Abstract
In surgeries where general anesthesia is required, the auscultation of heart and lung sounds is essential to provide information on the patient’s cardiorespiratory system. Heart and lung sounds can be recorded using an esophageal stethoscope; however, there is huge background noise when this device is used in an operating room. In this study, a digital esophageal stethoscope system was designed. A 3D-printed case filled with Polydimethylsiloxane material was designed to hold two electret-type microphones. One of the microphones was placed inside the printed case to collect the heart and lung sound signals coming out from the patient through the esophageal catheter, the other was mounted on the surface of the case to collect the operating room sounds. A developed adaptive noise canceling algorithm was implemented to remove the operating room noise corrupted with the main heart and lung sound signals and the output signal was displayed on software application developed especially for this study. Using the designed case, the noise level of the signal was reduced to some extent, and by adding the adaptive filter, further noise reduction was achieved. The designed system is lightweight and can provide noise-free heart and lung sound signals.
Highlights
A patient under general anesthesia is monitored by using a variety of techniques to observe the effect of the anesthetic and to safeguard the patient against progression into adverse conditions [1]
The signals picked up from the two microphones were fed to the processing unit, which mainly consisted of an amplification circuit to amplify the recorded signals to a certain level, and an adaptive noise canceling algorithm code was implemented using the Teensy 3.2 development board to filter out the operating room noise from the main heart and lung sound signals
The second graph shows the noise signal, which was measured from the second sound source only, and it represents the background noise, i.e., the operating room noise
Summary
A patient under general anesthesia is monitored by using a variety of techniques to observe the effect of the anesthetic and to safeguard the patient against progression into adverse conditions [1]. There have been many studies on developing digital esophageal stethoscope systems that can accurately measure heart and lung sound signals. It has been shown that digital esophageal stethoscope systems can help to detect the intratracheal accumulation of secretion [3], to measure cardiovascular function [4,5], and predict fluid responsiveness during surgery [6]. When using a digital esophageal stethoscope in an operating room, there is a lot of noise coming from outside of the patient, which corrupts the main heart and lung sound signals. Adding sound-absorbing materials and some filtering techniques can be effective in reducing the noise. Porous materials, which have sound absorption properties, can be considered as one of the most effective methods for noise reduction [7,8] because they reduce the energy of the noise signal and gradually weaken it as the thickness of the material increases [9]
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