Reduced heart rate variability predicts poor sleep quality in a case–control study of chronic fatigue syndrome

Parasympathetic function is important in the induction and maintenance of sleep. We examined whether nocturnal vagal modulation of heart rate is related to the poor sleep quality commonly reported in chronic fatigue syndrome (CFS). Heart rate (HR, as R–R intervals) was continuously monitored during sleep in 20 patients with CFS and 20 matched control subjects. Questionnaires assessed demographic information, symptoms, functional impairment, and subjective sleep quality. CFS was associated with more sleep problems in general and poorer subjective sleep quality on the study night (all p < 0.003), and reports of repeated awakening during the night were 7 times more likely compared to healthy subjects (p = 0.017). Time and frequency-domain parameters of HR variability during sleep were significantly lower in patients with CFS (all p < 0.006). Multiple regression analyses revealed that heart rate variability (HRV) parameters were the best predictors of subjective sleep measures. This study identified significant reductions in vagal modulation of heart rate during sleep in CFS. Low HRV strongly predicted sleep quality—suggesting a pervasive state of nocturnal sympathetic hypervigilance in CFS.     

Effects of exercise intensity and duration on nocturnal heart rate variability and sleep quality

Acute physical exercise may affect cardiac autonomic modulation hours or even days during the recovery phase. Although sleep is an essential recovery period, the information on nocturnal autonomic modulation indicated by heart rate variability (HRV) after different exercises is mostly lacking. Therefore, this study investigated the effects of exercise intensity and duration on nocturnal HR, HRV, HR, and HRV-based relaxation, as well as on actigraphic and subjective sleep quality. Fourteen healthy male subjects (age 36 ± 4 years, maximal oxygen uptake 49 ± 4 ml/kg/min) performed five different running exercises on separate occasions starting at 6 p.m. with HR guidance at home. The effect of intensity was studied with 30 min of exercises at intensities corresponding to HR level at 45% (easy), 60% (moderate) and 75% (vigorous) of their maximal oxygen uptake. The effect of duration was studied with 30, 60, and 90 min of moderate exercises. Increased exercise intensity elevated nocturnal HR compared to control day (p < 0.001), but it did not affect nocturnal HRV. Nocturnal HR was greater after the day with 90- than 30- or 60-min exercises (p < 0.01) or control day (p < 0.001). Nocturnal HRV was lower after the 90-min exercise day compared to control day (p < 0.01). Neither exercise intensity nor duration had any impact on actigraphic or subjective sleep quality. The results suggest that increased exercise intensity and/or duration cause delayed recovery of nocturnal cardiac autonomic modulation, although long exercise duration was needed to induce changes in nocturnal HRV. Increased exercise intensity or duration does not seem to disrupt sleep quality.     

Procedural memory consolidation is associated with heart rate variability and sleep spindles

Sleep and memory studies often focus on overnight rather than long‐term memory changes, traditionally associating overnight memory change (OMC) with sleep architecture and sleep patterns such as spindles. In addition, (para‐)sympathetic innervation has been associated with OMC after a daytime nap using heart rate variability (HRV). In this study we investigated overnight and long‐term performance changes for procedural memory and evaluated associations with sleep architecture, spindle activity (SpA) and HRV measures (R‐R interval [RRI], standard deviation of R‐R intervals [SDNN], as well as spectral power for low [LF] and high frequencies [HF]). All participants (N = 20, M_age = 23.40 ± 2.78 years) were trained on a mirror‐tracing task and completed a control (normal vision) and learning (mirrored vision) condition. Performance was evaluated after training (R1), after a full‐night sleep (R2) and 7 days thereafter (R3). Overnight changes (R2‐R1) indicated significantly higher accuracy after sleep, whereas a significant long‐term (R3‐R2) improvement was only observed for tracing speed. Sleep architecture measures were not associated with OMC after correcting for multiple comparisons. However, individual SpA change from the control to the learning night indicated that only “SpA enhancers” exhibited overnight improvements for accuracy and long‐term improvements for speed. HRV analyses revealed that lower SDNN and LF power was associated with better OMC for the procedural speed measure. Altogether, this study indicates that overnight improvement for procedural memory is specific for spindle enhancers, and is associated with HRV during sleep following procedural learning.     

