Twenty-four-hour ambulatory blood pressure in shift workers

Circadian Influences on Myocardial Ischemia-Reperfusion Injury and Heart Failure

The impact of circadian rhythms on cardiovascular function and disease development is well established, with numerous studies in genetically modified animals emphasizing the circadian molecular clock's significance in the pathogenesis and pathophysiology of myocardial ischemia and heart failure progression. However, translational preclinical studies targeting the heart's circadian biology are just now emerging and are leading to the development of a novel field of medicine termed circadian medicine. In this review, we explore circadian molecular mechanisms and novel therapies, including (1) intense light, (2) small molecules modulating the circadian mechanism, and (3) chronotherapies such as cardiovascular drugs and meal timings. These promise significant clinical translation in circadian medicine for cardiovascular disease. (4) Additionally, we address the differential functioning of the circadian mechanism in males versus females, emphasizing the consideration of biological sex, gender, and aging in circadian therapies for cardiovascular disease.

Pioneering new frontiers in circadian medicine chronotherapies for cardiovascular health

Cardiovascular disease (CVD) is a global health concern. Circadian medicine improves cardiovascular care by aligning treatments with our body's daily rhythms and their underlying cellular circadian mechanisms. Time-based therapies, or chronotherapies, show special promise in clinical cardiology. They optimize treatment schedules for better outcomes with fewer side effects by recognizing the profound influence of rhythmic body cycles. In this review, we focus on three chronotherapy areas (medication, light, and meal timing) with potential to enhance cardiovascular care. We also highlight pioneering research in the new field of rest, the gut microbiome, novel chronotherapies for hypertension, pain management, and small molecules that targeting the circadian mechanism.

Nighttime administration of antihypertensive medication: a review of chronotherapy in hypertension

Hypertension remains a global health concern because of suboptimal blood pressure control despite advancements in antihypertensive treatments. Chronotherapy, defined as evening or bedtime administration of medication based on biological rhythms, is emerging as a potential strategy to improve blood pressure control and treatment outcomes. Clinical trials have investigated the potential effects of nighttime administration of antihypertensive medication in the improvement of 24 hours blood pressure control and reduction of cardiovascular risk. Implementing chronotherapy in clinical practice could have significant implications in enhancing blood pressure control and improving clinical outcomes in patients with hypertension, particularly those with resistant hypertension. However, recent trials have reported contradictory results, causing confusion in real-world practice. Herein we review, analyze, and critique the current evidence and propose suggestions regarding the clinical application and future directions of chronotherapy.

Pressure Building Against the Clock: The Impact of Circadian Misalignment on Blood Pressure

PURPOSE OF REVIEW

Misalignment between the endogenous biological timing system and behavioral activities (i.e., sleep/wake, eating, activity) contributes to adverse cardiovascular health. In this review, we discuss the effects of recurring circadian misalignment on blood pressure regulation and the implications for hypertension development. Additionally, we highlight emerging therapeutic approaches designed to mitigate the negative cardiovascular consequences elicited by circadian disruption.

RECENT FINDINGS

Circadian misalignment elicited by work schedules that require individuals to be awake during the biological night (i.e., shift work) alters 24-h blood pressure rhythms. Mechanistically, circadian misalignment appears to alter blood pressure via changes in autonomic nervous system balance, variations to sodium retention, dysregulation of endothelial vasodilatory responsiveness, and activation of proinflammatory mechanisms. Recurring circadian misalignment produced by a mismatch in sleep timing on free days vs. work days (i.e., social jetlag) appears to have no direct effects on prevailing blood pressure levels in healthy adults; though, circadian disruptions resulting from social jetlag may increase the risk of hypertension through enhanced sympathetic activation and/or obesity. Furthermore, social jetlag assessment may be a useful metric in shift work populations where the magnitude of circadian misalignment may be greater than in the general population. Circadian misalignment promotes unfavorable changes to 24-h blood pressure rhythms, most notably in shift working populations. While light therapy, melatonin supplementation, and the timing of drug administration may improve cardiovascular outcomes, interventions designed to target the effects of circadian misalignment on blood pressure regulation are warranted.

Evaluation of the Diurnal Cycle of Blood Pressure and Sleep in Shift Workers

BACKGROUND

Circadian misalignment of physiological factors in shift workers is poorly studied in the Indian population. In the present study, 24-hour blood pressure measurements were taken on the same subject twice, once during his morning and night shifts. Sleep was also monitored by a self-reported sleep diary, which was confirmed with an activity monitor, and the sleep quality was assessed using sleep questionnaires.

OBJECTIVE

This study aimed to discover the pattern of blood pressure variation, the dipping and non-dipping status, and its correlation with sleep.

METHODOLOGY

This observational study was conducted in the Department of Physiology, All India Institute of Medical Sciences (AIIMS), Rishikesh, from April 2019 to September 2019, among security guards working rotating shifts in the Rishikesh hospital premises. Participants were given an activity sheet with instructions to document their daily activities for a complete 24-hour period on the designated measurement day, including recording the time of waking up and going to sleep. A wrist-worn activity monitor was utilised to assess the self-reported sleep duration provided by each participant on the activity sheet.

RESULTS

The present study showed the mean age of the participants as 27.03 ± 2.71 years, along with a mean body mass index (BMI) of 22.10 ± 1.64. Sleep duration was significantly higher during the morning shift (5.81 ± 1.08 hours) compared to the night shift (4.02 ± 1.70 hours) on the day of ambulatory blood pressure monitoring (ABPM) recording. The mean difference in systolic blood pressure between night shift workers between their awake and sleep periods was 15.91 ± 8.44 mmHg. However, no statistically significant disparity was seen when comparing the systolic blood pressure at the 24-hour mark during wakefulness and sleep between those working morning and night shifts (p >0.05).

CONCLUSION

The current study's findings indicate that participation in shift work, particularly night shift work, could potentially play a role in the emergence of irregular circadian blood pressure patterns and potentially lead to a lack of nocturnal blood pressure decline.

Short-term blood pressure variability as a potential therapeutic target for kidney disease

Short-term blood pressure variability (BPV) measured with ambulatory blood pressure (BP) monitoring has been demonstrated to be significant in predicting various clinical outcomes. Short-term BPV is distinguished from long-term BPV based on the time interval in which BP fluctuations are measured. Increased short-term BPV has been linked to detrimental effects on the microvascular structure and contributes to subclinical organ damage in the heart, blood vessels, and kidneys, regardless of the average 24-h BP levels. Short-term BPV can be defined by various measures, including calculated metrics (standard deviation, coefficient of variation, average real variability, weighted standard deviation, variability independent of the mean) or dipping patterns. Nevertheless, the additional role of short-term BPV beyond the predictive value of average 24-h BPs or established risk factors for cardiovascular disease and kidney disease remains unclear. In particular, longitudinal studies that evaluate the association between short-term BPV and kidney function impairment are limited and no conclusive data exist regarding which short-term BPV indicators most accurately reflect the prognosis of kidney disease. The issue of how to treat BPV in clinical practice is another concern that is frequently raised. This paper presents a review of the evidence for the prognostic role of short-term BPV in kidney outcomes. Additionally, this review discusses the remaining concerns about short-term BPV that need to be further investigated as an independent risk modifier.

