Heartbeats are Highly Interrelated During REM Sleep

Heartbeats are highly interelated during REM sleep, the stage in which the brain is very active and when most dreaming takes place. This is the finding of a German-Israeli research team (Armin Bunde and Jan Kantelhardt, Justus-Liebig-University, 011-49-641-99333-60 or -73, kantelhardt@physik.uni-giessen.de; Shlomo Havlin, Bar-Ilan University).

Examining heartbeat patterns in 15 healthy individuals and 26 with a sleep disorder, the researchers looked at interbeat intervals, the times between successive heartbeats. Looking at deep sleep and light sleep, they found that interbeat intervals exhibited no interrelationships for more than 5 successive heartbeats. But during the REM (rapid eye movement) stage, which takes up about 20 percent of total sleep time, they found the interbeat intervals at one time and those at much later times were correlated over a whole range of time scales--for example, a shorter-than-average interval would more likely be followed by another shorter-than-average interval instead of a longer one, even if the researchers selected two intervals that were minutes away from each other.

Therefore, the heartbeat during REM sleep seems to rely upon a sort of "memory" that does not appear during the other phases of sleep. This finding, the researchers believe, could provide insights into the biological regulatory processes that govern heart rate variability. In addition, they say that the heartbeat information could potentially lead to a convenient "sleep phase finder" which could determine sleep stage by monitoring heartbeat. The researchers point out that the overall situation is reminiscent to DNA--in which the sequences of "letters" (base pairs) in non-coding ("junk DNA") regions have correlations, while the coding (gene-containing) regions do not have correlations. (Bunde et al., Physical Review Letters, 23 October 2000; Select Article.)