Heart Rate Variability, Sleep Quality, and Depression in the Context of Chronic Stress

Predicting sleep based on physical activity, light exposure, and Heart rate variability data using wearable devices

OBJECTIVE

We aimed to improve the performance of sleep prediction algorithms by increasing the data amount, adding variables reflecting psychological state, and adjusting the data length.

MATERIALS AND METHODS

We used ActiGraph GT3X+® and Galaxy Watch Active2™ to collect physical activity and light exposure data. We collected heart rate variability (HRV) data with the Galaxy Watch. We evaluated the performance of sleep prediction algorithms based on different data sources (wearable devices only, sleep diary only, or both), data lengths (1, 2, or 3 days), and analysis methods. We defined the target outcome, 'good sleep', as ≥90% sleep efficiency.

RESULTS

Among 278 participants who denied having sleep disturbance, we used data including 2136 total days and nights from 230 participants. The performance of the sleep prediction algorithms improved with an increased amount of data and added HRV data. The model with the best performance was the extreme gradient boosting model; XGBoost, using both sources combined data with HRV, and 2-day data (accuracy=.85, area under the curve =.80).

CONCLUSIONS

The results show that the performance of the sleep prediction models improved by increasing the data amount and adding HRV data. Further studies targeting insomnia patients and applied researches on non-pharmacological insomnia treatment are needed.

Beyond HIV Shame: Effects of Self-Forgiveness in Improving Mental Health in HIV-Positive Individuals in Poland

Guided by the bio-psycho-socio-spiritual approach, this randomized controlled trial assessed the efficacy of a self-forgiveness intervention among 60 HIV-positive individuals in Poland. Participants underwent a 90-min "Restore: The Journey Toward Self-Forgiveness" session, in contrast to a wait-list control group. The intervention significantly enhanced self-forgiveness, spirituality, mental well-being, and heart rate variability in response to a cognitive stressor (i.e., a mental arithmetic challenge). Significant effects were observed in both between-group and within-subject comparisons. These results support the incorporation of self-forgiveness into psychological rehabilitation programs for HIV to improve quality of life and health outcomes.

Digital biomarkers in depression: A systematic review and call for standardization and harmonization of feature engineering

BACKGROUND

General physicians misclassify depression in more than half of the cases. Researchers have explored the feasibility of leveraging passively collected data points, also called digital biomarkers, to provide more granular understanding of depression phenotypes as well as a more objective assessment of disease.

METHOD

This paper provides a systematic review following the PRISMA guidelines (Page et al., 2021) to understand which digital biomarkers might be relevant for passive screening of depression. Pubmed and PsycInfo were systematically searched for studies published from 2019 to early 2024, resulting in 161 records assessed for eligibility. Excluded were intervention studies, studies focusing on a different disease or those with a lack of passive data collection. 74 studies remained for a quality assessment, after which 27 studies were included.

RESULTS

The review shows that depressed participants' real-life behavior such as reduced communication with others can be tracked by passive data. Machine learning models for the classification of depression have shown accuracies up to 0.98, surpassing the quality of many standardized assessment methods.

LIMITATIONS

Inconsistency of outcome reporting of current studies does not allow for drawing statistical conclusions regarding effectiveness of individual included features. The Covid-19 pandemic might have impacted the ongoing studies between 2020 and 2022.

CONCLUSION

While digital biomarkers allow real-life tracking of participant's behavior and symptoms, further work is required to align the feature engineering of digital biomarkers. With shown high accuracies of assessments, connecting digital biomarkers with clinical practice can be a promising method of detecting symptoms of depression automatically.

Post-adoption experiences of discrimination moderated by sleep quality are associated with depressive symptoms in previously institutionalized youth over and above deprivation-induced depression risk

The association of post-adoption experiences of discrimination with depressive symptoms was examined in 93 previously institutionalized (PI) youth (84% transracially adopted). Additionally, we explored whether sleep quality statistically moderated this association. Notably, we examined these associations after covarying a measure of autonomic balance (high/low frequency ratio in heart rate variability) affected by early institutional deprivation and a known risk factor for depression. PI youth exhibited more depressive symptoms and experiences of discrimination than 95 comparison youth (non-adopted, NA) raised in their biological families in the United States. In the final regression model, there was a significant interaction between sleep quality and discrimination, such that at higher levels of sleep quality, the association between discrimination and depression symptoms was non-significant. Despite being cross-sectional, the results suggest that the risk of depression in PI youth involves post-adoption experiences that appear unrelated to the impacts of early deprivation on neurobiological processes associated with depression risk. It may be crucial to examine methods of improving sleep quality and socializing PI youth to cope with discrimination as protection against discrimination and microaggressions.

Moderating effect of negative emotion differentiation in chronic stress and fatigue among Chinese employees

Introduction

According to the reactivity hypothesis and the diathesis-stress model, repeated activation of the stress system has a negative effect on health, and this effect may differ because of individual characteristics. Thus, the present study explores the effect of chronic stress on fatigue and investigates its mechanism.

Methods

A questionnaire survey of 288 participants selected from the northwest part of China was conducted (13.89% females; ages ranged from 18 to 34 years, with M ± SD = 23.14 ± 3.79 years) on chronic stress, fatigue, depression, anxiety, and negative emotion differentiation. SPSS 28.0 was used to process descriptive statistics and correlation analysis and the PROCESS macro was used to analyze the moderated chained multi-mediation.

Results

Chronic stress was found to be positively correlated with fatigue, depression, and anxiety; depression and anxiety played a chained multi-mediating role between chronic stress and fatigue, and negative emotion differentiation played a moderating role in the chained multi-mediation model.

Discussion

Compared with depression, anxiety plays a more important role in the influence of chronic stress on fatigue. Therefore, it is necessary to pay more attention to anxiety symptoms and take appropriate intervention measures. Negative emotion differentiation plays a moderating role. Improving negative emotion differentiation through mindfulness and adaptive emotion regulation is an effective way to reduce the influence of chronic stress on fatigue.

Evaluating the role of heart rate variability in monitoring stress and sleep quality among nurses in the aftermath of the COVID-19 pandemic

AIM

To assess heart rate variability (HRV) as a measure to assess job stress and sleep quality among nurses in the post-COVID-19 period.

BACKGROUND

The COVID-19 pandemic significantly affected nurses, with heightened job stress and impaired sleep quality impacting their well-being and effectiveness in patient care. HRV could offer insights for supporting strategies in the pandemic aftermath.