Redox Regulatory Changes of Circadian Rhythm by the Environmental Risk Factors Traffic Noise and Air Pollution

Significance: Risk factors in the environment such as air pollution and traffic noise contribute to the development of chronic noncommunicable diseases. Recent Advances: Epidemiological data suggest that air pollution and traffic noise are associated with a higher risk for cardiovascular, metabolic, and mental disease, including hypertension, heart failure, myocardial infarction, diabetes, arrhythmia, stroke, neurodegeneration, depression, and anxiety disorders, mainly by activation of stress hormone signaling, inflammation, and oxidative stress. Critical Issues: We here provide an in-depth review on the impact of the environmental risk factors air pollution and traffic noise exposure (components of the external exposome) on cardiovascular health, with special emphasis on the role of environmentally triggered oxidative stress and dysregulation of the circadian clock. Also, a general introduction on the contribution of circadian rhythms to cardiovascular health and disease as well as a detailed mechanistic discussion of redox regulatory pathways of the circadian clock system is provided. Future Directions: Finally, we discuss the potential of preventive strategies or "chrono" therapy for cardioprotection. Antioxid. Redox Signal. 37, 679-703.

Excessive Daytime Sleepiness and Its Associated Factors among Emergency Medicine Residents in South Korea: A Nationwide Survey

Objective

Excessive daytime sleepiness (EDS) in emergency medicine (EM) residents is associated with patient safety. However, studies regarding EDS in EM residents are limited. The objective of this study was to identify the prevalence of EDS and its associated factors among EM residents.

Methods

Epworth sleepiness scale scores, working hours per week (WHW), night working days per month, working environment, and depression were analyzed using data from the 2019 Korean Emergency Medicine Resident Survey.

Results

The survey response rate was 63.8% (384/601). Among 241 respondents, the prevalence rate of EDS was 32.4%. Multivariable logistic regression analysis demonstrated that WHW (odds ratio [OR] = 1.03, 95% confidence interval [CI] = 1.01–1.06) and depression (OR = 3.64, 95% CI = 1.91–6.96) had increased ORs for EDS.

Conclusions

Approximately one-third of EM residents had EDS. Depression and WHW were the associated factors.

Ambulatory blood pressure monitoring among emergency medical services night shift workers

OBJECTIVES

Higher 24-hour blood pressure (BP) and blunted BP dipping during sleep and night-time hours are associated with adverse health outcomes. Night shift work may affect 24-hour BP and dipping patterns, but empirical data in emergency medical services (EMS) clinician shift workers are sparse. We implemented ambulatory blood pressure monitoring (ABPM) in EMS workers to characterise BP during night shift work versus a non-workday, and sleep versus wake.

METHODS

Participants worked night shifts. Hourly ABPM and wrist actigraphy (to measure sleep) were collected during two 24-hour periods, one scheduled night shift and one non-workday. Blunted BP dipping was defined as a BP decrease of <10%.

RESULTS

Of 56 participants, 53 (53.6% female, mean age 26.5 (SD 7.5) years) completed the study. During daytime sleep on a workday, 49.1% of participants had blunted systolic BP (SBP) or diastolic BP (DBP) dipping. During night-time sleep on a non-workday, 25% had blunted SBP dipping and 3.9% blunted DBP dipping. Blunted SBP or DBP dipping occurred among all participants who did not nap during the night shift or who napped <60 min. Blunted SBP dipping occurred in only 14.3% of participants who napped 60-120 min.

CONCLUSIONS

During night shift work, the BP dipping of EMS shift workers is blunted; however, most who nap for 60 min or longer experience a healthy dip in BP. The potential health consequences of these observations in EMS clinicians warrant further study.

Diurnal Regulation of Renal Electrolyte Excretion: The Role of Paracrine Factors

Many physiological processes, including most kidney-related functions, follow specific rhythms tied to a 24-h cycle. This is largely because circadian genes operate in virtually every cell type in the body. In addition, many noncanonical genes have intrinsic circadian rhythms, especially within the liver and kidney. This new level of complexity applies to the control of renal electrolyte excretion. Furthermore, there is growing evidence that paracrine and autocrine factors, especially the endothelin system, are regulated by clock genes. We have known for decades that excretion of electrolytes is dependent on time of day, which could play an important role in fluid volume balance and blood pressure control. Here, we review what is known about the interplay between paracrine and circadian control of electrolyte excretion. The hope is that recognition of paracrine and circadian factors can be considered more deeply in the future when integrating with well-established neuroendocrine control of excretion.

Acute and Subacute Triggers of Cardiovascular Events

Inability to predict short-term cardiovascular (CV) events and take immediate preemptive actions has long been the Achilles heel of cardiology. However, certain triggers of these events have come to light. Although these triggers are nonspecific and are part of normal life, studying their temporal relationship with the onset of CV events provides an opportunity to alert high-risk atherosclerotic patients who may be most vulnerable to such triggers, the "vulnerable patient". Herein, we review the literature and shed light on the epidemiology and underlying pathophysiology of different triggers. We describe that certain adrenergic triggers can precipitate a CV event within minutes or hours; whereas triggers that elicit an immune or inflammatory response such as infections may tip an asymptomatic "vulnerable patient" to become symptomatic days and weeks later. In conclusion, healthcare providers should counsel high-risk CV patients (e.g., in secondary prevention clinics or those with coronary artery Calcium >75th percentile) on the topic, advise them to avoid such triggers, take protective measures once exposed, and seek emergency care immediately after becoming symptomatic after such triggers. Furthermore, clinical trials targeting triggers (prevention or intervention) are needed.

Implications of disturbances in circadian rhythms for cardiovascular health: A new frontier in free radical biology

Cell autonomous circadian "clock" mechanisms are present in virtually every organ, and generate daily rhythms that are important for normal physiology. This is especially relevant to the cardiovascular system, for example the circadian mechanism orchestrates rhythms in heart rate, blood pressure, cardiac contractility, metabolism, gene and protein abundance over the 24-h day and night cycles. Conversely, disturbing circadian rhythms (e.g. via shift work, sleep disorders) increases cardiovascular disease risk, and exacerbates cardiac remodelling and worsens outcome. Notably, reactive oxygen species (ROS) are important contributors to heart disease, especially the pathophysiologic damage that occurs after myocardial infarction (MI, heart attack). However, little is known about how the circadian mechanism, or rhythm desynchrony, is involved in these key pathologic stress responses. This review summarizes the current knowledge on circadian rhythms in the cardiovascular system, and the implications of rhythm disturbances for cardiovascular health. Furthermore, we highlight how free radical biology coincides with the pathogenesis of myocardial repair and remodelling after MI, and indicate a role for the circadian system in the oxidative stress pathways in the heart and brain after MI. This fusion of circadian biology with cardiac oxidative stress pathways is novel, and offers enormous potential for improving our understanding and treatment of heart disease.

Comparison of exogenous melatonin versus placebo on sleep efficiency in emergency medicine residents working night shifts: A randomized trial

BACKGROUND

Sleep deprivation resulting from night shifts, is a major cause of burnout among physicians. Exogenous melatonin may improve sleep quality in night-shift workers. The study aims to compare the effectiveness of melatonin versus placebo on sleep efficiency in emergency medicine (EM) residents.

