Chronobiology predicts actual and proxy outcomes when dipping fails

Chronobioethics: Symphony of biological clocks observed by 7-day/24-hour ambulatory blood pressure monitoring and cardiovascular health

BACKGROUND

The high prevalence of desynchronized biological rhythms is becoming a primary public health concern. We assess complex and diverse inter-modulations among multi-frequency rhythms present in blood pressure (BP) and heart rate (HR).

SUBJECTS

and Methods: We performed 7-day/24-hour Ambulatory BP Monitoring in 220 (133 women) residents (23 to 74 years) of a rural Japanese town in Kochi Prefecture under everyday life conditions.

RESULTS

A symphony of biological clocks contributes to the preservation of a synchronized circadian system. (1) Citizens with an average 12.02-h period had fewer vascular variability disorders than those with shorter (11.37-h) or longer (12.88-h) periods (P<0.05), suggesting that the circasemidian rhythm is potentially important for human health. (2) An appropriate BP-HR coupling promoted healthier circadian profiles than a phase-advanced BP: lower 7-day nighttime SBP (106.8 vs. 112.9 mmHg, P=0.0469), deeper nocturnal SBP dip (20.5% vs. 16.8%, P=0.0101), and less frequent incidence of masked non-dipping (0.53 vs. 0.86, P=0.0378), identifying the night as an important time window.

CONCLUSION

Adaptation to irregular schedules in everyday life occurs unconsciously at night, probably initiated from the brain default mode network, in coordination with the biological clock system, including a reinforced about 12-hour clock, as "a biological clock-guided core integration system".

Appropriate Circadian-Circasemidian Coupling Protects Blood Pressure from Morning Surge and Promotes Human Resilience and Wellbeing

Background

Blood pressure (BP) variability is involved in the appraisal of threat and safety, and can serve as a potential marker of psychological resilience against stress. The relationship between biological rhythms of BP and resilience was cross-sectionally assessed by 7-day/24-hour chronobiologic screening in a rural Japanese community (Tosa), with focus on the 12-hour component and the "circadian-circasemidian coupling" of systolic (S) BP.

Subjects and Methods

Tosa residents (N = 239, 147 women, 23-74 years), free of anti-hypertensive medication, completed 7-day/24-hour ambulatory BP monitoring. The circadian-circasemidian coupling was determined individually by computing the difference between the circadian phase and the circasemidian morning-phase of SBP. Participants were classified into three groups: those with a short coupling interval of about 4.5 hours (Group A), those with an intermediate coupling interval of about 6.0 hours (Group B), and those with a long coupling interval of about 8.0 hours (Group C).

Results

Residents of Group B who showed optimal circadian-circasemidian coordination had less pronounced morning and evening SBP surges, as compared to residents of Group A (10.82 vs 14.29 mmHg, P < 0.0001) and Group C (11.86 vs 15.21 mmHg, P < 0.0001), respectively. The incidence of morning or evening SBP surge was less in Group B than in Group A (P < 0.0001) or Group C (P < 0.0001). Group B residents showed highest measures of wellbeing and psychological resilience, assessed by good relation with friends (P < 0.05), life satisfaction (P < 0.05), and subjective happiness (P < 0.05). A disturbed circadian-circasemidian coupling was associated with elevated BP, dyslipidemia, arteriosclerosis and a depressive mood.

Conclusion

The circadian-circasemidian coupling of SBP could serve as a new biomarker in clinical practice to guide precision medicine interventions aimed at achieving properly timed rhythms, and thereby resilience and wellbeing.

Is there an association between socioeconomic status and the degree of diurnal variation in heart rate?

BACKGROUND

Disruption in circadian rhythms is associated with cardiovascular disease and may play a role in socioeconomic differences in cardiovascular disease prevalence. However, it is unclear whether low SES is associated with a lower diurnal rhythm in autonomic activity markers. We investigated the association between SES and the amplitude of the daily fluctuation of heart rate.

METHODS

We included data of 450 participants of a HELIUS sub-study in Amsterdam, the Netherlands. Participants wore an Actiheart monitor (CamNtech), a chest-worn monitor which measures heart rate every 15 s for several days. Cosinor analysis was performed on the time series of heart rate within each participant. We analyzed the association between the cosinor parameters (amplitude, midline and peak time of the diurnal HR rhythm) and SES indicators (education, occupational class and a proxy of income) in multivariate linear regression models, adjusting for age, sex and ethnicity.

