What affects the Lyapunov exponents of finger plethysmogram?

This study investigated the relations between the largest Lyapunov exponents of the finger plethysmogram and pulse indices. First, we made a sine wave that had various pulse intervals and examined the relations using a simulation. Consequently, the largest Lyapunov exponents decreased with the standard deviation of the pulse interval. Next, we carried out two experiments and reexamined the relations using actual measurements of finger plethysmogram recorded during rest and during two mental tasks. We found a significant positive correlation between the standard deviation of the pulse intervals of the finger plethysmogram and the largest Lyapunov exponent, and the correlation coefficient was the highest of pulse indices in two experiments. From these results, we concluded that the largest Lyapunov exponents of the finger plethysmogram are greatly affected by the standard deviation of pulse intervals may be a more reasonable measurement than the largest Lyapunov exponents of the finger plethysmogram.