METHODS

A randomized, double-blind, replicated crossover trial was performed on EM residents. This study consisted of 4 phases within a month with intervention periods of 2 nights and washouts of 6 days. In our study, EM residents had nine-hour shifts on 6 consecutive days, 2 mornings, 2 evenings and 2 nights and then 2 days off. At the end of shifts' cycle, 24 EM residents were given 3 mg melatonin or placebo (12 in each arm of the study) for 2 consecutive nights after the second night shift with crossover to the other arm after a six-day off drug. This crossover intervention was repeated for two more another time. Finally, we created 48 cases and comparisons in each arm. Different items related to sleep quality were assessed and compared both within the same group and between the two groups.

RESULTS

In the melatonin group, daytime sleepiness (calculated by Karolinska Sleep Scale) had a significant reduction after taking the second dose of drug (P=0.003) but the same result was not observed when comparing the 2 groups. Mood status (calculated by Profile of Mood States) showed no remarkable difference between the 2 groups.

CONCLUSION

Melatonin might have a limited benefit on sleep quality in EM residents working night shifts.

Cuffless Blood Pressure Estimation Based on Data-Oriented Continuous Health Monitoring System

Measuring blood pressure continuously helps monitor health and also prevent lifestyle related diseases to extend the expectancy of healthy life. Blood pressure, which is nowadays used for monitoring patient, is one of the most useful indexes for prevention of lifestyle related diseases such as hypertension. However, continuously monitoring the blood pressure is unrealistic because of discomfort caused by the tightening of a cuff belt. We have earlier researched the data-oriented blood pressure estimation without using a cuff. Remarkably, our blood pressure estimation method only uses a photoplethysmograph sensor. Therefore, the application is flexible for sensor locations and measuring situations. In this paper, we describe the implementation of our estimation method, the launch of a cloud system which can collect and manage blood pressure data measured by a wristwatch-type photoplethysmograph sensor, and the construction of our applications to visualize life-log data including the time-series data of blood pressure.

Circadian Misalignment Increases C-Reactive Protein and Blood Pressure in Chronic Shift Workers

Shift work is a risk factor for inflammation, hypertension, and cardiovascular disease. This increased risk cannot be fully explained by classical risk factors. Shift workers' behavioral and environmental cycles are typically misaligned relative to their endogenous circadian system. However, there is little information on the impact of acute circadian misalignment on cardiovascular disease risk in shift workers, independent of differences in work stress, food quality, and other factors that are likely to differ between night and day shifts. Thus, our objectives were to determine the independent effect of circadian misalignment on 24-h high-sensitivity C-reactive protein (hs-CRP; a marker of systemic inflammation) and blood pressure levels-cardiovascular disease risk factors-in chronic shift workers. Chronic shift workers undertook two 3-day laboratory protocols that simulated night work, comprising 12-hour inverted behavioral and environmental cycles (circadian misalignment) or simulated day work (circadian alignment), using a randomized, crossover design. Circadian misalignment increased 24-h hs-CRP by 11% ( p < 0.0001). Circadian misalignment increased 24-h systolic blood pressure (SBP) and diastolic blood pressure (DBP) by 1.4 mmHg and 0.8 mmHg, respectively (both p ≤ 0.038). The misalignment-mediated increase in 24-h SBP was primarily explained by an increase in SBP during the wake period (+1.7 mmHg; p = 0.017), whereas the misalignment-mediated increase in 24-h DBP was primarily explained by an increase in DBP during the sleep opportunity (+1.8 mmHg; p = 0.005). Circadian misalignment per se increases hs-CRP and blood pressure in shift workers. This may help explain the increased inflammation, hypertension, and cardiovascular disease risk in shift workers.

Shift work is associated with metabolic syndrome in male steel workers-the role of resistin and WBC count-related metabolic derangements

AIMS

There is increasing evidence linking a shift work schedule with various adverse health effects. The present study aimed to examine the relationship between shift work and the metabolic syndrome (MetS) in male steel workers, and also the possible mechanism of shift work-related metabolic derangements.

METHODS

A total of 1732 men aged 42 ± 8 years were enrolled in this cross-sectional study, including 862 day workers and 870 shift workers. Circulating levels of resistin were measured by ELISA using monoclonal specific antibodies.

RESULTS

The shift workers had higher rates of MetS and its components (central obesity, hypertension, and hypertriglyceridemia) than the day workers. In multiple logistic regression analysis, shift work was independently associated with MetS. In further analysis, the shift workers had elevated circulating levels of resistin (13 ± 10 vs. 10 ± 7 ng/mL) and total white blood cell (WBC) count (6.865 ± 1.819 vs. 6.304 ± 1.547 10⁹/L) than the day workers. In addition, both resistin level and total WBC count were significantly associated with shift work, MetS, and its components (body mass index, fasting glucose, triglyceride, and high-density lipoprotein-cholesterol levels), and plasma resistin levels were significantly associated with total WBC count (β = 0.34, p < 0.0001).

CONCLUSION

Shift work was independently associated with MetS in male steel workers. Resistin and WBC count were associated with shift work-related metabolic derangements.

Ambulatory Blood Pressure in Chronic Kidney Disease: Ready for Prime Time?

Hypertension is common in patients with chronic kidney disease (CKD) and is the most important modifiable risk factor for CKD progression and adverse cardiovascular events in these patients. Diagnosis and successful management of hypertension are critically dependent on accurate blood pressure (BP) measurement. This is most relevant to CKD patients, in whom BP control is difficult to achieve and in whom early antihypertensive treatment is imperative to prevent kidney and cardiovascular complications. Accumulated data indicate that ambulatory blood pressure monitoring (ABPM) is better in detecting hypertension than office BP measurement. ABPM is also a superior prognostic marker compared with office BP and has successfully identified hypertensive CKD patients at increased risk. Additionally, ABPM provides information on circadian BP variation and short-term BP variability, which is associated with cardiovascular and renal outcomes. This paper reviews the evidence for the usefulness of ABPM in detection and management of hypertension in CKD patients and discusses our current understanding of the pathophysiology of altered circadian BP rhythm and variability in CKD and the role of abnormal BP patterns detected by ABPM in relation to outcomes in CKD. In addition, this Review examines the emerging role of antihypertensive chronotherapy to tailor BP management to the circadian BP pattern abnormality detected by 24-hour ABPM.

Circadian misalignment increases cardiovascular disease risk factors in humans

Shift work is a risk factor for hypertension, inflammation, and cardiovascular disease. This increased risk cannot be fully explained by classic risk factors. One of the key features of shift workers is that their behavioral and environmental cycles are typically misaligned relative to their endogenous circadian system. However, there is little information on the impact of acute circadian misalignment on cardiovascular disease risk in humans. Here we show-by using two 8-d laboratory protocols-that short-term circadian misalignment (12-h inverted behavioral and environmental cycles for three days) adversely affects cardiovascular risk factors in healthy adults. Circadian misalignment increased 24-h systolic blood pressure (SBP) and diastolic blood pressure (DBP) by 3.0 mmHg and 1.5 mmHg, respectively. These results were primarily explained by an increase in blood pressure during sleep opportunities (SBP, +5.6 mmHg; DBP, +1.9 mmHg) and, to a lesser extent, by raised blood pressure during wake periods (SBP, +1.6 mmHg; DBP, +1.4 mmHg). Circadian misalignment decreased wake cardiac vagal modulation by 8-15%, as determined by heart rate variability analysis, and decreased 24-h urinary epinephrine excretion rate by 7%, without a significant effect on 24-h urinary norepinephrine excretion rate. Circadian misalignment increased 24-h serum interleukin-6, C-reactive protein, resistin, and tumor necrosis factor-α levels by 3-29%. We demonstrate that circadian misalignment per se increases blood pressure and inflammatory markers. Our findings may help explain why shift work increases hypertension, inflammation, and cardiovascular disease risk.

