Circadian variation of ambulatory myocardial ischemia. Triggering by daily activities and evidence for an endogenous circadian component

Silent Myocardial Ischemia: From Pathophysiology to Diagnosis and Treatment

Silent myocardial ischemia (SMI), characterized by a lack of overt symptoms despite an inadequate blood supply to the myocardium, remains a challenging entity in cardiovascular medicine. The pathogenesis involves intricate interactions of vascular, neurohormonal, and metabolic factors, contributing to perfusion deficits without the characteristic chest pain. Understanding these mechanisms is pivotal for recognizing diverse clinical presentations and designing targeted interventions. Diagnostic strategies for SMI have evolved from traditional electrocardiography to advanced imaging modalities, including stress echocardiography, single-photon emission computed tomography (SPECT), positron emission tomography (PET), and cardiac magnetic resonance imaging (MRI). Treating SMI is a matter of ongoing debate, as the available evidence on the role of invasive versus medical management is controversial. This comprehensive review synthesizes current knowledge of silent myocardial ischemia, addressing its pathophysiology, diagnostic modalities, and therapeutic interventions.

Complexities in cardiovascular rhythmicity: perspectives on circadian normality, ageing and disease

Biological rhythms exist in organisms at all levels of complexity, in most organs and at myriad time scales. Our own biological rhythms are driven by energy emitted by the sun, interacting via our retinas with brain stem centres, which then send out complex messages designed to synchronize the behaviour of peripheral non-light sensing organs, to ensure optimal physiological responsiveness and performance of the organism based on the time of day. Peripheral organs themselves have autonomous rhythmic behaviours that can act independently from central nervous system control but is entrainable. Dysregulation of biological rhythms either through environment or disease has far-reaching consequences on health that we are only now beginning to appreciate. In this review, we focus on cardiovascular rhythms in health, with ageing and under disease conditions.

Impact of Circadian Disruption on Cardiovascular Function and Disease

The circadian system, that is ubiquitous across species, generates ∼24 h rhythms in virtually all biological processes, and allows them to anticipate and adapt to the 24 h day/night cycle, thus ensuring optimal physiological function. Epidemiological studies show time-of-day variations in adverse cardiovascular (CV) events, and controlled laboratory studies demonstrate a circadian influence on key markers of CV function and risk. Furthermore, circadian misalignment, that is typically experienced by shift workers as well as by individuals who experience late eating, (social) jet lag, or circadian rhythm sleep-wake disturbances, increases CV risk factors. Therefore, understanding the mechanisms by which the circadian system regulates CV function, and which of these are affected by circadian disruption, may help to develop intervention strategies to mitigate CV risk.

Impact of mental stress, the circadian system and their interaction on human cardiovascular function

The risk for adverse cardiovascular events (e.g., myocardial infarction, sudden cardiac death) peaks in the morning, possibly due to the effects of the endogenous circadian system on cardiovascular risk factors, or the occurrence in the morning of specific triggers, such as mental stress. To assess any interacting effects on cardiovascular function of mental stress and the circadian system, 12 healthy adults underwent a 240-h protocol with all measurements and behaviors scheduled evenly across the circadian cycle. Mental stress was repeatedly induced by performance-motivated serial addition tasks. Cardiovascular measures included hemodynamic function (heart rate, blood pressure), circulating catecholamines (epinephrine, norepinephrine), and estimates of sympathovagal balance and cardiac vagal modulation derived from heart rate variability analyses. Mental stress increased hemodynamic function, sympathovagal balance and epinephrine, and decreased cardiac vagal modulation. Endogenous circadian variation occurred in all cardiovascular measures: sympathovagal balance peaked in the circadian morning (∼9 AM), cardiac vagal modulation in the circadian night (∼4 AM), and heart rate and circulating catecholamines in the late circadian morning/early afternoon (∼12 PM). Importantly, the effects of mental stress and the endogenous circadian system on cardiovascular function occurred in conjunction, such that mental stress in the circadian morning caused greatest sympathovagal balance. This summation of effects could contribute to the increased morning cardiovascular vulnerability.

In a Heartbeat: Light and Cardiovascular Physiology

Light impinging on the retina fulfils a dual function: it serves for vision and it is required for proper entrainment of the endogenous circadian timing system to the 24-h day, thus influencing behaviors that promote health and optimal quality of life but are independent of image formation. The circadian pacemaker located in the suprachiasmatic nuclei modulates the cardiovascular system with an intrinsic ability to anticipate morning solar time and with a circadian nature of adverse cardiovascular events. Here, we infer that light exposure might affect cardiovascular function and provide evidence from existing research. Findings show a time-of-day dependent increase in relative sympathetic tone associated with bright light in the morning but not in the evening hours. Furthermore, dynamic light in the early morning hours can reduce the deleterious sleep-to-wake evoked transition on cardiac modulation. On the contrary, effects of numerous light parameters, such as illuminance level and wavelength of monochromatic light, on cardiac function are mixed. Therefore, in future research studies, light modalities, such as timing, duration, and its wavelength composition, should be taken in to account when testing the potential of light as a non-invasive countermeasure for adverse cardiovascular events.

Chronobiology of Takotsubo Syndrome and Myocardial Infarction: Analogies and Differences

Several pathophysiologic factors, not harmful if taken alone, are capable of triggering unfavorable events when presenting together within the same temporal window (chronorisk), and the occurrence of many cardiovascular events is not evenly distributed in time. Both acute myocardial infarction and takotsubo syndrome seem to exhibit a temporal preference in their onset, characterized by variations according to time of day, day of the week, and month of the year, although with both analogies and differences.

Regulating sadness and fear from outside and within: mothers' emotion socialization and adolescents' parasympathetic regulation predict the development of internalizing difficulties

Multilevel models of developmental psychopathology implicate both characteristics of the individual and their rearing environment in the etiology of internalizing problems and disorders. Maladaptive regulation of fear and sadness, the core of anxiety and depression, arises from the conjoint influences of ineffective parasympathetic regulation of emotion and ineffective emotion socialization experiences. In 171 youths (84 female, M = 13.69 years, SD = 1.84), we measured changes of respiratory sinus arrhythmia (RSA) in response to sadness- and fear-inducing film clips and maternal supportive and punitive responses to youths' internalizing emotions. Youths and mothers reported on youths' internalizing problems and anxiety and depression symptoms concurrently and 2 years later at Time 2. Maternal supportive emotion socialization predicted fewer, and punitive socialization predicted more, mother-reported internalizing problems at Time 2 only for youths who showed RSA suppression to fear-inducing films. More RSA suppression to sadness-inducing films predicted more youth-reported internalizing problems at Time 2 in girls only. In addition, less supportive emotion socialization predicted more youth-reported depression symptoms at Time 2 only for girls who showed more RSA suppression to sadness. RSA suppression to sadness versus fear might reflect different patterns of atypical parasympathetic regulation of emotional arousal, both of which increase the risk for internalizing difficulties in youths, and especially girls, who lack maternal support for regulating emotions.

