Electronic Stethoscopes - Whitepaper

Auscultation as a tool for examining patients has been noted in writings as far back as 500 BCE. Physicians originally performed “direct auscultation” by placing their ears directly on the patient’s body to listen to their internal body sounds. The invention of the stethoscope occurred in 1816, when Rene Laennec invented what was essentially a wooden tube for listening to internal body sounds. Over the years the stethoscope has changed from the original monaural model to the widely recognized binaural model of today. As early as 1878 an electronic stethoscope was used to send a signal over 100 miles, but it has taken another 100 years for manufacturers to invent any truly practical models. It was not until 1929 that the “tunable diaphragm” was invented.

Stethoscopes as a tool for auscultation allow the clinician to have a window into their patient’s body. The stethoscope has become an indispensable tool in the physical examination of patients, perhaps one of the last reasons why a clinician needs to actually lay hands on a patient. With the evolution of telemedicine, clinicians have been looking for a way to do by proxy physical examinations of patients. Electronic stethoscopes allow for such a thing; they allow a clinician to be located in one place and the patient to be located in another, and still receive the same care as if they were in the room with the clinician. Electronic stethoscopes take sound energy and convert it to electronic energy, greatly opening the possibilities for their application in the field of telemedicine. Today’s electronic stethoscope can be used simply to amplify sounds, record and store digital sound files, send sounds files asynchronously in combination with store and forward software applications, and transmit a patient’s body sounds synchronously (real-time) over various videoconferencing and networking applications.

In order to select the electronic stethoscope that is most appropriate for your Telehealth program, it is important to do a thorough needs assessment, which can be a difficult task without some guidance and resources. This whitepaper looks at what factors should be considered in the course of choosing an appropriate electronic stethoscope.

Determining Minimum Requirements

Establishing a base set of requirements will help you select the most appropriate device for your program.  

Define Users

Knowing which users will be utilizing the digital camera is an important first step in creating the minimum requirements. Some questions to consider:

  • What is the clinical background of the electronic stethoscope users?
  • What clinical programs within your organization do the users belong to?
  • Are the users part of a clinical specialty group, will this stethoscope be utilized by general practitioners, or both?
  • What is the level of expertise of the users?
  • What are the different sounds and pathologies that your users will need to auscultate with the electronic stethoscope your program selects?
  • How often will the electronic stethoscopes be used by the user or user groups?
  • Are the users already skilled diagnosticians when utilizing a regular acoustic stethoscope?
  • How many additional skills will the users need to acquire to be able to utilize the new electronic stethoscope, i.e. computer software, videoconferencing equipment, communicating to a far site provider where to place the stethoscope, advanced diagnostic skills related to auscultation, etc…?

Define the Required Functionality

There are multiple ways that the electronic stethoscopes currently on the market can be utilized in a Telehealth program. It is best to have a clear picture of exactly how you will want to use the technology before you are bombarded with the various elements of what these electronic stethoscopes “can” do verses what you will need it to be able to do to suit your program’s needs. Knowing which of the functions an electronic stethoscope can perform will help you determine its usefulness to your program. Questions to consider:

  • Is the unit amplifying, digitizing, or both?
  • What is the power supply for the unit?
    • If it is battery operated, what type of battery is required?
    • What is the battery life?
    • Is there a low battery indicator?
  • Are there any power saving features, auto shutoff for example?
  • Does the unit automatically retain any settings when powered off?
  • What is the amount of amplification offered?
  • Does the data need to be transferred real time or can it be transferred at a later time after the patient encounter?
  • What are the data output options: audio, serial, USB, wireless/Bluetooth?
    • Will the stethoscopes be used in conjunction with PCs, laptops, and/or videoconferencing units?
    • Are the cables for transfer of the data all included with the units, or will they need to be purchased separately?
    • Are the units designed to work automatically with additional equipment, or will any special work in that area be required for setup?
    • Does the data output option that the electronic stethoscope offers work with the data input options required on the additional equipment?
  • What are the network transfer options: direct IP unit to unit over the network utilizing software, over the network utilizing videoconferencing codecs, over simple phone lines?
  • What modes are offered: bell, diaphragm, extended?
  • What are the frequency ranges of the modes offered?
  • Does the unit offer ambient noise reduction?
  • Is the diaphragm electronic or hardware based?
  • Are there binaurals or headphones?
  • Are replacement parts available?
  • How many pieces are in the unit?
  • Can the user adjust the volume?
    • Is adjusting the volume an easy process?
    • Are there specific volume adjustment buttons?
    • Are there any visual and/or sound indicators for volume adjustment?
  • Are there any special ways to care for, clean, or maintain the unit that need to be taken into consideration?
    • Can it be cleaned after each patient use?
      • What cleaning agents can be used, if any?
    • Can it be sterilized?
    • Are there any devices or additional hardware it cannot be used with?
    • Are there any special power considerations for use?
  • Is the usage range for temperature and humidity conducive to your proposed use environment?
  • How many years do you expect this technology to function for your program’s use?


