Acoustic Methods for Pulmonary Diagnosis

Abstract

Recent developments in sensor technology and computational analysis methods enable new strategies to measure and interpret lung acoustic signals that originate internally, such as breathing or vocal sounds, or are externally introduced, such as in chest percussion or airway insonification. A better understanding of these sounds has resulted in a new instrumentation that allows for highly accurate as well as portable options for measurement in the hospital, in the clinic, and even at home. This review outlines the instrumentation for acoustic stimulation and measurement of the lungs. We first review the fundamentals of acoustic lung signals and the pathophysiology of the diseases that these signals are used to detect. Then, we focus on different methods of measuring and creating signals that have been used in recent research for pulmonary disease diagnosis. These new methods, combined with signal processing and modeling techniques, lead to a reduction in noise and allow improved feature extraction and signal classification. We conclude by presenting the results of human subject studies taking advantage of both the instrumentation and signal processing tools to accurately diagnose common lung diseases. This paper emphasizes the active areas of research within modern lung acoustics and encourages the standardization of future work in this field.

Figure 1:

Summary of the different types of acoustic signals for pulmonary disease diagnosis. This includes both internal sounds, such as breath sounds, and external stimuli, such as percussion.

Figure 2:

(a) This soft tissue–bone boundary in which the ultrasound wave is highly reflected, and thus appears as a white (hyperechoic) line of the femur. (b) A-lines are static horizontal regularly-spaced hyperechoic lines that represent an aerated lung created by reverberation artifact. (c) B-lines are discrete, laser-like vertical projections arising from the pleural line and extending to the bottom of the screen without fading. (d) Shred (fractal) sign shows echo-poor areas of the pleura, represented as a non-smooth pleural line.