Effects of chronic sleep deprivation on autonomic activity by examining heart rate variability, plasma catecholamine, and intracellular magnesium levels

The Role of Sleep in Cardiovascular Disease

PURPOSE OF REVIEW

Sleep is an important component of cardiovascular (CV) health. This review summarizes the complex relationship between sleep and CV disease (CVD). Additionally, we describe the data supporting the treatment of sleep disturbances in preventing and treating CVD.

RECENT FINDINGS

Recent guidelines recommend screening for obstructive sleep apnea in patients with atrial fibrillation. New data continues to demonstrate the importance of sleep quality and duration for CV health. There is a complex bidirectional relationship between sleep health and CVD. Sleep disturbances have systemic effects that contribute to the development of CVD, including hypertension, coronary artery disease, heart failure, and arrhythmias. Additionally, CVD contributes to the development of sleep disturbances. However, more data are needed to support the role of screening for and treatment of sleep disorders for the prevention of CVD.

Sleep fragmentation exacerbates myocardial ischemia‒reperfusion injury by promoting copper overload in cardiomyocytes

Sleep disorders increase the risk and mortality of heart disease, but the brain-heart interaction has not yet been fully elucidated. Cuproptosis is a copper-dependent type of cell death activated by the excessive accumulation of intracellular copper. Here, we showed that 16 weeks of sleep fragmentation (SF) resulted in elevated copper levels in the male mouse heart and exacerbated myocardial ischemia-reperfusion injury with increased myocardial cuproptosis and apoptosis. Mechanistically, we found that SF promotes sympathetic overactivity, increases the germination of myocardial sympathetic nerve terminals, and increases the level of norepinephrine in cardiac tissue, thereby inhibits VPS35 expression and leads to impaired ATP7A related copper transport and copper overload in cardiomyocytes. Copper overload further leads to exacerbated cuproptosis and apoptosis, and these effects can be rescued by excision of the sympathetic nerve or administration of copper chelating agent. Our study elucidates one of the molecular mechanisms by which sleep disorders aggravate myocardial injury and suggests possible targets for intervention.

Overnight Heart Rate Variability During Sleep Disturbance In Peri- And Postmenopausal Women

OBJECTIVES

Disturbed sleep, common during the climacteric, is associated with increased sympathetic activity, a cardiovascular risk factor. We evaluated sleep disturbance effect on autonomic nervous function in climacteric women.

METHODS

Seventeen perimenopausal and 18 postmenopausal women underwent a sleep study protocol: an adaptation night, a reference night, and a sleep disturbance night, with a hand loosely tied to the bed to allow blood sampling. This procedure was repeated after six months of menopausal hormone therapy (MHT) or placebo. Sleep disturbance and MHT effects on overnight heart rate variability (HRV) were analyzed.

RESULTS

At baseline, sleep disturbance increased vagal HRV in postmenopausal women, but no changes were seen in perimenopausal women. At six months, sleep disturbance increased total HRV power in the perimenopausal placebo group, and increased nonlinear vagal HRV in the postmenopausal placebo group, but no other changes were seen. MHT did not have any effects on HRV, neither at perimenopause nor at postmenopause.

CONCLUSIONS

External sleep disturbance had only minor effects on HRV across menopause. MHT had no detectable HRV effects.

Preventive noninvasive vagal nerve stimulation reduces insufficient sleep-induced depression by improving the autonomic nervous system

BACKGROUND

Depression is closely linked to an imbalance in the autonomic nervous system (ANS). However, the role of this imbalance in mediating the effects of sleep deprivation (SD) and vagus nerve stimulation (VNS) on emotional well-being is not fully understood.

METHODS

A population-based analysis was conducted to explore the relationship between sleep duration, depression scores, and heart rate variability (HRV). Additionally, the chronic SD mouse model was established to assess the impact of preventive transcutaneous auricular VNS (taVNS) on pathological and behavioral changes.

RESULTS

Our study found a significant link between sleep duration, depression severity, and HRV. Shorter sleep duration was associated with higher depression scores and lower RMSSD (a measure of HRV). In our rat model, insufficient sleep consistently impaired HRV. This effect was mitigated by taVNS, accompanied by corresponding changes in levels of IL-1β and IL-6, astrocyte and microglia activation, and tail suspension times.

CONCLUSIONS

Using VNS as a preventive treatment for depression-risk individuals with insufficient sleep shows promise. It not only broadens the potential applications of VNS but also sheds light on its mechanism-particularly its role in enhancing vagal nerve function and balancing the ANS, as evidenced by HRV measurements.

The role of sleep and heart rate variability in metabolic syndrome: evidence from the Midlife in the United States study

STUDY OBJECTIVES

Poor sleep and autonomic dysregulation can both disrupt metabolic processes. This study examined the individual and combined effects of poor sleep and reduced heart rate variability (HRV) on metabolic syndrome among 966 participants in the Midlife in the United States II (MIDUS II) study.

METHODS

Self-reported sleep was assessed using the Pittsburgh Sleep Quality Index (PSQI). HRV was acquired from 11-minute resting heart rate recordings. Spearman correlations, general linear regression, and logistic regression models were used to examine the study hypotheses.

RESULTS

Poor sleep quality was associated with metabolic syndrome when global PSQI scores were evaluated as a continuous (odds ratio [OR]: 1.07, 95% confidence interval [CI]: 1.03 to 1.11) or categorical measure (cutoff > 5, OR: 1.58, 95% CI: 1.19 to 2.10), after adjustment for confounding. There also was an association between reduced HRV and metabolic syndrome (ln [HF-HRV] OR: 0.89, 95% CI: 0.80 to 0.99; ln [LF-HRV] OR: 0.82, 95% CI: 0.72 to 0.92; ln [SDRR] OR: 0.59, 95% CI: 0.43 to 0.79; ln [RMSSD] OR: 0.75, 95% CI: 0.60 to 0.94). When the combined effects of poor sleep and low HRV were examined, the association with metabolic syndrome was further strengthened relative to those with normal sleep and HRV.

CONCLUSIONS

To the best of the author's knowledge, this is the first study to suggest a combined effect of poor sleep and low HRV on the odds of metabolic syndrome.

