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

Time-domain methods for quantifying dynamic cerebral blood flow autoregulation: Review and recommendations. A white paper from the Cerebrovascular Research Network (CARNet)

Cerebral Autoregulation (CA) is an important physiological mechanism stabilizing cerebral blood flow (CBF) in response to changes in cerebral perfusion pressure (CPP). By maintaining an adequate, relatively constant supply of blood flow, CA plays a critical role in brain function. Quantifying CA under different physiological and pathological states is crucial for understanding its implications. This knowledge may serve as a foundation for informed clinical decision-making, particularly in cases where CA may become impaired. The quantification of CA functionality typically involves constructing models that capture the relationship between CPP (or arterial blood pressure) and experimental measures of CBF. Besides describing normal CA function, these models provide a means to detect possible deviations from the latter. In this context, a recent white paper from the Cerebrovascular Research Network focused on Transfer Function Analysis (TFA), which obtains frequency domain estimates of dynamic CA. In the present paper, we consider the use of time-domain techniques as an alternative approach. Due to their increased flexibility, time-domain methods enable the mitigation of measurement/physiological noise and the incorporation of nonlinearities and time variations in CA dynamics. Here, we provide practical recommendations and guidelines to support researchers and clinicians in effectively utilizing these techniques to study CA.

Clinical, Anamnestic, and Demographic Characteristics of Patients with Myocardial Infarction in Russian Federation According to the Russian Registry of Acute Myocardial Infarction - REGION-IM

AIM

Based on data from the Russian REGION-MI registry, to characterize patients with myocardial infarction (MI) hospitalized in Russian hospitals, describe their historical, demographic, and clinical characteristics, and compare the results with the data of previous Russian and international registries of acute coronary syndrome.

MATERIAL AND METHODS

REGION-MI is a multicenter prospective observational study. The follow-up period was divided into three stages: during the hospital stay, at 6 and 12 months after the inclusion in the registry. Demographic and historic data and information about the present case of MI were entered into the patient's individual record card.

RESULTS

The median age of all patients was 63 years; 68% of patients were men. The mean age of women was older than that of men. Among all MI cases, 70% were ST-segment elevation myocardial infarction (STEMI). Patients with non-ST-segment elevation myocardial infarction (NSTEMI) were older and had more comorbidities than patients with STEMI. The median time from the first symptoms to ECG recording was two hours, and from the first symptoms to CAG 7 hours. CAG was performed in 91% of patients with STEMI and 84% of patients with NSTEMI. Stenting was performed in 69% of patients. Although many patients had a complicated cardiovascular history, at the time of admission only 31.5% of patients were taking at least one drug from the groups of antiplatelets, oral anticoagulants, statins, and beta-blockers.

CONCLUSION

Patients with MI in the Russian Federation are younger than patients with MI in European countries. Among the clinical and historical characteristics, conspicuous is the presence of modifiable risk factors in many patients, as well as the presence of a previous diagnosis of ischemic heart disease. Furthermore, a small proportion of patients took statins, antiplatelet agents or anticoagulants at the outpatient stage, which indicates a great reserve of both primary and secondary prevention of cardiovascular diseases in the Russian Federation. The delayed seeking medical help is also noticeable, which indicates the need for increasing the public awareness of the symptoms of MI and the importance of timely hospitalization.

Circadian and sex differences in post-ischemic vasodilation and reactive hyperemia in young individuals and elderly with and without type 2 diabetes

OBJECTIVE

Cardiovascular events show morning preference and sex differences, and are related to aging and type 2 diabetes. We assessed circadian variations and sex differences in vascular conductance (VC) and blood flow (BF) regulations following a brief bout of forearm ischemia.

METHODS

Young healthy individuals (H18-30) and elderly without (H50-80) and with type 2 diabetes (T2DM50-80) of both sexes were included. Forearm VC and BF, and mean arterial pressure (MAP) at baseline and following circulatory reperfusion were measured at 6 a.m. and 9 p.m.

RESULTS

In the morning compared to evening, following reperfusion, the VC and BF increments were similar in H18-30 (p>.71), but lower in H50-80 (p<.001) and T2DM50-80 (p<.01). VC and BF following circulatory reperfusion were higher in men than women in H18-30 (p<.001), but similar between sexes in the older groups (p>.23).

CONCLUSIONS

Forearm vasodilation following reperfusion is attenuated in the morning in the elderly, impairing BF towards an ischemic area. Diabetes does not affect the circadian regulation of VC and BF, but that of MAP. There are sex differences in VC and BF at baseline and after circulatory reperfusion at a young age, being greater in men, which disappear with aging without being affected by diabetes.