RESULTS

There was a clear diurnal rhythm in the average heart rates, with a peak between noon and 18:00 and a trough between 04:00 and 06:00. This rhythm was present for all categories of education, occupation and income proxy. The estimates for the cosinor parameters did not differ consistently and significantly between categories of education, occupation or income proxy.

CONCLUSIONS

We did not find any consistent evidence to support our hypothesis of a diminished amplitude in the diurnal variation of heart rate in individuals with lower SES. Future studies should explore SES differences in the diurnal variation in markers of autonomic activity other than heart rate.

Applications of cosinor rhythmometry in pharmacology

Study design and data analysis are two important aspects relevant to chronopharmacometrics. Blunders can be avoided by recognizing that most physiological variables are circadian periodic. Both ill health and treatment can affect the amplitude, phase, and/or period of circadian (and other) rhythms, in addition to their mean. The involvement of clock genes in molecular pathways related to important physiological systems underlies the bidirectional relationship often seen between circadian rhythm disruption and disease risk. Circadian rhythm characteristics of marker rhythms interpreted in the light of chronobiologic reference values represent important diagnostic tools. A set of cosinor-related programs is presented. They include the least squares fit of multiple-frequency cosine functions to model the time structure of individual records; a cosinor-based spectral analysis to detect periodic signals; the population-mean cosinor to generalize inferences; the chronobiologic serial section to follow the time course of changing rhythm parameters over time; and parameter tests to assess differences among populations. Relative merits of other available cosinor and non-parametric algorithms are reviewed. Parameter tests to compare individual records and a self-starting cumulative sum (CUSUM) make personalized chronotherapy possible, where the treatment of each patient relies on an N-of-1 design. Methods are illustrated in a few examples relevant to endocrinology, cancer and cardiology. New sensing technology yielding large personal data sets is likely to change the healthcare system. Chronobiologic concepts and methods should become an integral part of these evolving systems.

Circadian rhythms and the molecular clock in cardiovascular biology and disease

The Earth turns on its axis every 24 h; almost all life on the planet has a mechanism - circadian rhythmicity - to anticipate the daily changes caused by this rotation. The molecular clocks that control circadian rhythms are being revealed as important regulators of physiology and disease. In humans, circadian rhythms have been studied extensively in the cardiovascular system. Many cardiovascular functions, such as endothelial function, thrombus formation, blood pressure and heart rate, are now known to be regulated by the circadian clock. Additionally, the onset of acute myocardial infarction, stroke, arrhythmias and other adverse cardiovascular events show circadian rhythmicity. In this Review, we summarize the role of the circadian clock in all major cardiovascular cell types and organs. Second, we discuss the role of circadian rhythms in cardiovascular physiology and disease. Finally, we postulate how circadian rhythms can serve as a therapeutic target by exploiting or altering molecular time to improve existing therapies and develop novel ones.

Cosinor-based rhythmometry

A brief overview is provided of cosinor-based techniques for the analysis of time series in chronobiology. Conceived as a regression problem, the method is applicable to non-equidistant data, a major advantage. Another dividend is the feasibility of deriving confidence intervals for parameters of rhythmic components of known periods, readily drawn from the least squares procedure, stressing the importance of prior (external) information. Originally developed for the analysis of short and sparse data series, the extended cosinor has been further developed for the analysis of long time series, focusing both on rhythm detection and parameter estimation. Attention is given to the assumptions underlying the use of the cosinor and ways to determine whether they are satisfied. In particular, ways of dealing with non-stationary data are presented. Examples illustrate the use of the different cosinor-based methods, extending their application from the study of circadian rhythms to the mapping of broad time structures (chronomes).

Chronobiologically Interpreted Ambulatory Blood Pressure Monitoring in Health and Disease

