Reviews

The Ultimate Acoustic Stethoscope Review

Page 1 (Introduction)

Eli Finkelstein MD, PhD 07/01/08

Abstract: (Twelve popular acoustic stethoscope models were tested for sound transmission characteristics and clinical utility in checking heart, breath, and vascular sounds and measuring blood pressure. Sound transmission was both measured on human volunteers, and in an acoustic laboratory using sine wave frequency sweeps, and Dirac pulses. The acoustic laboratory tests developed better simulate actual clinical usage than prior studies. Results are reported according to the measured sound pressure level as a function of frequency (transfer function). Power spectra were generated for the human heart using each stethoscope, with the test microphone as a control. The effect of varying diaphragm pressure on the transfer function (tunable diaphragm effect), and the difference in transmission between bell and diaphragm were measured. We verified the relative enhancement of low frequencies with light diaphragm pressure as claimed by Littmann, however the decreased sound transmission efficiency with light diaphragm pressure limits its clinical utility. The rank ordering of the stethoscopes tested were Littmann Cardiology III, Omron Sprague Rappaport, Littmann Master Classic II, Littmann Cardiology I, Littmann Classic II SE, Welch Allyn Harvey Tycos Elite, Prestige Sprague Rappaport, ADC Cardiology model 615, Single Head Nursing stethoscope, ADC dual head model 603, Allheart cardiology, and DRG Puretone Traditional PT3.)

There are many acoustic stethoscopes on the market, with a wide price range from $5 to $300. There have been very few comparative reviews of stethoscopes, and even fewer that rate them by brand and model name. No one has answered the question of whether price correlates with quality. The last real review by brand and model was done 16 years ago by a cardiologist who tested six different stethoscopes (Abella M, Formolo J, Penney DG. Comparison of the acoustic properties of six popular stethoscopes. J Acoust Soc Am 1992 Apr;91(4 Pt 1):2224-2228.) This study measured power spectra on six scopes to see which were most efficient at transmitting sound in the frequency range of 37.5-1000 Hz. A frequency generator and a model ear with a microphone was used. In this study the Littmann Cardiology II was felt to be the best stethoscope. A more recent study by Callahan et al evaluated 30 different stethoscopes by usage category in an artificial system, but unfortunately didn't list the brand or model. A pink noise source and a Radio Shack microphone were used. There have been no studies which have compared stethoscopes by brand and model in actual clinical usage. Why is there such a price range for a simple device consisting of a simple chestpiece attached to a couple of tubes? Or is an acoustic stethoscope like a fine musical instrument with its own sound and personality, justifying its high price tag?

In this issue of ForUsDocs we perform extensive testing of 12 different acoustic stethoscopes purchased from retail sources. We performed both subjective and objective tests. We used the stethoscopes in our office, took them on hospital rounds, and examined a wide variety of patients with different body habituses, and different physical findings. In this way we were able to discover practical issues with the use of each of these scopes. We also did objective testing on the scopes recording heart sounds on all 12 stethoscopes using two different volunteers. We varied the pressure of the scope head on the skin to see if that affected our measurements. We used acoustic test equipment to measure the frequency response of each scope on actual heart sounds from volunteers. We measured the frequency response from test sweeps using a transducer. We performed Fourier analysis, and power spectrum analysis of the frequency response. We tested the transient response of each scope to determine which were best at detecting clicks. We tested the freedom from interference from external noise of each scope. What we produced is the most extensive and practical test ever on acoustic stethoscopes. Read our study to find our conclusions.



Which Is The Best Stethoscope?: 1. Littmann Cardiology III, 2. Allheart Cardiology, 3. Welch Allyn Harvey Tycos Elite, 4. Littmann Cardiology (I), 5. ADC ADscope 603, 6. Littman Classic II SE, 7. DRG Puretone Traditional, 8. Nurses Single Head, 9. Littmann Master Classic II, 10. ADC Platinum Cardiology 615, 11. Prestige Stealth Sprague Rappaport, 12. Omron Sprague Rappaport.



The Test Stethoscopes; Photos and Prices:

We chose 12 different scopes to test. The choice of the scopes tested were based on Amazon’s sales rankings of the most popular scopes, and on anecdotal internet comments by physicians, nurses, and EMT workers as to which were the best scopes and the best scopes for the money. The model, thumbnail photo, lowest retail price at the time of this review, and Amazon sales rank at the time of the review are listed. All stethoscopes were bought at retail. They are listed alphabetically in the following table. Click on the name to see the vendor's description. Click on any thumbnail photo to see an enlarged photo.

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