The influence of regular walking at different times of day on blood lipids and inflammatory markers in sedentary patients with coronary artery disease

OBJECTIVE

To examine the influence of walking at different times of day on lipids and inflammatory markers in sedentary patients with coronary artery disease (CAD).

METHODS

A total of 330 patients recruited from Nanjing between September 2011 and November 2012 were randomly assigned to a control group (n=110), morning (n=110) or evening walking group (n=110). Both the walking groups were asked to walk 30 min/day or more on at least 5 days/week either in the morning or evening for 12 weeks. Lipids and inflammatory markers were measured before and after exercise intervention.

RESULTS

Compared with baseline, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) were improved in all groups. Significances were shown in the changes of fibrinogen, high sensitivity C-reactive protein (hsCRP), white blood cell (WBC) count, TC, triglycerides, LDL-C, lipoprotein(a) between groups. The evening walking group had a larger decrease in fibrinogen (0.16 ± 0.19 g/L, P<0.001), hsCRP (1.16 ± 1.07 mg/L, P<0.001), WBC count (0.76 ± 1.53·10(9)/L, P=0.004) and LDL-C (0.34 ± 0.31 mmol/L, P<0.001) than the other two groups.

CONCLUSIONS

Our walking program successfully resulted in a favorable change in lipids and inflammatory markers. Patients in the evening walking group gained more benefits than those walking in the morning walking group. NCT01887093.

Is there diurnal variation of the vestibulosympathetic reflex: implications for orthostatic hypotension

Incidences of adverse cardiac events and orthostatic hypotension are associated with diurnal variations. The primary purpose of the present study was to determine if the vestibulosympathetic reflex (VSR) follows a diurnal variation in humans. We hypothesized that the VSR would be attenuated at night based on the relation between melatonin and the VSR. Arterial blood pressure, heart rate, calf blood flow, and muscle sympathetic nerve activity (MSNA) were measured in nine healthy subjects (28 ± 1 yr, 5 men and 4 women) at rest and during head-down rotation. Each subject was tested during the day at 11:34 ± 13 and again at night 22:10 ± 5. MSNA was significantly decreased at night compared with day (8 ± 1 vs. 11 ± 2 bursts/min, respectively, P < 0.02). Heart rate and arterial blood pressure at rest were significantly increased at night compared with day (heart rate: 70 ± 4 vs. 66 ± 4 beats/min and mean arterial blood pressure: 91 ± 2 vs. 87 ± 1 mmHg, respectively). MSNA and hemodynamic responses to head-down rotation were not significantly altered at night compared with day (changes of 3 ± 1 bursts/min and 25 ± 6% for MSNA and calf blood flow, respectively). The data indicate that MSNA at rest decreases during the late evening hours and exhibits a diurnal variation, whereas the VSR does not. In summary, diurnal variation of orthostatic hypotension in humans does not appear to be associated with changes in the VSR and MSNA at rest.

Sleep-wake and circadian-dependent variation of cardiorespiratory coherence

The risk of adverse cardiovascular events is elevated in the morning compared to the rest of the day. A circadian and a sleep-wake dependent variation in the regulation of the cardiovascular system could contribute to this increased cardiovascular risk. Using an ultradian sleep-wake cycle (USW) procedure, our aim was to explore the effects of the sleep-wake and circadian cycles on cardiorespiratory coherence (CRC) as a measure of autonomic nervous system (ANS) state. Our results suggest a shift toward parasympathetic dominance with deepening of sleep. Conversely, REM sleep is associated with a sympathetic dominance comparable to levels observed during wakefulness. A circadian rhythm was observed for CRC during wakefulness and all sleep stages. Maximal sympathetic dominance was observed in the morning, as measured by CRC during wakefulness and REM sleep, consistent with studies showing increased cardiac risk in the morning. This study provides evidence that circadian and sleep processes interact to influence the ANS modulation of the heart.

The chronergy of recombinant streptokinase thrombolysis in acute myocardial infarction

The aim of this study was to explore the chronergy of intravenous recombinant streptokinase (r-SK) in patients with acute myocardial infarction (AMI). A total of 114 patients were divided into two groups according to the time of AMI onset: the morning onset (6:01-12:00, n=53) and non-morning onset (12:01-06:00, n=61) groups. The recanalization rate was recorded, as well as anticoagulant and fibrinolytic indices. Statistical analysis was performed to evaluate the recanalization rate following thrombolysis, as well as the anticoagulant and fibrinolytic activities. The recanalization rates following thrombolysis in the morning onset and non-morning onset groups were 60.4 and 82.0%, respectively (P<0.05). The level of plasminogen activator inhibitor-1 (PAI-1) antigen was significantly higher in the morning onset group compared with that in the non-morning onset group (P<0.05). This indicated a resistance to r-SK thrombolysis in the morning at the early stage of AMI, which possibly correlates with increased PAI-1 antigen levels and activity.

Protection of the heart against ischemia/reperfusion by silent information regulator 1

Myocardial ischemia followed by ischemia/reperfusion (I/R) induces irreversible damage to cardiac muscle. Medical treatment that effectively prevents I/R injury would alleviate the consequent development of cardiac remodeling and failure. Mechanisms that extend life span often make organisms resistant to stress, and an accumulation of such mechanisms may prevent aging and susceptibility to age-associated diseases. Sirtuins are a group of molecules involved in longevity and stress resistance. Stimulation of silent information regulator 1 (Sirt1), the mammalian ortholog of yeast Sir2 and a member of the sirtuin family, extends the life span of mice fed a high-fat diet and retards aging in the heart. Recent evidence suggests that stimulation of Sirt1 mimics ischemic preconditioning and protects the heart from I/R injury, suggesting an intriguing possibility of using longevity factors to treat cardiac disease. Here, we discuss the cardioprotective effects of Sirt1 and possible underlying mechanisms.

Circadian clock genes and implications for intestinal nutrient uptake

There has recently been increasing interest in the phenomenon of circadian rhythmicity. We have used circadian rhythms as a means to understanding the regulation of glucose absorption in the intestine. We and others have previously demonstrated rhythmicity in intestinal glucose uptake, mediated by rhythmicity in the expression of the sodium glucose cotransporter 1. Rhythmicity of clock gene expression was subsequently confirmed in the intestine, a phenomenon also demonstrated in other viscera. Clock genes have since been shown via a combination of in vitro and in vivo techniques to play a role in the transcriptional regulation of key absorptive proteins.