Effects of sleep fragmentation and partial sleep restriction on heart rate variability during night

We developed a cross-over study design with two interventions in randomized order to compare the effects of sleep fragmentation and partial sleep restriction on cardiac autonomic tone. Twenty male subjects (40.6 ± 7.5 years old) underwent overnight polysomnography during 2 weeks, each week containing one undisturbed baseline night, one intervention night (either sleep restriction with 5 h of sleep or sleep fragmentation with awakening every hour) and two undisturbed recovery nights. Parameters of heart rate variability (HRV) were used to assess cardiac autonomic modulation during the nights. Sleep restriction showed significant higher heart rate (p = 0.018) and lower HRV-pNN50 (p = 0.012) during sleep stage N1 and lower HRV-SDNN (p = 0.009) during wakefulness compared to the respective baseline. For HR and SDNN there were recovery effects. There was no significant difference comparing fragmentation night and its baseline. Comparing both intervention nights, sleep restriction had lower HRV high frequency (HF) components in stage N1 (p = 0.018) and stage N2 (p = 0.012), lower HRV low frequency (LF) (p = 0.007) regarding the entire night and lower SDNN (p = 0.033) during WASO during sleep. Sleep restriction increases sympathetic tone and decreases vagal tone during night causing increased autonomic stress, while fragmented sleep does not affect cardiac autonomic parameters in our sample.

The effect of extended shift work on autonomic function in occupational settings: A systematic review and meta-analysis

OBJECTIVE

To examine the effect of 24-h shift work on autonomic nervous system function via heart rate variability (HRV) methodologies.

METHODS

Electronic databases (indexed in either PubMed, MEDLINE, CINAHL, SPORTDiscus, or OpenDissertations) were searched from January 1964 to March 2023. A modified Downs and Black checklist was used for assessing methodological quality and the Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) approach was used to evaluate the quality of evidence. Study design, study population, study sample, shift work description, and assessment of HRV metrics and methods were extracted from each study.

FINDINGS

A total of 58 478 study articles were identified, of which 12 articles met inclusion criteria. Sample sizes varied from eight to 60 participants, with the ratio of low- to high-frequency HRV (LF/HF) as the most common frequency-domain variable reported. Of the nine included studies that observed LF/HF, three (33.3%) demonstrated a significant increase after 24-h shift work. Moreover, of the five studies that reported HF, two (40%) noted a significant decrease after 24-h shift work. When observing risk of bias, two (16.6%) studies were low quality, five (41.7%) were moderate quality, and five (41.7%) were high quality.

INTERPRETATION

There were inconsistent findings demonstrating an effect of 24-h shift work on autonomic function, with a suggested shift away from parasympathetic dominance. Discrepancies in HRV methodologies, such as the duration of recordings and hardware used for measurement, may have contributed to the disparity in findings. In addition, differences in roles and responsibilities across occupations may explain the incongruence in findings across studies.

Sleep Loss Influences the Interconnected Brain-Body Regulation of Cardiovascular Function in Humans

OBJECTIVE

Poor sleep is associated with hypertension, a major risk factor for cardiovascular disease. However, the mechanism(s) through which sleep loss affects cardiovascular health remains largely unknown, including the brain and body systems that regulate vascular function.

METHODS

Sixty-six healthy adults participated in a repeated-measures, crossover, experimental study involving assessments of cardiovascular function and brain connectivity after a night of sleep and a night of sleep deprivation.

RESULTS

First, sleep deprivation significantly increased blood pressure-both systolic and diastolic. Interestingly, this change was independent of any increase in heart rate, inferring a vasculature-specific rather than direct cardiac pathway. Second, sleep loss compromised functional brain connectivity within the vascular control network, specifically the insula, anterior cingulate, amygdala, and ventral and medial prefrontal cortices. Third, sleep loss-related changes in brain connectivity and vascular tone were not independent, but significantly interdependent, with changes within the vascular control brain network predicting the sleep-loss shift toward hypertension.

CONCLUSIONS

These findings establish an embodied framework in which sleep loss confers increased risk of cardiovascular disease through an impact upon central brain control of vascular tone, rather than a direct impact on accelerated heart rate itself.

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

ABSTRACT

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

Workplace Culture and Biomarkers of Health Risk

Workplace culture has been studied for impact on health risk; however, connections with robust biologic markers of health remain to be established. We examined associations between the work environment and urinary levels of catecholamines and their metabolites as biomarkers of sympathetic nervous system activity, indicative of stress. We recruited participants (n = 219; 2018-2019) from a cardiovascular risk cohort to investigate workplace culture, well-being, and stress. Participants completed seven questionnaires. Urine samples were used to measure catecholamines and their metabolites by LC/MS/MS. Pearson correlation and linear regression models were used after adjusting for demographics and creatinine. Participants reporting higher well-being had lower urinary levels of dopamine, serotonin, and 3-methoxytyramine. Participants reporting a more engaged and more positive workplace had lower levels of dopamine and 3-methoxytyramine. Reported workplace isolation was correlated with higher levels of dopamine and 3-methoxytyramine. Given correlations between catecholamines, we used 3-methoxytyramine for linear regression. In fully adjusted models, in environments with a more positive culture, levels of 3-methoxytyramine remained lower (β = -0.065 ± 0.025, p = 0.01) and indicated a positive association between workplace isolation and 3-methoxytyramine (β = 0.064 ± 0.030, p = 0.04). These findings are consistent with an important relationship between workplace environment and sympathetic nervous system activity.

Symptom phenotypes in Pulmonary Arterial Hypertension: The PAH “Symptome”

Women with pulmonary arterial hypertension (PAH) experience multiple symptoms, including dyspnea, fatigue, and sleep disturbance, that impair their health‐related quality of life (HRQOL). However, we know little about phenotypic subgroups of patients with PAH with similar, concurrent, multiple symptoms. The objectives of this study were to define the “symptome” by symptom cluster phenotypes and compare characteristics such as biomarkers, cardiac structure and function (echocardiography), functional capacity (6‐min walk distance), and HRQOL between the groups. This cross‐sectional study included 60 women with PAH. Subjects completed an assessment battery: Pulmonary Arterial Hypertension Symptom Scale, Pittsburgh Sleep Quality Index, Multidimensional Dyspnea Profile, Patient‐Reported Outcomes Measurement Information System (PROMIS®) Physical Function, PROMIS® Sleep‐Related Impairment, and the emPHasis‐10. Subjects also underwent transthoracic echocardiography, phlebotomy, 6‐min walk distance, and actigraphy. The three symptoms of dyspnea, fatigue, and sleep disturbance were used to define the symptom clusters. Other PAH symptoms, plasma and serum biomarkers, cardiac structure and function (echocardiography), exercise capacity (6‐min walk distance), sleep (actigraphy), and HRQOL were compared across phenotypes. The mean age was 50 ± 18 years, 51% were non‐Hispanic white, 32% were non‐Hispanic Black and 40% had idiopathic PAH. Cluster analysis identified Mild (n = 28, 47%), Moderate (n = 20, 33%), and Severe Symptom Cluster Phenotypes (n = 12, 20%). There were no differences for age, race, or PAH etiology between the phenotypes. WHO functional class (p < 0.001), norepinephrine levels (p = 0.029), right atrial pressure (p = 0.001), physical function (p < 0.001), sleep onset latency (p = 0.040), and HRQOL (p < 0.001) all differed significantly across phenotypes. We identified three distinctive symptom cluster phenotypes (Mild, Moderate, and Severe) for women with PAH that also differed by PAH‐related symptoms, physical function, right atrial pressure, norepinephrine levels, and HRQOL. These phenotypes could suggest targeted interventions to improve symptoms and HRQOL in those most severely affected.