It is very important that as part of your minimum requirements that you define what types of certifications and national safety standards you want the equipment that you are purchasing to have. Please refer to the section on FDA and Certifications for more information on what these certifications mean to the products that you purchase. You may need to eliminate some candidates based on what you are willing or able to accept.

Market Review

Being familiar with your minimum set of requirements will aide you in your market review process. If you know you users and what functionality you are looking for ahead of time, you can easily eliminate certain units on the market without much consideration.

The first step in the market review process is to simply review all of the electronic stethoscopes that are currently on the market. It is important to check for new units with each review, as these technologies advance rapidly and new manufacturers are entering the market on a fairly regular basis. Simply searching the internet will yield comparable results, usually in a faster time frame. You can use the internet to obtain initial information on the units, anywhere from product information sheets to full color user manuals. You may only be able to find models or units names in your search, but you can always find either phone or email contact methods for further contact with the vendors to obtain additional information. You can work directly with vendors that you already have established business relationships if you prefer, but just be sure to use caution that they do not bias your search results with the products that they are offering. It is probably wiser to involve vendors after the initial phases of your market review if at all possible, so you can get the broadest initial list of candidates.

The process of elimination can begin as soon as your list is compiled. Electronic stethoscopes that don’t fit your minimum requirements can be removed from the list and narrow your search field. From that point, constructing a table of the remaining candidate’s features and functionality may allow you to remove additional models from the running.

Considering the information you have learned by constructing the comparison table will help you decide which units you may want to bring in-house for further functional testing, or may even help you make your decision. If you decided you need to physically lay hands on a few units before deciding, you have a couple of options. You can either budget to purchase x number of units for testing purposes, or you can contact vendors to see if they offer any trial periods or loaner programs to get the equipment in-house and aid in your decision making process. Feel free to contact vendors and tell them about your program’s possible interest in their product. With some vendors this will be the beginning of your working business relationship, so pay special attention to how they behave as an organization and remember you may be forming a partnership with this organization or simply a purchasing relationship.

Working with Foreign Manufacturers

You may find that the technologies in which you are interested are made by foreign manufactures. You should not eliminate a product simply based on this fact, as many of the original designers and manufactures of the technology currently on the US market started in foreign markets. These units can be attractive, because they offer great functionality and feature sets generally at a lower price. You simply need to exercise caution, as you would with making any purchase, and ensure workmanship and quality before purchasing an excessive amount of units. We would recommend that you get at least one unit in-house and put it through some testing before selecting one of these models for your program. There is a possibility that you might encounter certain road blocks to working with these companies, mostly related to actually contacting the company in the first place. It is important that the products you purchase meet your minimum requirements for certifications and national safety standards, and that they can be serviced by the manufacturer in a timely and standardized fashion.

