A STATISTICAL-ANALYSIS OF SEQUENCES OF CARDIAC INTERBEAT INTERVALS DOES NOT SUPPORT THE CHAOS HYPOTHESIS

Series of cardiac interbeat intervals were recorded in 34 mice and des cribed using an original technique. The different intervals were divid ed into six classes according to their lengths. The different successi ons of pairs of intervals were counted with the help of a software pro gramme devoted to lexical analysis. Most of the mice showed a very sim ilar pattern of repeated sequences of interbeat intervals, statistical ly different from a random distribution. One-, two- or three-dimension al chaotic discrete maps were used to generate series that were then a nalyzed in the same way. They failed to give a distribution pattern of repeated sequences similar to the biological ones. On the contrary, s eries generated using a random component, and limited in amplitude by a feed-back correction occurring when the intervals reached a lower or an upper threshold, gave distributions of values very similar to biol ogical ones. Moreover, the natural diversity observed between mice was easily reproduced by fluctuation of these different parameters. It is suggested that a very simple process, not completely deterministic, c ould better explain interbeat interval regulation in normal mice than did chaotic phenomena, which would need complex biological processes. (C) 1997 Academic Press Limited.