DESIGN

A quantitative cross-sectional study.

METHODS

This study involved 403 clinical nurses recruited from a teaching hospital in Taiwan. Data on job stress, work frustration, sleep quality and HRV were collected and analysed.

RESULTS

Among the nurses surveyed during the COVID-19 pandemic, 72.7% reported poor sleep quality (PSQI = 9.369). Job stress emerged as a strong predictor of work frustration. High stress levels and poor sleep quality were correlated with significantly decreased HRV, indicating a potential physiological impact of stress on the nurses' health and well-being.

CONCLUSIONS

HRV is a valuable and cost-effective measure for monitoring and managing nurses' well-being in the post-COVID-19 era. Targeted interventions can be implemented to support nurses' overall performance and promote their well-being by identifying those at high risk of job stress and poor sleep quality.

Early adolescent development in the face of violence: A systematic review running

BACKGROUND

Exposure to violence has severe and lasting effects on development. Despite the body of research examining childhood exposures to violence and victimization, developmental outcomes during early adolescence are poorly understood.

OBJECTIVE

To synthesize existing research on the effects of violence exposure on early adolescent development (youth 9-14 years old) and highlight areas for future research.

METHOD

We conducted a systematic search of PubMed, CINAHL, Web of Science, Scopus, and EMBASE for articles published between 2012 and 2023. Included articles focused on violence exposure related to experiencing or observing community violence, witnessing domestic violence and/or being the victim of chronic physical abuse.

RESULTS

Twenty-eight articles spanning four developmental domains were included: behavioral, biological, neurological, and social development. Behaviorally, violence exposure posed significant effects on both internalizing and externalizing symptoms. Biologically, violence exposure was strongly associated with advanced epigenetic age, accelerated puberty, and insomnia. Neurologically, violence exposure had significant associations with both structural and functional differences in the developing brain. Socially, violence exposure was related to poor school engagement, peer aggression, and low social support.

CONCLUSION

This systematic review highlights varying effects of violence exposure on early adolescent development. The gaps presented should be addressed and implemented into clinical practice via evidence-based policies and procedures to ensure successful transition to adulthood.

Sleep experiences of parents of children 18 years or younger with sickle cell disease during the COVID-19 pandemic: a qualitative study

STUDY OBJECTIVES

The coronavirus disease pandemic has highlighted disparities in health care. Parents assist in sickle cell disease management in children. Understanding sleep in parents of children who are diagnosed with sickle cell disease is an important facet of disease management. Our objectives were to identify sleep characteristics of parents of children with sickle cell disease age 18 years or younger during the coronavirus disease pandemic, to investigate measures used by parents to achieve restful sleep, and to discuss how sleep may be improved in parents of children diagnosed with sickle cell disease.

METHODS

This study conducted 14 face-to-face semistructured interviews with parents of children diagnosed with sickle cell disease. A majority of the interviews (93%) were conducted at a hematology clinic. Qualitative thematic analysis was used to analyze data.

RESULTS

All parents reported that their child experienced pain because of sickle cell disease. Most parents (86.7%) reported that their child was diagnosed with sickle cell anemia. Four themes were identified: difficulty obtaining restful sleep during their child's sickle cell crisis, sleep during the coronavirus disease pandemic, factors affecting sleep, and effects of sleep disturbance and deprivation on parental performance.

CONCLUSIONS

This research has highlighted some of the difficulties experienced by parents of children who are diagnosed with sickle cell disease and allows for additional insight into the sleep experiences of parents as they attempt to manage their child's disease.

CITATION

Osborne JC, Odlum M, Sedrak A. Sleep experiences of parents of children 18 years or younger with sickle cell disease during the COVID-19 pandemic: a qualitative study. J Clin Sleep Med. 2024;20(5):777-782.

Intertwined depressive and cognitive trajectories and the risk of dementia and death in older adults: a competing risk analysis

Background

Depressive symptoms and cognitive impairment often interact, rendering their associations controversial. To date, their joint trajectories and associations with dementia and death remain underexplored.

Aims

To explore the interactions between depressive symptoms and cognitive function, their developmental trajectories and the associations with all-cause dementia, Alzheimer's disease (AD) and all-cause death in older adults.

Methods

Data were from the Health and Retirement Study. Depressive symptoms and cognitive function were measured using the 8-item Centre for Epidemiologic Studies Depression Scale and the Telephone Interview of Cognitive Status, respectively. All-cause dementia and AD were defined by self-reported or proxy-reported physician diagnoses. All-cause death was determined by interviews. The restricted cubic spline, group-based trajectory modelling and subdistribution hazard regression were used.

Results

Significant interactions between depressive symptoms and cognitive function in 2010 in their association with new-onset all-cause dementia and AD from 2010 to 2020 were found, especially in women (p for interaction <0.05). Independent trajectory analysis showed that emerging or high (vs no) depressive trajectories and poor or rapidly decreased cognitive trajectories (vs very good) from 1996 to 2010 were at significantly higher risk of subsequent all-cause dementia, AD and all-cause death. 15 joint trajectories of depressive symptoms and cognitive function from 1996 to 2010 were determined, where rapidly decreased cognitive function was more common in those with no depressive symptoms. Compared with older adults with the trajectory of no depressive symptoms and very good cognitive function, those with the trajectory of no depressive symptoms but rapidly decreased cognitive function were much more likely to develop new-onset all-cause dementia and death, with subdistribution hazard ratios (95% confidence intervals) of 4.47 (2.99 to 6.67) and 1.84 (1.43 to 2.36), especially in women.

Conclusions

To effectively mitigate the risk of dementia and death, it is crucial to acknowledge the importance of preventing cognitive decline in older adults without depressive symptoms, particularly in women.