Association of the time of day of peak physical activity with cardiovascular mortality: Findings from the UK Biobank study

Cardiovascular physiology and pathophysiology display pronounced circadian rhythms. The study is designed to examine whether the time of day of physical activity is associated with cardiovascular mortality. We analyzed 94,489 UK Biobank adults with objectively measured physical activity, including 53,328 morning-type participants and 30,962 evening-type participants based on self-reported chronotypes. The time of day of peak physical activity was categorized using a machine learning algorithm: early morning (n = 18,477), late morning (n = 25,700), midday (reference) (n = 27,803), and night (n = 22,509). Hazard ratios of cardiovascular mortality were examined using the Cox proportional hazards model. During a median follow-up of 6.9 years (interquartile range, 6.3-7.4 years), we identified 629 cardiovascular deaths. The hazard of cardiovascular mortality was elevated in the early morning group (hazard ratio = 1.56, 95% Confidence Interval [1.23-1.98]) and night group (1.49, [1.18-1.88]) but not in the late morning group (1.21, [0.98-1.47]) compared to the referent midday group. In the chronotype-stratified analysis, the increased cardiovascular mortality in the morning group was only observed in the evening-type participants, while the increased cardiovascular mortality in the night group was only observed in the morning-type participants. In conclusion, optimizing the timing of peak physical activity according to cardiovascular circadian rhythms and individual chronotypes could be a potential therapeutic target that brings additional health benefits.

Circadian Variations in Sympathetic Vasoconstriction in Older Adults with and Without Type 2 Diabetes

INTRODUCTION

An impact of the sympathetic nervous system in the higher rate of cardiovascular events in the early morning compared to the evening has been claimed. Augmented sympathetic vasoconstriction increases cardiovascular risk by augmenting pulse pressure and cardiac afterload. Type 2 diabetes (T2DM) further increases sympathetic neurovascular transduction and cardiovascular risk.

AIM

We assessed whether peripheral vasoconstriction triggered by a standardized sympathetic stressor is augmented at 6am vs 9pm in adults between 50-80 years with type 2 diabetes (T2DM50-80) vs healthy ones (H50-80).

METHODS

Mean values of sympathetic vasoconstrictor responsiveness (SVR), vascular conductance (VC), brachial artery blood flow, and mean arterial pressure were measured on the contralateral forearm over two 5-minute bouts of rest and handgrip-mediated sympathetic stimulation, respectively.

RESULTS

Although baseline VC values were lower (p < 0.01) in the morning vs evening in both groups, SVR values in response to sympathoexcitation were similar in H50-80 (- 0.43 ± 12.44 vs - 2.57 ± 11.63 %, p = 0.73) and T2DM50-80 (+6.64 ± 10.67 vs +5.21 ± 7.64 %, p = 0.90), but higher (p < 0.01) in T2DM50-80 vs H50-80 at both day hours. Individuals with T2DM reported positive SVR values and VC change-scores, while healthy individuals reported statistically different (p < 0.02) negative SVR values and VC change-scores.

CONCLUSION

Peripheral vasoconstriction triggered by a standardized sympathetic stressor is similar between morning and evening, regardless of T2DM and different baseline VC values. However, peripheral vasoconstriction responsiveness is blunted in individuals with T2DM as handgrip-mediated sympathoexcitation induces vasodilation in the contralateral forearm in adults with T2DM and vasoconstriction in healthy age-matched controls, highlighting a neurovascular response altered by T2DM.

Chronobiology of Exercise: Evaluating the Best Time to Exercise for Greater Cardiovascular and Metabolic Benefits

Physiological function fluctuates across 24 h due to ongoing daily patterns of behaviors and environmental changes, including the sleep/wake, rest/activity, light/dark, and daily temperature cycles. The internal circadian system prepares the body for these anticipated behavioral and environmental changes, helping to orchestrate optimal cardiovascular and metabolic responses to these daily changes. In addition, circadian disruption, caused principally by exposure to artificial light at night (e.g., as occurs with night-shift work), increases the risk for both cardiovascular and metabolic morbidity and mortality. Regular exercise is a countermeasure against cardiovascular and metabolic risk, and recent findings suggest that the cardiovascular benefits on blood pressure and autonomic control are greater with evening exercise compared to morning exercise. Moreover, exercise can also reset the timing of the circadian system, which raises the possibility that appropriate timing of exercise could be used to counteract circadian disruption. This article introduces the overall functional relevance of the human circadian system and presents the evidence surrounding the concepts that the time of day that exercise is performed can modulate the cardiovascular and metabolic benefits. Further work is needed to establish exercise as a tool to appropriately reset the circadian system following circadian misalignment to preserve cardiovascular and metabolic health. © 2022 American Physiological Society. Compr Physiol 12:3621-3639, 2022.

Day-To-Day Home Blood Pressure Variability and All-Cause Mortality in a Memory Clinic Population

BACKGROUND

High day-to-day blood pressure variability (BPV) has been associated with an increased risk for cognitive decline and mortality in the general population. Whether BPV is associated with increased all-cause mortality in older people with cognitive impairment is unknown.

OBJECTIVE

To investigate the association between day-to-day home BPV and all-cause mortality in older patients attending a memory clinic.

METHODS

We included 279 patients attending a memory clinic, who measured home blood pressure (BP) for 7 consecutive days in the morning and evening. Within-subject BPV was defined as the variation independent of the mean (VIM). Time-to-death was verified through the Dutch population registry. Cox proportional hazard regression was used. Separate analyses were performed for morning-to-morning and evening-to-evening BPV.

RESULTS

Mean age was 73±9 years, dementia and mild cognitive impairment were diagnosed in 35% and 34% respectively, and mean home BP was 139/79 mmHg. After a mean follow-up of 3.2 years, 52 patients had died. Neither day-to-day systolic nor diastolic VIM were associated with mortality (adjusted hazard ratio [HR] systolic VIM: 0.99, 95% -CI 0.92-1.06, p = 0.770, HR diastolic VIM: 1.04, 95% -CI 0.93-1.17, p = 0.517). When morning and evening measurements were analyzed separately, systolic morning-to-morning VIM was associated with mortality (adjusted HR: 1.09, 95% -CI 1.01-1.18, p = 0.033).