Gravitational Dose‐Response Curves for Acute Cardiovascular Hemodynamics and Autonomic Responses in a Tilt Paradigm

Background

The cardiovascular system is strongly dependent on the gravitational environment. Gravitational changes cause mechanical fluid shifts and, in turn, autonomic effectors influence systemic circulation and cardiac control. We implemented a tilt paradigm to (1) investigate the acute hemodynamic response across a range of directions of the gravitational vector, and (2) to generate specific dose‐response relationships of this gravitational dependency.

Methods and Results

Twelve male subjects were tilted from 45° head‐up tilt to 45° head‐down tilt in 15° increments, in both supine and prone postures. We measured the steady‐state hemodynamic response in a range of variables including heart rate, stroke volume, cardiac output, oxygen consumption, total peripheral resistance, blood pressure, and autonomic indices derived from heart rate variability analysis. There is a strong gravitational dependence in almost all variables considered, with the exception of oxygen consumption, whereas systolic blood pressure remained controlled to within ≈3% across the tilt range. Hemodynamic responses are primarily driven by differential loading on the baroreflex receptors, combined with differences in venous return to the heart. Thorax compression in the prone position leads to reduced venous return and increased sympathetic nervous activity, raising heart rate, and systemic vascular resistance while lowering cardiac output and stroke volume.

Conclusions

Gravitational dose‐response curves generated from these data provide a comprehensive baseline from which to assess the efficacy of potential spaceflight countermeasures. Results also assist clinical management of terrestrial surgery in prone posture or head‐down tilt positions.

Dysautonomia in Parkinson’s Disease: Impact of Glucocerebrosidase Gene Mutations on Cardiovascular Autonomic Control

Evidence from clinical practice suggests that PD patients with the Glucocerebrosidase gene mutations (GBA-PD) are characterized by more severe dysautonomic symptoms than patients with idiopathic PD (iPD). Therefore, an accurate assessment of cardiovascular autonomic control (CAC) is necessary to clarify the role of GBA mutations in the pathophysiology of PD. We evaluated the CAC at rest and during orthostatic challenge of 15 iPD, 15 GBA-PD and 15 healthy controls (CTR). ECG and respiration were recorded in supine position and during active standing. The analysis of Heart Rate Variability (HRV) was performed on ECG recordings using two different approaches, linear spectral analysis and non-linear symbolic analysis. GBA-PD patients presented more frequently an akinetic-rigid phenotype and cognitive dysfunction than iPD patients. Both iPD and GBA-PD group were characterized by a lower spectral HRV than CTR group. At rest, the GBA-PD group was characterized by a lower parasympathetic modulation and a shift of the sympathovagal balance toward a sympathetic predominance compared to the CTR group. Moreover, the GBA-PD patients presented a lower HR increment and a lower or absent reduction of the vagal modulation in response to the active standing than iPD patients. Lastly, the cardiovascular autonomic dysfunction in PD patients was associated with longer disease duration, and with the occurrence of REM sleep behavior disorder and constipation. Our findings suggest a more severe impairment of the CAC in PD patients with GBA mutations. These results and further studies on the role of GBA mutations could allow a stratification based on cardiovascular risk in PD patients and the implementation of specific prevention programs.

Sympathetic neural responses to sleep disorders and insufficiencies

Short sleep duration and poor sleep quality are associated with cardiovascular risk, and sympathetic nervous system (SNS) dysfunction appears to be a key contributor. The present review will characterize sympathetic function across several sleep disorders and insufficiencies in humans, including sleep deprivation, insomnia, narcolepsy, and obstructive sleep apnea (OSA). We will focus on direct assessments of sympathetic activation, e.g., plasma norepinephrine and muscle sympathetic nerve activity, but include heart rate variability (HRV) when direct assessments are lacking. The review also highlights sex as a key biological variable. Experimental models of total sleep deprivation and sleep restriction are converging to support several epidemiological studies reporting an association between short sleep duration and hypertension, especially in women. A systemic increase of SNS activity via plasma norepinephrine is present with insomnia and has also been confirmed with direct, regionally specific evidence from microneurographic studies. Narcolepsy is characterized by autonomic dysfunction via both HRV and microneurographic studies but with opposing conclusions regarding SNS activation. Robust sympathoexcitation is well documented in OSA and is related to baroreflex and chemoreflex dysfunction. Treatment of OSA with continuous positive airway pressure results in sympathoinhibition. In summary, sleep disorders and insufficiencies are often characterized by sympathoexcitation and/or sympathetic/baroreflex dysfunction, with several studies suggesting women may be at heightened risk.

Subjective and Objective Consequences of Stress in Subjects with Subjectively Different Sleep Quality-A Cross-Sectional Study

BACKGROUND

Restful sleep plays an important role in long-term health and occupational safety. Heart rate variability (HRV) is used as stress indicator. The aim of this study was to determine whether HRV at rest or during sleep, as an objective indicator of stress, reflects subjectively assessed sleep quality.

METHODS

84 subjects (37.3 ± 15.6 years) were classified into good sleepers and poor sleepers based on the results of the Pittsburgh Sleep Quality Index (PSQI). The cut-off value to distinguish between good and bad sleepers recommended by Buysse et al. 1989 is >5. Mental health status was determined using the 12-Item General Health Questionnaire (GHQ-12). A 24 h electrocardiogram (ECG) was recorded for HRV analysis (total and 6 h night phase).

RESULTS

The poor sleepers showed a significantly lower mental health status (p = 0.004). The multifactorial variance analysis of the total phase time parameters Min HR (p = 0.032, η² = 0.056) and SI (p = 0.015, η² = 0.072) showed significant interaction effects. In the 6h night phase, significant interaction effects were found for SDNN (p = 0.036, η² = 0.065) and SD2 (p = 0.033, η² = 0.067). In addition, there was a significant negative correlation between HRV and stress and a positive correlation between HRV and mental health.

CONCLUSIONS

Although this study did not demonstrate a direct relationship between sleep quality and HRV, it was shown that there are important connections between sleep quality and mental health, and between HRV and mental health.