Association of intra-shift nap duration with heart rate variability in medical night shift workers

Napping during night shifts effectively reduces disease risk and improves work performance, but few studies have investigated the association between napping and physiological changes, particularly in off-duty daily lives. Changes in the autonomic nervous system precede diseases like cardiovascular disease, diabetes, and obesity. Heart rate variability is a good indicator of autonomic nervous system. This study aimed to investigate the link between night shift nap durations and heart rate variability indices in the daily lives of medical workers. As indicators of chronic and long-term alterations, the circadian patterns of heart rate variability indices were evaluated. We recruited 146 medical workers with regular night shifts and divided them into four groups based on their self-reported nap durations. Heart rate variability circadian parameters (midline-estimating statistic of rhythm, amplitude, and acrophase) were obtained by obtaining 24-h electrocardiogram on a day without night shifts, plotting the data of the heart rate variability indices as a function of time, and fitting them into periodic cosine curves. Using clinical scales, depression, anxiety, stress, fatigue, and sleepiness were assessed. Linear regression analysis revealed a positive relationship between 61-120-min naps and 24-h, daytime, and night-time heart rate variability indices, and the parasympathetic activity oscillation amplitude (indexed by high-frequency power, the square root of the mean of the sum of squares of differences between adjacent normal intervals, standard deviation of short-term R-R-interval variability) within one circadian cycle. This study indicated that napping for 61-120 min during night shifts could benefit medical workers' health, providing physiological evidence to promote nap management.

Neurobiological Underpinnings of Hyperarousal in Depression: A Comprehensive Review

Patients with major depressive disorder (MDD) exhibit an abnormal physiological arousal pattern known as hyperarousal, which may contribute to their depressive symptoms. However, the neurobiological mechanisms linking this abnormal arousal to depressive symptoms are not yet fully understood. In this review, we summarize the physiological and neural features of arousal, and review the literature indicating abnormal arousal in depressed patients. Evidence suggests that a hyperarousal state in depression is characterized by abnormalities in sleep behavior, physiological (e.g., heart rate, skin conductance, pupil diameter) and electroencephalography (EEG) features, and altered activity in subcortical (e.g., hypothalamus and locus coeruleus) and cortical regions. While recent studies highlight the importance of subcortical-cortical interactions in arousal, few have explored the relationship between subcortical-cortical interactions and hyperarousal in depressed patients. This gap limits our understanding of the neural mechanism through which hyperarousal affects depressive symptoms, which involves various cognitive processes and the cerebral cortex. Based on the current literature, we propose that the hyperconnectivity in the thalamocortical circuit may contribute to both the hyperarousal pattern and depressive symptoms. Future research should investigate the relationship between thalamocortical connections and abnormal arousal in depression, and explore its implications for non-invasive treatments for depression.

Prevalence and correlates of depressive symptoms among professional drivers in Saudi Arabia: A cross-sectional study

BACKGROUND

Professional drivers in Saudi Arabia may be at increased risk for mental illness because of their expatriate status, long driving hours, and unhealthy lifestyles.

OBJECTIVE

To assess the prevalence and correlates of depressive symptoms among professional drivers in Saudi Arabia, most of whom are expatriates.

METHODS

Professional drivers (n = 324) were interviewed after convenient sampling of transportation companies. The Depression Anxiety Stress Scale-21 (DASS-21) was used to screen for depressive symptoms. Correlates of depressive symptoms were identified using Cox regression with a fixed follow-up time.

RESULTS

Of the drivers, 20.4% had moderate to severe depressive symptoms. Sleep quality was found to be a significant independent correlate of depressive symptoms. Drivers with poor and fair sleep quality had higher risk of depressive symptoms than drivers with excellent sleep quality (poor: OR = 5.8, CI: 1.95-17.11; fair: OR = 4.5, CI: 1.68-11.96).

CONCLUSION

The frequency of depressive symptoms among professional drivers in Saudi Arabia is high (one out of five). Companies should consider screening for depressive symptoms and sleep disorders among employees and should provide referrals as needed.

The sleep response to stress: how sleep reactivity can help us prevent insomnia and promote resilience to trauma

Sleep reactivity is a predisposition to sleep disturbance during environmental perturbations, pharmacological challenges, or stressful life events. Consequently, individuals with highly reactive sleep systems are prone to insomnia disorder after a stressor, engendering risk of psychopathology and potentially impeding recovery from traumatic stress. Thus, there is tremendous value in ameliorating sleep reactivity to foster a sleep system that is robust to stress exposure, ultimately preventing insomnia and its downstream consequences. We reviewed prospective evidence for sleep reactivity as a predisposition to insomnia since our last review on the topic in 2017. We also reviewed studies investigating pre-trauma sleep reactivity as a predictor of adverse post-traumatic sequelae, and clinical trials that reported the effect of behavioural treatments for insomnia on mitigating sleep reactivity. Most studies measured sleep reactivity via self-report using the Ford Insomnia Response to Stress Test (FIRST), demonstrating high scores on this scale reliably indicate a sleep system with a lower capacity to tolerate stress. Nascent evidence suggests elevated sleep reactivity prior to trauma increases the risk of negative posttraumatic outcomes, namely acute stress disorder, depression, and post-traumatic stress disorder. Lastly, sleep reactivity appears most responsive to behavioural insomnia interventions when delivered early during the acute phase of insomnia. Overall, the literature strongly supports sleep reactivity as a premorbid vulnerability to incident acute insomnia disorder when faced with an array of biopsychosocial stressors. The FIRST identifies individuals at risk of insomnia a priori, thereby guiding early interventions toward this vulnerable population to prevent insomnia and promote resilience to adversity.

Nighttime sleep quality & daytime sleepiness across inpatient psychiatric treatment is associated with clinical outcomes

Prior research has demonstrated the strong link between sleep disturbance and mental health outcomes, including the importance of examining nighttime sleep quality and daytime sleepiness as separate constructs in relation to mental health outcomes. As such, the current study examined patients' self-reported nighttime sleep quality and daytime sleepiness trajectories over the course of inpatient treatment and how these trajectories related to treatment outcomes. Participants were 1,500 adults who voluntarily admitted to an inpatient psychiatric hospital. Mental health outcomes measured were emotion regulation problems, anxiety severity, depression severity, nightmare severity, and suicide risk. Group-based trajectory modeling was used to determine nighttime sleep quality and daytime sleepiness trajectory groups. Multivariate analyses of covariance (MANCOVA) were used to determine between group differences on mental health outcomes. Patients fit into distinct groups based on their trajectories of nighttime sleep quality and daytime sleepiness across inpatient psychiatric treatment: Low, Moderate, and High. Individuals with greater nighttime sleep disturbance and greater daytime sleepiness throughout treatment (High group) demonstrated significantly increased suicide risk, higher nightmare severity, more anxiety, more depression, and more emotion regulation difficulties at discharge. Results suggest an important connection exists between nighttime sleep quality and excessive daytime sleepiness and mental health outcomes for inpatient psychiatry.