Cardiac oxygen supply is compromised during the night in hypertensive patients

The enhanced heart rate and blood pressure soon after awaking increases cardiac oxygen demand, and has been associated with the high incidence of acute myocardial infarction in the morning. The behavior of cardiac oxygen supply is unknown. We hypothesized that oxygen supply decreases in the morning and to that purpose investigated cardiac oxygen demand and oxygen supply at night and after awaking. We compared hypertensive to normotensive subjects and furthermore assessed whether pressures measured non-invasively and intra-arterially give similar results. Aortic pressure was reconstructed from 24-h intra-brachial and simultaneously obtained non-invasive finger pressure in 14 hypertensives and 8 normotensives. Supply was assessed by Diastolic Time Fraction (DTF, ratio of diastolic and heart period), demand by Rate-Pressure Product (RPP, systolic pressure times heart rate, HR) and supply/demand ratio by A_dia/A_sys, with A_dia and A_sys diastolic and systolic areas under the aortic pressure curve. Hypertensives had lower supply by DTF and higher demand by RPP than normotensives during the night. DTF decreased and RPP increased in both groups after awaking. The DTF of hypertensives decreased less becoming similar to the DTF of normotensives in the morning; the RPP remained higher. A_dia/A_sys followed the pattern of DTF. Findings from invasively and non-invasively determined pressure were similar. The cardiac oxygen supply/demand ratio in hypertensive patients is lower than in normotensives at night. With a smaller night-day differences, the hypertensives’ risk for cardiovascular events may be more evenly spread over the 24 h. This information can be obtained noninvasively.

The influence of circadian variations on echocardiographic parameters in healthy people

BACKGROUND

Our aim was to investigate whether diastolic functions, myocardial velocities and pulmonary vein flow show diurnal variation within a 24-hour day.

METHOD AND RESULTS

Fourty-four healthy subjects with no history of cardiovascular or systemic diseases (32 males, 12 females; mean age 34.7 ± 8.7 years, mean BMI: 25.5 ± 3.5 kg/m(2)) were enrolled in this study. None of the subjects had a history, symptoms or signs of cardiovascular or systemic diseases or were taking drugs of any kind. All underwent echocardiographic examination at 7 a.m., 1 p.m., 7 p.m., and 1 a.m. M-mode systolic, diastolic velocities and pulmonary vein flow measurements were obtained. There were no differences in systolic and diastolic blood pressures and heart rate. The left atrial diameter was greater at 1 p.m. (3.80 ± 0.44; P = 0.031). The isovolumic contraction time (ICT) was found to be the shortest (41 ± 12 msn; P = 0.050), and ejection time (ET) the longest (290 ± 31 msn; P = 0.017) at the 1 am measurements. The mitral myocardial performance index (MPI) was lowest during the 1 a.m. measurements (0.42 ± 0.11; P = 0.001). The systolic myocardial velocities (Sm) obtained from the septum and inferior region were significantly higher at 1 p.m. and lower at 7 a.m. (9.17 ± 1.79, 10.25 ± 2.29; 8.11 ± 1.06, 8.63 ± 1.49; P < 0.05). The late diastolic velocities obtained from the lateral, inferior and anterior regions were higher at 1 p.m. and 7 p.m.

CONCLUSION

The left ventricular diameter and ejection fraction did not exhibit circadian variations. However, our data indicate that some parameters reflecting diastolic function, systolic myocardial velocities and MPI, as well as left atrial diameter change at different times of the day, independent of blood pressure and heart rate.

Mood and transient cardiac dysfunction in everyday life

Emotion in daily life may be associated with transient myocardial ischemia, ventricular tachycardia and impaired autonomic function in cardiac patients, but the precise temporal sequence is unclear. Eighty-eight patients with suspected coronary artery disease underwent 24-h electrocardiographic monitoring, and affect was measured with the Day Reconstruction Method. Thirteen patients (15%) experienced one or more episodes of ST depression or ventricular tachycardia, nine of whom provided concurrent mood data. Mood and heart rate variability were analyzed for the 15 min before, during, and 15 min after each ST depression/ventricular tachycardia episode, and were compared with control periods not associated with cardiac dysfunction. Patients reported more negative mood in the 15 min preceding cardiac dysfunction compared with control periods (P = 0.02). Heart rate increased in the 5 min before cardiac dysfunction (P = 0.005), whereas low frequency heart rate variability was reduced at onset but not before cardiac dysfunction (P = 0.007). There were not changes in high frequency heart rate variability. This small study indicates that emotional state may contribute to vulnerability of cardiac dysfunction in everyday life.

Impact of the human circadian system, exercise, and their interaction on cardiovascular function

The risk of adverse cardiovascular events peaks in the morning (≈9:00 AM) with a secondary peak in the evening (≈8:00 PM) and a trough at night. This pattern is generally believed to be caused by the day/night distribution of behavioral triggers, but it is unknown whether the endogenous circadian system contributes to these daily fluctuations. Thus, we tested the hypotheses that the circadian system modulates autonomic, hemodynamic, and hemostatic risk markers at rest, and that behavioral stressors have different effects when they occur at different internal circadian phases. Twelve healthy adults were each studied in a 240-h forced desynchrony protocol in dim light while standardized rest and exercise periods were uniformly distributed across the circadian cycle. At rest, there were large circadian variations in plasma cortisol (peak-to-trough ≈85% of mean, peaking at a circadian phase corresponding to ≈9:00 AM) and in circulating catecholamines (epinephrine, ≈70%; norepinephrine, ≈35%, peaking during the biological day). At ≈8:00 PM, there was a circadian peak in blood pressure and a trough in cardiac vagal modulation. Sympathetic variables were consistently lowest and vagal markers highest during the biological night. We detected no simple circadian effect on hemostasis, although platelet aggregability had two peaks: at ≈noon and ≈11:00 PM. There was circadian modulation of the cardiovascular reactivity to exercise, with greatest vagal withdrawal at ≈9:00 AM and peaks in catecholamine reactivity at ≈9:00 AM and ≈9:00 PM. Thus, the circadian system modulates numerous cardiovascular risk markers at rest as well as their reactivity to exercise, with resultant profiles that could potentially contribute to the day/night pattern of adverse cardiovascular events.

Examining the relationship between triggering activities and the circadian distribution of acute aortic dissection

BACKGROUND AND OBJECTIVES

There are limited data examining triggering activities and circadian distribution at the onset of acute aortic dissection (AAD) in the context of diagnostic and anatomical classification. The aim of this study was to further investigate this relationship between triggering activities and circadian distribution at the onset of AAD according to diagnostic and anatomic classification.

SUBJECTS AND METHODS

A total of 166 patients with AAD admitted to Kyungpook National University Hospital between July 2001 and June 2009 were included. To assess the influence of diagnostic and anatomical classification, we categorized the patients into intramural hematoma (IMH) group (n=67)/non-IMH group (n=99) and Stanford type A (AAD-A, n=94)/type B (AAD-B, n=72). To evaluate circadian distribution, the day was divided into four 6-hour periods: night (00-06 hours), morning (06-12 hours), afternoon (12-18 hours), and evening (18-00 hours).

