Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Body’s biological clock found to affect cardiac rhythm patterns in healthy adults

21.12.2004


Statistical physics approach to analysis of heartbeat pattern uncovers link to circadian cycle



In a newly reported, first-ever finding, physicists from Boston University and physiologists from Boston’s Brigham and Women’s Hospital (BWH) have found that the body’s biological clock affects the patterns of heart-rate control in healthy individuals independent of sleep/wake cycle or other behavior influences. Their analysis of the heartbeat dynamics of the healthy individuals in the study showed significant circadian rhythm, including a notable response at the internal circadian phase corresponding to 10 a.m., the time of day most often linked to adverse cardiac events in individuals with heart disease.

The BU/BWH team reports its findings in the Dec. 28 issue of the Proceedings of the National Academy of Sciences. Sponsored by grants from the National Institutes of Health, the institutional teams were led by Plamen Ivanov, a research associate in BU’s Center for Polymer Studies, who undertook the analysis of the data, and Steven Shea, director of BWH’s medical chronobiology program and associate professor of medicine at Harvard Medical School, who conducted the experimental part of the research.


Cardiac disease is the leading cause of death in the United States, accounting for 29 percent of the deaths from the nation’s 10 leading causes (including homicides and accidents), according to the latest statistics (2001) available from the National Center for Health Statistics.

When designing their study of this deadly disease, the BU/BWH team drew on seemingly disparate findings in epidemiology, cardiology, circadian biology, biomedical engineering, and physics to construct an approach that would assess heartbeat fluctuations in healthy individuals at different circadian phases. In addition, they choose to analyze the data from these individuals using tools from statistical physics that describe relationships between the frequencies of large and small events. With these tools, the researchers hoped to find whether underlying patterns in the heartbeat data of the study participants were affected by the circadian phases.

For more than a decade, researchers at the Center for Polymer Studies have applied statistical physics methods to investigations of cardiac dynamics, probing for hidden patterns. Previous statistical evaluations of heartbeat fluctuations by Ivanov and others have shown that those of healthy subjects exhibit a self-similar structure over a range of time scales, that is, the fluctuations found in a window of 10 beats will be statistically similar to those found in a heartbeat interval of 100 beats and or one of 1000 beats.

"These studies have demonstrated that this self-similar structure in the temporal order of heartbeat fluctuations changes with certain behaviors, such as sleep or wake, rest or exercise," explains Ivanov. "Based on these observations, we hypothesized that these dynamic patterns will also change with circadian rhythm. This provided the impetus for the study design."

Epidemiological studies, too, have shown a pattern to events associated with heartbeat irregularities such as myocardial infarction, stroke, angina, arrhythmias and sudden cardiac death. These events have been found to have a strong 24-hour day/night pattern and, intriguingly, have been found to occur most often around 10 a.m.

Day/night patterns of disease severity are often associated with sleep/wake behavior but, the researchers hypothesized, they can also be linked to an internal body clock, the endogenous circadian pacemaker that controls much of our physiology, even when behaviors are unchanged. Body temperature, Shea notes, rises during the day and falls at night even when a person doesn’t sleep at night. The circadian cycle usually "resets" itself daily in response to certain external cues, most especially bright light, such as sunlight.

To remove any influence from the sleep/wake cycle, Shea and his team employed a "forced desynchrony" protocol on the five healthy volunteers who participated in the study. For 10 days, the participants lived in dimly lit rooms cut off from any outside stimuli or time cues. The researchers adjusted scheduled behaviors (sleeping periods, eating, and the like), gradually shifting the behavior patterns until the participants had a 28-hour day, about 19 hours awake and 9 hours asleep. This 28-hour sleep/wake schedule was sustained for seven "days," while core body temperatures, used to mark participants’ internal circadian phases, continued to oscillate with an approximate 24-hour period, indicating their sleep/wake cycles had been experimentally separated from their circadian cycles.

Using heartbeat data gathered from the participants throughout the 10-day desynchrony, Ivanov and BU team members Kun Hu and Zhi Chen, research assistants in physics, estimated correlations in the heartbeat fluctuations according to a power law function quantified using a method known as a detrended fluctuation analysis (DFA). The DFA mathematically describes the fluctuations at different time scales in the heartbeat signal and produces a scaling exponent that characterizes the degree of correlation between heartbeat intervals. If, for example, the scaling exponent, known as á, equaled 0.5, the interval fluctuations showed no correlation; if á equaled 1.5, the interval fluctuations were considered to be without control, exhibiting a so-called random walk property. If, however, á fell between 0.5 and 1.5, the interval fluctuations were considered to be organized and physiologically controlled. Interestingly, research studies have associated á values progressing toward 1.5 with pathological conditions, such as congestive heart failure.

When the team analyzed wake period data, they found a striking correlation: á values changed according to the internal body clock time. At 2 a.m., the value was 0.8; at 5 p.m., it was 1.0. However, at 10 a.m., the time of day found to have the greatest incidence of cardiac incidents, the team found the value was 1.2, edging toward the value linked with congestive heart failure. The team likewise found strong circadian rhythms whether data were considered only from the awake period or only from the sleep period.

"We are tempted to speculate that if the same circadian effect occurs in people with diseased hearts, then this may contribute to the day/night pattern of cardiac events," says BWH’s Shea. "But this was only a study on healthy subjects, and, therefore, we are a long way from making clinical recommendations. Further studies could, however, provide insight to the underlying cause of the disease -- and to therapies that might work better by being timed to the specific phases of the body clock."

Brigham and Women’s Hospital is a 735-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare System, an integrated health care delivery network. Internationally recognized as a leading academic health care institution, BWH is committed to excellence in patient care, medical research, and the training and education of health care professionals.

Ann Marie Menting | EurekAlert!
Further information:
http://www.bu.edu

More articles from Health and Medicine:

nachricht Finnish research group discovers a new immune system regulator
23.02.2018 | University of Turku

nachricht Minimising risks of transplants
22.02.2018 | Friedrich-Alexander-Universität Erlangen-Nürnberg

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>