Using in-seat electrical potential sensors for non-contact monitoring of heart rate, heart rate variability, and heart rate recovery

Detecting transient changes in heart rate and heart rate variability during experimental simulated autonomous driving scenarios can indicate participant arousal and cognitive load, providing valuable insights into the relationship between human and vehicle autonomy. Successfully detecting such parameters unobtrusively may assist these experimental situations as well as naturalistic driver monitoring systems within an autonomous vehicle. However, non-contact sensors must collect reliable and accurate signals. This study aims to compare the in-seat, non-contact Plessey EPIC sensor to the gold standard, contact Biopac sensor. Thirty participants took part in five-minute simulated autonomous vehicle journeys in a city environment and a rural environment, and a five-minute resting condition. To ensure the seat sensor was sensitive to elevated heart rate values, heart rate was also collected following the energetic Harvard Step Test. Lin concordance coefficients and Bland-Altman analyses were employed to assess the level of agreement between the non-contact Plessey EPIC sensor and the contact Biopac sensor for heart rate and heart rate variability. Analyses revealed a high level of agreement (r_c > 0.96) between both sensors for one-minute averaged heart rate and five-minute averaged heart rate variability during simulated autonomous driving and rest, and one-minute averaged heart rate following the Harvard Step Test. In addition, the non-contact sensor was sensitive to significant differences during tasks. This proof of principle study demonstrates the feasibility of using the non-contact Plessey EPIC sensor to accurately detect heart rate and heart rate variability during simulated autonomous driving environments.

Loss of nocturnal dipping pattern of skin sympathetic nerve activity during and following an extended-duration work shift in residents in training

BACKGROUND

Extended-duration work shifts (EDWSs) might affect the health of physician residents, causing autonomic alteration. Skin sympathetic nerve activity (SKNA) recorded by noninvasive neuro-electrocardiography (neuECG) is used to estimate cardiac sympathetic tone. In this study, we aim to evaluate the impact of EDWSs on nocturnal SKNA assessed in resident doctors.

METHODS

Twenty-four residents working EDWSs and 12 PhD students not working nightshift schedules were prospectively recruited. The neuECG was performed between 12 am and 6 am for 5 consecutive nights. SKNA was filtered from neuECG recorded signals. The questionnaires regarding work stress and sleep quality, blood pressure, and salivary alpha-amylase and cortisol levels were administered.

RESULTS

The hours of weekly working and sleep opportunities were similar between residents and students, while residents reported more work stress and worse sleep quality. In residents, SKNA at 6 am (SKNA_6am) was significantly higher than SKNA_2am during the precall night, revealing a dipping pattern. However, the SKNA dipping disappeared during the on-call night and prominently flattened during the first postcall night, the full recovery of which was delayed until the second postcall nights. The morning blood pressure and salivary alpha-amylase and cortisol levels were similar between the precall and postcall days. In contrast, SKNA in students exhibited a constant dipping profile for all recorded nights.

CONCLUSIONS

In healthy young adults, SKNA presents a dip night. The SKNA dip is impaired by working a nightshift, with a delayed recovery. The neuECG might serve as a useful tool to detect subclinical autonomic disturbances in shiftworkers.

Association between nocturnal activity of the sympathetic nervous system and cognitive dysfunction in obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is associated with repetitive breathing obstructions during sleep. These episodes of hypoxia and associated arousals from sleep induce physiological stress and nocturnal over-activation of the sympathetic nervous system (SNS). One consequence of OSA is impairment in a range of cognitive domains. Previous research into cognitive impairment in OSA have focussed on intermittent hypoxia and disrupted sleep, but not nocturnal over-activation of the SNS. Therefore, we investigated whether nocturnal over-activity of the SNS was associated with cognitive impairments in OSA. The extent of nocturnal SNS activation was estimated from heart rate variability (HRV), pulse wave amplitude (PWA) and stress response biomarkers (cortisol and glucose levels). OSA severity was significantly associated with PWA indices and the HRV low frequency/ high frequency ratio (p < 0.05). Morning blood glucose levels were significantly associated with the duration of a blood oxygen saturation (SaO₂) < 90% (p < 0.01). PWA and HRV were significantly associated with the time taken to perform a task involving visuospatial functioning (p < 0.05), but not with impairments in sustained attention, reaction time or autobiographical memory. These results suggest that the visuospatial dysfunction observed in people with OSA is associated with increased nocturnal activity of the SNS.

The association between heart rate variability, reaction time, and indicators of workplace fatigue in wildland firefighters

PURPOSE

To understand the association between heart rate variability and indices of fatigue, total sleep time, and reaction time in shift workers.

METHODS

Ten participants from the British Columbia Wildfire Service management team were examined over a 14-day active fire-line period. Daily measures of subjective fatigue, sleepiness, and alertness were recorded using a visual analog scale. Daily total sleep time was recorded using a wrist actigraph. Cardiac autonomic modulation was examined each morning using heart rate variability (HRV). Three measures of reaction time (simple reaction time, choice reaction tie, and discriminatory reaction time) was examined on days 1, 5, 10, and 14. Multiple linear regression analysis was utilized to examine the association between HRV and indices of fatigue, total sleep time, and reaction time.

RESULTS

Mean shift duration was 13.8 ± 0.77 h. Significant inverse associations were observed between HRV and sleepiness [r = - 0.60, p = 0.000] and fatigue [r = - 0.55, p = 0.000], and a positive association with total sleep time (min) [r = 0.28, p = 0.009]. There were no significant relationships between HRV and simple reaction time (ms) [r = - 0.32, p = 0.182], choice reaction time (ms) [r = - 0.10, p = 0.850], or discriminatory reaction time (ms) [r = - 0.09, p = 0.881].

CONCLUSIONS

HRV displayed significant associations with indices of fatigue and sleep, whereby demonstrating its utility as a practical tool for monitoring the development of fatigue in wildland firefighters and for providing insight when to make lifestyle modifications to preserve alertness.

Interhemispheric sleep depth coherence predicts driving safety in sleep apnea

Obstructive sleep apnea is associated with increased risk of car crashes; however, conventional measures of sleep apnea severity do not clearly identify those individuals who are at greatest risk. Here we tested whether, among individuals with sleep apnea, those with reduced interhemispheric sleep depth coherence, measured by correlation between right and left hemisphere odds ratio product, are at greater risk. The sample was derived from the Sleep Heart Health Study, a prospective observational cohort study, and included 1,378 adults with sleep apnea. The occurrence of a car crash was ascertained by a questionnaire administered 2 years after the sleep study, which asked about the occurrence of crashes during the year prior to questionnaire administration. We computed the sleep depth coherence from electroencephalograms recorded during baseline sleep studies and after 5 years. The weighted kappa coefficient and Bangdiwala's B were 0.34 and 0.59, respectively, indicating a fair to moderate stability over a 5-year interval. Multivariate logistic regression, adjusted for age, sex, race, body mass index and miles driven per year, was used to assess the risk of a car crash. Compared to the lowest quartile of sleep depth coherence (<0.86), individuals in the highest quartile (>0.93) had a 62% (95% confidence interval, 22%-81%) lower risk of an accident. Further adjustments for usual sleep duration and sleepiness did not meaningfully alter these findings. Higher interhemispheric sleep depth coherence is associated with significantly lower risk of motor vehicle crashes in individuals with sleep apnea. This suggests that high interhemispheric sleep depth coherence may be a marker of resistance to sleep apnea-related adverse neurocognitive outcomes.