The effects of auricular acupressure on blood pressure, stress, and sleep in elders with essential hypertension: a randomized single-blind sham-controlled trial

AIMS

Reduction of blood pressure and improvement of stress and sleep disorders in patients with essential hypertension were important factors. This study aimed to examine the effects of auricular acupressure on blood pressure, stress, and sleep quality among elderly with essential hypertension in Korea.

METHODS AND RESULTS

This study was a single-blind, randomized, placebo-controlled study. The experimental group (n = 23) received 8 weeks of auricular acupressure intervention on specific acupoints (superior triangular fossa, Shenmen, kidney, heart, and occiput) related to blood pressure, pulse rate, stress, and sleep, whereas the control group (n = 23) received auricular acupressure on non-specific acupoints. The primary outcomes were the systolic and diastolic blood pressure measured weekly. The secondary outcomes were the pulse rate, heart rate variability, actigraphy measured through Fitbit, and the Pittsburgh sleep quality index (PSQI) were measured before and after the experiment. There were statistically significant differences between two groups in systolic blood pressure (F = 5.67, P = 0.022), diastolic blood pressure (17.53, P < 0.001), and pulse rate (F = 6.78, P = 0.013) over time. Stress index (χ2 = 2.12, P = 0.040) and sleep efficiency (χ2 = 3.57, P = 0.001) were also significantly different before and after the experiment. However, there was no significant difference in the PSQI.

CONCLUSION

The findings showed that auricular acupressure leads to improvements in blood pressure, stress, and sleep in elderly people with essential hypertension. Therefore, auricular acupressure can be used as an alternative nursing intervention for hypertension prevention, stress, and sleep management.

REGISTRATION

WHO ICTRP KCT0007364.

Resting-state EEG as a potential indicator to predict sleep quality in depressive patients

OBJECTIVES

To investigate the changes in sleep quality, heart rate variability (HRV) and resting-state electroencephalogram (rsEEG) in patients with major depressive disorder (MDD), and to explore whether HRV and rsEEG may be served as more convenient tools to assess sleep quality in MDD patients.

METHOD

We included a total of 91 subjects (46 healthy controls and 45 MDD patients) and compared their sleep quality, HRV and power spectra of rsEEG. Correlation analyses were conducted to discuss the relationship between HRV and seven factors of PSQI. Multiple linear regression model was used to examine whether absolute band power could predict sleep quality in MDD patients.

RESULTS

We found higher PSQI scores and lower levels of HRV in depressive individuals compared with healthy controls. In MDD patients, sleep latency was negatively correlated with RMSSD and HF. Delta, theta, and alpha band power of rsEEG were higher in MDD patients. Regression analyses showed delta band power of TP8, as well as theta, alpha band power of AF3 predicts PSQI score of MDD patients.

CONCLUSIONS

The findings of our study show that some aspects of sleep problems had negative correlations with parasympathetic activity and the regression model supports that the band power of rsEEG may be used as a potential indicator to evaluate the sleep quality in MDD patients.

SIGNIFICANCE

Cortical hyperarousal may be one of the reasons leading to poor sleep quality of MDD patients. And resting-state EEG can be used as a potential indicator for clinical assessment of MDD patients' sleep quality.

Comprehensive evaluation of machine learning algorithms for predicting sleep-wake conditions and differentiating between the wake conditions before and after sleep during pregnancy based on heart rate variability

Introduction

Perinatal women tend to have difficulties with sleep along with autonomic characteristics. This study aimed to identify a machine learning algorithm capable of achieving high accuracy in predicting sleep-wake conditions and differentiating between the wake conditions before and after sleep during pregnancy based on heart rate variability (HRV).

Methods

Nine HRV indicators (features) and sleep-wake conditions of 154 pregnant women were measured for 1 week, from the 23rd to the 32nd weeks of pregnancy. Ten machine learning and three deep learning methods were applied to predict three types of sleep-wake conditions (wake, shallow sleep, and deep sleep). In addition, the prediction of four conditions, in which the wake conditions before and after sleep were differentiated-shallow sleep, deep sleep, and the two types of wake conditions-was also tested.

Results and Discussion

In the test for predicting three types of sleep-wake conditions, most of the algorithms, except for Naïve Bayes, showed higher areas under the curve (AUCs; 0.82-0.88) and accuracy (0.78-0.81). The test using four types of sleep-wake conditions with differentiation between the wake conditions before and after sleep also resulted in successful prediction by the gated recurrent unit with the highest AUC (0.86) and accuracy (0.79). Among the nine features, seven made major contributions to predicting sleep-wake conditions. Among the seven features, "the number of interval differences of successive RR intervals greater than 50 ms (NN50)" and "the proportion dividing NN50 by the total number of RR intervals (pNN50)" were useful to predict sleep-wake conditions unique to pregnancy. These findings suggest alterations in the vagal tone system specific to pregnancy.

Health Effects of Sleep Quality in Premutation Carrier Mothers of Individuals With Fragile X Syndrome

Sleep plays an integral role in supporting well-being, and sleep difficulties are common in mothers of individuals with developmental disabilities, including fragile X syndrome (FXS). This study assessed whether the effects of sleep quality on physical health and depression are exacerbated by genetic risk factors (CGG repeats) in FMR1 premutation carrier mothers of individuals with FXS. Poor sleep quality predicted a greater number of physical health conditions for mothers with CGG repeats in the mid-premutation range (90-110 repeats), but not for those in the lower (< 90 repeats) or higher (> 110 repeats) ends of the range. A significant association between poor sleep quality and maternal depressive symptoms was also observed, but there was no evidence that this effect varied by level of genetic vulnerability. This research extends our understanding of individual differences in the effects of sleep quality among mothers of individuals with FXS.

