Noise and the detection of coronary artery disease with an electronic stethoscope

Recent studies demonstrated that diastolic heart sounds, recorded with an electronic stethoscope, contain markers of coronary artery disease (CAD). A difficult is that the CAD-related sound is very weak and recordings are often contaminated by noise. The current study analyses the noise contamination of 633 stethoscope recordings from a clinical environment. Respiration noise, ambient noise, recording noise and abdominal noise were identified in the recordings and were classified according to duration and intensity. To monitor how noise influences the classification performance AR-pole magnitudes were extracted from both the 25-250 Hz frequency band and the 250-1000 Hz frequency band. The classification performance was quantified by the Area Under the receiver operating Characteristic (AUC). Ambient noise was present in 39.9% of the recordings and was the most common noise source. Abdominal noise was the least common noise source, present in 10.8% of the recordings. The best pole, with respect to detection of CAD, extracted from the 250-1000 Hz frequency band was sensitive to noise, since the AUC dropped from 0.70 in to 0.57 when noisy recordings were included. Contrary the best pole from the 25-250 Hz frequency band was relatively robust against noise, since the AUC dropped from 0.73 to only 0.70 when noisy recordings were included. The study demonstrated that noise contamination is a frequent problem and that features from lower frequency bands are more robust against noise than features from higher frequency bands.