To detect vascular variability anomalies (VVAs), a blood pressure and heart rate profile around the clock for at least 7 days is a start. As a minimum, measurement every 60 or preferably 30 minutes for a week is needed, to be continued if abnormality is found, to assess the about 24-hour (circadian) variability that exists in all individuals. As a first dividend, one then also obtains a glimpse of 2 of the very many longer-than-circadian periodicities, the biological half-week and week. Certainly if we can have sensors and computer chips in our cars that continuously monitor the pressure over a tire's life, we should be able to do the same job for ourselves for diagnostic and therapeutic decisions. Healthcare today emphasizes wellness with recommendations for exercise and a proper diet, yet these evaluations may not be adequate. BP may be measured at a visit to the doctor or before an exercise session, along with measuring body weight and performing a physical exam. The seeds of disease are planted long before they are visible, and what appears to be normal from a conventional point of view may in fact actually be abnormal. Hidden alterations of physiological function, masked by the body's remarkable adaptive capabilities, may become visible through a new diagnostic and therapeutic realm-chronobiology-that reveals hitherto unseen abnormalities. The tools of chronobiology may yield additional dividends, such as the detection of physiological "loads" related to stress and stress relief and the undesirable effcts of space weather upon personal events such as sudden cardiac death, societal events like terrorism and war, and natural disasters. Chronobiologi cally interpreted automatic ambulatory BP and heart rate (HR) monitoring (C-ABPM) may detect the antecedents of these types of events. C-ABPM is of interest in preventive cardiology, since it reveals new diagnoses as vascular variability anomalies (VVAs) and renders previous conventional diagnoses more reliable, such as that of an elevated BP. These VVAs include MESOR (midline-estimating statistic of rhythm)-hypertension, an elevation of the MESOR, which is diagnosed, like all other VVAs, only after I or preferably several replications of 7-day around-the-clock BP monitoring with available, affordable, and unobtrusive instrumentation. The recommendation for continuous C-ABPM recognizes several principles that constitute inseparably intertwined contributors to severe cardio-, cerebro- and renovascular diease. C-ABPM gauges wear and tear of genetics, physical loads, and in particular mental stress placed upon individuals from "womb to tomb" by daily life, including weather in extraterrestrial space as well as that on earth, as a continuous surveillance paradigm preventing us from flying blind to a change from less than 5% to near 100% in the risk of a stroke within 6 years.

Diagnosing vascular variability anomalies, not only MESOR-hypertension

Chronobiology is the study of biological rhythms. Chronomics investigates interactions with environmental cycles in a genetically coded autoresonance of the biosphere with wrangling space and terrestrial weather. Analytical global and local methods applied to human blood pressure records of around-the-clock measurements covering decades detect physiological-physical interactions, a small yet measurable response to solar and terrestrial magnetism. The chronobiological and chronomic interpretation of ambulatory blood pressure monitoring (C-ABPM) records in the light of time-specified reference values derived from healthy peers matched by sex and age identify vascular variability anomalies (VVAs) for an assessment of cardio-, cerebro-, and renovascular disease risk. Even within the conventionally accepted normal range, VVAs have been associated with a statistically significant increase in risk. Long-term C-ABPM records help to "know ourselves," serving for relief of psychological and other strain once transient VVAs are linked to the source of a load, prompting adjustment of one's lifestyle for strain reduction. Persistent circadian VVAs can be treated, sometimes by no more than a change in timing of the daily administration of antihypertensive medication. Circadian VVA assessment is an emergency worldwide, prompted in the United States by 1,000 deaths per day every day from problems related to blood pressure. While some heads of state met under United Nation and World Health Organization sponsorship to declare that noncommunicable diseases are a slow-motion disaster, a resolution has been drafted to propose C-ABPM as an added tool complementing purely physical environmental monitoring to contribute also to the understanding of social and natural as well as personal cataclysms.

Toward a personalized chronotherapy of high blood pressure and a circadian overswing

Timing can greatly affect the response to a stimulus, including antihypertensive medications. Herein, we assess the response of 30 patients to losartan/hydrochlorothiazide (L/H), administered for at least 1 month at a given circadian stage to each patient, this stage being changed during consecutive spans to cover six treatment times from awakening to bedtime at approximately 3-hour intervals. At the end of each stage, each patient underwent a 7-day around-the-clock ambulatory blood pressure (BP) profile, analyzed chronobiologically. A larger reduction of the midline estimating statistic of rhythm (MESOR; a rhythm-adjusted mean) of diastolic BP was achieved by L/H administration in the early morning for more patients (P < .05), while treatment upon awakening was the best choice for most patients to reduce the circadian amplitude of BP the most (P < .01). The optimal treatment time varied considerably among patients, however. Special attention should be given to the effect on the circadian amplitude since treatment can increase it above a threshold, beyond which there is a marked increase in cardiovascular disease risk. The results indicate the desirability to individualize the optimization of the antihypertensive effect of L/H by timing along the circadian scale.