Validating Force Sensitive Resistor Strip Sensors for Cardiorespiratory Measurement during Sleep: A Preliminary Study

Sleep disorders can impact daily life, affecting physical, emotional, and cognitive well-being. Due to the time-consuming, highly obtrusive, and expensive nature of using the standard approaches such as polysomnography, it is of great interest to develop a noninvasive and unobtrusive in-home sleep monitoring system that can reliably and accurately measure cardiorespiratory parameters while causing minimal discomfort to the user's sleep. We developed a low-cost Out of Center Sleep Testing (OCST) system with low complexity to measure cardiorespiratory parameters. We tested and validated two force-sensitive resistor strip sensors under the bed mattress covering the thoracic and abdominal regions. Twenty subjects were recruited, including 12 males and 8 females. The ballistocardiogram signal was processed using the 4th smooth level of the discrete wavelet transform and the 2nd order of the Butterworth bandpass filter to measure the heart rate and respiration rate, respectively. We reached a total error (concerning the reference sensors) of 3.24 beats per minute and 2.32 rates for heart rate and respiration rate, respectively. For males and females, heart rate errors were 3.47 and 2.68, and respiration rate errors were 2.32 and 2.33, respectively. We developed and verified the reliability and applicability of the system. It showed a minor dependency on sleeping positions, one of the major cumbersome sleep measurements. We identified the sensor under the thoracic region as the optimal configuration for cardiorespiratory measurement. Although testing the system with healthy subjects and regular patterns of cardiorespiratory parameters showed promising results, further investigation is required with the bandwidth frequency and validation of the system with larger groups of subjects, including patients.

Simultaneous Recording of Objective Sleep in Mothers and School-aged Children with Developmental Disabilities: A Pilot Study of Actigraphy and Videosomnography

Mothers of school-aged children ages 3 to 17 years with developmental disabilities (DDs) commonly report sleep problems in their children associated with impaired maternal sleep. However, existing research relies heavily on mothers' self-reported sleep. This study aimed to determine the feasibility of objectively measuring child and mother sleep-wake patterns using actigraphy and videosomnography. This was an observational pilot study. Mothers wore actigraphy watches and video-recorded their child's sleep for 7 nights. Mothers also completed a 7-day sleep diary and questionnaires on sleep quality, depressive symptoms, stress, and child sleep problems. Ten mothers (32-49 years) and ten children with DDs (8-12 years) completed this study. Half of the children were boys with autism spectrum disorders. We successfully recruited 77% of eligible mothers for the study during the pandemic. Eight mothers successfully wore the actigraphy, and nine successfully video-recorded their child's sleep. Mothers rated their participation positively and considered the data collection protocol acceptable. While mothers' sleep patterns from actigraphy were mostly within recommendations, self-reported sleep quality was poor. Child's sleep estimates from videosomnography showed children slept substantially less than recommended sleep hours. Mothers also reported a high frequency of child sleep problems. Consistent with this pattern, mothers also endorsed elevated stress and depression. The use of actigraphy and videosomnography is feasible. Objective sleep measurement for mothers' and children's sleep is needed with self-report to measure multidimensional aspects of sleep and discrepancies between objective and self-report sleep measures. Future studies can use multi-methods sleep measures and work toward interventions that can improve family sleep and reduce mothers' stress and depression.

Does Being Ignored on WhatsApp Hurt? A Pilot Study on the Effect of a Newly Developed Ostracism Task for Adolescents

(1) Background: Many studies have used a well-known social exclusion task, namely Cyberball, to assess the psychophysiological reactions to ostracism in laboratory settings. However, this task has been recently criticized for its lack of realism. Instant messaging communication platforms are currently central communication channels where adolescents conduct their social life. These should be considered when recreating the emotional experiences that fuel the development of negative emotions. To overcome this limitation, a new ostracism task, namely SOLO (Simulated On-Line Ostracism), recreating hostile interactions (i.e., exclusion and rejection) over WhatsApp was developed. The aim of this manuscript is to compare adolescents' self-reported negative and positive affect, as well as physiological reactivity (i.e., heat rate, HR; heart rate variability, HRV) exhibited during SOLO to Cyberball. (2) Method: A total of 35 participants (Mage = 15.16; SD = 1.48; 24 females) took part in the study. The first group (n = 23; transdiagnostic group), recruited at an inpatient and outpatient unit of a clinic for children and adolescent psychiatry, psychotherapy, and psychosomatic therapy in Baden-Württemberg (Germany), reported clinical diagnoses linked with emotional dysregulation (e.g., self-injury and depression). The second group (n = 12; control group), recruited in the district of Bavaria and Baden-Württemberg, had no pre-existing clinical diagnoses. (3) Results: The transdiagnostic group showed higher HR (b = 4.62, p < 0.05) and lower HRV (b = 10.20, p < 0.01) in SOLO than in Cyberball. They also reported increased negative affect (interaction b = -0.5, p < 0.01) after SOLO but not after Cyberball. In the control group, no differences in either HR (p = 0.34) or HRV (p = 0.08) between tasks were found. In addition, no difference in negative affect after either task (p = 0.83) was found. (4) Conclusion: SOLO could be an ecologically valid alternative to Cyberball when assessing reactions to ostracism in adolescents with emotional dysregulation.

mHealth interventions to reduce stress in healthcare workers (fitcor): study protocol for a randomized controlled trial

BACKGROUND

Causes and consequences of chronic stress levels in the context of healthcare work are well examined. Nevertheless, the implementation and evaluation of high-quality interventions to reduce stress of healthcare workers is still missing. Internet and app-based interventions are a promising venue for providing interventions for stress reduction to a population that is otherwise difficult to reach due to shift work and time constraints in general. To do so, we developed the internet and app-based intervention (fitcor), a digital coaching of individual stress coping for health care workers.

METHODS

We applied the SPIRIT (Standard Protocol Items: Recommendations for Interventional Trials) statement as a guideline for the present protocol. A randomized controlled trial will be conducted. There are five different intervention groups and one waiting control group. To achieve the sample sizes required by power analysis (G*Power) (β-error 80%; effect size 0.25), the sample sizes of the respective scenarios will be at best as follows: 336 care workers from hospitals, 192 administrative health personnel, 145 care workers from stationary elderly care homes, and 145 care workers from ambulatory care providers in Germany. Participants will randomly be assigned to one of five different intervention groups. A crossover design with a waiting control group is planned. Interventions will be accompanied by three measurement points, first a baseline measure, second a post-intervention measure directly after completion of the intervention, and a follow-up measure 6 weeks after completion of the intervention. At all three measurement points, perceived team conflict, work-related experience patterns, personality, satisfaction with internet-based training, and back pain will be assessed using questionnaires, as well as heart rate variability, sleep quality, and daily movement will be recorded using an advanced sensor.