CONCLUSION

In this study, day-to-day BPV was not associated with all-cause mortality in patients attending a memory clinic. However, morning-to-morning BPV was. Due to the short assessment window, there is still a lack of clarity; hence future research is warranted to clarify the role of all BPV components in aging.

Circadian Biology and Stroke

Circadian biology modulates almost all aspects of mammalian physiology, disease, and response to therapies. Emerging data suggest that circadian biology may significantly affect the mechanisms of susceptibility, injury, recovery, and the response to therapy in stroke. In this review/perspective, we survey the accumulating literature and attempt to connect molecular, cellular, and physiological pathways in circadian biology to clinical consequences in stroke. Accounting for the complex and multifactorial effects of circadian rhythm may improve translational opportunities for stroke diagnostics and therapeutics.

Evaluation of stroke related risk factors in wake up and non-wake up stroke patients

Wake-Up Stroke (WUS) is defined as a stroke with the unclear onset of symptoms and subsequent neurological deficits which perceived upon awakening. WUS patients are often excluded from acute fibrinolytic and reperfusion therapy due to the unknown exact time of symptoms onset. This study aimed to evaluate patients with and without WUS characteristics and associated risk factors at two tertiary hospitals. First, we prospectively evaluated consecutive patients with stroke symptoms and determined stroke sub groups by using Computed Tomography (CT) scan. Next, demographic and clinical characteristics including past medical and drug consumption history as well as cardiac function index (ejection fraction), LDL (mg/dl) level and hematologic parameters: hemoglobin (Hb); hematocrit (Hct); platelet (Plt) were assessed. Results: 510 patients (56.1% men and 43.9% women) with averaged age of 70 and 72 years were studied, respectively. Of 510 patients, 405 (79.4%) had non-WUS stroke (known-onset stroke) and 105 (20.6%) had WUS strokes (unknown-onset stroke). The WUS occurrence most likely was observed in ischemic stroke compared to hemorrhagic one. No significant differences were found between patients from both groups regarding stroke risk factors. However, hypertension and family history were more common in patients with WUS (p>0.05). Moreover, individuals with a previous cerebrovascular accident in WUS group were almost similar to non-WUS counterparts. No differences also detected in case of hematologic characteristics, heart function index and LDL levels between study groups (p>0.05). Together, wake-up stroke occurs in approximately 20% of stroke subjects. In this study, patients with WUS had more hypertension and family history.

Endovascular treatment for ischemic stroke beyond the time window: A meta-analysis

Currently, endovascular treatment has been proven to be effective when conducted within 6 hours of symptom onset. However, when patients have symptoms for more than 6 hours, have a daytime-unwitnessed stroke (DUS) or wake up with a stroke (wake-up stroke, WUS), the safety and efficacy of endovascular treatment need to be further elucidated. Therefore, we performed a systematic review and meta-analysis to compare the clinical outcomes of endovascular treatment in patients with ischemic stroke beyond the time window with that ≤6 hours. PubMed, EMBASE, and Ovid MEDLINE were searched from inception to November 2018. The following outcomes were evaluated by a random-effects model: efficacy outcomes, that is, functional independence and successful recanalization, and safety outcomes, that is, symptomatic intracranial hemorrhage and mortality. Subgroup analyses were also performed to examine whether patient or study characteristics were associated with the outcomes. Nine observational studies, including 5192 patients (1414 patients with extended time windows [ETWs]; 3778 patients ≤6 hours), were eligible for analysis. The overall analysis demonstrated that the functional independence was worse in patients with ETWs vs those ≤6 hours (OR, 0.78; 95% CI, 0.68-0.90, P = .0006). However, subgroup analysis showed that there was no significant difference in functional independence between the two groups when patients were selected for a perfusion mismatch by imaging (OR, 1.00; 95% CI, 0.70-1.43, P = 1.000). Therefore, compared with a window ≤6 hours, endovascular treatment with ETWs for ischemic stroke may not result in poor outcomes when patients are typically selected by perfusion techniques.