Testing and Assessment

After conducting a market review based on your minimum requirements you will most likely be ready to conduct further testing. You may have been able to narrow down your selection to a few units, and once you do that it is time to bring the units in-house to conduct further testing. Even if you were able to nearly make a product selection after your market review, if you budget permits, there may still be some hands-on tests that you want to conduct on your new equipment before making your final order. Testing can be a drain on your program’s budget if conducted haphazardly without much planning; it can cost a lot of personnel time and project time. You need to have a plan for what you wish to gain by testing the equipment and possibly some testing designs made out ahead of time, to help the process run smoothly. You need to consider your internal resources and budget and decide to use external resources to carry out testing. During the process of selecting a device, qualitative or subjective data is going to be very important to you. You may also want to test the system you intend to put in place as a whole, to check for feasibility. If you have allocated extra money in your budget, and you have the resources available, quantitative or objective testing may also be of interest to your program. Again, with quantitative testing, you must have concrete ideas of what data you intend to gain from such testing. The setup for the sound equipment and personnel support tends to be cost prohibitive for most programs.


The point of this testing is to get subjective data or opinions on the aspects of the technology that you want to evaluate. Although you are soliciting opinions, you need to design testing procedures to eliminate as many variables as possible to consistently get the data and information that you are seeking. If you are going to involve patients in these evaluations, make sure you are aware of your organization’s IRB policies and procedures in case your project requires approval.

When conducting qualitative testing, you need to be mindful of whom you involve. You want to have a well rounded appropriate group carry out this testing. You want to make sure to have clinical and technical representation. Your testing process will be different based on the parties involved in testing. For the TTAC testing, we utilized various testing parties for our qualitative testing process. For our broad initial functionality testing of all of the electronic stethoscope units, we utilized our TTAC team, which consisted of a technical person with extensive knowledge of the Telehealth field and two clinicians with clinical, informatics, and technical expertise. For additional testing related to specific unit performance issues, we utilized individual clinicians which were recognized as excellent diagnosticians and who relied heavily on stethoscopes in their day to day practice. If you have more than one unit that you are evaluating, you have to be mindful of involving too many practitioners or those with too broad of a skill set at different phases of the process. Your testing parties should be clearly laid out in your testing plan.

You will need to design documentation methods in order to keep records of the data that you are going to collect. Having your documentation organized will help you at the end of your testing phase when you are ready to make decisions and draw conclusions. For the more technical functional aspects testing group, the documentation will be much more detailed. For clinician opinions and unit specific testing, the documentation needs to be simple to gain participation and obtain valuable input, but also not be too difficult or time consuming. The TTAC team designed three sets of documentation for subjective data gathering. In our initial testing phases, we had a table with each stethoscope that we evaluated, looking at functional aspects. Each aspect was rated on a scale of 1-3, and each rating for each functional aspect was defined as a team. It was important to do this, so when we went back to look at the results we could see why we rated each device the way we rated it, and will lend some consistency if we need to retrospectively add additional devices. Having the results all in one table is also helpful when looking back at the data, for sorting purposes etc. Secondly, we designed documentation to evaluate the clinical utility of all of the electronic stethoscopes we were evaluating. In this documentation we were looking at how each stethoscope handled normal heart sounds, normal lung sounds, and normal lung sound maneuvers. We utilized the same 1-3 rating scale. Thirdly, we created a simplified clinician documentation form that was user friendly, concise, and had the 1-3 rating scale documented directly on it.

Useful documentation templates included in this Whitepaper are:


After the units have been purchased and arrive in your testing space, it is important to be organized from the beginning. Make sure to catalog the units and account for all of the piece and parts. There are often many boxes, parts, cables, and batteries. Devise a system to keep each unit and its components contained together. The TTAC team received the stethoscopes and then documented all aspects of each unit. We made a picture catalog of the stethoscopes and their user manuals. As part of our familiarization process with each unit, we filled out a product cut sheet on each unit. The cut sheet is a way to document the functional aspects of the units, and have one concise format to refer to during testing, as opposed to searching through user manuals and product information sheets. We also documented expected and observed behaviors for certain product features.

Once the units have been organized, find a common space large enough to fit all of the products, your evaluation team, and a documentation station with a common viewing monitor. It is best to plan a time when all the units can be evaluated in the same day by the same group of people. As you go through the evaluation, the group think and group memory will be invaluable collaboration tools for completing the task as you review, evaluate, and compare units.

