Acoustic analysis of snoring sounds with chaos theory

Snoring sounds are approximately periodic waves with noise. Therefore, the characteristics of snoring sound cannot be represented appropriately by frequency analysis. The snoring sounds of six patients with sleep apnea syndrome were evaluated using the chaos theory. To evaluate the chaotic nature of snoring sound, phase space, Poincare section, and time evolutions of Lyapunov exponents were calculated. At the same time, the snoring sound was analyzed by the conventional FFT method. Analytical results were as follows. An attractor of snoring sound was drawn in a four-dimensional space using the embedding theorem of Takens. The values of Lyapunov exponent (one of the indices of chaotic nature) were positive, suggesting that snoring sound demonstrates the characteristics of chaos. These nonlinear dynamic methods are expected to provide useful information for better understanding of irregular snoring sounds. (C) 2003 Elsevier B.V. All rights reserved.