RESULTS

Most (72%) AAD episodes were related to physical (53%) and mental activities (19%), with about one-third occurring during the afternoon, and only 12% occurring at night. No differences in triggering activities or circadian distribution were observed among the groups. Waking hours including morning, afternoon, and evening correlated with triggering activities (p=0.003). These relationships were observed for the non-IMH (p=0.008) and AAD-B (p=0.003) cases. The remaining categories had similar relationships, but did not reach statistical significance.

CONCLUSION

Our findings suggest differences in the relationship between triggering activities and the circadian distribution of the onset of AAD according to diagnostic and anatomical classification.

Melatonin and circadian biology in human cardiovascular disease

Diurnal rhythms influence cardiovascular physiology, i.e. heart rate and blood pressure, and they appear to also modulate the incidence of serious adverse cardiac events. Diurnal variations occur also at the molecular level including changes in gene expression in the heart and blood vessels. Moreover, the risk/benefit ratio of some therapeutic strategies and the concentration of circulating cardiovascular system biomarkers may also vary across the 24-hr light/dark cycle. Synchrony between external and internal diurnal rhythms and harmony among molecular rhythms within the cell are essential for normal organ biology. 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. specific genes that are differentially light/dark regulated) mechanisms. Neurohormones, which are particularly relevant to the cardiovascular system, such as melatonin, exhibit a diurnal variation and may play a role in the synchronization of molecular circadian clocks in the peripheral tissue and the suprachiasmatic nucleus. Moreover, mounting evidence reveals that the blood melatonin rhythm has a crucial role in several cardiovascular functions, including daily variations in blood pressure. Melatonin has antioxidant, anti-inflammatory, chronobiotic and, possibly, epigenetic regulatory functions. This article reviews current knowledge related to the biological role of melatonin and its circadian rhythm in cardiovascular disease.

Dynamic cardiovascular risk assessment in elderly people. The role of repeated N-terminal pro-B-type natriuretic peptide testing

OBJECTIVES

This study sought to determine whether serial measurement of N-terminal pro-B-type natriuretic peptide (NT-proBNP) in community-dwelling elderly people would provide additional prognostic information to that from traditional risk factors.

BACKGROUND

Accurate cardiovascular risk stratification is challenging in elderly people.

METHODS

NT-proBNP was measured at baseline and 2 to 3 years later in 2,975 community-dwelling older adults free of heart failure in the longitudinal CHS (Cardiovascular Health Study). This investigation examined the risk of new-onset heart failure (HF) and death from cardiovascular causes associated with baseline NT-proBNP and changes in NT-proBNP levels, adjusting for potential confounders.

RESULTS

NT-proBNP levels in the highest quintile (>267.7 pg/ml) were independently associated with greater risks of HF (hazard ratio [HR]: 3.05; 95% confidence interval [CI]: 2.46 to 3.78) and cardiovascular death (HR: 3.02; 95% CI: 2.36 to 3.86) compared with the lowest quintile (<47.5 pg/ml). The inflection point for elevated risk occurred at NT-proBNP 190 pg/ml. Among participants with initially low NT-proBNP (<190 pg/ml), those who developed a >25% increase on follow-up to >190 pg/ml (21%) were at greater adjusted risk of HF (HR: 2.13; 95% CI: 1.68 to 2.71) and cardiovascular death (HR: 1.91; 95% CI: 1.43 to 2.53) compared with those with sustained low levels. Among participants with initially high NT-proBNP, those who developed a >25% increase (40%) were at higher risk of HF (HR: 2.06; 95% CI: 1.56 to 2.72) and cardiovascular death (HR: 1.88; 95% CI: 1.37 to 2.57), whereas those who developed a >25% decrease to <or=190 pg/ml (15%) were at lower risk of HF (HR: 0.58; 95% CI: 0.36 to 0.93) and cardiovascular death (HR: 0.57; 95% CI: 0.32 to 1.01) compared with those with unchanged high values.

CONCLUSIONS

NT-proBNP levels independently predict heart failure and cardiovascular death in older adults. NT-proBNP levels frequently change over time, and these fluctuations reflect dynamic changes in cardiovascular risk.

Prokineticin 2 modulates the excitability of area postrema neurons in vitro in the rat

Despite recent evidence describing prokineticin 2 (PK2)-producing neurons and receptors in the dorsomedial medulla, little is known regarding the potential mechanisms by which this circadian neuropeptide acts in the medulla to influence autonomic function. Using whole cell electrophysiology, we have investigated a potential role for PK2 in the regulation of excitability in neurons of the area postrema (AP), a medullary structure known to influence autonomic processes in the central nervous system. In current-clamp recordings, focal application of 1 μM PK2 reversibly influenced the excitability of the majority of dissociated AP cells tested, producing depolarizations (38%) and hyperpolarizations (28%) in a concentration-dependent manner. Slow voltage ramps and ion-substitution experiments revealed that a PK2-induced Cl− current was responsible for membrane depolarization, whereas hyperpolarizations were the result of inhibition of a nonselective cation current. In contrast to these differential effects on membrane potential, nearly all neurons that displayed spontaneous activity responded to PK2 with a decrease in spike frequency. These observations are in accordance with voltage-clamp experiments showing that PK2 caused a leftward shift in Na+ channel activation and inactivation gating. Lastly, using post hoc single-cell RT-PCR technology, we have shown that 7 of 10 enkephalin-expressing AP neurons were depolarized by PK2 indicating that PK2 may have specific inhibitory actions on this population of neurons in the AP to reduce their sensitivity to homeostatic signals. These data suggest that the level of AP neuronal excitability may be regulated by PK2, ultimately affecting AP autonomic control.

Effects of circadian disruption on the cardiometabolic system

The presence of day-night variations in cardiovascular and metabolic functioning is well known. However, only recently it has been shown that cardiovascular and metabolic processes are not only affected by the behavioral sleep/wake cycle but are partly under direct control of the master circadian pacemaker located in the suprachiasmatic nucleus (SCN). Heart rate, cardiac autonomic activity, glucose metabolism and leptin-involved in appetite control-all show circadian variation (i.e., under constant behavioral and environmental conditions). This knowledge of behavioral vs. circadian modulation of cardiometabolic function is of clinical relevance given the morning peak in adverse cardiovascular incidents observed in epidemiological studies and given the increased risk for the development of diabetes, obesity, and cardiovascular disease in shift workers. We will review the evidence for circadian control of cardiometabolic functioning, as well its sensitivity to light and melatonin, and discuss potential implication for therapy.