Shift work and hypertension: Prevalence and analysis of disease pathways in a German car manufacturing company

BACKGROUND

Hypertension and cardiovascular disease (CVD) may share a similar pathophysiology. Despite shift workers' CVD excess risk, studies on shift work and hypertension are inconclusive.

METHODS

Blood pressure and shift status for 25,343 autoworkers were obtained from medical check-ups and company registers. Cross-sectional associations modeling the total effect from shift work (day shifts, shift work without nights, rotating shift work with nights, and night shifts) on hypertension were assessed. By sequential adjustments, the influence of behavioral, psychosocial, and physiological factors on the total effect was examined, with subsequent mediation and moderation analyses.

RESULTS

Adjusted for confounders, shift work without nights (vs. day shifts) was significantly associated with hypertension (OR 1.15, 95%CI 1.02-1.30). The total effect was mediated by BMI, physical inactivity, and sleep disorders. No moderation of the total effect by behaviors was found.

CONCLUSION

The association between shift work and hypertension seems mainly attributable to behavioral mechanisms.

Influence of the Cardiomyocyte Circadian Clock on Cardiac Physiology and Pathophysiology

Cardiac function and dysfunction exhibit striking time-of-day-dependent oscillations. Disturbances in both daily rhythms and sleep are associated with increased risk of heart disease, adverse cardiovascular events, and worsening outcomes. For example, the importance of maintaining normal daily rhythms is highlighted by epidemiologic observations that night shift workers present with increased incidence of cardiovascular disease. Rhythmicity in cardiac processes is mediated by a complex interaction between extracardiac (e.g., behaviors and associated neural and humoral fluctuations) and intracardiac influences. Over the course of the day, the intrinsic properties of the myocardium vary at the levels of gene and protein expression, metabolism, responsiveness to extracellular stimuli/stresses, and ion homeostasis, all of which affect contractility (e.g., heart rate and force generation). Over the past decade, the circadian clock within the cardiomyocyte has emerged as an essential mechanism responsible for modulating the intrinsic properties of the heart. Moreover, the critical role of this mechanism is underscored by reports that disruption, through genetic manipulation, results in development of cardiac disease and premature mortality in mice. These findings, in combination with reports that numerous cardiovascular risk factors (e.g., diet, diabetes, aging) distinctly affect the clock in the heart, have led to the hypothesis that aberrant regulation of this mechanism contributes to the etiology of cardiac dysfunction and disease. Here, we provide a comprehensive review on current knowledge regarding known roles of the heart clock and discuss the potential for using these insights for the future development of innovative strategies for the treatment of cardiovascular disease.

Workplace psychosocial factors associated with hypertension in the U.S. workforce: a cross-sectional study based on the 2010 national health interview survey

OBJECTIVE

To explore associations between self-reported hypertension and workplace psychosocial factors that are common among U.S. workers and to identify industries and occupations (I&Os) that are associated with a high prevalence of hypertension, even after adjustment for common known risk factors.

METHODS

Data from the 2010 National Health Interview Survey were used to examine relationships between the prevalence of self-reported hypertension and job insecurity, hostile work environment, work- family imbalance, work hours and I&O.

RESULTS

Job insecurity (adjusted prevalence ratio (aPR): 1.11; 95% confidence interval (CI): 1.04-1.19)) and hostile work environment (aPR: 1.15; 95% CI: 1.03-1.29) were significantly associated with hypertension. Hypertension prevalence was significantly elevated among those employed in Healthcare Support occupations and Public Administration industries.

CONCLUSION

Addressing hostile work environments and the stress associated with job insecurity may improve workers' health. Other occupational factors that contribute to the variation in prevalence of hypertension by I&O should be sought.

Association between light exposure at night and nighttime blood pressure in the elderly independent of nocturnal urinary melatonin excretion

Circadian misalignment between internal and environmental rhythms dysregulates blood pressure (BP) variability because of disruption of the biological clock, resulting in increased nighttime BP. Although exposure to light-at-night is associated with the circadian misalignment, it remains unclear whether exposure to light-at-night in home settings is associated with nighttime BP. In this cross-sectional analysis of 528 elderly individuals (mean age: 72.8 years), we measured bedroom light intensity at 1-min intervals on two consecutive nights along with ambulatory BP, overnight urinary melatonin excretion and actigraphy. With regard to adjusted mean comparisons using analysis of covariance, the light-at-night group (average: ≥5 lux; n = 109) showed significantly higher nighttime systolic BP (SBP; adjusted mean: 120.8 vs. 116.5 mmHg, p = 0.01) and diastolic BP (70.1 vs. 67.1 mmHg, p < 0.01) compared with the Darker group (average: <5 lux; n = 419) independently of potential confounding factors including overnight urinary melatonin excretion and actigraphic sleep quality. We observed consistent associations between light-at-night and nighttime BP in different cutoff values for light-at-night intensity (i.e. 3 and 10 lux). In conclusion, exposure to light-at-night in home settings is significantly associated with increased nighttime BP in elderly individuals independently of overnight urinary melatonin excretion. A 4.3 mmHg increase in nighttime SBP is associated with a 6.1% increase in total mortality, which corresponds to approximately 10 000 annual excess deaths in Japanese elderly population.

Disruption of Transitional Stages in 24-h Blood Pressure Recording in Renal Transplant Recipients

Patients with kidney replacement exhibit disrupted circadian rhythms. Most studies measuring blood pressure use the dipper/non-dipper classification, which does not consider analysis of transitional stages between low and high blood pressure, confidence intervals nor shifts in the time of peak, while assuming subjective onsets of night and day phases. In order to better understand the nature of daily variation of blood pressure in these patients, we analyzed 24 h recordings from 41 renal transplant recipients using the non-symmetrical double-logistic fitting assessment which does not assume abruptness nor symmetry in ascending and descending stages of the blood pressure profile, and a cosine best-fitting regression method (Cosinor). Compared with matched controls, double-logistic fitting showed that the times for most transitional stages (ascending systolic and descending systolic, diastolic, and mean arterial pressure) had a wider distribution along the 24-h. The proportion of individuals without daily blood pressure rhythm in the transplanted group was larger only for systolic arterial pressure, and the amplitude showed no significant difference. Furthermore, the transplant recipient group had a less pronounced slope in descending systolic and ascending mean blood pressure. Cosinor analysis confirmed this phase-related changes, showing a wider distribution of times of peak (acrophases). We conclude that daily disruptions in renal transplant recipients can be explained not necessarily by an absence in diurnal variation, but also by changes in waveform-related parameters of the rhythm, and that alterations in the phase of the rhythm are the most consistent finding in these patients.

Diurnal blood pressure variation and related behavioral factors

Blood pressure (BP) varies according to many internal and external factors, and behavioral factors have an important role in diurnal BP variation. BP rises sharply on waking in the morning and falls during sleep at night, although it varies throughout the day and night. These changes in BP are closely related to mental and physical activities, and the sympathetic nervous system mainly contributes to the diurnal variation in BP. Other behavioral factors, such as food consumption and obesity, dietary intake of sodium, drinking and smoking habits, consumption of coffee and tea, and bathing, also affect the diurnal variation in BP. Alterations in diurnal BP variation due to behavioral factors are frequently seen in patients with hypertension and can be classified as morning hypertension, daytime hypertension and nighttime hypertension. Appropriate lifestyle modifications may normalize or improve both the level and rhythm of BP in these patients.