Anticipated next‐day demand affects the magnitude of the cortisol awakening response,but not subjective or objective sleep

Whilst the association between sleep and stress is well established, few studies have examined the effects of an anticipated stressor upon sleep and relevant physiological markers. The aim of the present study was to examine whether an anticipated stressor in the form of next‐day demand affects subjective and objective sleep, and multiple indices of the cortisol awakening response. Subjective and objective sleep and the cortisol awakening response were measured over three consecutive nights in 40 healthy adults in a sleep laboratory. During their second night, participants were informed that they would either be required to complete a series of demanding cognitive tasks, in a competition format, during the next day (anticipation condition; n = 22), or were given no instruction (sedentary condition; n = 18). Sleep was measured subjectively using sleep diaries, objectively using polysomnography, and saliva was measured at awakening, +15, +30, +45 and +60 min each morning, from which cortisol awakening response measurement indices were derived: awakening cortisol levels, the mean increase in cortisol levels and total cortisol secretion. There were no between‐group differences in subjective or objective sleep in the night preceding the anticipated demand; however, compared with the sedentary condition, those in the anticipation group displayed a larger mean increase in cortisol levels, representing the cortisol awakening response magnitude, on the morning of the anticipated demand. Overall, the results suggest that whilst anticipated stress affected the subsequent cortisol awakening response, subjective and objective sleep remained undisturbed. It is possible that the timing of an anticipated stressor, rather than its expected duration, may influence subsequent sleep disruption.     

Time‐varying correlations between delta EEG power and heart rate variability in midlife women: The SWAN Sleep Study

No studies have evaluated the dynamic, time‐varying relationship between delta electroencephalographic (EEG) sleep and high frequency heart rate variability (HF‐HRV) in women. Delta EEG and HF‐HRV were measured during sleep in 197 midlife women (M_age = 52.1, SD = 2.2). Delta EEG–HF‐HRV correlations in nonrapid eye movement (NREM) sleep were modeled as whole‐night averages and as continuous functions of time. The whole‐night delta EEG–HF‐HRV correlation was positive. The strongest correlations were observed during the first NREM sleep period preceding and following peak delta power. Time‐varying correlations between delta EEG–HF‐HRV were stronger in participants with sleep‐disordered breathing and self‐reported insomnia compared to healthy controls. The dynamic interplay between sleep and autonomic activity can be modeled across the night to examine within‐ and between‐participant differences including individuals with and without sleep disorders.     

Children's heart rate variability as stress indicator: Association with reported stress and cortisol

Stress is a complex phenomenon coordinated by two main neural systems: the hypothalamic–pituitary–adrenal system with cortisol as classical stress biomarker and the autonomic nervous system with heart rate variability (HRV) as recently suggested stress marker. To test low HRV (5 minute measurements) as stress indicator in young children (5-10y), associations with self-reported chronic stress aspects (events, emotions and problems) (N = 334) and salivary cortisol (N = 293) were performed. Peer problems, anger, anxiety and sadness were associated with lower root mean square of successive differences (RMSSD) and high frequency power (i.e. lower parasympathetic activity). Anxiety and anger were also related to a higher low frequency to high frequency ratio. Using multilevel modelling, higher cortisol levels, a larger cortisol awakening response and steeper diurnal decline were also associated with these HRV patterns of lower parasympathetic activity. Conclusion: Low HRV (lower parasympathetic activity) might serve as stress indicator in children.     

Impact of sleep inertia on visual selective attention for rare targets and the influence of chronotype

