Abstract
Fluctuations in heartbeat and interbreath intervals have been confirmed to exhibit scale-invariance. This property can be used to examine the effect of gender, aging, health or disease of a patient from his heartbeat and respiration signals. Sophisticated methods of scale-invariant signal analysis are based on the estimation of multifractal spectrum of the scale exponent. In this study we used an algorithm to estimate multifractal spectrum to confirm the existence of nonlinear relationship between heartbeat and interbreath interval under supine resting condition for 20 young and 20 elderly people. Using two border and one peak scale exponents which are selected from each spectrum, we constructed a 3-dimensonal feature space. The distance and the angle of the line connecting features estimated from heartbeat and respiratory dynamics for each patient were calculated and compared in both age group. Results showed that long range dependency in heartbeat dynamics degrades in elderly people which results to a large difference between heartbeat and respiratory dynamics. Exponents for heartbeat and respiratory dynamics for young people have no significant difference reinforcing the evidence of a possible nonlinear relationship of heartbeat and respiratory dynamics for young people.