Nondipping in Parkinson's disease

Objective. The aim of this study was to identify patients with Parkinson's disease who showed loss or decrease of nocturnal blood pressure fall (nondipper patients) as a marker of autonomic dysfunction. Presence or absence of orthostatic hypotension was considered to investigate whether alterations in circadian blood pressure pattern are associated with posture-related dysregulation of blood pressure. Methods. 40 patients with Parkinson's disease underwent 24-hour blood pressure monitoring. 21 patients were diagnosed with arterial hypertension and received anti-hypertensive drugs. Nondipper patients were defined as having nocturnal decrease of mean systolic and diastolic blood pressure less than 10%. Presence or absence of orthostatic hypotension was determined by Schellong's test. Results. We identified 35 nondipper patients (88%). Nondipping was detected in 20 patients with orthostatic hypotension (95%) and in 15 patients without orthostatic hypotension (79%). 18 patients with hypertensive and 22 patients with normal blood pressure values were detected. Conclusions. In conclusion 24-hour blood pressure monitoring showed a high prevalence of nondipping in 40 patients with Parkinson's disease with and without orthostatic hypotension independent of coexisting arterial hypertension and antihypertensive treatment. 24-hour blood pressure monitoring may be useful to identify non-dipping as a marker of autonomic dysfunction in patients with Parkinson's disease.

Circadian blood pressure variability in type 1 diabetes subjects and their nondiabetic siblings - influence of erythrocyte electron transfer

BACKGROUND

Normotensive non-diabetic relatives of type 1 diabetes (T1D) patients have an abnormal blood pressure response to exercise testing that is associated with indices of metabolic syndrome and increased oxidative stress. The primary aim of this study was to investigate the circadian variability of blood pressure and the ambulatory arterial stiffness index (AASI) in healthy siblings of T1D patients vs healthy control subjects who had no first-degree relative with T1D. Secondary aims of the study were to explore the influence of both cardiovascular autonomic function and erythrocyte electron transfer activity as oxidative marker on the ambulatory blood pressure profile.

METHODS

Twenty-four hour ambulatory blood pressure monitoring (ABPM) was undertaken in 25 controls, 20 T1D patients and 20 siblings. In addition to laboratory examination (including homeostasis model assessment of insulin sensitivity) and clinical testing of autonomic function, we measured the rate of oxidant-induced erythrocyte electron transfer to extracellular ferricyanide (RBC vfcy).

RESULTS

Systolic blood pressure (SBP) midline-estimating statistic of rhythm and pulse pressure were higher in T1D patients and correlated positively with diabetes duration and RBC vfcy; autonomic dysfunction was associated with diastolic BP ecphasia and increased AASI. Siblings had higher BMI, lower insulin sensitivity, larger SBP amplitude, and higher AASI than controls. Daytime SBP was positively, independently associated with BMI and RBC vfcy. Among non-diabetic people, there was a significant correlation between AASI and fasting plasma glucose.

CONCLUSIONS

Siblings of T1D patients exhibited a cluster of sub-clinical metabolic abnormalities associated with consensual perturbations in BP variability. Moreover, our findings support, in a clinical setting, the proposed role of transplasma membrane electron transport systems in vascular pathobiology.

The role of clock genes in pharmacology

The physiology of a wide variety of organisms is organized according to periodic environmental changes imposed by the earth's rotation. This way, a large number of physiological processes present diurnal rhythms regulated by an internal timing system called the circadian clock. As part of the rhythmicity in physiology, drug efficacy and toxicity can vary with time. Studies over the past four decades present diurnal oscillations in drug absorption, distribution, metabolism, and excretion. On the other hand, diurnal variations in the availability and sensitivity of drug targets have been correlated with time-dependent changes in drug effectiveness. In this review, we provide evidence supporting the regulation of drug kinetics and dynamics by the circadian clock. We also use the examples of hypertension and cancer to show current achievements and challenges in chronopharmacology.

COSMIC INHERITANCE RULES: IMPLICATIONS FOR HEALTH CARE AND SCIENCE

Countering the trend in specialization, we advocate the trans-disciplinary monitoring of blood pressure and heart rate for signatures of environmental cyclic and other variabilities in space as well as terrestrial weather on the one hand, and for surveillance of personal and societal health on the other hand. New rules (if confirmed novel laws) emerge as we recognize our inheritance from the cosmos of cycles that constitute and characterize life and align them with inheritance from parents. In so doing, we happen to follow the endeavors of Gregor Mendel, who recognized the segregation and independent assortment of what became known as genes. Circadians, rhythms with periods, τ, between 20 and 28 hours, and cycles with frequencies that are higher (ultradian) or lower (infradian) than circadian, are genetically anchored. An accumulating long list of very important but aeolian (nonstationary) infradian cycles, characterizing the incidence patterns of sudden cardiac death, suicide and terrorism, with drastically different τs, constitutes the nonphotic (corpuscular emission from the sun, heliogeomagnetics, ultraviolet flux, gravitation) Cornélissen-series.

