Chest
Volume 104, Issue 5, November 1993, Pages 1518-1525
Journal home page for Chest

Clinical Investigations: Miscellaneous: Comparative Study: Journal Article: Research Support, Non-U.S. Gov't: Research Support, U.S. Gov't, Non-P.H.S.
Measurement of Respiratory Acoustical Signals: Comparison of Sensors

https://doi.org/10.1378/chest.104.5.1518Get rights and content

We assessed the performance of three air-coupled and four contact sensors under standardized conditions of lung sound recording. Recordings were obtained from three of the investigators at the best site on the posterior lower chest as determined by auscultation. Lung sounds were band-pass filtered between 100 and 2,000 Hz and sampled simultaneously with calibrated airflow at a rate of 10 kHz. Fourier techniques were used for power spectral analysis. Average spectra for inspiratory sounds at flows of 2±0.5 L/s were referenced against background noise at zero flow. Air-coupled and contact sensors had comparable maximum signal-to-noise ratios and gave similar values for most spectral parameters. Unexpectedly, less sensitivity (lower signal-to-noise ratio) at high frequencies was observed in the air-coupled devices. Sensor performance needs to be characterized in studies of lung sounds. We suggest that lung sound spectra should be averaged at known airflows over several breaths and that all measurements should be reported relative to sounds recorded at zero flow.

Section snippets

Subjects and Methods

We used seven sensors that are representative of those commonly used for respiration acoustic studies (Table 1). Three of us served as subjects for the recording of lung sounds after giving informed consent. The study protocol was approved by the Purdue University Committee on the use of human subjects. All three participants were healthy male nonsmokers, ranging in age from 24 to 47 years, in height from 166 to 183 cm, and in weight from 62 to 83 kg. None of the subjects had a respiratory

Results

On average, the length of recording was 20.8 s (range, 16.0 to 30.3 s) for each subject and sensor, and contained six inspirations (range, 4 to 9). The average number of spectra within the target flow range was 34 (range, 18 to 57). We computed the background noise spectra from an average of 31 samples (range, 9 to 70).

The slopes of the spectral curves of inspiratory sounds recorded with air-coupled microphones were steeper compared with those recorded with contact sensors (Table 2). A

Discussion

Our observations on inspiratory lung sounds confirm once again their well-known spectral characteristics,10 showing 99 percent of sound intensity below 600 Hz and greatest amplitudes between 100 and 300 Hz. Expiratory sounds at the same airflows were quieter and not necessarily similar to inspiratory sounds. For this comparison of sensors, however, we concentrated on data acquired during inspiration. Unexpectedly we found steeper spectral slopes with air-coupled microphones compared with

ACKNOWLEDGMENTS

We would like to thank Dr. Ignacio Sanchez for his help and participation as a study subject. We gratefuly acknowledge the technical assistance of Mr. Yuns Oh and secretarial help from Mrs. Doris Jensen.

References (24)

  • PasterkampH et al.

    Tracheal sounds in upper airway obstruction

    Chest

    (1992)
  • PasterkampH et al.

    Digital respirosono-graphy: new images of lung sounds

    Chest

    (1989)
  • AndersonK et al.

    Variation of breath sound and airway caliber induced by histamine challenge

    Am Rev Respir Dis

    (1990)
  • SpenceDPS et al.

    Effect of methacholine induced bronchoconstriction on the spectral characteristics of breath sounds in asthma

    Thorax

    (1992)
  • ColemanRF et al.

    A basic model to study acoustic evaluation of airway obstruction

    Arch Orolaryngol Head Neck Surg

    (1991)
  • MusselMJ

    The need for standards in recording and analysing respiratory sounds

    Med Biol Eng Comput

    (1992)
  • DruzgalskiCK et al.

    Techniques of recording respiratory sounds

    J Clin Engineer

    (1980)
  • HassardTH
  • CohenA

    Biomedical signal processing

  • KramanSS

    Vesicular (normal) lung sounds: how are they made, where do they come from, and what do they mean?

    Semin Respir Med

    (1985)
  • ForgacsP
  • GavrielyN et al.

    Spectral characteristics of normal breath sounds

    J Appl Physiol

    (1981)
  • Cited by (64)

    • Multi-channel lung sound classification with convolutional recurrent neural networks

      2020, Computers in Biology and Medicine
      Citation Excerpt :

      For a detailed description of the lung sound recording device, we refer to [26]. We developed a lung sound transducer (LST) in accordance with the air-coupled microphone approach [34]. As a basis for the LST, we use a Littmann Classic II chest piece (see Fig. 6).

    • An experimental study on the role and function of the diaphragm in modern acoustic stethoscopes

      2019, Applied Acoustics
      Citation Excerpt :

      Some of those devices are equipped with diaphragms and air-coupled microphones, other use contact transducers – such as piezoelectric foil or ceramic discs[11]. Different methods for acoustic characterization of those transducers were proposed, based on phantoms[12,13] or actual body sounds[14,15]. However, due to the applied signal processing, direct comparison of various models of electronic stethoscopes is a complex issue.

    • Investigating a compact phantom and setup for testing body sound transducers

      2011, Computers in Biology and Medicine
      Citation Excerpt :

      Sensor characteristics are often not accurately known apriori and there is no standardized calibration setup or procedure for testing these sensors [2]. However, many attempts to compare the characteristics of the different sensors were carried out [3–10]. These comparisons can aid optimal sensor selection and facilitate evaluating the results from different studies that used different sensors.

    View all citing articles on Scopus

    This study was supported in part by a grant from the Whitaker Foundation and a National Science Foundation Young Investigator Award BCS-9257488 to Dr. Wodicka. Dr. Pasterkamp is supported by the Childrens Hospital of Winnipeg Research Foundation.

    This study was presented in part at the 17th International Conference on Lung Sounds, August, 1992, Helsinki, Finland.

    View full text