions: CovidRhythm demonstrates that biobehavioral rhythms derived from consumer-grade wearable data can facilitate timely Covid-19 detection. To the best of our knowledge, our work is the first to detect Covid-19 using deep learning and biobehavioral rhythms features derived from consumer-grade wearable data.

The Multiple Functions of Melatonin: Applications in the Military Setting

The aim of this review is to provide the reader with a general overview on the rationale for the use of melatonin by military personnel. This is a technique that is being increasingly employed to manage growing psycho-physical loads. In this context, melatonin, a pleotropic and regulatory molecule, has a potential preventive and therapeutic role in maintaining the operational efficiency of military personnel. In battlefield conditions in particular, the time to treatment after an injury is often a major issue since the injured may not have immediate access to medical care. Any drug that would help to stabilize a wounded individual, especially if it can be immediately administered (e.g., per os) and has a very high safety profile over a large range of doses (as melatonin does) would be an important asset to reduce morbidity and mortality. Melatonin may also play a role in the oscillatory synchronization of the neuro-cardio-respiratory systems and, through its epigenetic action, poses the possibility of restoring the main oscillatory waves of the cardiovascular system, such as the Mayer wave and RSA (respiratory sinus arrhythmia), which, in physiological conditions, result in the oscillation of the heartbeat in synchrony with the breath. In the future, this could be a very promising field of investigation.

Monitoring Effects of Sleep Extension and Restriction on Endurance Performance Using Heart Rate Indices

ABSTRACT

Roberts, SSH, Aisbett, B, Teo, W-P, and Warmington, S. Monitoring effects of sleep extension and restriction on endurance performance using heart rate indices. J Strength Cond Res 36(12): 3381-3389, 2022-Heart rate (HR) indices are useful for monitoring athlete fatigue or "readiness to perform." This study examined whether HR indices are sensitive to changes in readiness following sleep restriction (SR) and sleep extension (SE). Nine athletes completed a crossover study with 3 conditions: SR, normal sleep (NS), and SE. Each condition required completion of an endurance time trial (TT) on 4 consecutive days (D1-D4). Athletes slept habitually before D1; however, time in bed was reduced by 30% (SR), remained normal (NS), or extended by 30% (SE), on subsequent nights (D1-D3). Daily resting HR and HR variability were recorded. The maximal rate of HR increase and HR recovery was determined from a constant-load test before TTs. Exercise intensity ratios incorporating mean HR, mean power (W), and perceived exertion (RPE) were recorded at steady state during constant-load tests (W:HR SS ) and during TTs (W:HR TT , RPE:HR TT ). Compared with D4 of NS, RPE:HR TT was lower on D4 of SE ( p = 0.008)-when TT performances were faster. Compared with D1 of SR, RPE:HR TT was higher on D3 and D4 of SR ( p < 0.02). Moderate correlations were found between percentage changes in W:HR TT and changes in TT finishing time in SR ( r = -0.67, p = 0.049) and SE ( r = -0.69, p = 0.038) conditions. Intensity ratios incorporating mean HR seem sensitive to effects of sleep duration on athlete readiness to perform. When interpreting intensity ratios, practitioners should consider potential effects of prior sleep duration to determine whether sleep-promoting interventions are required (e.g., SE).

Maternal melatonin treatment rescues endocrine, inflammatory, and transcriptional deregulation in the adult rat female offspring from gestational chronodisruption

Introduction

Gestational chronodisruption impact maternal circadian rhythms, inhibiting the nocturnal increase of melatonin, a critical hormone that contributes to maternal changes adaptation, entrains circadian rhythms, and prepares the fetus for birth and successful health in adulthood. In rats, we know that gestational chronodisruption by maternal chronic photoperiod shifting (CPS) impaired maternal melatonin levels and resulted in long-term metabolic and cardiovascular effects in adult male offspring. Here, we investigated the consequences of CPS on mother and adult female offspring and explored the effects of melatonin maternal supplementation. Also, we tested whether maternal melatonin administration during gestational chronodisruption rescues maternal circadian rhythms, pregnancy outcomes, and transcriptional functions in adult female offspring.

Methods

Female rats raised and maintained in photoperiod 12:12 light: dark were mated and separated into three groups: (a) Control photoperiod 12:12 (LD); (b) CPS photoperiod; and (c) CPS+Mel mothers supplemented with melatonin in the drinking water throughout gestation. In the mother, we evaluated maternal circadian rhythms by telemetry and pregnancy outcomes, in the long-term, we study adult female offspring by evaluating endocrine and inflammatory markers and the mRNA expression of functional genes involved in adrenal, cardiac, and renal function.