The cardiomyocyte circadian clock: emerging roles in health and disease

Circadian misalignment has been implicated in the development of obesity, diabetes mellitus, and cardiovascular disease. Time-of-day-dependent synchronization of organisms with their environment is mediated by circadian clocks. This cell autonomous mechanism has been identified within all cardiovascular-relevant cell types, including cardiomyocytes. Recent molecular- and genetic-based studies suggest that the cardiomyocyte circadian clock influences multiple myocardial processes, including transcription, signaling, growth, metabolism, and contractile function. Following an appreciation of its physiological roles, the cardiomyocyte circadian clock has recently been linked to the pathogenesis of heart disease in response to adverse stresses, such as ischemia/reperfusion, in animal models. The purpose of this review is therefore to highlight recent advances regarding the roles of the cardiomyocyte circadian clock in both myocardial physiology and pathophysiology (ie, health and disease).

Increased levels of resistin in rotating shift workers: a potential mediator of cardiovascular risk associated with circadian misalignment

OBJECTIVE

Shift work schedule has been associated with several health problems, including deleterious effects on the cardiovascular system. The present study aimed to evaluate the circulating levels of four biomarkers of atherosclerosis (soluble CD40 ligand [sCD40L], monocyte chemoattractant protein-1 [MCP-1], resistin, and plasminogen activator inhibitor-1 [PAI-1]) in a population-based sample of young adult men exposed to rotating shift work schedule in comparison with day workers.

DESIGN AND PARTICIPANTS

A total of 439 men aged 34.4+/-8.6 years were included in a cross-sectional study comparing 255 day workers with 184 rotating shift workers. Circulating levels of the biomarkers were measured in duplicate by ELISA using monoclonal specific antibodies.

RESULTS

Rotating shift workers had elevated (6440+/-4510 pg/mL) (mean+/-SD) circulating levels of resistin in comparison with day workers (5450+/-3780 pg/mL), and significance remains after adjusting for age and blood leukocyte count (p<0.045, ANCOVA). Shift work schedule explains 1% of the proportion of the total variation in the circulating resistin levels. Multiple regression analysis showed that resistin levels significantly correlate with rotating shift work (p<0.04) and blood leukocyte count (p<0.00003) independently of age, BMI, waist-hip ratio, HOMA, and cardiovascular risk %. Circulating levels of sCD40L, MCP-1, and PAI-1 did not significantly differ between day workers and shift workers.

CONCLUSION

Shift work schedule was significantly associated with elevated plasma resistin levels. Resistin, which is probably produced by leukocytes, may play an important role in the pathogenesis of early metabolic syndrome components in young men chronically exposed to circadian misalignment.

When and why do heart attacks occur? Cardiovascular triggers and their potential role

Coronary heart disease affects 7.6% of the population in the United States, where > 900,000 myocardial infarctions (MIs) occur annually. Approximately half of all MIs have an identifiable clinical trigger. Myocardial ischemia, MI, sudden cardiac death, and thrombotic stroke each occur with circadian variation and peak after waking in the morning. In addition, physical exertion and mental stress are common precipitants of MI. Waking in the morning, physical exertion, and mental stress influence a number of physiologic parameters, including blood pressure, heart rate, plasma epinephrine levels, coronary blood flow, platelet aggregability, and endothelial function. Upregulation of sympathetic output and catecholamines increase myocardial oxygen demand and can decrease myocardial oxygen supply and promote thrombosis. Ischemia ensues when myocardial oxygen demand exceeds supply. Increases in blood pressure and ventricular contractility increase intravascular shear stress and may cause vulnerable atherosclerotic plaques to rupture, forming a nidus for thrombosis that can precipitate MI. Numerous clinical triggers of MI have been identified, including blizzards, the Christmas and New Year's holidays, experiencing an earthquake, the threat of violence, job strain, Mondays for the working population, sexual activity, overeating, smoking cigarettes, smoking marijuana, using cocaine, and particulate air pollution. Avoiding clinical triggers or participating in therapies that prevent clinical triggers from precipitating cardiac events could potentially postpone clinical events by several years and improve cardiovascular morbidity and mortality. Direct or indirect evidence suggests that the risk of triggered MIs is reduced with β-blockers, aspirin, statins, stress management, and transcendental meditation.

Nocturnal blood pressure dipping in the hypertension of autonomic failure

Blood pressure (BP) normally decreases during the night. Absence of this phenomenon (nondipping) is associated with increased cardiovascular risk. Altered autonomic and endocrine circadian rhythms are suspected to play a role. Patients with peripheral autonomic failure offer a unique opportunity to study this phenomenon, because approximately 50% develop supine hypertension despite very low autonomic function. The purpose of this study was to define the prevalence of dipping in these patients and to determine whether dipping is associated with less severe autonomic impairment or exaggerated nocturnal sodium excretion. We collected BP and urine from 8:00 pm to 8:00 am in 41 peripheral autonomic failure patients with supine hypertension. Dipping (systolic BP fall >or=10% during 12 am to 6 am from baseline [8 pm to 10 pm]) occurred in 34% of patients, with an average decrease of -44+/-4 mm Hg at 4 am. Systolic BP, averaged from 12 am to 6 am, decreased to normotensive levels in 50% (n=7) of dippers and 15% (n=7) of nondippers. There were no significant differences in the severity of autonomic failure, nocturnal diuresis, or natriuresis (0.18+/-0.01 in dippers versus 0.18+/-0.01 mEq/mg of creatinine in nondippers; P=0.522) between groups. At 8:00 am, orthostatic hypotension was similar between groups (-84/-35+/-9/4 mm Hg in dippers versus -93/-39+/-6/3 mm Hg in nondippers; P=0.356 for systolic BP). In conclusion, dipping was observed in one third of patients with peripheral autonomic failure, so that a significant percentage of patients would not require treatment for supine hypertension. Dipping was not associated with increased nocturnal urinary sodium or volume excretion or less severe autonomic failure. Thus, mechanisms independent of autonomic pathways contribute to BP dipping in these patients.

Dynamic blood pressure changes and recovery under different work shifts in young women

BACKGROUND

Some studies have reported that shift work can affect blood pressure (BP), but few have studied recovery from BP changes occurring during different shifts.

METHODS

We recruited 16 young female nurses working rotating shifts and six working the regular day shift. All received repeated ambulatory BP monitoring (ABPM) during their workdays and following day off.

RESULTS

Our linear mixed-effect model showed that both systolic and diastolic BPs were significantly decreased during sleeping period and significantly increased while on working period, on a work day, but increased during sleeping period after a night shift or evening shift. BP measurements that changed after evening shift usually returned to baseline on consecutive off-duty day after day shift, but they did not completely return to baseline after a night shift (P < 0.05). We also found 69% of those working rotating shifts had at least changed once in dipper/nondipper status. The rates of change in dipper/nondipper status between work day and off-duty day were 33, 44, 50, and 38% for nurses worked in outpatient clinic, night shift, evening shift, and day shift, respectively.

CONCLUSION

Shift work is significantly associated with BP and possibly dipper/nondipper status in young female nurses. Except for those working night shifts, BP levels returned to baseline the off-duty day after day shift. We recommend that potential influence of shift work be considered when evaluating a person's BP.