Effects of functional water on heart rate, heart rate variability, and salivary immunoglobulin a in healthy humans: a pilot study

OBJECTIVE

This study was designed to explore the effects of drinking an average dietary volume of functional water on blood pressure, short-term cardiovascular variables, and salivary immunoglobulin A.

DESIGN

Subjects were studied in a randomized pre-post crossover design the morning after an overnight fast.

SUBJECTS

Fifteen (15) healthy nonsmoking subjects, 8 males and 7 females, aged between 15 and 49 years, participated in the study.

INTERVENTION

Short-term (10 minute) electrocardiography was measured in the participants before and after drinking either control mineral or functional water. The measurements were randomized, double blinded, and held two weeks apart. Saliva was collected for 4 minutes before the start of each electrocardiograph measurement. Blood pressure was monitored at 5 minute intervals for one hour as the mean of triplicate consecutive measurements.

RESULTS

Drinking 100 mL of control mineral or functional water did not alter arterial blood pressure in the 60 minutes post-drinking. Drinking control mineral water led to a significant fall in the heart rate, although all time domain and power density parameters remained unaffected. Consumption of functional water resulted in a significant difference in all time domain measures and in three of the power density parameters. The heart rate fell, while RR interbeat intervals, standard deviation of the normal-to-normal heartbeats (SDNN), and the square root of the mean squared differences of successive NN intervals (RMSSD) increased. A large rise in low (LF) and high frequency (HF) power had a significant effect on total power, indicating homeodynamic balance. Elevated LF power indicated intensified spectral power at frequencies in the range of 0.1 Hz, thus improving autonomic stability. The effect on the heart rate may confirm changes in cellular metabolism. Parasympathetic pathway activation stimulated secretory immunoglobulin A on mucosal surfaces, which protects against pathogenic invasion.

CONCLUSIONS

The drinking of functional water in healthy subjects elicited a rapid parasympathetic restorative response from the heart as well as stimulating mucosal humoral immunity. Functional water acts as an unconditional natural stimulus that elicits an involuntary response and facilitates physiological homeostasis.

Volume-associated ambulatory blood pressure patterns in hemodialysis patients

Although volume excess causes hypertension, whether it also affects circadian patterns of arterial pressures among hemodialysis patients remains unknown. To test the notion of whether volume overload is associated with a unique blood pressure (BP) "signature," a posthoc analysis was performed among 145 patients participating in the Dry-Weight Reduction in Hypertensive Hemodialysis Patients randomized, controlled trial. Using 400 ambulatory BP recordings over 8 weeks composed of 35 302 measurements, the trended cosinor model was found to be the best descriptor of BP chronobiology. The trended cosinor model may be described as a pattern of sinusoidal oscillation around a straight line with an upward trend during the interdialytic period that has an intercept at the postdialysis time. Augmented volume removal therapy reduced the intercept systolic BP and increased the rate of rise in systolic BP over the interdialytic interval but had no effect on the systolic BP fluctuation (amplitude). Thus, an elevated intercept and blunted slope pattern characterize the "volume-overload BP pattern" on ambulatory BP monitoring. Similar changes were seen for diastolic BP. Augmented volume removal therapy neither restored dipping nor was associated with a lag phenomenon for either the wake or the sleep systolic BP. Lowering of systolic BP was greater than diastolic BP such that pulse pressure was reduced. An observational cohort of 37 patients followed for 6 months confirmed these findings. Randomized trials are now needed to evaluate the clinical impact of augmented volume removal therapy on hard outcomes, because reduction of pulse pressure with this simple expedient has the potential to improve survival in hemodialysis patients.

Chronobiological analysis techniques. Application to blood pressure

Most variables of clinical interest show predictable changes with different frequencies, mainly, but not exclusively, along the rest-activity cycle (circadian variation). Methods of linear least-squares estimation have been designed for the detection of periodic components in sparse and noisy time series (as they are usually present in clinical situations). They include the single and population-mean cosinor methods. In cases where more than one period is statistically significant over the span of time investigated, or when the waveform is non-sinusoidal, the use of multiple components analysis to fit a model consisting of several cosine functions (harmonics or not from a given fundamental period) is recommended. We describe these methods, from the characterization of the underlying models to the process of parameter estimation. As an application example, we describe the modelling of the circadian variation of blood pressure (BP). In most individuals, BP presents a morning increase, a small postprandial valley and a deeper descent during nocturnal rest. This pattern can be easily modelled by means of a model with periods of 24 and 12 hours. Individuals that differ from this model might be considered to present increased cardiovascular risk.