Sleep inertia is affected by circadian phase, with worse performance upon awakening from sleep during the biological night than biological day. Visual search/selective visual attention performance is known to be sensitive to sleep inertia and circadian phase. Individual differences exist in the circadian timing of habitual wake time, which may contribute to individual differences in sleep inertia. Because later chronotypes awaken at an earlier circadian phase, we hypothesized that later chronotypes would have worse visual search performance during sleep inertia than earlier chronotypes if awakened at habitual wake time. We analysed performance from 18 healthy participants [five females (22.1 ± 3.7 years; mean ± SD)] at ~1, 10, 20, 30, 40 and 60 min following electroencephalogram‐verified awakening from an 8 h in‐laboratory sleep opportunity. Cognitive throughput and reaction times of correct responses were impaired by sleep inertia and took ~10–30 min to improve after awakening. Regardless whether chronotype was defined by dim light melatonin onset or mid‐sleep clock hour on free days, derived from the Munich ChronoType Questionnaire, the duration of sleep inertia for cognitive throughput and reaction times was longer for later chronotypes (n = 7) compared with earlier chronotypes (n = 7). Specifically, performance for earlier chronotypes showed significant improvement within ~10–20 min after awakening, whereas performance for later chronotypes took ~30 min or longer to show significant improvement (P < 0.05). Findings have implications for decision making immediately upon awakening from sleep, and are consistent with circadian theory suggesting that sleep inertia contributes to longer‐lasting impairments in morning performance in later chronotypes.     

Sleep as a tool for evaluating autonomic drive to the heart in cardiac transplant patients

STUDY OBJECTIVES: The aim of this study was to investigate the autonomic drive to the heart in cardiac transplant patients (CTP) using heart rate (HR) and HR variability (HRV) analysis during non-rapid eye movement (NREM)-rapid eye movement (REM) sleep cycles, in particular during arousal associated with the emergence from slow wave sleep (SWS). In healthy subjects, this arousal is characterized by a pronounced HR surge, and HRV is lower during SWS than during the subsequent "active" sleep stage 2 and REM sleep. PARTICIPANTS: The participants were 24 adults, 14 CTP (men, n = 11; women, n = 3; mean age, 62.2 +/- 2.2 years; time after transplantation, 4-14 years) and 10 control subjects (men, n = 7; women, n = 3; mean age, 61.0 +/- 1.8 years). DESIGN: The subjects underwent polygraphic sleep, cardiac, and respiratory recordings during an experimental night. HR was measured during the arousal. HRV was estimated from the R-R intervals in 5-minute stationary segments preceding and following arousal, ie, during SWS and active sleep stage 2 from the first 2 complete NREM-REM sleep cycles. RESULTS: In controls, HR increased during arousal associated with the emergence from SWS during the 2 sleep cycles (P < .05). Sleep-stage-dependent increases of all HRV indexes were observed in the 2 sleep cycles. Concerning CTP, 5 of them displayed a smaller HR increase at arousal, whereas 9 other patients had no HR variation. This distinction between the 2 groups of CTP was confirmed by HRV analysis. The patients with HR reactivity to arousal presented significant sleep-stage-dependent increases in global HRV and sympathetic HRV indexes, whereas the nonreactive group was characterized by an inability of HRV to change with sleep-stage alternation. Sympathetic HRV indexes were significantly higher in the reactive patients than in nonreactive patients, but high frequency power reflecting parasympathetic activity did not differ. However, the absolute HRV indexes were greatly decreased in both groups of patients compared to controls. CONCLUSION: HR reactivity during arousal associated with the emergence from SWS, corroborated by HRV surrounding arousal, may suggest a partial improvement of the sympathetic drive to the heart in some CTP, with no indication of increased parasympathetic activity. Other signs of reinnervation have to be identified to validate this hypothesis.     

Sleep‐disordered breathing in children is associated with impairment of sleep stage‐specific shift of cardiac autonomic modulation

