title: Regularity analysis of nocturnal oximetry recordings to assist in the diagnosis of sleep apnoea syndrome.
abstract: The relationship between sleep apnoea-hypopnoea syndrome (SAHS) severity and the regularity of nocturnal oxygen saturation (SaO2) recordings was analysed. Three different methods were proposed to quantify regularity: approximate entropy (AEn), sample entropy (SEn) and kernel entropy (KEn). A total of 240 subjects suspected of suffering from SAHS took part in the study. They were randomly divided into a training set (96 subjects) and a test set (144 subjects) for the adjustment and assessment of the proposed methods, respectively. According to the measurements provided by AEn, SEn and KEn, higher irregularity of oximetry signals is associated with SAHS-positive patients. Receiver operating characteristic (ROC) and Pearson correlation analyses showed that KEn was the most reliable predictor of SAHS. It provided an area under the ROC curve of 0.91 in two-class classification of subjects as SAHS-negative or SAHS-positive. Moreover, KEn measurements from oximetry data exhibited a linear dependence on the apnoea-hypopnoea index, as shown by a correlation coefficient of 0.87. Therefore, these measurements could be used for the development of simplified diagnostic techniques in order to reduce the demand for polysomnographies. Furthermore, KEn represents a convincing alternative to AEn and SEn for the diagnostic analysis of noisy biomedical signals.
authors.affiliation: Grupo de Ingeniería Biomédica, E.T.S. Ingenieros de Telecomunicación, Universidad de Valladolid, Paseo de Belén 15, Valladolid 47011, Spain. Electronic address: jvmarcos@gmail.com.
authors.forename: J Víctor
authors.initials: JV
authors.lastname: Marcos
authors.affiliation: Grupo de Ingeniería Biomédica, E.T.S. Ingenieros de Telecomunicación, Universidad de Valladolid, Paseo de Belén 15, Valladolid 47011, Spain. Electronic address: robhor@tel.uva.es.
authors.forename: Roberto
authors.initials: R
authors.lastname: Hornero
authors.affiliation: Non-linearity and Complexity Research Group, Aston University, Aston Triangle, Birmingham B4 7ET, United Kingdom. Electronic address: i.t.nabney@aston.ac.uk.
authors.forename: Ian T
authors.initials: IT
authors.lastname: Nabney
authors.affiliation: Grupo de Ingeniería Biomédica, E.T.S. Ingenieros de Telecomunicación, Universidad de Valladolid, Paseo de Belén 15, Valladolid 47011, Spain. Electronic address: dalvgon@gmail.com.
authors.forename: Daniel
authors.initials: D
authors.lastname: Álvarez
authors.affiliation: Grupo de Ingeniería Biomédica, E.T.S. Ingenieros de Telecomunicación, Universidad de Valladolid, Paseo de Belén 15, Valladolid 47011, Spain. Electronic address: gguttob@gmail.com.
authors.forename: Gonzalo C
authors.initials: GC
authors.lastname: Gutiérrez-Tobal
authors.affiliation: Hospital Universitario Pío del Río Hortega de Valladolid, Dulzaina 2, Valladolid 47013, Spain. Electronic address: fsas@telefonica.net.
authors.forename: Félix
authors.initials: F
authors.lastname: del Campo
mesh_terms: D019277:Entropy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism; D012815:Signal Processing, Computer-Assisted; D012891:Sleep Apnea Syndromes / Q000175:diagnosis* / Q000378:metabolism
chemical_list: D010100:Oxygen
keywords: Approximate entropy; Density estimation; Entropy rate; Kernel entropy; Oxygen saturation; Sample entropy