Stress, geomagnetic disturbance, infradian and circadian sampling for circulating corticosterone and models of human depression?

While certain circadian hormonal changes are prominent, their predictable assessment requires a standardization of conditions of sampling. The 24-hour rhythm in circulating corticosterone of rodents, known since the 1950s, was studied as a presumed proxy for stress on 108 rats divided into 9 groups of 6 male and 9 groups of 6 female animals sampled every 4 hours for 24 hours. In a first stress study, the "no-rhythm" (zero-amplitude) assumption failed to be rejected at the 5% probability level in the two control groups and in 16 out of the 18 groups considered. A circadian rhythm could be detected with statistical significance, however, in three separate follow-up studies in the same laboratory, each on 168 rats kept on two antiphasic lighting regimens, with 4-hourly sampling for 7 or 14 days. In the first stress study, pooling of certain groups helped the detection and assessment of the circadian corticosterone rhythm. Without extrapolating to hormones other than corticosterone, which may shift more slowly or adjust differently and in response to different synchronizers, the three follow-up studies yielded uncertainty measures (95% confidence intervals) for the point estimate of its circadian period, of possible use in any future study as a reference standard. The happenstance of a magnetic disturbance at the start of two follow-up studies was associated with the detection of a circasemiseptan component, raising the question whether a geomagnetic disturbance could be considered as a "load". Far beyond the limitations of sample size, the methodological requirements for standardization in the experimental laboratory concerning designs of studies are considered in the context of models of depression. Lessons from nature's unforeseen geomagnetic contribution and from human studies are noted, all to support the advocacy, in the study of loads, of sampling schedules covering more than 24 hours.

Prediabetes is associated with abnormal circadian blood pressure variability

Blood pressure (BP) exhibits a circadian variation characterized by a morning increase, followed by a small postprandial valley and a deeper descent during nocturnal rest. Although abnormal 24-h variability (abnormal circadian variability (ACV)) predicts adverse cardiovascular disease (CVD) outcomes, a 7-day automatic ambulatory BP monitoring (ABPM) and subsequent chronobiologic analysis of the gathered data, permits identification of consistency of any abnormal circadian variation. To test whether normal overweight healthy men and women with prediabetes differed from subjects with normoglycemia in having ACV with a 7-day ABPM. Consent for a 7-day ABPM was obtained from subjects with family history of diabetes mellitus, who were participating in the screening phase for a randomized, double blind, placebo-controlled weight loss trial in prediabetics to prevent progression to diabetes mellitus. The automatic 7-day ABPM device recorded BP and heart rate every 30 min during the day and every 60 min during the night. Normoglycemic and prediabetic subjects matched for age, sex, race, BP, BMI, waist circumference and glycemic control, differed statistically significantly only in their fasting and/or 2-h postprandial serum glucose concentrations. Chronobiologically-interpreted 7-day ABPM uncovered no abnormalities in normoglycemics, whereas prediabetics had a statistically significantly higher incidence of high mean BP (MESOR-hypertension), excessive pulse pressure and/or circadian hyper-amplitude-tension (CHAT) (P<0.001). ACV detected with 7-day ABPM may account for the enhanced CVD risk in prediabetes. These findings provide a basis for larger-scale studies to assess the predictive value of 7-day ABPM over the long term.

Peripheral Circadian Clocks in the Vasculature

Living organisms have adapted to the daily rotation of the earth and regular changes in the light environment. Life forms anticipate environmental transitions, adapt their own physiology, and perform activities at behaviorally advantageous times during the day. This is achieved by means of endogenous circadian clocks that can be synchronized to the daily changes in external cues, most notably light and temperature. For many years it was thought that neurons of the suprachiasmatic nucleus (SCN) uniquely controlled circadian rhythmicity of peripheral tissues via neural and humoral signals. The cloning and characterization of mammalian clock genes revealed that they are expressed in a circadian manner throughout the body. It is now accepted that peripheral cells, including those of the cardiovascular system, contain a circadian clock similar to that in the SCN. Many aspects of cardiovascular physiology are subject to diurnal variation, and serious adverse cardiovascular events including myocardial infarction, sudden cardiac death, and stroke occur with a frequency conditioned by time of day. This has raised the possibility that biological responses under the control of the molecular clock might interact with environmental cues to influence the phenotype of human cardiovascular disease.