Results

In the mothers, CPS disrupted circadian rhythms of locomotor activity, body temperature, and heart rate and increased gestational length by almost 12-h and birth weight by 12%, all of which were rescued by maternal melatonin administration. In the female offspring, we found blunted day/night differences in circulating levels of melatonin and corticosterone, abnormal patterns of pro-inflammatory cytokines Interleukin-1a (IL1a), Interleukin-6 (IL6), and Interleukin-10 (IL10); and differential expression in 18 out of 24 adrenal, cardiac, and renal mRNAs evaluated.

Conclusion

Maternal melatonin contributed to maintaining the maternal circadian rhythms in mothers exposed to CPS, and the re-establishing the expression of 60% of the altered mRNAs to control levels in the female offspring. Although we did not analyze the effects on kidney, adrenal, and heart physiology, our results reinforce the idea that altered maternal circadian rhythms, resulting from exposure to light at night, should be a mechanism involved in the programming of Non-Communicable Diseases.

Physiological and pharmacological perspectives of melatonin

The pineal gland is a interface between light-dark cycle and shows neuro-endocrine functions. Melatonin is the primary hormone of pineal gland, secreted at night. The night-time melatonin peak regulates the physiological functions at dark. Melatonin has several unique features as it synchronises internal rhythm with daily and seasonal variations, regulates circadian rhythm and sleep-wake cycle. Physiologically melatonin involves in detoxification of free radicals, immune functions, neuro-protection, oncostatic effects, cardiovascular functions, reproduction, and foetal development. The precise functions of melatonin are exhibited by specific receptors. In relation to pathophysiology, impaired melatonin secretion promotes sleep disorder, cancer progression, type-2 diabetes, and neurodegenerative diseases. Several reports have highlighted the therapeutic benefits of melatonin specially related to cancer protection, sleep disorder, psychiatric disorders, and jet lag problems. This review will touch the most of the area of melatonin-oriented health impacts and its therapeutic aspects.

Increase in cardioprotective SUR2A does not alter heart rate and heart rate regulation by physical activity and diurnal rhythm

OBJECTIVES

SUR2A is an ABC protein serving as a regulatory subunit of ATP-sensitive (KATP) channels. An increase in SUR2A levels is cardioprotective and it is a potential therapeutic strategy against ischaemic heart disease, heart failure and other diseases. However, whether overexpression of this protein has any adverse effects is yet to be fully understood. Here, we examined the heart rate and the heart rate diurnal variation in mice overexpressing SUR2A (SUR2A+) and their littermate controls (WT) using ECG telemetry that was continuously recorded for 14 days (days 8-23 post-radiotransmitter implantation).

METHODS

Using SigmaPlot 14.0 and Microsoft Excel, Area Under the Curve (AUC) for each parameter was calculated and plotted in a graph.

RESULTS

Both WT and SUR2A+ mice were more physically active during nights and there were no significant differences between two phenotypes. Physical activity was associated with increased heart rate in both phenotypes, but there were no differences in heart rate between phenotypes irrespective of physical activity or time of the day. A diurnal heart rate variation was preserved in the SUR2A+ mice. As area under the curve (AUC) analysis has the potential to reveal differences that are invisible with other statistical methods, we compared AUC of heart rate in SUR2A+ and WT mice. This analysis did not yield anything different from traditional analysis.

CONCLUSIONS

We conclude that increased SUR2A levels are not associated with changes in physical activity, heart rate and/or circadian rhythm influence on the heart rate. This lack of adverse effects supports a notion that manipulation with SUR2A levels is a promising cardioprotective strategy.

Heart rate variability during sleep after two, four and seven consecutive night shifts and recovery days: a cross-over intervention study

OBJECTIVE

Recovery after shift work is an important part reducing the health problems related to shift work. Heart rate variability (HRV) is an indicator of the balance between sympathetic and parasympathetic activity in the autonomic nervous system and can be used as a measure of recovery after night shifts. The aim of the study is to investigate autonomic recovery during sleep in response to night work in a crossover intervention study.

