Comparison of RR-interval scaling exponents derived from long and short segments at different wake periods

Heartbeat fluctuations show fractal-like correlations that are associated with highly adaptive cardiovascular regulatory systems. Moreover, the short-range fractal or scaling exponent a I extracted from these correlations has been found to be a predictor of mortality for subjects with an impaired left ventricular function. In general, the RR-interval data required for this analysis are derived from long-term ECG recordings during free-running conditions. Yet short-term recordings are more likely to be obtained in some practical circumstances, so becoming relevant to assess the possibility of obtaining representative alpha(1) exponents from these recordings. Here, we compare the a I exponents extracted from the RR-interval series (9:00 am-6:00 pm) of 51 healthy adults in normal sinus rhythm and the a, calculated from three shorted segments of only 700 beats obtained from the same series at 9:00 am, 1:30 pm and 5:00 pm. We found no significant differences between the scaling exponents derived from the whole 9 h series and the short segments at 9:00 am and 5:00 pm, but did find significant differences when comparing the whole series with the short segment at 1:30 pm. Thus, only if the time of day is taken into consideration can short segments of heartbeat fluctuation data be used to obtain representative a, exponents.