We examined the effects of sleep stages and sleep‐disordered breathing (SDB) on autonomic modulation in 700 children. Apnea hypopnea index (AHI) during one 9 h night‐time polysomnography was used to define SDB. Sleep stage‐specific autonomic modulation was measured by heart rate variability (HRV) analysis of the first available 5 min RR intervals from each sleep stage. The mean [standard deviation (SD)] age was 112 (21) months (49% male and 25% non‐Caucasian). The average AHI was 0.79 (SD = 1.03) h^?1, while 73.0%, 25.8% and 1.2% of children had AHI <1 (no SDB), 1–5 (mild SDB) and ≥5 (moderate SDB), respectively. In the no SDB group, the high frequency (HF) and root mean square SD (RMSSD) increased significantly from wake to Stage 2 and slow wave sleep (SWS), and then decreased dramatically when shifting into rapid eye movement (REM) sleep. In the moderate SDB group, the pattern of HRV shift was similar to that of no SDB. However, the decreases in HF and RMSSD from SWS to REM were more pronounced in moderate SDB children [between‐group differences in HF (?24% in moderate SDB versus ?10% in no SDB) and RMSSD (?27% versus ?12%) were significant (P < 0.05)]. The REM stage HF is significantly lower in the moderate SDB group compared to the no SDB group [mean (standard error): 4.49 (0.43) versus 5.80 (0.05) ms², respectively, P < 0.05]. Conclusions are that autonomic modulation shifts significantly towards higher parasympathetic modulation from wake to non‐rapid eye movement sleep, and reverses to a less parasympathetic modulation during REM sleep. However, the autonomic modulation is impaired among children with moderate SDB in the directions of more reduction in parasympathetic modulation from SWS to REM sleep and significantly weaker parasympathetic modulation in REM sleep, which may lead to higher arrhythmia vulnerability, especially during REM sleep.     

Impact of chronic obstructive pulmonary disease on linear and nonlinear dynamics of heart rate variability in patients with heart failure

The objective of this study was to investigate the impact of chronic obstructive pulmonary disease (COPD)-heart failure (HF) coexistence on linear and nonlinear dynamics of heart rate variability (HRV). Forty-one patients (14 with COPD-HF and 27 HF) were enrolled and underwent pulmonary function and echocardiography evaluation to confirm the clinical diagnosis. Heart rate (HR) and R-R intervals (iRR) were collected during active postural maneuver (APM) [supine (10 min) to orthostasis (10 min)], respiratory sinus arrhythmia maneuver (RSA-M) (4 min), and analysis of frequency domain, time domain, and nonlinear HRV. We found expected autonomic response during orthostatic changes with reduction of mean iRR, root mean square of successive differences between heart beats (RMSSD), RR tri index, and high-frequency [HF (nu)] and an increased mean HR, low-frequency [LF (nu)], and LF/HF (nu) compared with supine only in HF patients (P<0.05). Patients with COPD-HF coexistence did not respond to postural change. In addition, in the orthostatic position, higher HF nu and lower LF nu and LF/HF (nu) were observed in COPD-HF compared with HF patients. HF patients showed an opposite response during RSA-M, with increased sympathetic modulation (LF nu) and reduced parasympathetic modulation (HF nu) (P<0.05) compared with COPD-HF patients. COPD-HF directly influenced cardiac autonomic modulation during active postural change and controlled breathing, demonstrating an autonomic imbalance during sympathetic and parasympathetic maneuvers compared with isolated HF.     

Usefulness of cardiac parasympathetic index in CPAP‐treated patients with obstructive sleep apnea: A preliminary study

Cardiac autonomic indexes, including cardiac parasympathetic index and cardiac sympathetic index, have been reported to accurately identify patients with sleep disorders such as obstructive sleep apnea. Our study aimed to assess cardiac autonomic indexes in patients with obstructive sleep apnea before and during a single full‐night continuous positive airway pressure therapy using a combined approach. Our simultaneous heart rate variability‐polysomnographic study included 16 never‐treated obstructive sleep apnea patients. Two patients dropped out. Patients underwent combined recordings in two consecutive days, at baseline and during a single full‐night of acute continuous positive airway pressure treatment. We calculated cardiac parasympathetic index and cardiac sympathetic index as night/day ratio for high‐frequency and low‐frequency heart rate variability spectral components, respectively. Continuous positive airway pressure treatment significantly reduced cardiac autonomic indexes values in comparison with baseline values (cardiac parasympathetic index: p < .0001; cardiac sympathetic index: p = .001). After acute continuous positive airway pressure treatment, the percentage of decrease of cardiac parasympathetic index was greater than that of cardiac sympathetic index (51.02 ± 15.72 versus 34.64 ± 26.93). A positive statistical correlation was also found between decrease of cardiac parasympathetic index and decrease of apnea–hypopnea index after continuous positive airway pressure (p < .001). This study improves the knowledge on cardiac autonomic modulation during acute continuous positive airway pressure therapy in obstructive sleep apnea. Our results demonstrate that both autonomic indexes decreased significantly after a single‐night of acute continuous positive airway pressure therapy. Cardiac parasympathetic index more than cardiac sympathetic index was related to decrease of apnea–hypopnea index after continuous positive airway pressure therapy, thus representing a potential help in everyday clinical practice.     

