Time domain analysis of R-wave attenuation envelope for sleep apnea detection

Time domain analysis was carried out on the R-wave attenuation (RWA) envelope of the subjects with and without obstructive sleep apnea. The RWA envelope is derived from the morphology of the electrocardiogram (ECG) obtained during polysomnography data collection of the subjects. Nocturnal polysomnography was performed on 16 normal subjects and 14 obstructive sleep apnea (OSA) patients. The ECG from the polysomnography data was divided into fifteen minute epochs for analysis. The QRS detection was carried out by an algorithm using Hilbert transform. Standard deviation of each of the fifteen one minute epochs in fifteen minute epoch of the RWA envelope was calculated. Standard deviation of these fifteen parameters was observed to have considerably good sensitivity and specificity to sleep apnea. For the clips selected from normal subjects, the parameter produced a sensitivity of 78.57% and specificity of 70.33% for the training set and sensitivity of 87.5% and specificity of 80.95 for the testing set. For the clips selected from OSA subjects, the parameter produced a sensitivity of 72.46% and specificity of 73.53% for the training set and sensitivity of 82.86% and specificity of 66.67% for the testing set.