Aerobic Training and Mobilization Early Post-stroke: Cautions and Considerations

Knowledge gaps exist in how we implement aerobic exercise programs during the early phases post-stroke. Therefore, the objective of this review was to provide evidence-based guidelines for pre-participation screening, mobilization, and aerobic exercise training in the hyper-acute and acute phases post-stroke. In reviewing the literature to determine safe timelines of when to initiate exercise and mobilization we considered the following factors: arterial blood pressure dysregulation, cardiac complications, blood-brain barrier disruption, hemorrhagic stroke transformation, and ischemic penumbra viability. These stroke-related impairments could intensify with inappropriate mobilization/aerobic exercise, hence we deemed the integrity of cerebral autoregulation to be an essential physiological consideration to protect the brain when progressing exercise intensity. Pre-participation screening criteria are proposed and countermeasures to protect the brain from potentially adverse circulatory effects before, during, and following mobilization/exercise sessions are introduced. For example, prolonged periods of standing and static postures before and after mobilization/aerobic exercise may elicit blood pooling and/or trigger coagulation cascades and/or cerebral hypoperfusion. Countermeasures such as avoiding prolonged standing or incorporating periodic lower limb movement to activate the venous muscle pump could counteract blood pooling after an exercise session, minimize activation of the coagulation cascade, and mitigate potential cerebral hypoperfusion. We discuss patient safety in light of the complex nature of stroke presentations (i.e., type, severity, and etiology), medical history, comorbidities such as diabetes, cardiac manifestations, medications, and complications such as anemia and dehydration. The guidelines are easily incorporated into the care model, are low-risk, and use minimal resources. These and other strategies represent opportunities for improving the safety of the activity regimen offered to those in the early phases post-stroke. The timeline for initiating and progressing exercise/mobilization parameters are contingent on recovery stages both from neurobiological and cardiovascular perspectives, which to this point have not been specifically considered in practice. This review includes tailored exercise and mobilization prescription strategies and precautions that are not resource intensive and prioritize safety in stroke recovery.

Effect of morning blood pressure peak on early progressive ischemic stroke: a prospective clinical study

OBJECTIVE

To prospectively evaluate the effect of morning blood pressure peak (MBPP) on early progressive ischemic stroke (EPIS).

PATIENTS AND METHODS

A total of 135 patients with acute ischemic stroke were enrolled and completed all assessments. The patients were divided into EPIS group and non-EPIS group, with 22 and 113 cases in each group, respectively, according to the assessment of Scandinavian stroke scale within three days after onset. All cases received conventional treatment for stroke and its risk factors. 24 -h dynamic blood pressure monitoring was performed within 24 h after admission. Based on the 24 -h mean blood pressure, MBPP, morning blood pressure, and other risk factors for EPIS, we conducted a logistic regression analysis to evaluate whether MBPP was an independent risk factor for EPIS.

RESULTS

Mean systolic blood pressure, systolic and diastolic MBPP, morning systolic and diastolic blood pressure were all significantly higher in EPIS group than in non-EPIS group (p = 0.037, p = 0.001, p = 0.035, p = 0.003, p = 0.042, respectively). Logistic regression analysis showed that MBPP was an independent risk factor for EPIS (OR = 1.057, 95% CI 1.014-1.102, p = 0.009). Further stratified analysis showed that incidences of EPIS in patients with elevated MBPP combined with large artery atherosclerosis or small artery occlusion were comparable (41.2% vs. 25.0%, p = 0.367), and the systolic MBPP was significantly higher in morning EPIS group than in non-morning EPIS group (p = 0.041).

CONCLUSION

Elevated systolic MBPP might be an independent risk factor for EPIS, and play a more obvious effect on EPIS manifesting in the morning especially.

Circadian Rhythm of Cardiovascular Disease: The Potential of Chronotherapy With Aspirin

Almost all the systems in our body adhere to a daily 24 h rhythm. The cardiovascular system is also affected by this 24 h rhythm. In the morning there is a change in various cardiovascular processes, including platelet aggregability. These changes may play a role in the relative excess of early morning cardiovascular events. The number of recurrent cardiovascular diseases (CVD) could, in theory, be reduced by responding to this 24 h rhythm with timed medication intake (chronotherapy), which also applies to aspirin. Multiple studies on chronotherapy with low-dose aspirin are promising, showing a decrease in early morning platelet activity with evening intake compared with morning intake. However, in order to further demonstrate its clinical impact, randomized trials with cardiovascular events as a primary outcome are needed. This review discusses the available evidence of the effects of circadian rhythm on CVD and the potential positive effect of chronotherapy with aspirin.

Circadian variations in electric current responses at ryodoraku points across the waking stage: A prospective observational study

Human body undergoes the 24-hour daily rhythm in response primarily to light and darkness. The circadian rhythms of biomarkers reflect bodily conditions including the prognosis of some pathologies. As a sensitive index of sympathetic nervous response (SNR), electrodermal activity (EDA) is a recent research topic in healthcare industry as a noninvasive and easy-access biosignal. The EDA response at Ryodoraku points (RPs) is of potential clinical usage in relation to SNR and meridian theory, but still remains in its primitive development stage.In this study, the 24-hour variations of EDA for 14 hospitalized participants were monitored over 3 days using a Ryodoraku device, and a circadian model of EDA was constructed using a cosinor analysis based on the linear mixed effect model.As a result, EDA at every RP showed a circadian cycle with its value the lowest in the morning and increased gradually until the late afternoon, and monotonically decreased again until the next morning. Circadian variations were observed in EDAs of all 12 RPs. However, Ryodoraku-specific features were not detected. Midline estimating statistic of rhythm (MESOR) values in men and young group were higher than in women and old group, and cosinor analysis showed significant circadian rhythms, especially for men and young groups. Especially, circadian variation in EDA in the young group went above 35% of the MESOR value.It implies that the circadian rhythm should be considered for the Ryodoraku analysis to examine bodily conditions or the prognosis of some pathologies.