Cardiac autonomic dynamics during sleep are lost in patients with TIA and stroke

Ischaemic stroke is accompanied by important alterations of cardiac autonomic control, which have an impact on stroke outcome. In sleep, cardiac autonomic control oscillates with a predominant sympathetic modulation during REM sleep. We aimed to assess cardiac autonomic control in different sleep stages in patients with ischaemic stroke. Forty‐five patients enrolled in the prospective, multicentre SAS‐CARE study but without significant sleep‐disordered breathing (apnea–hypopnea index < 15/hr) and without atrial fibrillation were included in this analysis. The mean age was 56 years, 68% were male, 76% had a stroke (n = 34, mean National Institutes of Health Stroke Scale [NIHSS] score of 5, 11 involving the insula) and 24% (n = 11) had a transitory ischaemic attack. Cardiac autonomic control was evaluated using three different tools (spectral, symbolic and entropy analysis) according to sleep stages on short segments of 250 beats in all patients. Polysomnographic studies were performed within 7 days and 3 months after the ischaemic event. No significant differences in cardiac autonomic control between sleep stages were observed in the acute phase and after 3 months. Predominant vagal modulation and decreased sympathetic modulation were observed across all sleep stages in ischaemic stroke involving the insula. Patients with ischaemic stroke and transitory ischaemic attack present a loss of cardiac autonomic dynamics during sleep in the first 3 months after the ischaemic event. This change could represent an adaptive phenomenon, protecting the cardiovascular system from the instabilities of autonomic control, or a risk factor for stroke, which precedes the ischaemic event.     

Integrating nap and night‐time sleep into sleep patterns reveals differential links to health‐relevant outcomes

Both night‐time sleep and nap behaviour have been linked consistently to health outcomes. Although reasons for napping are usually tied to night‐time sleep, the majority of studies assess their effects independently. The current study thus aimed to examine the health relevance of patterns of sleep behaviour that take into account both night‐time and daytime sleep habits. Night‐time sleep, recorded during 7 days via actigraphy from 313 participants (aged 34–82 years) of the Midlife in the United States II Biomarker study, was assessed. Blood and urine specimens were assayed for noradrenaline, interleukin‐6 and C‐reactive protein. Participants self‐reported nap behaviour, depressive symptoms, perceived chronic stress and the presence of medical symptoms and conditions. Overall, nappers (n = 208) showed elevated waist–hip ratios, C‐reactive protein and interleukin‐6 levels compared to non‐nappers and reported more physiological symptoms and conditions (all P ≤ 0.019). Within nappers, cluster analysis revealed three patterns of sleep behaviour—infrequent nappers with good night‐time sleep, frequent nappers with good night‐time sleep and nappers with poor night‐time sleep. Nappers with poor night‐time sleep thereby exhibited elevated noradrenaline levels, depressive symptoms and perceived stress scores compared to other groups (all P ≤ 0.041). These findings support the idea that nap–health relationships are complex, in that frequency of napping and accumulation of nap sleep is not related linearly to health consequences. Assessing nap behaviour in conjunction with night‐time sleep behaviour appeared crucial to elucidate further the health relevance of napping, particularly in terms of psychological health outcomes, including chronic stress and depressive symptoms.     