The Effects of Psychological and Environmental Stress on Micronutrient Concentrations in the Body: A Review of the Evidence

Stress is the nonspecific response of the body to any demand for change. Excess or chronic psychological or environmental stress is associated with an increased risk of mental and physical diseases, with several mechanisms theorized to be associated with its detrimental effects. One underappreciated potential mechanism relates to the effects of psychological and environmental stress on micronutrient concentrations. Micronutrients (vitamins and minerals) are essential for optimal physical and mental function, with deficiencies associated with an array of diseases. In this article, animal and human studies investigating the effects of various psychological and environmental stressors on micronutrient concentrations are reviewed. In particular, the effects of psychological stress, sleep deprivation, and physical exercise on micronutrient concentrations and micronutrient excretion are summarized. Micronutrients identified in this review include magnesium, zinc, calcium, iron, and niacin. Overall, the bulk of evidence suggests stress can affect micronutrient concentrations, often leading to micronutrient depletion. However, before definitive conclusions about the effects of stress can be made, the impact of different stressors, stress severity, and acute versus chronic stress on micronutrient concentrations requires investigation. Moreover, the impact of stress on micronutrients in different populations varying in age, gender, and premorbid health status and the durability of changes after a stressor is resolved require examination. The medical, physical, and psychological implications of nutrient changes caused by a stressor also remain to be determined.

Short Sleep, Insomnia, and Cardiovascular Disease

PURPOSE OF REVIEW

This review summarizes key findings linking insomnia, short sleep duration, and cardiovascular health.

RECENT FINDINGS

Early studies associations between insomnia with short sleep and cardiovascular disease Recent studies have incorporated objective data to assess sleep and identify comorbid sleep disorders (e.g. sleep apnea). Use of objective metrics has facilitated understanding of the impacts of insufficient sleep on autonomic dysregulation, metabolic syndrome, coronary artery disease and overall cardiovascular mortality. Emerging research suggests treatment of insomnia (CBT-I) may be beneficial in terms of reducing cardiovascular disease risk.

SUMMARY

From short term effects on the autonomic nervous system to lasting effects on metabolic syndrome and coronary artery disease, there is growing evidence to support a physiologic pathway by which insomnia with short sleep contributes to cardiovascular disease. More research is needed to understand the effect of insomnia treatment on cardiovascular risk.

Heart rate variability related to season of birth: A replication study

Low heart rate variability (HRV) has strongly been associated with an increased risk for cardiovascular disease. With cardiovascular disease being the number one cause of global deaths, factors that influence its development are relevant to understand. Season of birth has been suggested as one of the factors influencing the development of HRV. The current study was set up to replicate the finding that men born in winter have higher HRV later in life compared to those born in other seasons. To this end, we studied a sample of 1,871 healthy participants from the Brain Resource International Database during rest and during task. Furthermore, sex and age differences and associations with personality traits and psychiatric symptoms were explored. We replicated the earlier finding that men born in winter have a lower ratio of low frequency (LF) power to high frequency (HF) power during rest compared to summer and fall, and, although less pronounced, higher HF compared to summer. A difference between summer and winter for LF/HF in men was internally replicated using data recorded during task. Additionally, for both sexes, LF/HF ratio increased with age, and LF and HF both decreased. In general, LF/HF was lower in women, but heart rate was higher. In men, low HRV was associated with depression and the personality trait openness. In conclusion, results from a large multicenter data set covering the entire lifespan demonstrate that HRV changes with age in both sexes and confirm that season of birth influences HRV later in life in men.

This is a replication study, showing heart rate variability (HRV) to vary with season of birth (SoB). Since both HRV and SoB have been related to cardiovascular disease, the relationship is relevant to understand. We used an almost five times larger sample than the original sample, covering wider geographic areas and the full lifespan. Additionally, age and sex differences in HRV were found. Replicating earlier findings provides solid evidence for a relationship between SoB and HRV later in life, thereby providing insights on how HRV develops and ultimately how increased risk for cardiovascular disease can be reduced.

Healthy hearts at hectic pace: From daily life stress to abnormal cardiomyocyte function and arrhythmias

The hectic pace of contemporary life is a major source of acute and chronic stress, which may have a deleterious impact on body health . In the field of cardiovascular disease, acute emotional stress has been associated with coronary spasm and Takotsubo cardiomyopathy, whereas the manifestations of chronic stress have been overlooked, and most underlying pathophysiology remains to be elucidated. Chronic stress affects the neuronal circuitry composed of cortico-limbic structures and the nuclei regulating autonomic function, eliciting a sympatho-vagal imbalance, characterised by adrenergic activation and vagal withdrawal. Sympathetic terminals are connected to cardiomyocytes in a quasi-synaptic way, producing the so called 'neuro-cardiac junction'. During chronic stress, norepinephrine release is increased, leading to overstimulation of cardiomyocytes via β₁-adrenergic receptors, influencing mainly calcium dynamics, and β₂-adrenergic receptors, which control housekeeping functions. The circadian rhythm of cardiomyocytes is then impaired, with elongation of the catabolic ('light' phase) over the anabolic ('nocturnal') phase. This leads to a depletion of cell energy storage, and a decreased turnover of cell constituents. Even cell interactions are affected, as coupling between cardiomyocytes decreases while coupling between cardiomyocytes and fibroblasts increases. The ultimate results are changes in the shape and velocity of action potential, fibroblast activation and deposition of extracellular matrix. These alterations may predispose to arrhythmias and may favour the development of a stress-related cardiomyopathy. A better comprehension of this cascade of events may allow us to identify screening protocols and treatment strategies (meditation, yoga, physical activity, psychological assistance, β-blockers) to prevent or relieve ongoing cardiac damage.

Physiological and autonomic stress responses after prolonged sleep restriction and subsequent recovery sleep in healthy young men

Purpose

Sleep restriction is increasingly common and associated with the development of health problems. We investigated how the neuroendocrine stress systems respond to prolonged sleep restriction and subsequent recovery sleep in healthy young men.

Methods

After two baseline (BL) nights of 8 h time in bed (TIB), TIB was restricted to 4 h per night for five nights (sleep restriction, SR, n = 15), followed by three recovery nights (REC) of 8 h TIB, representing a busy workweek and a recovery weekend. The control group (n = 8) had 8 h TIB throughout the experiment. A variety of autonomic cardiovascular parameters, together with salivary neuropeptide Y (NPY) and cortisol levels, were assessed.

Results

In the control group, none of the parameters changed. In the experimental group, heart rate increased from 60 ± 1.8 beats per minute (bpm) at BL, to 63 ± 1.1 bpm after SR and further to 65 ± 1.8 bpm after REC. In addition, whole day low-frequency to-high frequency (LF/HF) power ratio of heart rate variability increased from 4.6 ± 0.4 at BL to 6.0 ± 0.6 after SR. Other parameters, including salivary NPY and cortisol levels, remained unaffected.