METHODS

Seventeen male police officers working in call centres in five different police district participated in the HRV measurements. The participants were exposed to three interventions: 2 + 2: two consecutive night shifts followed by two consecutive day recovery days; 4 + 4: four consecutive night shifts followed by four consecutive recovery days; 7 + 7: seven consecutive night shifts followed by seven consecutive recovery days. On the last day with night shift and the last recovery day in each intervention the participants underwent 24 h HRV recordings. We analysed HRV during sleep. The five 5-min intervals with the lowest heart rate during each sleep period were chosen for spectral analysis of the heart interbeat interval time series. The five 5-min intervals could occur at any time during sleep.

RESULTS

There were overall differences in HRV during sleep between days with night shifts and recovery days, primarily in parasympathetic activity. There was no difference in the lowest heart rate obtained, but the timing was different for the three interventions. The lowest heart rate after night shifts occurred 112 (SD 79) min, 174 (SD 115) min and 135 (SD 94) min after sleep onset for the 2 + 2 night shift, the 4 + 4 night shift and the 7 + 7 night shift, respectively.

CONCLUSION

Overall sleep-related autonomic recovery had higher parasympathetic modulation of cardiac rhythm on the 2 + 2 shift system compared to the 4 + 4 and 7 + 7 shift system.

Evidence for the Benefits of Melatonin in Cardiovascular Disease

The pineal gland is a neuroendocrine gland which produces melatonin, a neuroendocrine hormone with critical physiological roles in the circadian rhythm and sleep-wake cycle. Melatonin has been shown to possess anti-oxidant activity and neuroprotective properties. Numerous studies have shown that melatonin has significant functions in cardiovascular disease, and may have anti-aging properties. The ability of melatonin to decrease primary hypertension needs to be more extensively evaluated. Melatonin has shown significant benefits in reducing cardiac pathology, and preventing the death of cardiac muscle in response to ischemia-reperfusion in rodent species. Moreover, melatonin may also prevent the hypertrophy of the heart muscle under some circumstances, which in turn would lessen the development of heart failure. Several currently used conventional drugs show cardiotoxicity as an adverse effect. Recent rodent studies have shown that melatonin acts as an anti-oxidant and is effective in suppressing heart damage mediated by pharmacologic drugs. Therefore, melatonin has been shown to have cardioprotective activity in multiple animal and human studies. Herein, we summarize the most established benefits of melatonin in the cardiovascular system with a focus on the molecular mechanisms of action.

Treatment of Circadian Rhythm Sleep-Wake Disorders

Circadian rhythm sleep-wake disorders (CRSWDs) are a distinct class of sleep disorders caused by alterations to the circadian time-keeping system, its entrainment mechanisms, or a mismatch between the endogenous circadian rhythm and the external environment. The main clinical manifestations are insomnia and excessive daytime sleepiness that often lead to clinically meaningful distress or cause mental, physical, social, occupational, educational, or other functional impairment. CRSWDs are easily mistaken for insomnia or early waking up, resulting in inappropriate treatment. CRSWDs can be roughly divided into two categories, namely, intrinsic CRSWDs, in which sleep disturbances are caused by alterations to the endogenous circadian rhythm system due to chronic changes in the regulation or capture mechanism of the biological clock, and extrinsic circadian rhythm sleep-wake disorders, in which sleep disorders, such as jet lag or shift-work disorder, result from environmental changes that cause a mismatch between sleep-wakefulness times and internal circadian rhythms. Sleep diaries, actigraphy, and determination of day and night phase markers (dim light melatonin onset and core body temperature minimum) have all become routine diagnostic methods for CRSWDs. Common treatments for CRSWD currently include sleep health education, time therapy, light therapy, melatonin, and hypnotic drug therapy. Here, we review the progress in the epidemiology, etiology, diagnostic evaluation, diagnostic criteria, and treatment of intrinsic CRSWD, with emphasis on the latter, in the hope of bolstering the clinical diagnosis and treatment of CRSWDs.