Exercise before bed does not impact sleep inertia in young healthy males

Sleep inertia is the transitional state marked by impaired cognitive performance and reduced vigilance upon waking. Exercising before bed may increase the amount of slow‐wave sleep within the sleep period, which has previously been associated with increased sleep inertia. Healthy males (n = 12) spent 3 nights in a sleep laboratory (1‐night washout period between each night) and completed one of the three conditions on each visit – no exercise, aerobic exercise (30 min cycling at 75% heart rate), and resistance exercise (six resistance exercises, three sets of 10 repetitions). The exercise conditions were completed 90 min prior to bed. Sleep was measured using polysomnography. Upon waking, participants completed five test batteries every 15 min, including the Karolinska Sleepiness Scale, a Psychomotor Vigilance Task, and the Spatial Configuration Task. Two separate linear mixed‐effects models were used to assess: (a) the impact of condition; and (b) the amount of slow‐wave sleep, on sleep inertia. There were no significant differences in sleep inertia between conditions, likely as a result of the similar sleep amount, sleep structure and time of awakening between conditions. The amount of slow‐wave sleep impacted fastest 10% reciprocal reaction time on the Psychomotor Vigilance Task only, whereby more slow‐wave sleep improved performance; however, the magnitude of this relationship was small. Results from this study suggest that exercise performed 90 min before bed does not negatively impact on sleep inertia. Future studies should investigate the impact of exercise intensity, duration and timing on sleep and subsequent sleep inertia.     

Assessment of autonomic function in the late term fetus: The effects of sex and state

Researchers have reported associations between fetal sex and heart rate (FHR) and heart rate variability (FHRV) but rarely in the context of fetal behavioral sleep state. We examined differences in measures of fetal autonomic function by sex and sleep state. Fetal abdominal ECG monitoring technology was used to measure FHR and two measures of FHRV—standard deviation of FHR (SD) and beat-to-beat variability (RMSSD). FHR and movement patterns were also recorded with standard Doppler ultrasound monitor technology employed to code sleep states. Data were collected from 82 healthy fetuses ranging from 36 to 39 weeks gestation. A one-way MANOVA showed that FHR was significantly lower and SD was significantly higher for males than females. Independent samples t tests found that these sex differences were only in the active sleep state. There were no significant differences in RMSSD by sex. Repeated measures MANOVA for a subset that exhibited more than one state (N = 22) showed that SD was significantly different by state. RMSSD showed a marginally significant sleep state difference. In conclusion, fetal sex differences in HR and HRV may indicate more mature autonomic functioning in near-term males than females and fetal sleep state can influence abdominal fECG derived measures of FHR and FHRV.     

The effect of 60-h sleep deprivation on cardiovascular regulation and body temperature

This study examined cardiovascular regulation and body temperature (BT) during 60 h of sleep deprivation in 20 young healthy cadets. Heart rate variability was measured during an active orthostatic test (AOT). Measurements were performed each day in the morning and evening after 2, 14, 26, 38, 50 and 60 h of sleep deprivation. In AOT, in the sitting and standing positions, heart rate decreased (P < 0.001), while high frequency and low frequency power increased (P < 0.05–0.001) during sleep deprivation. Body temperature also decreased (P < 0.001), but no changes were detected in blood pressure. In conclusion, the accumulation of 60 h of sleep loss resulted in increased vagal outflow, as evidenced by decreased heart rate. In addition, BT decreased during sleep deprivation. Thus, sleep deprivation causes alterations in autonomic regulation of the heart, and in thermoregulation.     

Cardiac autonomic activity during daytime nap in young adults

The current study investigated both sympathetic and vagal autonomic patterns during a daytime sleep in 25 healthy adults (23.2 ± 2.4 years). Pre‐ejection period (PEP; related inversely to beta‐adrenergic sympathetic activity), the interval between consecutive R‐waves (RR) and frequency‐domain heart rate variability (HRV) were computed during pre‐nap wakefulness and undisturbed sleep stages. Results showed sleep‐related changes in RR and HRV measures, whereas PEP decreased significantly from pre‐nap to sleep, showing no differences across sleep stages. Moreover, pre‐nap PEP and HFnu (the normalized unit of the high‐frequency component of HRV) were associated negatively with sleep latency and wake after sleep onset. These results indicate a marked autonomic output reduction during daytime sleep, with different stage‐dependent fluctuations for sympathetic and vagal activity. Importantly, pre‐nap autonomic activity seems to modulate subsequent sleep quality.     

