Comparison of phonocardiographic monitoring locations

This is a pilot study comparing phonocardiographic (PCG, or heart sound) monitoring locations used during anaesthesia and surgery. Heart sounds from anaesthetised surgical patients were simultaneously recorded from a precordial stethoscope, an esophageal stethoscope, and a special endotracheal tube (ETT) designed for PCG monitoring (Teves ETT). These heart sounds were then analysed using digital signal processing techniques. The first heart sounds (S1) were characterized using signal-to-noise ratio estimates, maximum-to-minimum amplitude differences, and S1 power spectra. The first heart sound obtained from the esophageal stethoscope had the best signal strength and clarity. However, the strength and clarity of the first heart sound obtained from the precordial stethoscope and Teves ETT were quite satisfactory. Thus, from a signal analysis perspective there is little difference between S1 obtained from the different monitoring sites. Consequently a choice of PCG monitoring site should be based on practical considerations such as patient safety or ease of use.