Dynamic Cerebral Autoregulation Remains Stable During the Daytime (8 a.m. to 8 p.m.) in Healthy Adults

Many functions of the human body possess a daily rhythm, disruptions of which often lead to disease. Dynamic cerebral autoregulation (dCA) stabilizes the cerebral blood flow to prompt normal neural function. However, whether dCA is stable across the day remains unknown. This study aimed to investigate the daily rhythm of dCA. Fifty-one healthy adults (38.294 ± 13.279 years, 40 females) were recruited and received six dCA measurements per individual that were conducted at predefined time points: 8:00, 9:00, 11:00, 14:00, 17:00, and 20:00. Although the blood pressure fluctuated significantly, there was no statistical difference in phase difference and gain (autoregulatory parameters) across the six time points. This study demonstrates that dCA remains stable during the interval from 8 a.m. to 8 p.m. and underscores the importance of stable dCA in maintaining cerebral blood flow and neural function.

Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion

The purpose of this study was to identify the dose-dependent effects of heat strain and orthostasis [via lower body negative pressure (LBNP)], with and without mild hypohydration, on systemic function and cerebral perfusion. Eleven men (means ± SD: 27 ± 7 y; body mass 77 ± 6 kg), resting supine in a water-perfused suit, underwent progressive passive heating [0.5°C increments in core temperature (T_c; esophageal to +2.0°C)] while euhydrated (EUH) or hypohydrated (HYPO; 1.5-2% body mass deficit). At each thermal state, mean cerebral artery blood velocity (MCAv_mean; transcranial Doppler), partial pressure of end-tidal carbon dioxide ([Formula: see text]), heart rate (HR) and mean arterial blood pressure (MAP; photoplethysmography) were measured continuously during LBNP (0, -15, -30, and -45 mmHg). Four subjects became intolerant before +2.0°C T_c, unrelated to hydration status. Without LBNP, decreases in [Formula: see text] accounted fully for reductions in MCAv_mean across all T_c. With LBNP at heat tolerance (+1.5 or +2.0°C), [Formula: see text] accounted for 69 ± 25% of the change in MCAv_mean. The HYPO condition did not affect MCAv_mean or any cardiovascular variables during combined LBNP and passive heat stress (all P > 0.13). These findings indicate that hypocapnia accounted fully for the reduction in MCAv_mean when passively heat stressed in the absence of LBNP and for two- thirds of the reduction when at heat tolerance combined with LBNP. Furthermore, when elevations in T_c are matched, mild hypohydration does not influence cerebrovascular or cardiovascular responses to LBNP, even when stressed by a combination of hyperthermia and LBNP.

Differences in emergency ambulance demand between older adults living in residential aged care facilities and those living in the community in Melbourne, Australia

OBJECTIVE

To describe the clinical presentation and temporal variation in ambulance service cases involving patients aged 65 years or older (older adults) from residential aged care facilities and those who are community dwelling (CD).

METHODS

This study used four years of electronic case records from Ambulance Victoria in Melbourne, Australia. Trigonometric regression was used to analyse demand patterns.

RESULTS

Residential aged care facility cases included proportionally more falls and infection-related problems and fewer circulatory-related incidents than CD cases. Community dwelling demand patterns differed between weekdays and weekends and peaked late morning. Residential aged care facility cases peaked late morning, with a secondary peak early evening, but with no significant difference between days.

CONCLUSIONS

Older adult ambulance demand has distinct temporal patterns that differ by place of residence and are associated with different clinical presentations. These results provide a basis for informing ambulance planning and the identification of alternate health services.

Circadian Phenotype Composition is a Major Predictor of Diurnal Physical Performance in Teams

Team performance is a complex phenomenon involving numerous influencing factors including physiology, psychology, and management. Biological rhythms and the impact of circadian phenotype have not been studied for their contribution to this array of factors so far despite our knowledge of the circadian regulation of key physiological processes involved in physical and mental performance. This study involved 216 individuals from 12 different teams who were categorized into circadian phenotypes using the novel RBUB chronometric test. The composition of circadian phenotypes within each team was used to model predicted daily team performance profiles based on physical performance tests. Our results show that the composition of circadian phenotypes within teams is variable and unpredictable. Predicted physical peak performance ranged from 1:52 to 8:59 p.m. with performance levels fluctuating by up to 14.88% over the course of the day. The major predictor for peak performance time in the course of a day in a team is the occurrence of late circadian phenotypes. We conclude that circadian phenotype is a performance indicator in teams that allows new insight and a better understanding of team performance variation in the course of a day as often observed in different groupings of individuals.

Post-Exercise Hypotension and Its Mechanisms Differ after Morning and Evening Exercise: A Randomized Crossover Study

Post-exercise hypotension (PEH), calculated by the difference between post and pre-exercise values, it is greater after exercise performed in the evening than the morning. However, the hypotensive effect of morning exercise may be masked by the morning circadian increase in blood pressure. This study investigated PEH and its hemodynamic and autonomic mechanisms after sessions of aerobic exercise performed in the morning and evening, controlling for responses observed after control sessions performed at the same times of day. Sixteen pre-hypertensive men underwent four sessions (random order): two conducted in the morning (7:30am) and two in the evening (5pm). At each time of day, subjects underwent an exercise (cycling, 45 min, 50%VO₂peak) and a control (sitting rest) session. Measurements were taken pre- and post-interventions in all the sessions. The net effects of exercise were calculated for each time of day by [(post-pre exercise)-(post-pre control)] and were compared by paired t-test (P<0.05). Exercise hypotensive net effects (e.g., decreasing systolic, diastolic and mean blood pressure) occurred at both times of day, but systolic blood pressure reductions were greater after morning exercise (-7±3 vs. -3±4 mmHg, P<0.05). Exercise decreased cardiac output only in the morning (-460±771 ml/min, P<0.05), while it decreased stroke volume similarly at both times of day and increased heart rate less in the morning than in the evening (+7±5 vs. +10±5 bpm, P<0.05). Only evening exercise increased sympathovagal balance (+1.5±1.6, P<0.05) and calf blood flow responses to reactive hyperemia (+120±179 vs. -70±188 U, P<0.05). In conclusion, PEH occurs after exercise conducted at both times of day, but the systolic hypotensive effect is greater after morning exercise when circadian variations are considered. This greater effect is accompanied by a reduction of cardiac output due to a smaller increase in heart rate and cardiac sympathovagal balance.