Circadian variation in the circulatory responses to exercise: relevance to the morning peaks in strokes and cardiac events

Sudden cardiac and cerebral events are most common in the morning. A fundamental question is whether these events are triggered by the increase in physical activity after waking, and/or a result of circadian variation in the responses of circulatory function to exercise. Although signaling pathways from the master circadian clock in the suprachiasmatic nuclei to sites of circulatory control are not yet understood, it is known that cerebral blood flow, autoregulation and cerebrovascular reactivity to changes in CO(2) are impaired in the morning and, therefore, could explain the increased risk of cerebrovascular events. Blood pressure (BP) and the rate pressure product (RPP) show marked 'morning surges' when people are studied in free-living conditions, making the rupture of a fragile atherosclerotic plaque and sudden cardiac event more likely. Since cerebral autoregulation is reduced in the morning, this surge in BP may also exacerbate the risk of hemorrhagic and ischemic strokes in the presence of other acute and chronic risk factors. Increased sympathetic activity, decreased endothelial function, and increased platelet aggregability could also be important in explaining the morning peak in cardiac and cerebral events but how these factors respond to exercise at different times of day is unclear. Evidence is emerging that the exercise-related responses of BP and RPP are increased in the morning when prior sleep is controlled. We recommend that such 'semi-constant routine' protocols are employed to examine the relative influence of the body clock and exogenous factors on the 24-h variation in other circulatory factors.

Circadian Variation in Stroke Onset: Identical Temporal Pattern in Ischemic and Hemorrhagic Events

Stroke is the culmination of a heterogeneous group of cerebrovascular diseases that is manifested as ischemia or hemorrhage of one or more blood vessels of the brain. The occurrence of many acute cardiovascular events--such as myocardial infarction, sudden cardiac death, pulmonary embolism, critical limb ischemia, and aortic aneurysm rupture--exhibits prominent 24 h patterning, with a major morning peak and secondary early evening peak. The incidence of stroke exhibits the same 24 h pattern. Although ischemic and hemorrhagic strokes are different entities and are characterized by different pathophysiological mechanisms, they share an identical double-peak 24 h pattern. A constellation of endogenous circadian rhythms and exogenous cyclic factors are involved. The staging of the circadian rhythms in vascular tone, coagulative balance, and blood pressure plus temporal patterns in posture, physical activity, emotional stress, and medication effects play central and/or triggering roles. Features of the circadian rhythm of blood pressure, in terms of their chronic and acute effects on cerebral vessels, and of coagulation are especially important. Clinical medicine has been most concerned with the prevention of stroke in the morning, when population-based studies show it is of greatest risk during the 24 h; however, improved protection of at-risk patients against stroke in the early evening, the second most vulnerable time of cerebrovascular accidents, has received relatively little attention thus far.

The autonomic nervous system and ischemic stroke: a reciprocal interdependence

Signs and symptoms of autonomic nervous system (ANS) dysfunction are frequently reported after ischemic or haemorrhagic stroke and in many cases they exhibit peculiar patterns in relationship with the site and the extension of brain lesion. However if an ANS disorder can cause or predispose to a stroke is far from being correctly known. Evidences in favor of a pathogenetic mechanism of an ANS dysfunction are reported for myocardial infarction and such data are likely to be appropriate also for atherothrombotic type of ischemic stroke. On the other hand, it is well known that many risk factors for this pathology are strongly correlated with an altered functioning of ANS so that a reciprocal interdependence between ANS and stroke can be hypothesized. This review points to evidence the possible relationship existing between these two conditions and suggests a quite different diagnostic and therapeutic approach to both on the basis of their pathogenetic mechanisms.

Coagulation activity before and after acute psychosocial stress increases with age

OBJECTIVE

To assess whether stress further increases hypercoagulation in older individuals. We investigated whether acute stress-induced changes in coagulation parameters differ with age. It is known that hypercoagulation occurs in response to acute stress and that a shift in hemostasis toward a hypercoagulability state occurs with age. However, it is not yet known whether acute stress further increases hypercoagulation in older individuals, and thus may increase their risk for cardiovascular disease (CVD).

METHODS

A total of 63 medication-free nonsmoking men, aged between 20 and 65 years (mean +/- standard error of the mean = 36.7 +/- 1.7 years), underwent an acute standardized psychosocial stress task combining public speaking and mental arithmetic in front of an audience. We measured plasma clotting factor VII activity (FVII:C), fibrinogen, and D-dimer at rest, immediately, and 20 minutes after stress.

RESULTS

Increased age predicted greater increases in fibrinogen (beta = 0.26, p = 0.041; DeltaR(2) = 0.05), FVII:C (beta = 0.40, p = .006; DeltaR(2) = 0.11), and D-dimer (beta = 0.51, p < .001; DeltaR(2) = 0.18) from rest to 20 minutes after stress independent of body mass index and mean arterial blood pressure. General linear models revealed significant effects of age and stress on fibrinogen, FVII:C, and D-dimer (main effects: p < .04), and greater D-dimer stress reactivity with older age (interaction age-by-stress: F(1.5/90.4) = 4.36, p = .024; f = 0.33).

CONCLUSIONS

Our results suggest that acute stress might increase vulnerability in the elderly for hypercoagulability and subsequent hemostasis-associated diseases like CVD.

Psychobiology of depression/distress in congestive heart failure

Heart failure affects millions of Americans and new diagnosis rates are expected to almost triple over the next 30 years as our population ages. Affective disorders including clinical depression and anxiety are common in patients with congestive heart failure. Furthermore, the presence of these disorders significantly impacts quality of life, medical outcomes, and healthcare service utilization. In recent years, the literature has attempted to describe potential pathophysiologic mechanisms relating affective disorders and psychosocial stress to heart failure. Several potential mechanisms have been proposed including autonomic nervous system dysfunction, inflammation, cardiac arrhythmias, and altered platelet function. These mechanisms are reviewed in this article. Additional novel mechanisms such as mental stress-induced myocardial ischemia are also discussed.

Neurovascular responses to mental stress in the supine and upright postures

The purpose of this study was to determine neurovascular responses to mental stress (MS) in the supine and upright postures. MS was elicited in 23 subjects (26 +/- 1 yr) by 5 min of mental arithmetic. In study 1 (n = 9), Doppler ultrasound was used to measure mean blood flow velocity in the renal (RBFV) and superior mesenteric arteries (SMBFV), and venous occlusion plethysmography was used to measure forearm blood flow (FBF). In study 2 (n = 14), leg blood flow (LBF; n = 9) was measured by Doppler ultrasound, and muscle sympathetic nerve activity (MSNA; n = 5) was measured by microneurography. At rest, upright posture increased heart rate and MSNA and decreased LBF, FBF, RBFV, and SMBFV and their respective conductances. MS elicited similar increases in mean arterial blood pressure ( approximately 12 mmHg) and heart rate ( approximately 17 beats/min), regardless of posture. MS in both postures elicited a decrease in RBFV, SMBFV, and their conductances and an increase in LBF, FBF, and their conductances. Changes in blood flow were blunted in the upright posture in all vascular beds examined, but the pattern of the vascular response was the same as the supine posture. MS did not change MSNA in either posture (change: approximately 1 +/- 3 and approximately 3 +/- 3 bursts/min, respectively). In conclusion, the augmented sympathetic activity of the upright posture does not alter heart rate, mean arterial blood pressure, or MSNA responses to MS. MS elicits divergent vascular responses in the visceral and peripheral vasculature. These results indicate that, although the upright posture attenuates vascular responses to MS, the pattern of neurovascular responses does not differ between postures.