Wearable device assessments of antiseizure medication effects on diurnal patterns of electrodermal activity, heart rate, and heart rate variability

Patient-generated health data provide a great opportunity for more detailed ambulatory monitoring and more personalized treatments in many diseases. In epilepsy, robust diagnostics applicable to the ambulatory setting are needed as diagnosis and treatment decisions in current clinical practice are primarily reliant on patient self-reports, which are often inaccurate. Recent work using wearable devices has focused on methods to detect and forecast epileptic seizures. Whether wearable device signals may also contain information about the effect of antiseizure medications (ASMs), which may ultimately help to better monitor their efficacy, has not been evaluated yet. Here we systematically investigated the effect of ASMs on different data modalities (electrodermal activity, EDA, heart rate, HR, and heart rate variability, HRV) simultaneously recorded by a wearable device in 48 patients with epilepsy over several days in the epilepsy long-term monitoring unit at a tertiary hospital. All signals exhibited characteristic diurnal variations. HRV, but not HR or EDA-based metrics, were reduced by ASMs. By assessing multiple signals related to the autonomic nervous system simultaneously, our results provide novel insights into the effects of ASMs on the sympathetic and parasympathetic interplay in the setting of epilepsy and indicate the potential of easy-to-wear wearable devices for monitoring ASM action. Future work using longer data may investigate these metrics on multidien cycles and their utility for detecting seizures, assessing seizure risk, or informing treatment interventions.

The impact of heart rate circadian rhythm on in-hospital mortality in stroke and critically ill patients: insights from the eICU Collaborative Research Database

BACKGROUND

Data showing the impact of dysregulated heart rate circadian rhythm in stroke and critically ill patients are scarce.

OBJECTIVE

The purpose of this study was to investigate whether the circadian rhythm of heart rate was an independent risk factor for in-hospital mortality in stroke and critically ill patients.

METHODS

Study patients from the recorded eICU Database were included in the current analyses. Three variables, Mesor, Amplitude, and Peak time were used to evaluate the heart rate circadian rhythm. The incremental value of circadian rhythm variables in addition to Acute Physiology and Chronic Health Evaluation (APACHE) IV score to predict in-hospital mortality was also explored.

RESULTS

A total of 6,201 Patients whose heart rate have cosinor rhythmicity. After adjustments, Mesor per 10 beats per min (bpm) increase was associated with a 1.18-fold (95%CI: 1.12, 1.25, P<0.001) and Amplitude per 5 bpm was associated with a 1.17-fold (95%CI: 1.07, 1.27, P<0.001) increase in the risk of in-hospital mortality, respectively. The risk of in-hospital mortality was highest in patients who had Peak time reached between 12:00-18:00 (OR: 1.35, 95%CI: 1.06, 1.72, P=0.015). Compared with APACHE IV score only (c-index=0.757), combining APACHE IV score and circadian rhythm variables of heart rate (c-index=0.766) was associated with increased discriminative ability (P=0.003).

CONCLUSION

Circadian rhythm of heart rate is an independent risk factor of the in-hospital mortality in stroke and critically ill patients. Including circadian rhythm variables regarding heart rate might increase the discriminative ability of the risk score to predict the prognosis of patients.

Time-specific associations of wearable sensor-based cardiovascular and behavioral readouts with disease phenotypes in the outpatient setting of the Chronic Renal Insufficiency Cohort

Patients with chronic kidney disease are at risk of developing cardiovascular disease. To facilitate out-of-clinic evaluation, we piloted wearable device-based analysis of heart rate variability and behavioral readouts in patients with chronic kidney disease from the Chronic Renal Insufficiency Cohort and controls (n  =  49). Time-specific partitioning of heart rate variability readouts confirm higher parasympathetic nervous activity during the night (mean RR at night 14.4  ±  1.9 ms vs. 12.8  ±  2.1 ms during active hours; n  =  47, analysis of variance (ANOVA) q  =  0.001). The α2 long-term fluctuations in the detrended fluctuation analysis, a parameter predictive of cardiovascular mortality, significantly differentiated between diabetic and nondiabetic patients (prominent at night with 0.58  ±  0.2 vs. 0.45  ±  0.12, respectively, adj. p  =  0.004). Both diabetic and nondiabetic chronic kidney disease patients showed loss of rhythmic organization compared to controls, with diabetic chronic kidney disease patients exhibiting deconsolidation of peak phases between their activity and standard deviation of interbeat intervals rhythms (mean phase difference chronic kidney disease 8.3 h, chronic kidney disease/type 2 diabetes mellitus 4 h, controls 6.8 h). This work provides a roadmap toward deriving actionable clinical insights from the data collected by wearable devices outside of highly controlled clinical environments.

Nomogram predicting testicular torsion in Japanese patients with acute scrotal pain using physical examination findings and environmental conditions: Development and prospective external validation

OBJECTIVES

To develop a prediction tool based on physical findings and environmental conditions without utilizing color Doppler ultrasonography to guide non-urologists and patients' families in determining the testicular torsion possibility among patients with acute scrotal pain.

