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 de
'"/>
Contact: Ann Marie Menting
amenting@bu.edu
617-358-1240
Boston University
20-Dec-2004