In the DFA method, the root-mean-square fluctuation of integrated and detrended time series is measured at different observation windows and plotted against the size of the observation window on a log-log scale. The scaling exponent a is then derived from the slope of line fitting to the obtained log-log plot. The short-term exponent a 1 (4 to 11 heartbeats) and the longterm scaling exponents a 2 (.11 heartbeats) were also calculated [27, 30, 31] . Low-exponent values represent reduced fractal propertiy of heart rate dynamics and have been implicated in the risk of fatal cardiac arrhythmia, increased mortality, or poor prognosis in cardiovascular diseases [32, 33, 34, 35] .