DISCUSSION

Workers in the health care sector increasingly face high job demands and stress levels. Traditional health interventions fail to reach the respective population due to organizational constraints. Implementation of digital health interventions has been found to improve stress coping behavior; however, the evidence in health care settings has not been established. To the best of our knowledge, fitcor is the first internet and app-based intervention to reduce stress among nursing and administrative health care personnel.

TRIAL REGISTRATION

The trial was registered at DRKS.de on 12 July 2021, registration number: DRKS00024605.

Biomarkers of sleep disturbance in adults with chronic illness: A scoping review

OBJECTIVES

The purpose of this scoping review was to identify which biomarkers for sleep disturbance were the most prevalent and significant in the literature across chronic illnesses.

METHODS

A scoping review was conducted, following Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines, to provide a map of the existing literature on the biomarkers of sleep disturbance in adults with chronic illness. Peer-reviewed articles published between 2010-2020 were included if they measured a biomarker and discussed sleep deprivation, disturbance, or dysfunction secondary to a chronic illness.

RESULTS

A total of 21 articles were included and synthesized using data charting. There were 24 different biomarkers identified, most commonly collected through serum. Biomarkers were grouped, then biomarkers and correlations with sleep were identified and mapped.

DISCUSSION

Overall, the most common biomarkers studied were interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), c-reactive protein (CRP), and interleukin-1 beta (IL-1β). Cytokines were the most commonly studied biomarkers, with a majority of studies focusing on pro-inflammatory cytokines. Based on the results of this review, CRP, IL-6, TNF-α, and erythrocyte sedimentation rate (ESR) showed themost significant correlations with sleep across all chronic illnesses. Future research is still needed to identify an ideal biomarker for sleep disturbance that can be used across chronic illnesses.

Efficacy of Individualized Sensory-Based mHealth Interventions to Improve Distress Coping in Healthcare Professionals: A Multi-Arm Parallel-Group Randomized Controlled Trial

Detrimental effects of chronic stress on healthcare professionals have been well-established, but the implementation and evaluation of effective interventions aimed at improving distress coping remains inadequate. Individualized mHealth interventions incorporating sensor feedback have been proposed as a promising approach. This study aimed to investigate the impact of individualized, sensor-based mHealth interventions focusing on stress and physical activity on distress coping in healthcare professionals. The study utilized a multi-arm, parallel group randomized controlled trial design, comparing five intervention groups (three variations of web-based training and two variations of an app training) that represented varying levels of individualization to a control group. Both self-reported questionnaire data (collected using Limesurvey) as well as electrocardiography and accelerometry-based sensory data (collected using Mesana Sensor) were assessed at baseline and post-intervention (after eight weeks). Of the 995 eligible participants, 170 (26%) completed the post-intervention measurement (Group 1: N = 21; Group 2: N = 23; Group 3: N = 7; Group 4: N = 34; Group 5: N = 16; Control Group: N = 69). MANOVA results indicated small to moderate time-by-group interaction effects for physical activity-related outcomes, including moderate to vigorous physical activity (F(1,5) = 5.8, p = ≤0.001, η2p = 0.057) and inactivity disruption (F(1,5) = 11.2, p = <0.001, η2p = 0.100), in the app-based intervention groups, but not for step counts and inactivity. No changes were observed in stress-related heart rate variability parameters over time. Despite a high dropout rate and a complex study design, the individualized interventions showed initial positive effects on physical activity. However, no significant changes in stress-related outcomes were observed, suggesting that the intervention duration was insufficient to induce physiological adaptations that would result in improved distress coping.

Continuous heart rate variability monitoring of freely moving chicken through a wearable electrocardiography recording system

Identification and quantification of stress and stress inducing factors are important components of animal welfare assessment and essential parts of poultry management. Measurement of the autonomic nervous system's influence on cardiac function using heart rate and heart rate variability (HR/HRV) indices can provide a non-invasive assessment of the welfare status of an animal. This paper presents a preliminary study showing the feasibility of continuous long-term measurement of HR/HRV indices in freely moving chicken. We developed and evaluated an electrocardiography (ECG) based HR/HRV recording system that can be used as a poultry wearable backpack for research studies. The backpack system was first validated against a commercial ECG amplifier, and the corresponding estimations of HR values matched well with each other. Then, an in vivo proof-of-concept experiment was conducted on floor-reared chickens to collect ECG data for 2 weeks. The extracted HR/HRV values show strong alignment with circadian patterns and well-defined sleep cycles. Wearable devices, like the backpack ECG system used in this study, may be best suited for application in freely moving poultry to get an insight into circadian abnormalities and sleep quality for stress and welfare management.

Health and social relationships of mothers of children in special education schools

BACKGROUND AND AIMS

The number of children in special education schools has increased in Japan. This study aimed to examine the association between special education school enrollment and the health and social relationships of mothers with children in these schools using population-based samples in Japan.

METHODS AND PROCEDURES

This study used data from the Kochi Child Health Impact of Living Difficulty (K-CHILD) study in 2016. First, fifth, eighth, and eleventh-grade children in all schools in Kochi prefecture were included (n = 12,623). Associations between school type (regular or special education school) and maternal physical and mental health and social relationships were investigated by multivariate regression models.

OUTCOMES AND RESULTS

There were 134 children in special education schools (1.1 %) and 12,489 children in regular schools. Mothers of children in special education schools were more likely to have higher body mass index (BMI), poorer mental health and lower neighborhood relations score. Mothers of children in regular schools had higher BMI when their children had higher behavioral problems.

CONCLUSION AND IMPLICATIONS

Mothers of children in special education schools are at risk of obesity, poor mental health, and having fewer social networks. Services and support should be expanded for caregivers based on their child's behavioral problems and school system.

Conflict at Work Impairs Physiological Recovery during Sleep: A Daily Diary Study

Sleep plays an essential role in maintaining employees' health and well-being. However, stressors, such as conflict at work, may interfere with employees' sleep. Drawing on previous literature on the relationship between conflict at work and sleep outcomes, we proposed a negative relationship between daily conflict at work and physiological changes during early sleep, particularly nocturnal heart rate variability (HRV). Furthermore, building on the perseverative cognition hypothesis, we proposed that daily work-related rumination mediates the relationship between conflict at work and nocturnal HRV. Ninety-three healthcare employees participated in a daily diary study for five workdays, resulting in 419 observations. Multilevel analysis revealed a significant relationship between daily conflict at work and nocturnal HRV, specifically high-frequency (HF) power. Daily conflict at work was found to predict rumination; however, rumination did not significantly predict nocturnal HRV. Our results suggest that daily conflict at work increases rumination during the off-job time and may directly alter nocturnal HRV, specifically parasympathetic function in early sleep.