Novel two-step release system for the traditional Chinese medicine compound Danshen

A novel two-step release system for the traditional Chinese medicine compound Danshen was developed by combining an effervescent osmotic pump tablet (EOPT) and a pulsed-released tablet (PT) of compound Danshen into one hard capsule. The EOPT of Danshen was prepared with sodium chloride, mannitol, hydroxypropylmethylcellulose (HPMC), and sodium bicarbonate as osmotic agents. The osmotic pressure from EOPT was greatly enhanced by carbon dioxide generated from the reaction between sodium bicarbonate and acidic components from Danshen. It was shown that the tested Danshen components could be completely released from the prepared EOPT following a zero-order release for up to 12 h. The PT of compound Danshen was a three-layer coated tablet composed of organic acid and osmotic agents. Eudragit RL, HPMC and the mixture of EC and Eudragit RS, RL were the major constituents of the separation layer, swelling layer and controlling release membrane, respectively. The swelling test of the PT indicated that swelling is a prerequisite for drug release from this PT device. In addition, the swelling behavior further suggested the drug release mechanism of PT involves diffusion, the osmotic pumping effect, and organic acid-induced effect, among which the osmotic pumping effect was the most important. Moreover, there was no significant difference among the five active constituents in their release profiles from the final combined two-step release system of compound Danshen.

Acute risk factors for myocardial infarction

Increased knowledge concerning the triggering of acute cardiovascular diseases has yielded a change in philosophical approach to this field. During the last decade, clinical evidence suggested that the term acute risk factors can be used for the activities and events that suddenly and transiently increase the risk of acute cardiac diseases. External triggers, such as heavy physical activity, emotional stress, eating, cold or heat exposure, coffee or alcohol consumption, cocaine or marijuana use and sexual intercourse are recognized as most important acute risk factors. It is likely that the morning hours may be considered as an endogenous, external triggering independent acute risk factor related to physiological sympathetic arousal. The features of triggering have been best described for an acute myocardial infarction whose moment of onset appears to be the result of a dynamic interaction between an endogenous response to acute risk factors and patient vulnerability. In this article, pathophysiological changes implicated as internal triggering mechanisms are summarized and the terms sympathetic and parasympathetic triggering patterns are introduced. A highly individual approach tailored both to protect against acute risk factors and to reduce patient vulnerability could provide a more complete protection from myocardial infarction and other coronary incidents. Lifestyle modifications, regular physical activity and adequate drug regimens may at least prove able to defer the occurrence of coronary thrombosis, thereby providing time for the development of collateral vessels, plaque stabilization or invasive/surgical treatment.

Chronobiological considerations for exercise and heart disease

Although regular physical activity is beneficial for many clinical conditions, an acute bout of exercise might increase the risk of an adverse clinical event, such as sudden cardiac death or myocardial infarction, particularly in vulnerable individuals. Since it is also known that the incidence of these events peaks in the morning and that some cardiac patients prefer to schedule leisure-time physical activity before lunch, the question arises as to whether morning exercise is 'inherently' more risky than physical activity performed at other times of day. We attempt to answer this question by reviewing the relevant epidemiological data as well as the results of chronobiological and exercise-related studies that have concentrated on the pathophysiological mechanisms for sudden cardiac events. We also consider generally how chronobiology might impact on exercise prescription in heart disease. We performed a structured literature search in the PubMed and WEBofSCIENCE databases for relevant studies published between 1981 and 2004. The limited amount of published epidemiological data did not allow us to conclude that a bout of vigorous exercise in the morning increases the relative risk of either primary cardiac events in apparently healthy individuals, or secondary events in cardiac patients enrolled in supervised exercise programmes. Nevertheless, these data are not directly relevant to individuals who have a history of heart disease and perform uncontrolled habitual activities. It appears as though the influence of time of day on the cardiovascular safety of this type of exercise has not been examined in this population. There is evidence that several pathophysiological variables (e.g. blood pressure, endothelial function, fibrinolysis) vary in parallel with typical diurnal changes in freely chosen activity. Nevertheless, few studies have been designed to examine specifically whether such variables respond differently to a 'set' level of exercise in the morning compared with the afternoon or evening. Even fewer researchers have adequately separated the influences of waking from sleep, adopting an upright posture and physical exertion per se on these pathophysiological responses at different times of day. In healthy individuals, exercise is generally perceived as more difficult and functional performance is decreased in the morning hours. These observations have been confirmed for patients with heart disease in only one small study. It has also not been confirmed, using an adequately powered study involving cardiac patients, that the responses of heart rate and oxygen consumption (VO(2)) to a set bout of exercise show the highest reactivity in the afternoon and evening, which is the case with healthy individuals. Confirmation of this circadian variation would be important, since it would mean that exercise might be prescribed at too high an intensity in the morning if heart rate or VO(2) responses are employed as markers of exercise load. We conclude that there is some parallelism between the diurnal changes in physical activity and those in the pathophysiological mechanisms associated with acute cardiac events. Nevertheless, more studies are needed to ascertain whether the responses of endothelial function, fibrinolysis and blood pressure to a set exercise regimen differ according to time of day. The results of epidemiological studies suggest that morning exercise is just as safe as afternoon exercise for cardiac patients enrolled in a supervised rehabilitation programme. Nevertheless, it is unclear whether time of day alters the risk of a cardiac event occurring during spontaneous physical activity performed by individuals with established risk factors for heart disease.

Myocardial ischemia during everyday life in patients with arterial hypertension: prevalence, risk factors, triggering mechanism and circadian variability

INTRODUCTION

The objective of the present study was to investigate the prevalence, the risk factors, the hemodynamic triggering mechanisms, the circadian variability of ST segment depression (ST depression) and the effect of day and night fall in blood pressure on the prevalence of ST depression in hypertensive patients.

MATERIALS AND METHODS

In a multicentric study in Germany, 1,244 CardioTens registrations (combined 24-h ambulatory blood pressure measurement/electrocardiography with ST segment triggering; Meditech, Budapest, Hungary) from patients with arterial hypertension were consecutively monitored and evaluated centrally at the University of Bonn. Inclusion criterion was treated or untreated arterial hypertension. The ST segment was measured in accordance with the "1 : 1 : 1 rule" (horizontal or descending ST depression by 1 mm, 1 min duration, 1 min interval from the previous episode).

