<title>Approach to blood oxygen level analysis by nonlinear dynamics methods</title>

Abstract

Blood oxygen saturation level dynamics measured during sleep simultaneously with pulse rate data by means of standard pulseoxymeter with a 1 second time resolution are analyzed in a number of obstructive sleep apnoea (OSA) and control cases by nonlinear dynamics methods. Minima of the blood oxygen saturation level and maxima of the pulse rate were analyzed and used to construct three types of return maps. On a global time scale, in OSA cases, a long term relaxation type oscillation was found. A group of OSA cases may be defined for which the characteristic times of such oscillations seem to be a feature specific for the individual. On a local timescale--when the data is viewed through a time window of 20 - 45 minutes-- characteristic, complex shapes of the return maps have been identified. For controls these shapes universal and can be found in different controls. For OSA cases there is only a similarity between the shapes of the maps which, upon comparison, appear distorted and rescaled.