The impact of circadian phenotype and time since awakening on diurnal performance in athletes

Circadian rhythms, among other factors, have been shown to regulate key physiological processes involved in athletic performance. Personal best performance of athletes in the evening was confirmed across different sports. Contrary to this view, we identified peak performance times in athletes to be different between human "larks" and "owls" (also called "morningness/eveningness types" or "chronotypes" and referred to as circadian phenotypes in this paper), i.e., individuals with well-documented genetic and physiological differences that result in disparities between their biological clocks and how they entrain to exogenous cues, such as the environmental light/dark cycle and social factors. We found time since entrained awakening to be the major predictor of peak performance times, rather than time of day, as well as significant individual performance variations as large as 26% in the course of a day. Our novel approach combining the use of an athlete-specific chronometric test, longitudinal circadian analysis, and physical performance tests to characterize relevant sleep/wake and performance parameters in athletes allows a comprehensive analysis of the link between the circadian system and diurnal performance variation. We establish that the evaluation of an athlete's personal best performance requires consideration of circadian phenotype, performance evaluation at different times of day, and analysis of performance as a function of time since entrained awakening.

Wake-up stroke and stroke of unknown onset: a critical review

Patients, who wake up with an ischemic stroke, account for a large number of the total stroke population, due to circadian morning predominance of stroke. Currently, this subset of patients is excluded from revascularization-therapy since no exact time of onset is known. A large group of these patients might be eligible for therapy. In this review, we assessed the current literature about the hypothesis that wake-up-strokes occur just prior on awakening and if this subgroup differs in characteristics compared to the overall stroke population. We looked at the safety and efficacy of thrombolysis and interventional techniques in the group of patients with unknown stroke-onset. We performed a meta-analysis of the diagnostic accuracy of the diffusion-FLAIR mismatch in identifying stroke within 3 and 4.5 h. The different imaging-selection criteria that can be used to treat these patients are discussed. Additional research on imaging findings associated with recent stroke and penumbral imaging will eventually lead to a shift from a rigid time-frame based therapy to a tissue-based individualized treatment approach.

Diurnal variation of haemostatic response to exercise in young sedentary males

The aim of this study was to evaluate diurnal variations in the haemostatic response to submaximal exercise performed by young, sedentary men. Fifteen healthy young sedentary males aged 25.6 ± 1.34 (mean ± SD) years performed two exercise sessions, morning and evening, at 70% of maximal oxygen consumption (V.O₂max) on a cycle ergometer for 30 min. Platelet count (PC), activated partial thromboplastin time (aPTT), prothrombin time (PT), fibrinogen, tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) activity were measured as dependent variables. Exercise produced significant increases in PC and fibrinogen for both sessions (P ≤ 0.05), which returned to the resting values after recovery only in the evening session. APTT and PT shortened immediately after exercise, which remained after recovery for both sessions (P ≤ 0.01). Exercise presented significant increases in tPA activity (P ≤ 0.001), which returned to the baseline after recovery in both exercises. PAI-1 activity was significantly higher during the morning than evening (P ≤ 0.05), but no longer demonstrated exercise-related changes. It was found that exercise caused activation of both coagulation and fibrinolysis processes, partly related to the time of the day when the exercise was performed.

Circadian rhythms in leukocyte trafficking

A broad range of immunological processes oscillates over the course of a day. Recent findings have identified a molecular basis for the circadian clock in the regulation of the immune system. These rhythms manifest themselves in oscillatory behavior of immune cells and proinflammatory mediators, which causes a time-dependent sensitivity in the reaction to pathogens. This rhythmicity impacts disease manifestations and severity and provides an option for therapy that incorporates chronopharmacological considerations. This review will focus on the current knowledge and relevance of rhythmic immune cell trafficking. It will provide an overview of the molecular clock machinery and its interrelations with leukocyte migration and the immune response.

Blood pressure control and primary prevention of stroke: summary of the recent clinical trial data and meta-analyses

Stroke is the second most common cause of death worldwide and of adult disability, but in the near future the global burden of cerebrovascular diseases will rise due to ageing and adverse lifestyle changes in populations worldwide. The risk of stroke increases at blood pressure levels above 115/75 mm Hg and high blood pressure (BP) is the most important modifiable risk factor for stroke, associated with 54 % episodes of stroke worldwide. There is strong evidence from clinical trials that antihypertensive therapy reduces substantially the risk of any type of stroke, as well as stroke-related death and disability. The risk attributed to BP is associated not only with absolute values but also with certain parameters describing BP diurnal pattern as well as short-term and long-term variability. Many studies reported that certain features of BP like nocturnal hypertension, morning surge or increased variability predict an increased stroke risk. However, there is no accepted effective modality for correction of these disturbances (chronotherapy, certain classes of antihypertensive drugs). In the elderly, who are mostly affected by stroke, the primary prevention guidelines recommend treatment with diuretics and calcium channel blockers to lower blood pressure to the standard level.

