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

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

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

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

Modern acoustic stethoscopes David Littmann, An approach to the ideal stethoscope, Journal of the American Medical Association, Vol 178 (5), 1961, pp :504-505. 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

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

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

Auscultation sounds real world vs. ideal world

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

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 695-698. 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 899-909.

Bell vs. diaphragm measurements and results Lung auscultation sounds spectra

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

Tunable diaphragms facts or myths?

Hollow tubes facts & measurements

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?

Thank you for your attention email: lnowak@ippt.pan.pl 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