METHODS

Overall, 110 consecutive patients aged ≤30 years with acute scrotal pain at Saitama Medical Center between 2012 and 2014 were retrospectively evaluated. Physical examination results, including scrotal inspection, palpation and gait observation, and environmental conditions at pain onset (time range and ambient temperature) were collected. Multivariate analysis identified significant and independent risk factors for testicular torsion, and a nomogram predicting testicular torsion was constructed. The model underwent prospective validation in an independent set of 123 consecutive patients admitted with acute scrotal pain to our institution between 2015 and 2017.

RESULTS

Testicular torsion diagnosis rates were 27% (30/110) and 26% (32/123) in the training and validation cohorts, respectively. Logistic regression analysis showed four risk factors for developing testicular torsion: abnormal testicular position, walking difficulty, midnight to early morning onset and ambient temperature <15°C at pain onset. The constructed nomogram showed that the areas under the receiver operating characteristic curves were 0.92 and 0.84 for the training and validation cohorts, respectively. The calibration plot showed an acceptable fitness between the predicted probability and the observed rate of testicular torsion.

CONCLUSIONS

A novel nomogram was developed solely based on physical findings and environmental conditions to predict testicular torsion in Japanese patients with acute scrotal pain.

Is there an association between socioeconomic status and the degree of diurnal variation in heart rate?

BACKGROUND

Disruption in circadian rhythms is associated with cardiovascular disease and may play a role in socioeconomic differences in cardiovascular disease prevalence. However, it is unclear whether low SES is associated with a lower diurnal rhythm in autonomic activity markers. We investigated the association between SES and the amplitude of the daily fluctuation of heart rate.

METHODS

We included data of 450 participants of a HELIUS sub-study in Amsterdam, the Netherlands. Participants wore an Actiheart monitor (CamNtech), a chest-worn monitor which measures heart rate every 15 s for several days. Cosinor analysis was performed on the time series of heart rate within each participant. We analyzed the association between the cosinor parameters (amplitude, midline and peak time of the diurnal HR rhythm) and SES indicators (education, occupational class and a proxy of income) in multivariate linear regression models, adjusting for age, sex and ethnicity.

RESULTS

There was a clear diurnal rhythm in the average heart rates, with a peak between noon and 18:00 and a trough between 04:00 and 06:00. This rhythm was present for all categories of education, occupation and income proxy. The estimates for the cosinor parameters did not differ consistently and significantly between categories of education, occupation or income proxy.

CONCLUSIONS

We did not find any consistent evidence to support our hypothesis of a diminished amplitude in the diurnal variation of heart rate in individuals with lower SES. Future studies should explore SES differences in the diurnal variation in markers of autonomic activity other than heart rate.

Relationship between the proficiency level and anxiety-reducing effect in a one-time heart rate variability biofeedback: A randomized controlled trial

INTRODUCTION

Previous studies have reported that the proficiency level of heart rate variability biofeedback (HRVBF) contributes significantly to the anxiety-reducing effects in continuous HRVBF interventions. Meanwhile, anxiety-reducing effects have been confirmed in one-time HRVBF interventions as well as continuous HRVBF; however, no study has analyzed the relationship between the proficiency level of a one-time HRVBF and its anxiety-reducing effects. To pursuit the effectiveness of a one-time HRVBF intervention, it is necessary to clarify whether the proficiency level is an important predictor of anxiety-reducing effects from a dose-response relationship between these 2 variables. The purpose of this study was to examine the dose-response relationship between the proficiency level and anxiety-reducing effects of a one-time HRVBF.

METHODS

This study was a single-blinded, randomized, controlled trial with stratification based on trait anxiety of the State-Trait Anxiety Inventory-JYZ. In total, 45 healthy young males aged 20 to 30 years were allocated to the HRVBF or control group with simple breathing at rest. The intervention was performed for 15 minute in each group. The state anxiety score of the State-Trait Anxiety Inventory-JYZ was measured to evaluate the anxiety-reducing effect before and after training.

RESULTS

The results showed no significant linear relationship between the proficiency level and anxiety-reducing effect, and variations in the proficiency level were observed post-intervention in the HRVBF group. A significant anxiety-reducing effect was only observed in the HRVBF group (P = .001, effect size r = 0.62).

CONCLUSIONS

These results suggest that there is no close relationship between the proficiency level and anxiety-reducing effect in one-time HRVBF and that HRVBF is effective in reducing anxiety regardless of individual differences in the proficiency level. Therefore, a one-time HRVBF may be a useful breathing technique for reducing state anxiety without specific education and breathing techniques.

