• Evangelos Kaimakamis, Charalambos Bratsas, Lazaros Sichletidis, Charalambos Karvounis, and Nikolaos Maglaveras.
• Lab of Medical Informatics, Medical School, Aristotle University of Thessaloniki, Greece. vkaimak@med.auth.gr
• Conf Proc IEEE Eng Med Biol Soc. 2009 Jan 1; 2009: 3465-9.

AimTo classify patients with possible diagnosis of Obstructive Sleep Apnea Syndrome (OSAS) into groups according to the severity of the disease using a decision tree producing algorithm based on nonlinear analysis of 3 respiratory signals instead of the use of full polysomnography.Patients MethodsEighty-six consecutive patients referred to the Sleep Unit of a Pulmonology Department underwent full polysomnography and their tests were manually scored. Three nonlinear indices (Largest Lyapunov Exponent-LLE, Detrended Fluctuation Analysis-DFA and Approximate Entropy-APEN) were extracted from two respiratory signals (nasal cannula flow-F and thoracic belt-T). The oxygen saturation signal (SpO(2)) was also selected. The above measurements provided data to the C4.5 algorithm using a data mining application.ResultsTwo decision trees were produced using linear and nonlinear data from 3 respiratory signals. The discrimination between normal subjects and sufferers from OSAS presented an accuracy of 84.9% and a recall of 90.3% using the variables age, sex, DFA from F and Time with SpO(2)<90% (T90). The classification of patients into severity groups had an accuracy of 74.2% and a recall of 81.1% using the variables APEN from F, DFA from F and T90.ConclusionIt is possible to have reliable predictions of the severity of OSAS using linear and nonlinear indices from only two respiratory signals during sleep instead of performing full polysomnography. The proposed algorithm could be used for screening patients suspected to suffer from OSAS.

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