Heart rate (HR) and heart rate variability (HRV) response to inhaled N, N-dimethyltryptamine (N, N-DMT): A case report

Background

N, N-Dimethyltryptamine (N, N-DMT) is a naturally occurring tryptamine-based alkaloid and classic psychedelic. The potent psychoactive properties of N, N-DMT are mediated by serotonin 2A (5-HT2A) receptor agonism. There are limited investigations into the physiologic effects of inhaled N, N-DMT, despite this being one of the most common routes of administration. Heart rate variability (HRV) is an emergent non-invasive marker of cardiac autonomic nervous system (ANS) regulation and reductions in HRV have been negatively associated with multiple health outcomes.

Methods

A case is described with a brief review of supportive findings.

Results

Heart rate (HR) and HRV responses following three naturalistic inhaled N, N-DMT experiences were documented in a healthy 31-year-old male. Acute transient elevations in HR immediately following N, N-DMT administration and a pronounced elevation in the average daily HRV one-day following the experiences were observed. The duration of experience shortened across the three experiences despite similar N, N-DMT doses.

Conclusion

These findings offer preliminary evidence into the effect of inhaled N, N-DMT on HR and HRV. Given the emergent understanding of reductions in HRV as a hazardous marker of stress, psychiatric conditions, and mental health outcomes, further research into the effects of psychedelics on HRV is warranted.

The cumulative effect of chronic stress and depressive symptoms affects heart rate in a working population

BACKGROUND

Chronic stress and depressive symptoms have both been linked to increased heart rate (HR) and reduced HR variability. However, up to date, it is not clear whether chronic stress, the mechanisms intrinsic to depression or a combination of both cause these alterations. Subclinical cases may help to answer these questions. In a healthy working population, we aimed to investigate whether the effect of chronic stress on HR circadian rhythm depends on the presence of depressive symptoms and whether chronic stress and depressive symptoms have differential effects on HR reactivity to an acute stressor.

METHODS

1,002 individuals of the SWEET study completed baseline questionnaires, including psychological information, and 5 days of electrocardiogram (ECG) measurements. Complete datasets were available for 516 individuals. In addition, a subset (n = 194) of these participants completed a stress task on a mobile device. Participants were grouped according to their scores for the Depression Anxiety Stress Scale (DASS) and Perceived Stress Scale (PSS). We explored the resulting groups for differences in HR circadian rhythm and stress reactivity using linear mixed effect models. Additionally, we explored the effect of stress and depressive symptoms on night-time HR variability [root mean square of successive differences (RMSSD)].

RESULTS

High and extreme stress alone did not alter HR circadian rhythm, apart from a limited increase in basal HR. Yet, if depressive symptoms were present, extreme chronic stress levels did lead to a blunted circadian rhythm and a lower basal HR. Furthermore, blunted stress reactivity was associated with depressive symptoms, but not chronic stress. Night-time RMSSD data was not influenced by chronic stress, depressive symptoms or their interaction.

CONCLUSION

The combination of stress and depressive symptoms, but not chronic stress by itself leads to a blunted HR circadian rhythm. Furthermore, blunted HR reactivity is associated with depressive symptoms and not chronic stress.

Behavioural, physical, and psychological predictors of cortisol and C-reactive protein in breast cancer survivors: A longitudinal study

Background

Breast cancer survivors (BCS) can exhibit a dysregulation of cortisol and elevated C-reactive protein (CRP) levels post-treatment, which increase the risk of diverse health outcomes. Certain behavioural, physical, and psychological variables may help to predict cortisol and CRP levels post-treatment. The aims of this study were to: (1) describe naturally occurring changes in absolute diurnal cortisol and CRP levels over a period of 1.5 years post-treatment among BCS, (2) assess if absolute diurnal cortisol and CRP levels change in tandem, and (3) assess behavioural, physical, and psychological variables as predictors of absolute diurnal cortisol levels and CRP levels.

Methods

Capillary blood and saliva samples were collected from 201 BCS, on average, 3.5 months post-treatment (T1) and again 3, 6, 9, and 12 months later (T2−T5). At each time point, five saliva samples were collected on two nonconsecutive days: at awakening, 30 ​min after awakening, 2:00 p.m., 4:00 p.m., and at bedtime. At each time point, participants also completed self-report questionnaires and wore an accelerometer for seven consecutive days. Data were analyzed using multilevel modeling.

Results

Absolute diurnal cortisol levels did not change significantly over time. CRP levels decreased across time points (B_linear ​= ​−0.31, p ​= ​.01), though the rate of decrease slowed over time (B_quadratic ​= ​0.05, p ​= ​.03). Generally, greater sedentary time predicted higher overall absolute diurnal cortisol levels (B ​< ​0.01, p ​= ​.01); whereas higher physical activity (B ​= ​−0.004, p ​< ​.01), lower body mass index (B ​= ​0.10, p ​< ​.01), and lower health- and cancer-related stress (B ​= ​0.24, p ​= ​.04) predicted lower overall CRP levels. Also, lower absolute diurnal cortisol levels were evident when participants engaged in more sedentary time, as compared to their own average sedentary time (B ​= ​−0.01, p ​< ​.01).

Conclusions

Results offer insight into the nature of change in diurnal cortisol and CRP levels among BCS from treatment completion onwards and offer clinical implications. Helping BCS manage their weight, reduce stress, increase physical activity participation, and decrease sedentary time as soon as possible after treatment may help to reduce physiological dysregulations, thereby lowering the risk of adverse health outcomes in this population. Further research investigating specific intervention parameters such as type, context, frequency, and intensity are warranted for the development of the most optimal interventions.

A mysterious sensation about sleep and health: the role of interoception

Background

Interoception is mental awareness, recognition and acknowledgement of physiological body signals. Understanding the role of sleep and interoception may provide a better understanding surrounding the sleep-health connection. Our primary objective was to examine the potential relationships between subjective sleep quality and multiple dimensions of interoceptive abilities in a large sample of young adults, a group who are vulnerable to sleep impairment and its widespread health consequences.