TRIAL REGISTRATION

University Hospital Medical Information Network Clinical Trial Registry (UMIN000041760).

Acute cardiovascular effects of traffic-related air pollution (TRAP) exposure in healthy adults: A randomized, blinded, crossover intervention study

Exposure to traffic-related air pollution (TRAP) may enhance the risk of cardiovascular disease. However, the short-term effects of TRAP components on the cardiovascular system are not well understood. We conducted a randomized, double-blinded, crossover intervention study in which 39 healthy university students spent 2 h next to a busy road. Participants wore a powered air-purifying respirator (PAPR) or an N95 mask. PAPRs were equipped with a filter for particulate matter (PM), a PM and volatile organic compounds (VOCs) filter or a sham filter. Participants were blinded to PAPR filter type and underwent randomized exposures four times, once for each intervention mode. Blood pressure (BP), heart rate (HR) and heart rate variability (HRV) were measured before, during and for 6 h after the roadside exposure. Linear mixed-effect models were used to evaluate the effects of the interventions relative to baseline controlling for other covariates. All HRV measures increased during and following exposure for all intervention modes. Some HRV measures (SDNN and rMSSD during exposure and SDNN after exposure) were marginally affected by PM filtration. Wearing the N95 mask affected VLF power and rMSSD responses to traffic exposure differently than the PAPR interventions. Both systolic and diastolic BP increased slightly during exposure, but then were generally lower than baseline after exposure for the sham and filter interventions. HR, which fell during exposure and mostly remained lower than baseline after exposure, was lower yet with all filter interventions compared to the sham mode following exposure. Therefore, short-term exposure to traffic acutely affects HRV, BP and HR, but N95 mask and PAPR interventions generally show little efficacy in reducing these effects. Removing the PM component of TRAP has some limited effects on HRV responses to exposure but exaggerates the traffic-related decrease in HR. HRV findings from N95 mask interventions need to be interpreted cautiously.

Increase in rear-end collision risk by acute stress-induced fatigue in on-road truck driving

Increasing road crashes related to occupational drivers’ deteriorating health has become a social problem. To prevent road crashes, warnings and predictions of increased crash risk based on drivers’ conditions are important. However, in on-road driving, the relationship between drivers’ physiological condition and crash risk remains unclear due to difficulties in the simultaneous measurement of both. This study aimed to elucidate the relationship between drivers’ physiological condition assessed by autonomic nerve function (ANF) and an indicator of rear-end collision risk in on-road driving. Data from 20 male truck drivers (mean ± SD, 49.0±8.2 years; range, 35–63 years) were analyzed. Over a period of approximately three months, drivers’ working behavior data, such as automotive sensor data, and their ANF data were collected during their working shift. Using the gradient boosting decision tree method, a rear-end collision risk index was developed based on the working behavior data, which enabled continuous risk quantification. Using the developed risk index and drivers’ ANF data, effects of their physiological condition on risk were analyzed employing a logistic quantile regression method, which provides wider information on the effects of the explanatory variables, after hierarchical model selection. Our results revealed that in on-road driving, activation of sympathetic nerve activity and inhibition of parasympathetic nerve activity increased each quantile of the rear-end collision risk index. The findings suggest that acute stress-induced drivers’ fatigue increases rear-end collision risk. Hence, in on-road driving, drivers’ physiological condition monitoring and ANF-based stress warning and relief system can contribute to promoting the prevention of rear-end truck collisions.

Comprehensive Parent-Metabolite PBPK/PD Modeling Insights into Nicotine Replacement Therapy Strategies

Background

Nicotine, the pharmacologically active substance in both tobacco and many electronic cigarette (e-cigarette) liquids, is responsible for the addiction that sustains cigarette smoking. With 8 million deaths worldwide annually, smoking remains one of the major causes of disability and premature death. However, nicotine also plays an important role in smoking cessation strategies.

Objectives

The aim of this study was to develop a comprehensive, whole-body, physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model of nicotine and its major metabolite cotinine, covering various routes of nicotine administration, and to simulate nicotine brain tissue concentrations after the use of combustible cigarettes, e-cigarettes, nicotine gums, and nicotine patches.