Efeito da inversão dos turnos de trabalho sobre capacidade aeróbia e respostas cardiovasculares ao esforço máximo

Os distúrbios do sono e alterações associadas atingem grande parte da população que trabalha no turno noturno, afetando a sua qualidade de vida. O objetivo do presente trabalho foi comparar a capacidade aeróbia e as respostas cardiovasculares ao exercício máximo em indivíduos com ciclo sono vigília fisiológico e com inversão dos turnos de trabalho. Foram analisados 18 indivíduos do sexo masculino, sedentários, com idade entre 23-35 anos, divididos em 2 grupos: a) grupo controle, formado por estudantes (n=9) e b) grupo experimental, composto por controladores de tráfego aéreo que trabalhavam com inversão dos turnos de trabalho (n=9). Para a medida da capacidade aeróbia, foi determinado o VO2máx. por meio do analisador de gases metabólicos (VO-2000, Aerosport, Medgraphics). Para o teste de esforço máximo foi realizado o protocolo de rampa em esteira (Millenniun ATL Inbramed) e as respostas cardiovasculares (FC, PAS e PAD) foram verificadas antes e após a realização do exercício. De acordo com os resultados, o grupo experimental apresentou valores inferiores de FC no repouso (79,8 ± 11,5 bpm vs. 70,3 ± 3,8 bpm), no 5º (112,7± 15,1 bpm vs. 98,7 ± 6,3 bpm) e no 7º minuto (108,7 ± 16,6 bpm vs. 93,9 ± 6,8 bpm) de recuperação. Quanto à PAS, foram observados valores superiores durante o repouso (110,0 ± 11,2 mmHg vs. 104,0 ± 5,7 mmHg), nos indivíduos do grupo controle. Já a PAD, mostrou níveis superiores no 5º minuto da recuperação no grupo experimental (67,0 ± 4,4 mmHg vs. 58,9 ± 6,0 mmHg). Por fim, foram verificados valores superiores de VO2máx. para os indivíduos do grupo controle (58,9 ± 6,1 ml/kg/min) em relação ao experimental (53,7 ± 2,5 ml/kg/min). Desta forma, podemos concluir que a inversão nos turnos de trabalho, afetando o ciclo sono-vigília, altera não apenas o ciclo circadiano das variáveis cardiovasculares no repouso e na recuperação do esforço, como também traz prejuízos à capacidade funcional, podendo comprometer o desempenho das atividades ocupacionais.

Serotonin and serotonin transporter gene variant in rotating shift workers

STUDY OBJECTIVES

Because serotonin (5-HT) is a neurotransmitter associated with circadian rhythm regulation, we explored a possible relation among 5-HT, serotonin metabolite, 5-hydroxyindolacetic acid (5HIAA), and the functional polymorphism of the serotonin transporter gene (SLC6A4) promoter with rotating shift work.

DESIGN AND PARTICIPANTS

683 men were included in this study: 437 day workers were compared with 246 rotating shift workers.

RESULTS

Platelet 5-HT content differed significantly (P = 0.002) between day workers (41.28+/-1.99 pg/mg) and rotating shift workers (37.91+/-4.16 pg/mg); 5-HIAA content was also significantly (P = 0.00004) higher in day workers (11.40+/-0.82 pg/mg) than in rotating shift workers (9.33+/-1.02 pg/ mg). We looked for further differences in SLC6A4 promoter (5-HTTLPR, 44 bp insertion: long (L)/deletion: short (S) alleles). We found a significant (P = 0.016) difference in genotype distribution between day workers LL: 126 (28.8%), LS: 202 (46.2%), and SS: 109 (24.9%), and rotating shift workers LL: 47 (19.1%), LS: 124 (50.4%), and SS: 75 (30.5%). When we divided the subjects between workers with less and more than 60 month rotating shift-work exposure, the difference in SLC6A4 genotypes frequency was only significant in the group with > or =60 months (P = 0.011). In addition, there was a significantly lower content of platelet 5-HIAA in S allele carriers in comparison with the other genotypes (SS: 9.2+/-1.0 pg/mg vs. SL/LL: 11.0+/-0.8 pg/mg, P <0.02).

CONCLUSIONS

Platelet 5-HT and 5-HIAA contents were significantly lower in rotating shift workers than day workers, and there was a significant association between the S variant of SLC6A4 promoter and shift work. These findings may be important for targeting effective therapeutic strategies to ameliorate the associated comorbidities and behavioral problems in rotating shift workers.

Rapid attenuation of circadian clock gene oscillations in the rat heart following ischemia-reperfusion

The intracellular circadian clock consists of a series of transcriptional modulators that together allow the cell to perceive the time of day. Circadian clocks have been identified within various components of the cardiovascular system (e.g. cardiomyocytes, vascular smooth muscle cells) and possess the potential to regulate numerous aspects of cardiovascular physiology and pathophysiology. The present study tested the hypothesis that ischemia/reperfusion (I/R; 30 min occlusion of the rat left main coronary artery in vivo) alters the circadian clock within the ischemic, versus non-ischemic, region of the heart. Left ventricular anterior (ischemic) and posterior (non-ischemic) regions were isolated from I/R, sham-operated, and naïve rats over a 24-h period, after which mRNAs encoding for both circadian clock components and known clock-controlled genes were quantified. Circadian clock gene oscillations (i.e. peak-to-trough fold differences) were rapidly attenuated in the I/R, versus the non-ischemic, region. Consistent with decreased circadian clock output, we observe a rapid induction of E4BP4 in the ischemic region of the heart at both the mRNA and protein levels. In contrast with I/R, chronic (1 week) hypobaric chamber-induced hypoxia did not attenuate oscillations in circadian clock genes in either the left or right ventricle of the rat heart. In conclusion, these data show that in a rodent model of myocardial I/R, circadian clocks within the ischemic region become rapidly impaired, through a mechanism that appears to be independent of hypoxia.

Circadian variation of blood pressure: the basis for the chronotherapy of hypertension

Ambulatory blood pressure (BP) measurements present a close correlation with target organ damage and cardiovascular events, including myocardial infarction, stroke and cardiovascular mortality. With the use of this measurement technique, a significant circadian variation has been shown to characterize BP. This circadian BP variation, although affected by a variety of external factors, represents the influence of internal factors such as ethnicity, gender, autonomic nervous system tone, vasoactive hormones, and hematologic and renal variables. In most individuals, BP presents a morning increase, a small post-prandial valley, and a deeper descent during nocturnal rest. However, under certain pathophysiological conditions, the nocturnal BP decline may be reduced or even reversed. This cannot be determined by traditional clinical or home BP assessments. Subjects with a diminished nocturnal BP decline (non-dipper pattern) have a significantly worse prognosis than the ones with a normal dipper pattern. In particular, the non-dipper circadian BP pattern represents a risk factor for left ventricular hypertrophy, microalbuminuria, cerebrovascular disease, congestive heart failure, vascular dementia and myocardial infarction. The normalization of the circadian BP pattern to a dipper profile is a novel therapeutic goal, and accumulating medical evidence suggests this can delay the progression towards the renal and cardiovascular pathology known to be a consequence of the non-dipper BP pattern. The features of the circadian BP profile have direct implications for improving the drug-delivery of antihypertensive therapies as well as the qualification of patients for medication trials and assessment.