Effects of stress on heart rate complexity—A comparison between short-term and chronic stress

This study examined chronic and short-term stress effects on heart rate variability (HRV), comparing time, frequency and phase domain (complexity) measures in 50 healthy adults. The hassles frequency subscale of the combined hassles and uplifts scale (CHUS) was used to measure chronic stress. Short-term stressor reactivity was assessed with a speech task. HRV measures were determined via surface electrocardiogram (ECG). Because respiration rate decreased during the speech task (p < .001), this study assessed the influence of respiration rate changes on the effects of interest. A series of repeated-measures analyses of covariance (ANCOVA) with Bonferroni adjustment revealed that short-term stress decreased HR D2 (calculated via the pointwise correlation dimension PD2) (p < .001), but increased HR mean (p < .001), standard deviation of R–R (SD_RR) intervals (p < .001), low (LF) (p < .001) and high frequency band power (HF) (p = .009). Respiratory sinus arrhythmia (RSA) and LF/HF ratio did not change under short-term stress. Partial correlation adjusting for respiration rate showed that HR D2 was associated with chronic stress (r = −.35, p = .019). Differential effects of chronic and short-term stress were observed on several HRV measures. HR D2 decreased under both stress conditions reflecting lowered functionality of the cardiac pacemaker. The results confirm the importance of complexity metrics in modern stress research on HRV.     

Disrupted rapid eye movement sleep predicts poor declarative memory performance in post‐traumatic stress disorder

Successful memory consolidation during sleep depends on healthy slow‐wave and rapid eye movement sleep, and on successful transition across sleep stages. In post‐traumatic stress disorder, sleep is disrupted and memory is impaired, but relations between these two variables in the psychiatric condition remain unexplored. We examined whether disrupted sleep, and consequent disrupted memory consolidation, is a mechanism underlying declarative memory deficits in post‐traumatic stress disorder. We recruited three matched groups of participants: post‐traumatic stress disorder (n = 16); trauma‐exposed non‐post‐traumatic stress disorder (n = 15); and healthy control (n = 14). They completed memory tasks before and after 8 h of sleep. We measured sleep variables using sleep‐adapted electroencephalography. Post‐traumatic stress disorder‐diagnosed participants experienced significantly less sleep efficiency and rapid eye movement sleep percentage, and experienced more awakenings and wake percentage in the second half of the night than did participants in the other two groups. After sleep, post‐traumatic stress disorder‐diagnosed participants retained significantly less information on a declarative memory task than controls. Rapid eye movement percentage, wake percentage and sleep efficiency correlated with retention of information over the night. Furthermore, lower rapid eye movement percentage predicted poorer retention in post‐traumatic stress disorder‐diagnosed individuals. Our results suggest that declarative memory consolidation is disrupted during sleep in post‐traumatic stress disorder. These data are consistent with theories suggesting that sleep benefits memory consolidation via predictable neurobiological mechanisms, and that rapid eye movement disruption is more than a symptom of post‐traumatic stress disorder.     

Determinants of perceived sleep quality in normal sleepers

Objective: This study aimed to establish the determinants of perceived sleep quality over a longer period of time, taking into account the separate contributions of actigraphy-based sleep measures and self-reported sleep indices. Methods: Fifty participants (52 ± 6.6 years; 27 females) completed two consecutive weeks of home monitoring, during which they kept a sleep–wake diary while their sleep was monitored using a wrist-worn actigraph. The diary included questions on perceived sleep quality, sleep–wake information, and additional factors such as well-being and stress. The data were analyzed using multilevel models to compare a model that included only actigraphy-based sleep measures (model Acti) to a model that included only self-reported sleep measures to explain perceived sleep quality (model Self). In addition, a model based on the self-reported sleep measures and extended with nonsleep-related factors was analyzed to find the most significant determinants of perceived sleep quality (model Extended). Results: Self-reported sleep measures (model Self) explained 61% of the total variance, while actigraphy-based sleep measures (model Acti) only accounted for 41% of the perceived sleep quality. The main predictors in the self-reported model were number of awakenings during the night, sleep onset latency, and wake time after sleep onset. In the extended model, the number of awakenings during the night and total sleep time of the previous night were the strongest determinants of perceived sleep quality, with 64% of the variance explained. Conclusion: In our cohort, perceived sleep quality was mainly determined by self-reported sleep measures and less by actigraphy-based sleep indices. These data further stress the importance of taking multiple nights into account when trying to understand perceived sleep quality.