Conclusions

Increased heart rate and LF/HF power ratio are early signs of an increased sympathetic activity after prolonged sleep restriction. To reliably interpret the clinical significance of these early signs of physiological stress, a follow-up study would be needed to evaluate if the stress responses escalate and lead to more unfavourable reactions, such as elevated blood pressure and a subsequent elevated risk for cardiovascular health problems.

The Association Between Extreme Sleep Duration and Cardiac Autonomic Control in Community-Dwelling Older Adults: The Yilan Study, Taiwan

Backgrounds

The aims of the present study were to determine the associations and sex-specific relationships between extreme sleep duration and cardiac autonomic control in a cohort of older individuals.

Methods

A community-based survey was conducted in Yilan City, Taiwan. Community-dwelling older adults aged ≥65 were randomly selected to participate. Extreme sleep durations were defined as either short sleep (≤5 hours) or long sleep (≥8 hours). Cardiac autonomic control was evaluated using the parameters of frequency-domain analysis of heart rate variability.

Results

Of 1,721 participants, 58.7% were female. In multiple logistic regression analyses, short sleep duration did not correlate with any of the unhealthier parameters of heart rate variability. In contrast, long sleep duration was associated with elevated risk for poor high-frequency values (odds ratio [OR]: 1.83, 95% confidence interval [CI]: 1.34-2.50) and the unfavorable low-frequency values (OR: 1.44, 95% CI: 1.05-1.97). When stratified by sex, the associations between extreme sleep duration and poor heart rate variability were more robust in males.

Conclusions

Poor cardiac autonomic control may underlie the link between extreme sleep duration and adverse health outcomes in older adults. A sex-specific relationship between poor cardiac autonomic function and extreme sleep duration also was found.

Sleep Duration and Quality in Relation to Autonomic Nervous System Measures: The Multi-Ethnic Study of Atherosclerosis (MESA)

STUDY OBJECTIVES

Short sleep duration and poor sleep quality are associated with adverse cardiovascular outcomes. Potential pathophysiological mechanisms include sleep-associated alterations in the autonomic nervous system. The objective of this study was to examine the associations of shorter sleep duration and poorer sleep quality with markers of autonomic tone: heart rate (HR), high-frequency HR variability (HF-HRV) and salivary amylase.

METHODS

Cross-sectional analysis of data from actigraphy-based measures of sleep duration and efficiency and responses to a challenge protocol obtained from 527 adult participants in the Multi-Ethnic Study of Atherosclerosis.

RESULTS

Participants who slept fewer than 6 h per night (compared to those who slept 7 h or more per night) had higher baseline HR (fully adjusted model 0.05 log beats/min, 95% confidence interval [CI] 0.01, 0.09) and greater HR orthostatic reactivity (fully adjusted model 0.02 log beats/min, 95% CI 0.002, 0.023). Participants who slept 6 to less than 7 h/night (compared to those who slept 7 h or more per night) had lower baseline HF-HRV (fully adjusted model -0.31 log msec², 95% CI -0.60, -0.14). Participants with low sleep efficiency had lower baseline HF-HRV than those with higher sleep efficiency (fully adjusted model -0.59 log msec², 95% CI -1.03, -0.15). Participants with low sleep efficiency had higher baseline levels of amylase than those with higher sleep efficiency (fully adjusted model 0.45 log U/mL, 95% CI 0.04, 0.86).

CONCLUSIONS

Short sleep duration, low sleep efficiency, and insomnia combined with short sleep duration were associated with markers of autonomic tone that indicate lower levels of cardiac parasympathetic (vagal) tone and/or higher levels of sympathetic tone.

Atrial Fibrillation: The Science behind Its Defiance

Atrial fibrillation (AF) is the most prevalent arrhythmia in the world, due both to its tenacious treatment resistance, and to the tremendous number of risk factors that set the stage for the atria to fibrillate. Cardiopulmonary, behavioral, and psychological risk factors generate electrical and structural alterations of the atria that promote reentry and wavebreak. These culminate in fibrillation once atrial ectopic beats set the arrhythmia process in motion. There is growing evidence that chronic stress can physically alter the emotion centers of the limbic system, changing their input to the hypothalamic-limbic-autonomic network that regulates autonomic outflow. This leads to imbalance of the parasympathetic and sympathetic nervous systems, most often in favor of sympathetic overactivation. Autonomic imbalance acts as a driving force behind the atrial ectopy and reentry that promote AF. Careful study of AF pathophysiology can illuminate the means that enable AF to elude both pharmacological control and surgical cure, by revealing ways in which antiarrhythmic drugs and surgical and ablation procedures may paradoxically promote fibrillation. Understanding AF pathophysiology can also help clarify the mechanisms by which emerging modalities aiming to correct autonomic imbalance, such as renal sympathetic denervation, may offer potential to better control this arrhythmia. Finally, growing evidence supports lifestyle modification approaches as adjuncts to improve AF control.

Chronic occupational exposures can influence the rate of PTSD and depressive disorders in first responders and military personnel

BACKGROUND

First responders and military personnel experience rates of post-traumatic stress disorder (PTSD) far in excess of the general population. Although exposure to acute traumatic events plays a role in the genesis of these disorders, in this review, we present an argument that the occupational and environmental conditions where these workers operate are also likely contributors.

PRESENTATION OF THE HYPOTHESIS

First responders and military personnel face occupational exposures that have been associated with altered immune and inflammatory activity. In turn, these physiological responses are linked to altered moods and feelings of well-being which may provide priming conditions that compromise individual resilience, and increase the risk of PTSD and depression when subsequently exposed to acute traumatic events. These exposures include heat, smoke, and sleep restriction, and physical injury often alongside heavy physical exertion. Provided the stimulus is sufficient, these exposures have been linked to inflammatory activity and modification of the hypothalamic-pituitary axis (HPA), offering a mechanism for the high rates of PTSD and depressive disorders in these occupations.

TESTING THE HYPOTHESIS

To test this hypothesis in the future, a case-control approach is suggested that compares individuals with PTSD or depressive disorders with healthy colleagues in a retrospective framework. This approach should characterise the relationships between altered immune and inflammatory activity and health outcomes. Wearable technology, surveys, and formal experimentation in the field will add useful data to these investigations.

IMPLICATIONS OF THE HYPOTHESIS

Inflammatory changes, linked with occupational exposures in first responders and military personnel, would highlight the need for a risk management approach to work places. Risk management strategies could focus on reducing exposure, ensuring recovery, and increasing resilience to these risk contributors to minimise the rates of PTSD and depressive disorders in vulnerable occupations.