The effect of telmisartan and ramipril on early morning blood pressure surge: a pooled analysis of two randomized clinical trials

OBJECTIVES

The period of early morning blood pressure surge is associated with a higher incidence of cardiovascular events than at other times of the day. Antihypertensive medication given once daily in the morning may not protect against this surge if its duration of action is too short. We compared telmisartan, an angiotensin II receptor blocker with a trough-to-peak ratio >90%, with ramipril, an angiotensin-converting enzyme inhibitor with a trough-to-peak ratio of around 50%.

METHODS

Data from two prospective, randomized, open-label, blinded endpoint studies comparing telmisartan force titrated to 80 mg once daily and ramipril 10 mg once daily were pooled. Patients had mild-to-moderate hypertension and were assessed using 24-h ambulatory blood pressure monitoring at baseline and endpoint. Early morning blood pressure surge was defined as the difference between mean blood pressure within 2 h after arising and night-time low. Patients were grouped into quartiles according to their baseline systolic surge.

RESULTS

Data from 1279 patients were analyzed. Telmisartan changed the overall mean (SE) systolic surge by -1.5 (0.47) mmHg, and ramipril by +0.3 (0.47) mmHg (P=0.0049). The magnitude of surge reduction was greatest in the quartile with highest baseline systolic surge: telmisartan -12.7 (0.91), ramipril -7.8 (1.02) mmHg (P=0.0004). Telmisartan also reduced the surge compared with ramipril in dippers, but there were no differences between the two groups in nondippers.

CONCLUSIONS

Telmisartan significantly reduced the early morning systolic blood pressure surge compared with ramipril. A reduction in this surge may help to reduce cardiovascular events in the morning period.

Role of sleep-wake cycle on blood pressure circadian rhythms and hypertension

Stages of different depth characterize the temporal organization of sleep. Each stage exerts an effect on blood pressure (BP) regulation and contributes to its 24-h variation. The main determinant of the circadian influences of sleep and wakefulness on BP is the daytime sympathetic and nighttime parasympathetic prevalence, but many other physiologic mechanisms known either to induce sleep or determine arousal may play an important role in the mediation of sleep influences on BP. Alteration of one or more of such mechanisms may be reflected in altered circadian BP rhythms. Sleep- and arousal-related mechanisms and phenomena that affect circadian BP rhythms include neurohumoral sleep factors (arginine vasopressin, vasoactive intestinal peptide, somatotropin, insulin, steroid hormones and metabolites, and serotonin among others) and waking factors (corticotropin-releasing factor, adrenocorticotropin, thyrotropin-releasing hormone, endogenous opioids, and prostaglandin (E(2))). Pathologic respiratory variations (sleep-disordered breathing) and insomnia are major causes of the sleep-related alteration of the circadian BP profile, including loss of the expected normal decline in BP by 10-20% from the daytime level. A great number of medical disorders can cause insomnia, but objective sleep studies have been performed only in a minority of them. Overall, the sleep-related pathophysiological mechanisms actually involved in causing altered circadian BP rhythms in different normotensive and hypertensive conditions are not completely understood. In any case, changes in the circadian BP rhythm are known to be strongly related to one's risk of cardiovascular morbidity and mortality, thus representing strong prognostic indicators worthy of further investigation.

Potential role for peripheral circadian clock dyssynchrony in the pathogenesis of cardiovascular dysfunction

Circadian clocks are intracellular molecular mechanisms designed to allow the cell, organ, and organism to prepare for an anticipated stimulus prior to its onset. In order for circadian clocks to maintain their selective advantage, they must be entrained to the environment. Light, sound, temperature, physical activity (including sleep/wake transitions), and food intake are among the strongest environmental factors influencing mammalian circadian clocks. Normal circadian rhythmicities in these environmental factors have become severely disrupted in our modern day society, concomitant with increased incidence of type 2 diabetes mellitus, obesity, and cardiovascular disease. Here, we review our current knowledge regarding the roles of peripheral circadian clocks, concentrating on those found within tissues directly involved in metabolic homeostasis and cardiovascular function. We propose that both inter- and intra-organ dyssynchronization, through alteration/impairment of peripheral circadian clocks, accelerates the development of cardiovascular disease risk factors associated with cardiometabolic syndrome.

Effects of rotating shift work on biomarkers of metabolic syndrome and inflammation

OBJECTIVE

The major function of the circadian system is the internal cycling of physiological and metabolic events. The present study sought to explore the effect of rotating shift work schedule on leucocyte count and its relationship with risk factors of metabolic syndrome (MS).

DESIGN AND PARTICIPANTS

From a population-based design, 1351 men of self-reported European ancestry were included in a cross-sectional study: 877 day workers were compared with 474 rotating shift workers. Medical history, health examination including anthropometric and arterial blood pressure measurements, a questionnaire on health-related behaviours and biochemical determinations was given to all participants.

RESULTS

In comparison with day workers, rotating shift workers had elevated (mean +/- SE) body mass index (27.1 +/- 0.3 vs. 26.3 +/- 0.2, P < 0.0154), waist-hip ratio (0.95 +/- 0.01 vs. 0.93 +/- 0.01, P < 0.00024), diastolic arterial blood pressure (78 +/- 1 vs. 76 +/- 1, P < 0.033), fasting insulin (65.5 +/- 2.9 vs. 55.9 +/- 1.9 pmol L(-1), P < 0.017), Homeostasis Model Assessment index (2.12 +/- 0.11 vs. 1.77 +/- 0.07, P < 0.0027), triglycerides (1.71 +/- 0.1 vs. 1.5 +/- 0.1 mmol L(-1), P < 0.002), uric acid (292.7 +/- 2.8 vs. 282 +/- 3.4 micromol L(-1), P < 0.01) and leucocyte count (7030 +/- 84 vs. 6730 +/- 58, P < 0.0094). In multiple regression analysis, leucocyte count was correlated with rotating shift work independently of age, smoking, education and components of MS.

CONCLUSION

The odds ratio for MS in rotating shift workers compared with day workers was 1.51 (95% CI 1.01-2.25), independently of age and physical activity. Increased leucocyte count, a biological marker of systemic inflammation, was associated with rotating shift work.

The circadian clock within the cardiomyocyte is essential for responsiveness of the heart to fatty acids

Cells/organs must respond both rapidly and appropriately to increased fatty acid availability; failure to do so is associated with the development of skeletal muscle and hepatic insulin resistance, pancreatic beta-cell dysfunction, and myocardial contractile dysfunction. Here we tested the hypothesis that the intrinsic circadian clock within the cardiomyocytes of the heart allows rapid and appropriate adaptation of this organ to fatty acids by investigating the following: 1) whether circadian rhythms in fatty acid responsiveness persist in isolated adult rat cardiomyocytes, and 2) whether manipulation of the circadian clock within the heart, either through light/dark (L/D) cycle or genetic disruptions, impairs responsiveness of the heart to fasting in vivo. We report that both the intramyocellular circadian clock and diurnal variations in fatty acid responsiveness observed in the intact rat heart in vivo persist in adult rat cardiomyocytes. Reversal of the 12-h/12-h L/D cycle was associated with a re-entrainment of the circadian clock within the rat heart, which required 5-8 days for completion. Fasting rats resulted in the induction of fatty acid-responsive genes, an effect that was dramatically attenuated 2 days after L/D cycle reversal. Similarly, a targeted disruption of the circadian clock within the heart, through overexpression of a dominant negative CLOCK mutant, severely attenuated induction of myocardial fatty acid-responsive genes during fasting. These studies expose a causal relationship between the circadian clock within the cardiomyocyte with responsiveness of the heart to fatty acids and myocardial triglyceride metabolism.