Methods

A parent–metabolite, PBPK/PD model of nicotine for a non-smoking and a smoking population was developed using 91 plasma and brain tissue concentration–time profiles and 11 heart rate profiles. Among others, cytochrome P450 (CYP) 2A6 and 2B6 enzymes were implemented, including kinetics for CYP2A6 poor metabolizers.

Results

The model is able to precisely describe and predict both nicotine plasma and brain tissue concentrations, cotinine plasma concentrations, and heart rate profiles. 100% of the predicted area under the concentration–time curve (AUC) and maximum concentration (C_max) values meet the twofold acceptance criterion with overall geometric mean fold errors of 1.12 and 1.15, respectively. The administration of combustible cigarettes, e-cigarettes, nicotine patches, and nicotine gums was successfully implemented in the model and used to identify differences in steady-state nicotine brain tissue concentration patterns.

Conclusions

Our PBPK/PD model may be helpful in further investigations of nicotine dependence and smoking cessation strategies. As the model represents the first nicotine PBPK/PD model predicting nicotine concentration and heart rate profiles after the use of e-cigarettes, it could also contribute to a better understanding of the recent increase in youth e-cigarette use.

Electronic supplementary material

The online version of this article (10.1007/s40262-020-00880-4) contains supplementary material, which is available to authorized users.

Cluster Headache Pathophysiology—A Disorder of Network Excitability?

Patients’ accounts of cluster headache attacks, ictal restlessness, and electrophysiological studies suggest that the pathophysiology involves Aδ-fibre nociceptors and the network processing their input. Continuous activity of the trigeminal autonomic reflex throughout the in-bout period results in central sensitization of these networks in many patients. It is likely that several factors force circadian rhythmicity upon the disease. In addition to sensitization, circadian changes in pain perception and autonomic innervation might influence the excitability of the trigeminal cervical complex. Summation of several factors influencing pain perception might render neurons vulnerable to spontaneous depolarization, particularly at the beginning of rapid drops of the pain threshold (“summation headache”). In light of studies suggesting an impairment of short-term synaptic plasticity in CH patients, we suggest that the physiologic basis of CH attacks might be network overactivity—similarly to epileptic seizures. Case reports documenting cluster-like attacks support the idea of distinct factors being transiently able to induce attacks and being relevant in the pathophysiology of the disorder. A sustained and recurring proneness to attacks likely requires changes in the activity of other structures among which the hypothalamus is the most probable candidate.

Taking the time for our bodies: How wearables can be used to assess circadian physiology

Consumer wearables, such as smart watches, are a promising tool for monitoring circadian health in "real world" settings. Bowman et al. demonstrate that circadian signals can be accurately captured through heart rate data obtained from wearables, opening up new possibilities for population-level studies on heart rate and circadian rhythm.

A method for characterizing daily physiology from widely used wearables

Millions of wearable-device users record their heart rate (HR) and activity. We introduce a statistical method to extract and track six key physiological parameters from these data, including an underlying circadian rhythm in HR (CRHR), the direct effects of activity, and the effects of meals, posture, and stress through hormones like cortisol. We test our method on over 130,000 days of real-world data from medical interns on rotating shifts, showing that CRHR dynamics are distinct from those of sleep-wake or physical activity patterns and vary greatly among individuals. Our method also estimates a personalized phase-response curve of CRHR to activity for each individual, representing a passive and personalized determination of how human circadian timekeeping continually changes due to real-world stimuli. We implement our method in the "Social Rhythms" iPhone and Android app, which anonymously collects data from wearable-device users and provides analysis based on our method.

Positive Relationship Between Precompetitive Sympathetic Predominance and Competitive Performance in Elite Extreme Sports Athletes

Elite athletes achieve superior performance under high pressure in competitive situations. Although it is known that such situations affect the precompetitive activity of their autonomic nervous system (ANS), the relationship between precompetitive ANS activity and performance remains controversial. Especially in extreme sports, it has been shown that cardiac sympathetic tone occurs in athletes before competition attempts. However, the relationship between precompetitive sympathetic tone and performance is unclear. To investigate this relationship in extreme sports, we organized a freestyle snowboard jumping competition and examined competitors' physiological states and performance during this event. The electrocardiograms (ECGs) of 20 elite snowboarders were measured 10 min before each jump in different competitive situations: practice, qualifying, and final sessions. The mean heart rate (HR), the low-frequency to high-frequency component ratio (LF/HF ratio), the logarithm of the HF (lnHF) component of the frequency-domain of the heart rate variability (HRV), the ratio of the standard deviation of all R-R intervals to the root mean square of successive differences of R-R intervals (SDNN/rMSSD ratio), and the rMSSD of the time-domain of the HRV were calculated from the ECG data. The results showed a significant increase in the mean HR as well as significant decreases in the lnHF component and rMSSD of the HRV as the sessions progressed. Interestingly, the mean HR, LF/HF ratio and SDNN/rMSSD ratio of the HRV showed significant positive correlations with competitive scores, and the lnHF component and rMSSD of the HRV showed significant negative correlations with the scores. Our results indicate that precompetitive ANS activity becomes predominantly sympathetic in elite extreme athletes, such as freestyle snowboarders, when the competition intensifies, and that this sympathetic predominance is positively related to competitive performance.