Ambulance demand: random events or predicable patterns?

BACKGROUND

Occupational, social and recreational routines follow temporal patterns, as does the onset of certain acute medical diseases and injuries. It is not known if the temporal nature of injury and disease transfers into patterns that can be observed in ambulance demand. This review examines eligible study findings that reported temporal (time of day, day of week and seasonal) patterns in ambulance demand.

METHODS

Electronic searches of Medline and Cumulative Index of Nursing and Allied Health Literature were conducted for papers published between 1980 and 2011. In addition, hand searching was conducted for unpublished government and ambulance service documents and reports for the same period.

RESULTS

38 studies examined temporal patterns in ambulance demand. Six studies reported trends in overall workload and 32 studies reported trends in a subset of ambulance demand, either as a specific case type or demographic group. Temporal patterns in overall demand were consistent between jurisdictions for time of day but varied for day of week and season. When analysed by case type, all jurisdictions reported similar time of day patterns, most jurisdictions had similar day of week patterns except for out-of-hospital cardiac arrest and similar seasonal patterns, except for trauma. Temporal patterns in case types were influenced by age and gender.

CONCLUSIONS

Temporal patterns are present in ambulance demand and importantly these populations are distinct from those found in hospital datasets suggesting that variation in ambulance demand should not be inferred from hospital data alone. Case types seem to have similar temporal patterns across jurisdictions; thus, research where demand is broken down into case types would be generalisable to many ambulance services. This type of research can lead to improvements in ambulance service deliverables.

[Relation between myocardial infarction and circadian rhythm in patients attended in a prehospital emergency service]

BACKGROUND AND OBJECTIVES

The aim of this study is to analyze the presence of circadian rhythm in the time of onset of symptoms of acute myocardial infarction treated by a prehospital emergency system and the influence of modifiable cardiovascular risk factors and non-modifiable as modulators of that circadian rhythm.

PATIENTS AND METHODS

Retrospective analysis of 709 patients clinically diagnosed with acute myocardial infarction on-site in the prehospital setting. The variables were time to onset of symptoms, age, sex, previous ischemic heart disease, hypertension, diabetes mellitus, hyperlipidemia and smoking. We analyzed the rhythm with cosinor multiple sinusoid method, with 3 harmonics (24, 12 and 8h) for the adjustment.

RESULTS

The time of onset of pain showed circadian rhythm (P <,001), peaking at 10.39 and a valley at 4.28, showing a sinusoidal curve fitting bimodal aspect with a predominant morning peak and another evening one of lower amplitude. All subgroups categorized by the study variables showed circadian rhythm, with a cosine curve similar to the global infarction. Smokers had a predominantly evening peak.

CONCLUSIONS

Acute myocardial infarction shows a circadian rhythm. Smoking and diabetes mellitus can modify the standard incidence rate of occurrence of myocardial infarction.

Evaluation of strength and irradiated movement pattern resulting from trunk motions of the proprioceptive neuromuscular facilitation

Introduction. The proprioceptive neuromuscular facilitation (PNF) is a physiotherapeutic concept based on muscle and joint proprioceptive stimulation. Among its principles, the irradiation is the reaction of the distinct regional muscle contractions to the position of the application of the motions. Objective. To investigate the presence of irradiated dorsiflexion and plantar flexion and the existing strength generated by them during application of PNF trunk motions. Methods. The study was conducted with 30 sedentary and female volunteers, the PNF motions of trunk flexion, and extension with the foot (right and left) positioned in a developed equipment coupled to the load cell, which measured the strength irradiated in Newton. Results. Most of the volunteers irradiated dorsal flexion in the performance of the flexion and plantar flexion during the extension motion, both presenting an average force of 8.942 N and 10.193 N, respectively. Conclusion. The distal irradiation in lower limbs became evident, reinforcing the therapeutic actions to the PNF indirect muscular activation.

Diurnal variation in vascular function: role of sleep

Although vascular function is lower in the morning than afternoon, previous studies have not assessed the influence of prior sleep on this diurnal variation. The authors employed a semiconstant routine protocol to study the contribution of prior nocturnal sleep to the previously observed impairment in vascular function in the morning. Brachial artery vascular function was assessed using the flow-mediated dilation technique (FMD) in 9 healthy, physically active males (mean ± SD: 27 ± 9 yrs of age), at 08:00 and 16:00 h following, respectively, 3.29 ± .37 and 3.24 ± .57 h prior sleep estimated using actimetry. Heart rate and systolic and diastolic blood pressures were also measured. The data of the experimental sleep condition were compared with the data of the "normal" diurnal sleep condition, in which FMD measurements were obtained from 21 healthy individuals who slept only during the night, as usual, before the morning test session. The morning-afternoon difference in FMD was 1 ± 4% in the experimental sleep condition compared with 3 ± 4% in the normal sleep condition (p = .04). This difference was explained by FMD being 3 ± 3% lower in afternoon following the prior experimental sleep (p = .01). These data suggest that FMD is more dependent on the influence of supine sleep than the endogenous circadian timekeeper, in agreement with our previous finding that diurnal variation in FMD is influenced by exercise. These findings also raise the possibility of a lower homeostatic "set point" for vascular function following a period of sleep and in the absence of perturbing hemodynamic fluctuation.