Brain-heart interactions: physiology and clinical implications

The brain controls the heart directly through the sympathetic and parasympathetic branches of the autonomic nervous system, which consists of multi-synaptic pathways from myocardial cells back to peripheral ganglionic neurons and further to central preganglionic and premotor neurons. Cardiac function can be profoundly altered by the reflex activation of cardiac autonomic nerves in response to inputs from baro-, chemo-, nasopharyngeal and other receptors as well as by central autonomic commands, including those associated with stress, physical activity, arousal and sleep. In the clinical setting, slowly progressive autonomic failure frequently results from neurodegenerative disorders, whereas autonomic hyperactivity may result from vascular, inflammatory or traumatic lesions of the autonomic nervous system, adverse effects of drugs and chronic neurological disorders. Both acute and chronic manifestations of an imbalanced brain-heart interaction have a negative impact on health. Simple, widely available and reliable cardiovascular markers of the sympathetic tone and of the sympathetic-parasympathetic balance are lacking. A deeper understanding of the connections between autonomic cardiac control and brain dynamics through advanced signal and neuroimage processing may lead to invaluable tools for the early detection and treatment of pathological changes in the brain-heart interaction.

Perceived Stress and Coffee and Energy Drink Consumption Predict Poor Sleep Quality in Podiatric Medical Students A Cross-sectional Study

BACKGROUND

A cross-sectional survey administered to first- and second-year podiatric medical students aimed to investigate the effect of coffee intake, energy drink consumption, and perceived stress on sleep quality in medical students during their preclinical studies.

METHODS

Ninety-eight of 183 students contacted (53.6%) completed a questionnaire comprising standard instruments measuring sleep quality (Pittsburgh Sleep Quality Index), daytime sleepiness (Epworth Sleepiness scale), and perceived stress (ten-item Perceived Stress Scale). Furthermore, we investigated coffee and energy drink consumption. Logistic regression was conducted to identify factors associated with poor sleep quality and the relation between sleep quality and academic performance (grade point average).

RESULTS

High prevalences of poor sleep quality, excessive daytime sleepiness, and perceived stress were reported. In addition, higher odds of developing poor sleep quality were associated with coffee and energy drink intake, perceived stress, and excessive daytime sleepiness. The total Pittsburgh Sleep Quality Index score was inversely correlated with grade point average.

CONCLUSIONS

First- and second-year podiatric medical students have poor sleep quality. Further research is needed to identify effective strategies to reduce stress and decrease coffee and energy drink intake to minimize their negative effect on sleep quality and academic performance in podiatric medical students.

Sleep duration during the school week is associated with C-reactive protein risk groups in healthy adolescents

BACKGROUND

The prevalence of short sleep duration in adolescence and the relevance of early risk factors to cardiovascular disease in adulthood suggest that adolescence is an opportune time to evaluate links between sleep duration and cardiovascular disease risk. We examined associations among actigraphy-assessed sleep duration and sleep debt with elevated C-reactive protein (CRP), a known risk factor for cardiovascular disease.

METHODS

Participants were 244 (56% Black, 48% male) healthy high school students, each of whom wore wrist actigraphs for one week and provided a fasting blood draw. CRP was examined as both a continuous and categorical outcome, with CRP >3 mg/L identifying a High Risk Group.

RESULTS

Sleep duration and sleep debt were significantly associated with CRP High Risk Group in covariate-adjusted analyses. Shorter sleep duration on school nights was associated with a greater likelihood of being in the High Risk CRP Group. Likelihood of being in the High Risk CRP Group was doubled in students who obtained an average of two or more hours of "catch up" sleep on weekend nights.

CONCLUSIONS

Reduced weekday sleep duration and sleep debt were both associated with CRP Risk Group in adolescence. That these relationships may be observed prior to the onset of clinical disease suggests that adolescence may provide an opportune period for disease prevention.

Cardiovascular function alterations induced by acute paradoxical sleep deprivation in rats

Sleep loss has been implicated in triggering the hypertension. The goal of the present study was investigated the possible mechanisms underlying cardiovascular alterations after acute paradoxical sleep deprivation (PSD). Male Wistar rats were assigned in two experimental groups: (1) control and (2) PSD for 24 h using the modified single platform method. Paradoxical sleep deprived rats exhibited higher blood pressure, heart rate (HR) and impaired baroreceptor sensitivity. After pharmacological autonomic double blockade (propranolol and methylatropine administration), intrinsic heart rate was decreased after PSD. The PSD rats showed a reduction in the vagal tone without affecting sympathetic tone. Isoproterenol administration (0.001, 0.01 and 1 µg/kg) induced an increase in ΔHR responses in PSD group. Electrocardiographic analysis in response to β-adrenergic stimulation indicated that PSD contributed to ventricular cardiac arrhythmias. Our findings suggest that acute paradoxical sleep loss induce cardiovascular alterations, autonomic imbalance accompanied by impaired baroreflex sensitivity and increased arrhythmia susceptibility.

Measuring quality of sleep and autonomic nervous function in healthy Japanese women

The purpose of this study was to determine the relationship between quality of sleep and autonomic nervous functioning in healthy adult Japanese women using three measures, namely, the Pittsburgh Sleep Quality Index (PSQI) for subjective assessment of sleep quality, actigraphy for objective assessment of sleep, and heart rate variability using high frequency and low frequency domains. Participants were 31 healthy women in their 20s to 40s who met the selection criteria, including having normal monthly menstrual periods. Participants were categorized as good or poor sleepers according to their PSQI score. Median correlation coefficients of activity count and high frequency were -0.62 (range -0.43 to -0.84) for good sleepers and -0.45 (range 0.003 to -0.64) for poor sleepers. Good sleepers showed a significantly higher correlation of activity count and high frequency (Z=-2.11, P<0.05). Median correlation coefficients of activity count and low frequency/high frequency were 0.54 (range 0.29-0.73) for good sleepers and 0.41 (range 0.11-0.63) for poor sleepers. The PSQI, actigraphy data, and heart rate variability results showed positive correlations between sleep time as measured by PSQI and duration of inactivity as measured by actigraphy (r=0.446, P<0.05) and sleep time as measured by actigraphy (r=0.377, P<0.05), and a negative correlation between sleep time as measured by PSQI and the correlation coefficients of activity count and high frequency (r=-0.460, P<0.01). These results support the finding that sleep-wake rhythms can be monitored efficiently with actigraphy, providing accurate data that can support the diagnosis of sleeping disorders. Furthermore, actigraphy data were associated with heart rate variability and PSQI findings, but only in subjects who were poor sleepers. Actigraphy is an accurate, efficient, rapid, and inexpensive test for determining objective and subjective sleeping problems, and can also be used in clinical tests for sleep assessment.