Traumatic Injury to the Developing Brain: Emerging Relationship to Early Life Stress

Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.

Regulation of sinus node pacemaking and atrioventricular node conduction by HCN channels in health and disease

The funny current, I_f, was first recorded in the heart 40 or more years ago by Dario DiFrancesco and others. Since then, we have learnt that I_f plays an important role in pacemaking in the sinus node, the innate pacemaker of the heart, and more recently evidence has accumulated to show that I_f may play an important role in action potential conduction through the atrioventricular (AV) node. Evidence has also accumulated to show that regulation of the transcription and translation of the underlying Hcn genes plays an important role in the regulation of sinus node pacemaking and AV node conduction under normal physiological conditions - in athletes, during the circadian rhythm, in pregnancy, and during postnatal development - as well as pathological states - ageing, heart failure, pulmonary hypertension, diabetes and atrial fibrillation. There may be yet more pathological conditions involving changes in the expression of the Hcn genes. Here, we review the role of I_f and the underlying HCN channels in physiological and pathological changes of the sinus and AV nodes and we begin to explore the signalling pathways (microRNAs, transcription factors, GIRK4, the autonomic nervous system and inflammation) involved in this regulation. This review is dedicated to Dario DiFrancesco on his retirement.

Clocks, Rhythms, Sex, and Hearts: How Disrupted Circadian Rhythms, Time-of-Day, and Sex Influence Cardiovascular Health

Cardiovascular diseases are the top cause of mortality in the United States, and ischemic heart disease accounts for 16% of all deaths around the world. Modifiable risk factors such as diet and exercise have often been primary targets in addressing these conditions. However, mounting evidence suggests that environmental factors that disrupt physiological rhythms might contribute to the development of these diseases, as well as contribute to increasing other risk factors that are typically associated with cardiovascular disease. Exposure to light at night, transmeridian travel, and social jetlag disrupt endogenous circadian rhythms, which, in turn, alter carefully orchestrated bodily functioning, and elevate the risk of disease and injury. Research into how disrupted circadian rhythms affect physiology and behavior has begun to reveal the intricacies of how seemingly innocuous environmental and social factors have dramatic consequences on mammalian physiology and behavior. Despite the new focus on the importance of circadian rhythms, and how disrupted circadian rhythms contribute to cardiovascular diseases, many questions in this field remain unanswered. Further, neither time-of-day nor sex as a biological variable have been consistently and thoroughly taken into account in previous studies of circadian rhythm disruption and cardiovascular disease. In this review, we will first discuss biological rhythms and the master temporal regulator that controls these rhythms, focusing on the cardiovascular system, its rhythms, and the pathology associated with its disruption, while emphasizing the importance of the time-of-day as a variable that directly affects outcomes in controlled studies, and how temporal data will inform clinical practice and influence personalized medicine. Finally, we will discuss evidence supporting the existence of sex differences in cardiovascular function and outcomes following an injury, and highlight the need for consistent inclusion of both sexes in studies that aim to understand cardiovascular function and improve cardiovascular health.

Circadian control of human cardiovascular function

Endogenous circadian rhythms prepare the cardiovascular (CV) system for optimal function to match the daily anticipated behavioral and environmental cycles, including variable activities when awake during the day and recuperation when sleeping at night. The overall day-night patterns in most CV variables result from the summation of predictable circadian effects with variable behavioral and environmental effects on the CV system. The circadian system has also been implicated in the morning peak in the incidence of adverse CV events, including myocardial infarction, stroke, and sudden cardiac death. We discuss the resting and stress-reactive circadian control of CV physiology in humans and suggest future research opportunities, including improving CV therapy by optimally timing therapy relative to a person's internal body clock time.