Diagnosing Obstructive Sleep Apnea: Using Predictive Analytics Based on Wavelet Analysis in SAS/IML® Software and Spectral Analysis in PROC SPECTRA

This paper presents an application based on predictive analytics and feature-extraction techniques to develop the alternative method for diagnosis of obstructive sleep apnea (OSA). Our method reduces the time and cost associated with the gold standard or polysomnography (PSG), which is operated manually, by automatically determining the OSA’s severity of a patient via classification models using the time-series from a one-lead electrocardiogram (ECG). The data is from Dr. Thomas Penzel of Philipps-University, Germany, and can be downloaded at www.physionet.org. The selected data consists of 10 recordings (7 OSAs, and 3 controls) of ECG collected overnight, and non-overlapping-minute-by-minute OSA episode annotations (apnea and non-apnea states). This accounts for a total of 4,998 events (2,532 non-apnea and 2,466 apnea minutes). This paper highlights the nonlinear decomposition technique, wavelet analysis (WA) in SAS/IML® software, to maximize the information of OSA symptoms from ECG, resulting in useful predictor signals. Then, the spectral and cross-spectral analyses via PROC SPECTRA are used to quantify important patterns of those signals to numbers (features), namely power spectral density (PSD), cross power spectral density (CPSD), and coherency, such that the machine learning techniques in SAS® Enterprise MinerTM, can differentiate OSA states. To eliminate variations such as body build, age, gender, and health condition, we normalize each feature by the feature of its original signal (that is, ratio of PSD of ECGs WA by PSD of ECG). Moreover, because different OSA symptoms occur at different times, we account for this by taking features from adjacency minutes into analysis, and select only important ones using a decision tree model. The best classification result in the validation data (70:30) obtained from the Random Forest model is 96.83% accuracy, 96.39% sensitivity, and 97.26% specificity. The results suggest our method is well comparable to the gold standard.