One night on-call: sleep deprivation affects cardiac autonomic control and inflammation in physicians

BACKGROUND

Sleep loss is associated with increased cardiovascular morbidity and mortality. It is known that chronic sleep restriction affects autonomic cardiovascular control and inflammatory response. However, scanty data are available on the effects of acute sleep deprivation (ASD) due to night shifts on the cardiovascular system and its capability to respond to stressor stimuli. The aim of our study was to investigate whether a real life model of ASD, such as "one night on-call", might alter the autonomic dynamic response to orthostatic challenge and modify the immune response in young physicians.

METHODS

Fifteen healthy residents in Internal Medicine were studied before and after one night on-call at Rest and during a gravitational stimulus (head up-tilt test, HUT). Heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) were analyzed during Rest and HUT before and after ASD. Plasmatic hormones (epinephrine, norepinephrine, cortisol, renin, aldosterone, ACTH) and tissue inflammatory cytokines were measured at baseline and after ASD.

RESULT

HRV analysis revealed a predominant sympathetic modulation and a parasympathetic withdrawal after ASD. During HUT, the sympathovagal balance shifted towards a sympathetic predominance before and after ASD. However, the magnitude of the autonomic response was lower after ASD. BPV and BRS remained unchanged before and after ASD as the hormone levels, while IFN-γ increased after ASD compared to baseline.

CONCLUSION

In summary, one night of sleep deprivation, at least in this real-life model, seems to affect cardiovascular autonomic response and immune modulation, independently by the activation of the hypothalamic-pituitary axis.

Sleep and its Relationship to Racial and Ethnic Disparities in Cardiovascular Disease

There are substantial racial/ethnic disparities in cardiovascular disease in the U.S., but few mechanisms have emerged as feasible intervention targets. A growing body of research suggests that racial/ethnic differences in sleep deficiency, including extreme sleep duration, sleep-disordered breathing, and insomnia, may help explain disparities in cardiovascular disease. However, little is known about the mechanisms underlying racial/ethnic disparities in sleep. In this article, we review the extant literature on sleep and cardiovascular outcomes (e.g., hypertension, stroke, cardiovascular disease) and racial/ethnic differences in these relations. We also discuss possible mechanisms that might help explain racial/ethnic sleep disparities, including neighborhood disadvantage, psychosocial and occupational stressors, acculturation, and treatment access and adherence. More research is needed to establish causal linkages among race/ethnicity, sleep, and these mechanisms, but existing evidence suggests that targeting these factors in interventions may reduce racial/ethnic sleep disparities and improve primary prevention of cardiovascular disease among all racial/ethnic groups.

Cardiovascular effects of partial sleep deprivation in healthy volunteers

Sleep deprivation is common in Western societies and is associated with increased cardiovascular morbidity and mortality in epidemiological studies. However, the effects of partial sleep deprivation on the cardiovascular system are poorly understood. In the present study, we evaluated 13 healthy male volunteers (age: 31 ± 2 yr) monitoring sleep diary and wrist actigraphy during their daily routine for 12 nights. The subjects were randomized and crossover to 5 nights of control sleep (>7 h) or 5 nights of partial sleep deprivation (<5 h), interposed by 2 nights of unrestricted sleep. At the end of control and partial sleep deprivation periods, heart rate variability (HRV), blood pressure variability (BPV), serum norepinephrine, and venous endothelial function (dorsal hand vein technique) were measured at rest in a supine position. The subjects slept 8.0 ± 0.5 and 4.5 ± 0.3 h during control and partial sleep deprivation periods, respectively ( P < 0.01). Compared with control, sleep deprivation caused significant increase in sympathetic activity as evidenced by increase in percent low-frequency (50 ± 15 vs. 59 ± 8) and a decrease in percent high-frequency (50 ± 10 vs. 41 ± 8) components of HRV, increase in low-frequency band of BPV, and increase in serum norepinephrine (119 ± 46 vs. 162 ± 58 ng/ml), as well as a reduction in maximum endothelial dependent venodilatation (100 ± 22 vs. 41 ± 20%; P < 0.05 for all comparisons). In conclusion, 5 nights of partial sleep deprivation is sufficient to cause significant increase in sympathetic activity and venous endothelial dysfunction. These results may help to explain the association between short sleep and increased cardiovascular risk in epidemiological studies.

Heart rate variability, sleep and sleep disorders

Heart rate (HR) is modulated by the combined effects of the sympathetic and parasympathetic nervous systems. Therefore, measurement of changes in HR over time (heart rate variability or HRV) provides information about autonomic functioning. HRV has been used to identify high risk people, understand the autonomic components of different disorders and to evaluate the effect of different interventions, etc. Since the signal required to measure HRV is already being collected on the electrocardiogram (ECG) channel of the polysomnogram (PSG), collecting data for research on HRV and sleep is straightforward, but applications have been limited. As reviewed here, HRV has been applied to understand autonomic changes during different sleep stages. It has also been applied to understand the effect of sleep-disordered breathing, periodic limb movements and insomnia both during sleep and during the daytime. HRV has been successfully used to screen people for possible referral to a Sleep Lab. It has also been used to monitor the effects of continuous positive airway pressure (CPAP). A novel HRV measure, cardiopulmonary coupling (CPC) has been proposed for sleep quality. Evidence also suggests that HRV collected during a PSG can be used in risk stratification models, at least for older adults. Caveats for accurate interpretation of HRV are also presented.

Sympathomodulatory effects of Saam acupuncture on heart rate variability in night-shift-working nurses

OBJECTIVE

We assessed the effects of Saam (traditional Korean) acupuncture on the autonomic nervous system in night-shift nurses using power-spectral heart-rate variability (HRV) analysis.

METHODS

This study had a 2 × 4 cross-over design with a series of six (n = 1) controlled trials. Six night-shift nurses were randomly divided into two groups, and each nurse received four acupuncture treatments on the third day of night-shift work. One group started with Saam acupuncture (gallbladder jeonggyeok), while the other started with sham acupuncture. Saam acupuncture and sham acupuncture were applied in turn. HRV was measured before and after treatment. For statistical analysis, the results of the two groups were combined, and a Bayesian model was used to compare the changes in HRV values before and after treatment, between Saam and sham acupuncture.

RESULTS

As the ratio of low- to high-frequency power (LF/HF) for HRV increased on the third day of night-shift work in the pilot study, HRV measurements were made on the third day. Compared with sham acupuncture, Saam acupuncture reduced sympathetic activity; the overall median treatment effect estimate in LF normalised units decreased by -17.4 (confidence interval (CI): -26.67, -8.725) and that for LF/HF decreased by -1.691 (CI: -3.222, -0.3789). The overall median treatment effect estimate in HF normalised units increased by 17.41 (CI: 6.393, 27.13) with Saam acupuncture, suggesting an increase in parasympathetic activity.

CONCLUSION

Saam acupuncture may attenuate the imbalance between sympathetic and parasympathetic activities induced by night-shift work in nurses.