RESULTS

ST segment depression was observed in 250 (20.1%) patients; 90.3% of the transient ST-segment depression was silent (without angina pectoris). Ambulatory 24-h blood pressure measurement, but not office-based blood pressure measurement, was predictive for the occurrence of ST-segment depression. Risk factors for ST-segment depression were the Sokolow index > or =3.5 mV, smoking status, severity of coronary heart disease, use of diuretics, reduced left ventricular function, pulse pressure > or =60 mmHg and increase of double product (1,000 mmHg/min). A significant rise of the systolic/diastolic blood pressure (+8+ or -18/+7+ or -10 mmHg), of the heart rate (+12+ or -13/min) and of the double product (+2,471+ or -2,517 mmHg/min) was found during the transient ST depression as compared with the corresponding 24-h ambulatory blood pressure measurement mean values (P<0.0001 for all parameters specified). In most intermittent ST depressions, a rise of the double product was seen (n=789 episodes), and in the remaining 239 ST depressions, a fall of the double product was observed. ST depressions with fall of the double product showed a circadian distribution with a peak in the late evening. ST depression accompanied by a rise in double product showed two peaks (one in the early morning and one in the late evening). The prevalence of ST depression was significantly higher (28.6%) in extreme dippers than in dippers (18.2%), risers (21.8%) and non-dippers (19.6%).

CONCLUSIONS

ST depressions have a high prevalence of 20.1% in hypertensive patients. Clinical predictors for the occurrence of ST-segment depression were classical risk factors and cardiac target organ damage. Office-based blood pressure measurement was not a useful measuring tool for forecasting the likelihood of ST-segment depression. ST depressions were triggered inter alia by variations of blood pressure and the heart rate. The circadian variability of the ST depressions is crucially affected by the pressure double product characteristics on which the ST depression is based.

Temporal Variations at the Onset of Spontaneous Acute Aortic Dissection

There have only been a few studies of the chronobiological occurrence of acute aortic dissection (AAD), and most were international and multicentered. The aim of the present study, conducted at only one center, was to determine the most frequent daily, monthly, and seasonal occurrences of AAD. The study population included 204 patients (66.5% male) treated at our institute between January 1, 1998 and January 1, 2004. A significantly higher frequency of AAD occurred from 6:00 AM to 12:00 noon, compared with other time periods (P < 0.001). The results showed a significant circadian variation in AAD (P < 0.001) with a peak between 9:00 AM and 10:00 AM. No significant variation was found for the day of the week; however, AAD occurred most frequently on Wednesday and Monday. The frequency of AAD was found to be significantly higher during winter versus other seasons (P < 0.001). The analysis of monthly variations of the onset of AAD confirmed a peak in February (12.9%) and in January (12.3%). Similar to other cardiovascular diseases, AAD exhibits significant circadian and seasonal/monthly variations. Our findings indicate that the prevention of AAD, especially during the aforementioned vulnerable periods, is possible by adequate tailoring of the treatment of hypertension, which is the main AAD predisposing factor.

Temporal variation in inhospital mortality with percutaneous coronary intervention: a report from the National Heart, Lung and Blood Institute Dynamic Registry

BACKGROUND

Cardiovascular morbidity and mortality display a distinct time dependence also known as circadian variation. Whether such time dependence extends to the risk of procedural-related mortality after percutaneous coronary intervention (PCI) is presently unknown.

METHODS

Inhospital mortality was analyzed in 6,347 patients with PCI start times from 8:00 am to 6:59 pm ("usual" workday). The sample was divided into 3 evenly populated groups (morning start 8:00-10:59 AM, midday start 11:00 AM-1:59 PM, afternoon start 2:00-6:59 PM). The association between procedural start time and mortality was assessed using multivariable analysis including a propensity score accounting for factors associated with procedural start time.

RESULTS

There was a significant, nonlinear relationship between procedural-related mortality and start time (P = .03). Afternoon start patients were at higher adjusted risk of mortality compared with midday start patients (OR 2.03, 95% CI 1.07-3.83, P = .03 ). Morning start patients were also at higher risk compared with midday start patients although the association was not statistically significant (OR 1.73, 95% CI 0.89-3.39, P = .11).

CONCLUSIONS

There is a significant time-dependent variation in the risk of inhospital PCI-related mortality during usual working hours. The highest risk period, taking into account numerous factors that confound this association, is the latter part of the workday. A second period of apparent greater risk occurs during the early part of the workday and is consistent with our present understanding of circadian variation in cardiovascular disease processes.

The influence of hydration status on stress-induced hemoconcentration

This study examined the effects of hydration status on rheological and hemodynamic activity during rest, mental stress, postural stress, and combined mental/postural stress in 24 men when euhydrated and hyperhydrated. The stress tasks elicited hemoconcentration, although the effects were less pronounced during mental stress. Hyperhydration was associated with higher plasma volume throughout. All stress tasks also perturbed hemodynamic activity, irrespective of hydration status, with the exception of heart rate reactivity, which was attenuated when hyperhydrated. As expected the combined stress during euhydration was associated with an unfavorable rheological and cardiovascular profile, which may help explain the increased incidence of cardiovascular events in the morning.

Psychological traits and emotion-triggering of ICD shock-terminated arrhythmias

OBJECTIVE

We have previously reported on the triggering of arrhythmia and hence, implanted cardioverter-defibrillators (ICD) shock by strong emotion. The purpose of the present study was to examine whether concordant psychological traits distinguish patients who experience emotion-triggered ICD shock.

METHODS

Two hundred forty ICD patients completed the Speilberger Trait Anxiety and Anger Inventories and Anger Expression Scale, and the abridged Cook-Medley Hostility Scale approximately 2 months after ICD implantation. Patients were also given a structured diary to record mood states retrospectively for the period 0 to 15 minutes preceding ICD shock and for a period corresponding to the same time of day 1 week later. Patients who reported emotion-triggered ICD shock were compared on concordant psychological measures to patients who did not.

RESULTS

Patients who reported at least moderate anger in the 0 to 15 minutes before ICD shock scored significantly higher on Speilberger Trait Anger (24.18 +/- 3.97 vs. 17.04 +/- 2.17, p < .0001), and Cook-Medley Aggressive Responding (5.76 +/- 0.75 vs. 3.96 +/- 1.30, p < .0001) and Hostile Affect (3.59 +/- 0.80 vs. 2.04 +/- 1.02, p < .0001), and lower on Speilberger Anger Control (7.94 +/- 1.43 vs. 10.64 +/- 1.19, p < .001) than those who did not. In multivariate analysis, only Trait Anger remained a significant predictor of anger-triggered shock (chi2 = 7.10, p < .008). Patients who reported at least moderate anxiety in the 0 to 15 minutes before ICD shock scored significantly higher on Speilberger Anxiety (22.43 +/- 1.65 vs. 19.96 +/- 1.71, p < .0001) than those who did not.

