{"id":770222,"date":"2014-09-24T09:55:07","date_gmt":"2014-09-24T13:55:07","guid":{"rendered":"http:\/\/www.futurity.org\/?p=770222"},"modified":"2014-09-24T09:55:07","modified_gmt":"2014-09-24T13:55:07","slug":"heart-rate-variability-770222","status":"publish","type":"post","link":"https:\/\/www.futurity.org\/heart-rate-variability-770222\/","title":{"rendered":"Heart rate varies to keep body in balance"},"content":{"rendered":"
Although the heart beats out a very familiar “lub-dub” pattern that speeds up or slows down as our activity increases or decreases, the pattern itself isn’t as regular as you might think. In fact, even a “constant” heart rate varies a bit between beats. Now, doctors have found that variability is a good thing.<\/p>\n
Reduced heart rate variability (HRV) is predictive of a number of illnesses, such as congestive heart failure and inflammation.<\/p>\n
For athletes, a drop in HRV has also been linked to fatigue and overtraining. However, the underlying physiological mechanisms that control HRV\u2014and exactly why this variation is important for good health\u2014are still a bit of a mystery.<\/p>\n
By combining heart rate data from real athletes with a branch of mathematics called control theory, researchers have devised a way to better understand the relationship between HRV and health\u2014a step that could soon inform better monitoring technologies for athletes and medical professionals.<\/p>\n
To run smoothly, complex systems, such as computer networks, cars, and even the human body, rely upon give-and-take connections and relationships among a large number of variables. If one variable must remain stable to maintain a healthy system, another variable must be able to flex to maintain that stability.<\/p>\n
[related]<\/p>\n
Because it would be too difficult to map each individual variable, the mathematics and software tools used in control theory allow engineers to summarize the ups and downs in a system and pinpoint the source of a possible problem.<\/p>\n
Researchers who study control theory are increasingly discovering that these concepts can also be extremely useful in studies of the human body. In order for a body to work optimally, it must operate in an environment of stability called homeostasis.<\/p>\n
When the body experiences stress\u2014for example, from exercise or extreme temperatures\u2014it can maintain a stable blood pressure and constant body temperature in part by dialing the heart rate up or down. And HRV plays an important role in maintaining this balance, says John Doyle, professor of control and dynamical systems, electrical engineering, and bioengineering at California Institute of Technology (Caltech).<\/p>\n
“A familiar related problem is in driving,” Doyle says. “To get to a destination despite varying weather and traffic conditions, any driver\u2014even a robotic one\u2014will change factors such as acceleration, braking, steering, and wipers. If these factors suddenly became frozen and unchangeable while the car was still moving, it would be a nearly certain predictor that a crash was imminent. Similarly, loss of heart rate variability predicts some kind of malfunction or ‘crash,’ often before there are any other indications,” he says.<\/p>\n
To study how HRV helps maintain this version of “cruise control” in the human body, Doyle and his colleagues measured the heart rate, respiration rate, oxygen consumption, and carbon dioxide generation of five healthy young athletes as they completed experimental exercise routines on stationary bicycles.<\/p>\n
By combining the data from these experiments with standard models of the physiological control mechanisms in the human body, the researchers were able to determine the essential tradeoffs that are necessary for athletes to produce enough power to maintain an exercise workload while also maintaining the internal homeostasis of their vital signs.<\/p>\n