Heartbeat and breathing cycles can become synchronized, a new study shows.
Looking for patterns in the sequence of human heartbeats is a much studied subject; evidence for pattern-revealing characteristics such as chaos and fractal or spiral geometry have been sought. Breathing, which is more under direct conscious control than heartbeat, is much less studied.
Part of the problem with searching for a breathing-heartbeat correlation is that these systems have very different rhythms. The heart normally beats 60 to 70 times per minute, while the breathing rate is about one-fifth of that. Furthermore, the heart and breathing phenomena are complex; consequently at least for periods of awakeness or rapid-eye-movement (REM) sleep little or no phase synchrony (that is, breathing and heartbeat recurring with a consistent relation to each other) can be found.
However, solid evidence has now been found for a breathing-heartbeat correlation for periods of deep sleep. Some signs of phase synchrony have been found before, but only in small samples of a dozen or so subjects. By contrast, the study performed by scientists at Bar-Ilan University (Israel), and the Martin-Luther University and the Philipps University (both in Germany), includes 112 healthy subjects of varying ages, men and women, for a variety of sleep stages.
The researchers conclude, for one thing, that the breathing rate affects the heart rate but not the other way around. Both the breathing oscillation and heartbeat oscillation are disturbed by the kinds of noise superimposed by higher brain activity present, such as in REM sleep. Jan Kantelhardt is sure enough of the heart-breathing correlation that he believes the sleep stages could now be determined by measuring heartbeat rather than measuring brain waves.
The researchers are also hoping to establish careful heart-breathing correlations for patients with heart problems, the better to develop diagnostic devices.