CONCLUSION

Stable psychological factors are associated with risk for ICD-shock triggered by concordant strong emotion.

Ritmo circadiano e doença vascular encefálica: um estudo de correlação com fatores de risco

Os mecanismos biológicos humanos exibem variabilidade clínica previsível no tempo, o que tem permitido reavaliação das práticas médicas atuais, do estudo mais aprofundado do ritmo circadiano (RC) e dos mecanismos que geram as oscilações sustentadas em todos os níveis biológicos. Fizemos um estudo procurando relacionar o RC e o momento do aparecimento do quadro clínico neurológico decorrente da lesão vascular do encéfalo com os fatores de risco modificáveis identificados no momento da internação. Foram estudados 53 pacientes, sendo 50,94% (n =27) do sexo feminino e 49,50%(n =26) do masculino, com média de idade de 66,4 anos. Quatro intervalos de 6 horas (0-6; 6-12; 12-18; 18-24) foram usados para análise da freqüência do ictus e da incidência em cada intervalo. Os resultados mostraram 6 (11,32%) pacientes no intervalo 0-6 hs; 21 (39,62%) no intervalo 6-12 hs; 10 (18,86%) no intervalo 12-18 hs; 16 (30,18%) no intervalo 18-24 hs. Estudo de correlação com os fatores de risco, baseado nos dados clínicos no momento da internação, mostrou que a hipertensão arterial [(81,25%)] e o tabagismo[ (56,25%)] predominaram no intervalo 18-24 hs, enquanto o sedentarismo[11; (52,38%)] o estresse[11 (52,38%)] o diabetes [(47,61%)] a hiperlipidemia [8 (38,09%)] e o alcoolismo[8 (38,09%)] predominaram no intervalo 6-12 hs; as cardiopatias [(50,00%)] predominaram no intervalo de 12-18 hs.

Light and diurnal cycle affect autonomic cardiac balance in human; possible role for the biological clock

The morning shift in cardiac sympatho-vagal balance seems involved in the increased risk of cardiovascular incidents at that time. To investigate the contribution of the biological clock in autonomic cardiac control, we investigated the presence of a diurnal rhythm independent of external factors, and of a circadian phase-dependent effect of moderate light in healthy volunteers. Recordings of heart rate (HR) and vagal and sympathetic cardiac tone were performed at different times over the day-night cycle during supine, awake, resting conditions, during exposure to different light intensities. The similarity between the diurnal rhythm in resting HR and that during previous constant routine conditions, demonstrated that our setup allowed accurate estimation of the endogenous circadian rhythm in HR. The present study suggests that, while a circadian rhythm in vagal cardiac tone is the main cause for the circadian rhythm in resting heart rate, the increase in sympathetic cardiac tone participates in the HR increase caused by early morning light.

Cardiovascular control by the suprachiasmatic nucleus: neural and neuroendocrine mechanisms in human and rat

The risk for cardiovascular incidents is highest in the early morning, which seems partially due to endogenous factors. Endogenous circadian rhythms in mammalian physiology and behavior are regulated by the suprachiasmatic nucleus (SCN). Recently, anatomical evidence has been provided that SCN functioning is disturbed in patients with essential hypertension. Here we review neural and neuroendocrine mechanisms by which the SCN regulates the cardiovascular system. First, we discuss evidence for an endogenous circadian rhythm in cardiac activity, both in humans and rats, which is abolished after SCN lesioning in rats. The immediate impact of retinal light exposure at night on SCN-output to the cardiovascular system, which signals 'day' in both diurnal (human) and nocturnal (rat) mammals with opposite effects on physiology, is discussed. Furthermore, we discuss the impact of melatonin treatment on the SCN and its potential medical relevance in patients with essential hypertension. Finally, we argue that regional differentiation of the SCN and autonomous nervous system is required to explain the multitude of circadian rhythms. Insights into the mechanisms by which the SCN affects the cardiovascular system may provide new strategies for the treatment of disease conditions known to coincide with circadian rhythm disturbances, as is presented for essential hypertension.

Sleep processes exert a predominant influence on the 24-h profile of heart rate variability

Adverse cardiovascular events are known to exhibit 24-h variations with a peak incidence in the morning hours and a nonuniform distribution during the night. The authors examined whether these 24-h variations could be related to circadian or sleep-related changes in heart rate (HR) and in HR variability (HRV). To differentiate the effect of circadian and sleep-related influences, independent of posture and of meal ingestion, seven normal subjects were studied over 24 h, once with nocturnal sleep from 2300 to 0700 h and once after a night of sleep deprivation followed by 8 h of daytime sleep from 0700 to 1500 h. The subjects were submitted to constant conditions (continuous enteral nutrition and bed rest). HRV was calculated every 5 min using two indexes: the standard deviation of normal R-R intervals (SDNN) and the ratio of low-frequency to low-frequency plus high-frequency power. Sleep processes exerted a predominant influence on the 24-h profiles of HR and HRV, with lowest HRV levels during slow wave sleep, high levels during REM sleep and intrasleep awakenings, and abrupt increases in HR at each transition from deeper sleep to lighter sleep or awakenings. The circadian influence was smaller, except for SDNN, which displayed a nocturnal increase of 140% whether the subjects slept or not. This study demonstrates that 24-h variations in HR and HRV are little influenced by the circadian clock andare mainly sleep-stage dependent. The results suggest an important role for exogenous factors in the morning increase in cardiovascular events. During sleep, the sudden rises in HR at each transition from deeper sleep to lighter sleep or awakenings might precipitate the adverse cardiac events.

Sleep-disordered breathing and stroke

Sleep-disordered breathing (obstructive and central sleep apnea) is common in persons who have had a cerebrovascular accident (CVA). This article describes both sleep-disordered breathing and CVAs and reviews the related risk factors that link them together. In addition, the article discusses sleep-disordered breathing after CVA. The article concludes by presenting the clinical implications of this topic for nurses.

Psychosocial influences on the development and course of coronary heart disease: current status and implications for research and practice

Psychosocial characteristics predict the development and course of coronary heart disease (CHD). In this review, the authors discussed human and animal research on psychophysiological mechanisms influencing coronary artery disease and its progression to CHD. They then reviewed literature on personality and characteristics of the social environment as risk factors for CHD. Hostility confers increased risk, and a group of risk factors involving depression and anxiety may be especially important following myocardial infarction. Social isolation, interpersonal conflict, and job stress confer increased risk. Psychosocial interventions may have beneficial effects on CHD morbidity and mortality, although inconsistent results and a variety of methodological limitations preclude firm conclusions. Finally, they discussed implications for clinical care and the agenda for future research.