Methods

We conducted an online cross-sectional survey targeting young adults, aged 18–25 years. The Pittsburgh Sleep Quality Index (PSQI) was used to identify subjective sleep quality and the Multidimensional Assessment of Interoceptive Awareness Version 2 was used to assess eight domains of interoception. We conducted a series of Spearman’s bivariate correlations to assess the relationships between global sleep quality as well as the seven PSQI sub-components in relation to the eight interoception outcomes. We then conducted quantile regression to assess if global PSQI score was an independent predictor of interoception. Participants (n = 609) consented and provided data.

Results

After adjustment, the global PSQI was a significant predictor of ‘Non-Distracting’, ‘Emotional Awareness’ and ‘Trusting’, where β = − 0.10 (95% CI: − 0.14, − 0.07), β = 0.05 (0.01, 0.09), and β = − 0.10 (− 0.14, − 0.05), respectively.

Conclusions

Our findings reveal a small, significant relationship between sleep quality and interoceptive abilities amongst young adults. Sleep impairment may inhibit interoceptive skills, thus adding value to the mechanistic explanation of the sleep-health relationship. Experimental and prospective studies are needed to determine temporal associations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-11603-0.

Moderation of the Stressor-Strain Process in Interns by Heart Rate Variability Measured with a Wearable and Smartphone App: a Within-Subject Design Using Continuous Monitoring

Background

The emergence of smartphones and wearable sensor technologies enables easy and unobtrusive monitoring of physiological and psychological data related to an individual’s resilience. Heart rate variability (HRV) is a promising biomarker for resilience based on between-subject population studies, but observational studies that apply a within-subject design and use wearable sensors in order to observe HRV in a naturalistic real-life context are needed.

Objective

This study aims to explore whether resting HRV and total sleep time (TST) are indicative and predictive of the within-day accumulation of the negative consequences of stress and mental exhaustion. The tested hypotheses are that demands are positively associated with stress and resting HRV buffers against this association, stress is positively associated with mental exhaustion and resting HRV buffers against this association, stress negatively impacts subsequent-night TST, and previous-evening mental exhaustion negatively impacts resting HRV, while previous-night TST buffers against this association.

Methods

In total, 26 interns used consumer-available wearables (Fitbit Charge 2 and Polar H7), a consumer-available smartphone app (Elite HRV), and an ecological momentary assessment smartphone app to collect resilience-related data on resting HRV, TST, and perceived demands, stress, and mental exhaustion on a daily basis for 15 weeks.

Results

Multiple linear regression analysis of within-subject standardized data collected on 2379 unique person-days showed that having a high resting HRV buffered against the positive association between demands and stress (hypothesis 1) and between stress and mental exhaustion (hypothesis 2). Stress did not affect TST (hypothesis 3). Finally, mental exhaustion negatively predicted resting HRV in the subsequent morning but TST did not buffer against this (hypothesis 4).

Conclusions

To our knowledge, this study provides first evidence that having a low within-subject resting HRV may be both indicative and predictive of the short-term accumulation of the negative effects of stress and mental exhaustion, potentially forming a negative feedback loop. If these findings can be replicated and expanded upon in future studies, they may contribute to the development of automated resilience interventions that monitor daily resting HRV and aim to provide users with an early warning signal when a negative feedback loop forms, to prevent the negative impact of stress on long-term health outcomes.

Salidroside Improves Chronic Stress Induced Depressive Symptoms Through Microglial Activation Suppression

Depression is a severe neurological disorder highly associated with chronic mental stress stimulation, which involves chronic inflammation and microglial activation in the central nervous system (CNS). Salidroside (SLDS) has been reported to exhibit anti-neuroinflammatory and protective properties on neurological diseases. However, the mechanism underlying the effect of SLDS on depressive symptoms has not been well elaborated. In the present study, the effects of SLDS on depressive behaviors and microglia activation in mice CNS were investigated. Behavioral tests, including Forced swimming test (FST), Open field test (OFT) and Morris water maze (MWM) revealed that SLDS treatment attenuated the depressive behaviors in stress mice. SLDS treatment significantly reduced the microglial immunoreactivity for both Iba-1 and CD68, characteristic of deleterious M1 phenotype in hippocampus of stress mice. Additionally, SLDS inhibited microglial activation involving the suppression of ERK1/2, P38 MAPK and p65 NF-κB activation and thus reduced the expression and release of neuroinflammatory cytokines in stress mice as well as in lipopolysaccharide (LPS)-induced primary microglia. Also, SLDS changed microglial morphology, attachment and reduced the phagocytic ability in LPS-induced primary microglia. The results demonstrated that SLDS treatment could improve the depressive symptoms caused by unpredictable chronic stress, indicating a potential therapeutic application of SLDS in depression treatment by interfering microglia-mediated neuroinflammation.

Using 24-h Heart Rate Variability to Investigate the Sleep Quality and Depression Symptoms of Medical Students

There have been numerous studies on the relationship between sleep and depression, as well as the relationship between sleep and depression, and heart rate variability (HRV), respectively. Even so, few studies have combined 24-h HRV analysis to study sleep quality and depressive symptoms. The purpose of this cross-sectional study was to investigate the relationship between depressed symptoms, sleep quality, and 24-h HRV in medical students. The particiants were all students at a medical university in Guangdong province, China. A total of 74 college students participated. They were asked to complete a questionnaire that included the Pittsburgh Sleep Quality Index (PSQI), the Beck Depression Inventory-II (BDI-II), the Positive and Negative Affect Scale (PANAS), and 24-h ECG monitoring. The results showed that 41.7% of the medical students had poor sleep quality, with higher levels of depressive symptoms and more negative emotions, and there was no difference in 24-h HRV indices between the low PSQI group and the high one. Correlation analysis showed that there was a significant relationship between sleep quality and depressive symptoms (r = 0.617), but the relationship between 24-h HRV indices and PSQI global scores, BDI scores were not significant. However, the correlation analysis of PSQI components and 24-h HRV showed that sleep disturbance was significantly negatively correlated with SDNN and LF in waking period (r = -0.285, -0.235), and with SDNN in sleeping period (r = -0.317). In general, the sleep disturbance in PSQI components can sensitively reflect the relationship between sleep quality and 24-h HRV of medical students. Individuals with higher sleep disturance may have lower SDNN during awake period and bedtime period, and lower LF in awake period. Twenty-four hour HRV has certain application value in clinical sleep quality monitoring, and its sensitivity and specificity in clinical application and daily life are still worth further investigation.