The circadian clock within the heart: potential influence on myocardial gene expression, metabolism, and function

It is becoming increasingly clear that the intrinsic properties of both the heart and vasculature exhibit dramatic oscillations over the course of the day. Diurnal variations in the responsiveness of the cardiovascular system to environmental stimuli are mediated by a complex interplay between extracellular (i.e., neurohumoral factors) and intracellular (i.e., circadian clock) influences. The intracellular circadian clock is composed of a series of transcriptional modulators that together allow the cell to perceive the time of day, thereby enabling preparation for an anticipated stimulus. These molecular timepieces have been characterized recently within both vascular smooth muscle cells and cardiomyocytes, giving rise to a multitude of hypotheses relating to the potential role(s) of the circadian clock as a modulator of physiological and pathophysiological cardiovascular events. For example, evidence strongly supports the hypothesis that the circadian clock within the heart modulates myocardial metabolism, which in turn facilitates anticipation of diurnal variations in workload, substrate availability, and/or the energy supply-to-demand ratio. The purpose of this review is therefore to summarize our current understanding of the molecular events governing diurnal variations in the intrinsic properties of the heart, with special emphasis on the intramyocardial circadian clock. Whether impairment of this molecular mechanism contributes toward cardiovascular disease associated with hypertension, diabetes mellitus, shift work, sleep apnea, and/or obesity will be discussed.

Effect of diet and exercise on pulse pressure and cardiac function in morbid obesity: analysis of 24-hour ambulatory blood pressure

Blood pressure is a major risk factor for cardiovascular events, although the role of pulse pressure, an independent predictor of arterial stiffness, has recently been emphasized. This study examines the baseline relationship between body mass index (BMI) and blood pressure indexes in 215 obese African Americans enrolled in a diet-exercise program. The subject population was 77% female, with a mean +/- SD age of 46.7+/-10.7 years and a mean BMI of 42.5+/-7.5 kg/m2. In addition, the authors prospectively examined the effect of weight loss on cardiovascular parameters in a subset of 25 participants. The results show a closer significant correlation between pulse pressure and BMI (b=1.97 kgm-1; p=0.001) than between systolic blood pressure and BMI (b=1.58 kgm-1; p=0.020). After 3 months of diet and exercise, average reductions were as follows: BMI, 4.2 kg/m2 (p<0.01); systolic blood pressure, 7.2 mm Hg (p<0.01); pulse pressure, 4.8 mm Hg (p<0.01); and cardiac output, 975 mL/min (p<0.01). Compliance index increased by 0.1 mL/mm Hg/m2 (p=0.03). The results highlight the potential value to cardiovascular health of a modest reduction in body weight in obese individuals.

Nonsymmetrical double logistic analysis of ambulatory blood pressure recordings

We developed an asymmetric double logistic curve-fitting procedure for circadian analysis that can determine the rate of change in variables during the day-to-night separately from the night-to-day transition for use in animal studies. We now have applied this procedure to 24-h systolic (SAP) and diastolic arterial pressure (DAP) and heart rate ambulatory recordings from 302 patients. In 292 cases, all parameters showed a pattern of higher day and lower night values. In men there was a similar rate of transition between day and night or from night to day for both SAP and DAP that lasted 3–4 h, indicating a symmetrical diurnal pattern. By contrast, women showed a faster rate of decrease in mean arterial pressure in the evening compared with men ( P < 0.05) and therefore showed an asymmetric diurnal SAP pattern. For both men and women, there was a markedly greater rate of morning increase in heart rate compared with the rate of evening decrease (2.2- and 1.9-fold, respectively, P < 0.001). The logistic method provided a better fit than the square-wave or the cosinor method ( P < 0.001) and more appropriately detected nondippers. We conclude that analysis of ambulatory recordings by a new logistic curve-fitting method reveals more rapid reductions in evening SAP in women than men but both have two- to threefold more rapid morning rates of tachycardia. The ability of the double logistic method to determine the diurnal blood pressure rates of change independently is key to determining new markers for cardiovascular risk.

An occupational health physician's report on the improvement in the sleeping conditions of night shift workers

This paper reviews briefly our research findings on sleep and health for shift workers at a bakery and a dish factory and aims to give some information on health protection with improved sleep. Our medical examinations revealed that rises in blood pressure (BP) were frequently observed in male bakery workers on the fixed night shift. They took a two-hour nap from 1:00 to 3:00 during the night shifts according to our advice. As a result, their diastolic BP significantly decreased in subsequent years. Women working shifts before 3:00 at a dish factory seemed to show more sleep disturbance, higher daytime sleepiness, and more fatigue than those working shits from 3:00. Total sleep hours taken during the daytime was similar between two groups. Among the dish, factory workers who switched to midnight or night shifts, 70% reported slow recovery from fatigue and 30% felt deteriorated health. These women also reported increased efforts to obtain a deep sleep, probably making up for shortened sleep. Occupational physicians can act to improve shift work conditions through monitoring the health of workers, applying naps, and designing possible schedules to secure deep, sufficient sleep.

Analysis of blood pressure in children and adolescents reporting siesta during ambulatory blood pressure monitoring

BACKGROUND

In adults, a siesta yields a blood pressure profile similar to that seen in nocturnal sleep. It is therefore stressed that siestas should not be included in daytime blood pressure measurement.

OBJECTIVES

To evaluate blood pressure profiles in pediatric and adolescent patients who reported a siesta during 24 h ambulatory blood pressure monitoring (ABPM).

METHODS

Patients' diaries of actual sleep times were used to determine the periods of sleep (night-time and siesta) and daytime wakefulness. Ambulatory systolic and/or diastolic daytime and/or night-time hypertension was determined by comparing patients' measurements with normal values taken from published standards for healthy children and adolescents. Data obtained from 12 patients with ambulatory normotension and 12 patients with ambulatory hypertension, who were referred for an evaluation of hypertension or management of known hypertension, were analysed separately.

RESULTS

Mean systolic (SBP) and diastolic (DBP) blood pressure values during the daytime awake period were significantly higher than the mean values for the period of daytime, including the siesta, both in patients with ambulatory normotension and in those with ambulatory hypertension (P<0.001 and P<0.01 for SBP and DBP, and P<0.001 and P<0.001 for SBP and DBP, respectively). The percentage night-time falls in SBP and DBP were 12.9+/-0.5 and 19.1+/-1.4 in patients with ambulatory normotension, and 7.1+/-1.5 and 12.9+/-2.2 in patients with ambulatory hypertension. These values were significantly higher when the siesta was excluded from the analysis in both groups (13.9+/-0.5% and 20.7+/-1.5%, P<0.001 and P<0.01 for SBP and DBP in patients with ambulatory normotension; 8+/-1.6% and 14.8+/-2.4%, P<0.001 and P<0.001 for SBP and DBP in patients with ambulatory hypertension, respectively).

CONCLUSIONS

By ignoring the effect of the siesta, both the calculation of daytime blood pressure values and the analysis of day-night variability in children and adolescents undergoing ABPM may be erroneously interpreted.