1. Discovering new facts and revealing existing myths about the acoustic stethoscope 200 years after its invention
Lukasz Nowak(a), Karolina Nowak(b)
(a) Institute of Fundamental Technological Research, Polish Academy of Sciences, Poland
(b) Centre of Postgraduate Medical Education, Poland

2. Introduction
Research project: „New Methods and Technologies for Acoustic Medical Diagnotics”
Aim of the project: to develop a new generation of methods and technologies for acoustic medical diagnostics
Multidisciplinary team of scientists and physicians combining clinical knowledge and strong background in acoustics, electronics and signal processing

3. What do we do?
Theoretical and experimental investigations on the physical phenomena underlying the auscultation examinations
State of the art revision
Auscultation signals database: heart, breath, and other sounds
Signal analysis and processing: algorithms and software
Electronic stethoscopes: development, construction, measurements

4. Stethoscope - facts
Invented 200. years ago, in 1816, by French physician, Rene Laennec
The first non-lethal instrument for exploring internal anatomy
1850s: binaural stethoscope
The symbol of healthcare professionals
The most widespread and commonly used medical diagnostic device

5. Modern acoustic stethoscopes
David Littmann, An approach to the ideal stethoscope, Journal of the American Medical Association, Vol 178 (5), 1961, pp :
basic assumptions concerning the construction and theory of operation of the modern acoustic stethoscopes – „desireable features”
Two chest pieces (bell and diaphragm), tubing, binaural and earpieces
Single-chestpiece stethoscopes with „tunable” diaphragm

6. Stethoscope – myths Simplest diagnostic device you can imagine?
Just a few silmple components…
binaural
chestpiece
earpieces
tubing

7. Stethoscope – facts Underlying phenomena still not really well understood…
Patient -> stethoscope -> Physician: coupled acoustic system
PHYSICIAN
binaural
chestpiece
earpieces
tubing
PATIENT

8. Auscultation sounds real world vs. ideal world

9. Bell vs. diaphragm facts or myths?
„amplifying low-pitched sounds”
skin as a diaphragm
heart auscultation
„lower natural resonances” [large chestpiece]
DIAPHRAGM:
„attenuating low-pitched sounds”
stiff diaphragm
lung auscultation

10. Bell vs. diaphragm experimental methodology
Welsby P. D., Parry G. and Smith D. The stethoscope: some preliminary investigations, Postgraduate Medical Journal, Vol 79 (938), 2003, pp
Ertel P. Y., Lawrence M., Brown R. K. and Stern A. M. Stethoscope Acoustics II.Transmission and Filtration Patterns, Circulation, Vol 34 (5), 1966, pp

11. Bell vs. diaphragm measurements and results
Lung auscultation sounds spectra

12. Bell vs. diaphragm measurements and results cont’d
Heart auscultation sounds spectra

13. Tunable diaphragms facts or myths?

14. Hollow tubes facts & measurements

15. Summary future of auscultation?
Stethoscope is a simple acoustic device, but mechanisms and phenomena underlying auscultation are very complex and not yet properly understood
Many common theses concerning stethoscope have no proper scientific justification…
…and some of them seem to be just wrong
Much of a scientific effort in the field is devoted to Computer Aided Auscultation systems…
…but can it really repleace the physician on the other side of the stethoscope?

16. Thank you for your attention
The authors would like to acknowledge the financial support from the Polish National Centre for Research and Development (NCBiR), grant no.
LIDER/034/037/L-5/13/NCBR/2014