Prognostic value of the variability in home-measured blood pressure and heart rate: the Finn-Home Study

The objective of the study was to assess the prognostic value of variability in home-measured blood pressure (BP) and heart rate (HR) in a general population. We studied a representative sample of the Finnish adult population with 1866 study subjects aged 45-74 years. BP and HR self-measurements were performed on 7 consecutive days. The variabilities of BP and HR were defined as the SDs of morning minus evening, day-by-day, and first minus second measurements. The primary end point was incidence of a cardiovascular event. The secondary end point was total mortality. During a follow-up of 7.8 years, 179 subjects had experienced a cardiovascular event, and 130 subjects had died. In Cox proportional hazard models adjusted for age, sex, BP/HR, and other cardiovascular risk factors, morning-evening home BP variability (systolic/diastolic relative hazard: 1.04/1.10 [95% CI: 1.01-1.07/1.05-1.15] per 1-mm Hg increase in BP variability) and morning day-by-day home BP variability (relative hazard: 1.04/1.10 [95% CI: 1.00-1.07/1.04-1.16] per 1-mm Hg increase in BP variability) were predictive of cardiovascular events. Morning-evening home HR variability (relative hazard: 1.07 [95% CI: 1.02-1.12] per 1-bpm increase in HR variability) and morning day-by-day home HR variability (relative hazard: 1.11 [95% CI: 1.05-1.17] per 1-bpm increase in HR variability) were also independent predictors of cardiovascular events. Greater variabilities of morning home BP and HR are independent predictors of cardiovascular events. Because the variabilities of home BP and HR are easily acquired in conjunction with home BP and HR level, they should be used as the additive information in the assessment of cardiovascular risk.

Time-of-day effect on cardiac responses to progressive exercise

This study was designed to examine time-of-day effects on markers of cardiac functional capacity during a standard progressive cycle exercise test. Fourteen healthy, untrained young males (mean ± SD: 17.9 ± 0.7 yrs of age) performed identical maximal cycle tests in the morning (08:00-11:00 h) and late afternoon (16:00-19:00 h) in random order. Cardiac variables were measured at rest, submaximal exercise, and maximal exercise by standard echocardiographic techniques. No differences in morning and afternoon testing values at rest or during exercise were observed for oxygen uptake, heart rate, cardiac output, or markers of systolic and diastolic myocardial function. Values at peak exercise for Vo(2) at morning and afternoon testing were 3.20 ± 0.49 and 3.24 ± 0.55 L min(-1), respectively, for heart rate 190 ± 11 and 188 ± 15 bpm, and for cardiac output 19.5 ± 2.8 and 19.8 ± 3.5 L min(-1). Coefficients of variation for morning and afternoon values for these variables were similar to those previously published for test-retest reproducibility. This study failed to demonstrate evidence for significant time-of-day variation in Vo(2)max or cardiac function during standard progressive exercise testing in adolescent males.

Diurnal variation in time to presyncope and associated circulatory changes during a controlled orthostatic challenge

Epidemiological data indicate that the risk of neurally mediated syncope is substantially higher in the morning. Syncope is precipitated by cerebral hypoperfusion, yet no chronobiological experiment has been undertaken to examine whether the major circulatory factors, which influence perfusion, show diurnal variation during a controlled orthostatic challenge. Therefore, we examined the diurnal variation in orthostatic tolerance and circulatory function measured at baseline and at presyncope. In a repeated-measures experiment, conducted at 0600 and 1600, 17 normotensive volunteers, aged 26 ± 4 yr (mean ± SD), rested supine at baseline and then underwent a 60° head-up tilt with 5-min incremental stages of lower body negative pressure until standardized symptoms of presyncope were apparent. Pretest hydration status was similar at both times of day. Continuous beat-to-beat measurements of cerebral blood flow velocity, blood pressure, heart rate, stroke volume, cardiac output, and end-tidal Pco2 were obtained. At baseline, mean cerebral blood flow velocity was 9 ± 2 cm/s (15%) lower in the morning than the afternoon ( P < 0.0001). The mean time to presyncope was shorter in the morning than in the afternoon (27.2 ± 10.5 min vs. 33.1 ± 7.9 min; 95% CI: 0.4 to 11.4 min, P = 0.01). All measurements made at presyncope did not show diurnal variation ( P > 0.05), but the changes over time (from baseline to presyncope time) in arterial blood pressure, estimated peripheral vascular resistance, and α-index baroreflex sensitivity were greater during the morning tests ( P < 0.05). These data indicate that tolerance to an incremental orthostatic challenge is markedly reduced in the morning due to diurnal variations in the time-based decline in blood pressure and the initial cerebral blood flow velocity “reserve” rather than the circulatory status at eventual presyncope. Such information may be used to help identify individuals who are particularly prone to orthostatic intolerance in the morning.