Your first evaluation should be a functional evaluation of each electronic stethoscope. Evaluate each piece of equipment following your documentation in a systematic fashion for best results. When you have finished evaluating all the products, go back to your documentation and evaluate two things. First, were you consistent in sticking with your rating criterion for each function? If not, be sure and modify the criterion. Second, consider in retrospect if your ratings were consistent across all products. If not, you may need to review a certain functional rating and make sure you are consistent.

In the case of the electronic stethoscope as a technology, it is not only the electronic stethoscope hardware that needs to be taken into consideration in an evaluation. In general in a Telehealth related program or project, these electronic stethoscopes are going to be used in conjunction with a software or some sort of networking and/or videoconferencing solutions. You must also take these into consideration when conducting your testing. The TTAC team reviewed each of the types of software on the market that can be utilized with an electronic stethoscope. We created a table that highlights each software’s functionality. We also used the software with its appropriate electronic stethoscope to evaluate the sound quality of the clips obtained. It was very apparent that the computer system setup, soundcard, and speakers made the sound output quality variable. We tested an audio data output scenario with various models and manufacturers of video conferencing equipment. We also tested serial data output scenarios with various models and manufactures of video conferencing equipment. The purpose of this testing was to determine the functionality of the units with various equipment setups, document the setup possibilities, document the cabling and networking necessary to make the connections happen, and document the quality of the auscultations obtained utilizing these different setups. You can see our documentation on these various tests here. This additional testing just reiterates the point that once an electronic stethoscope system is decided upon, it needs to be tested with your intended hardware setup to make sure that it will be the best fit for your program as a whole.

After functional testing of all of the electronic stethoscopes in your review, along with their accompanying software and adjunct hardware, are complete, you are ready to conduct some clinical testing. Make sure you have IRB approval if necessary within your organization. Initially it is important to conduct clinical testing with a small group of clinical experts to simply document the clinical utility of each electronic stethoscope. To conduct this testing we utilized one volunteer test subject. The clinicians utilized an acoustic Littmann stethoscope and identified 5 significant locations that each electronic stethoscope chest piece would auscultate which corresponded with our evaluation documentation. The clinicians drew circles at the point of maximum intensity for each desired clinical sound. This method reduced the variability related to having multiple clinicians listening with multiple electronic stethoscopes, and served to speed up the testing process. Another variable related to sound quality and clinical utility that we could not control for in different clinicians was the pressure utilized when they placed the electronic stethoscope chest piece on the patient. In this case, each clinician was encouraged to use a consistent methodology among the different electronic stethoscopes. From this point the clinicians each completed a physical assessment of the patient’s normal heart sounds, normal lung sounds, and normal lung sound maneuvers. The clinicians listened independently, one after another utilizing the same stethoscope. Each rated the sound heard utilizing the documentations 1-3 rating scale independently, and then the two came to consensus for each sound on each stethoscope, and documented the results real time.  At the end the documentation was reviewed for each stethoscope and scanned for inconsistencies. Once verified as complete, the electronic stethoscopes were given a preliminary ranking based on their clinical utility and functional testing to this point.

Once you have completed functional testing and preliminary clinical utility testing, you will be able to eliminate certain units that do not meet your minimum requirements and/or align with your program goals for the technology. Also, you will have an idea on your top choices for the technology based on the assigned ratings. From these ratings you will be able to single out about two units on which you still might want additional clinical feedback. We had our expert clinicians use the top two stethoscopes to conduct some normal auscultation examinations. We documented their feedback on our evaluation documentation utilizing the agreed upon 1-3 rating scale. In the case of the electronic stethoscopes, clinicians noted that to a certain extent, using normal heart and lung sounds made it hard to give meaningful feedback on the units because each could give diagnostic quality normal heart and lung sounds. So, with that in mind, we set up another functional testing session for each clinician. We had the clinicians examine patients with known pathologies utilizing both of the electronic stethoscopes side by side. The clinicians then were asked to document their rating evaluations and additional comments.

Completing these phases of qualitative testing will most likely yield the data that you need, in combination with your program plan and minimum requirements, to make an informed decision and select the best electronic stethoscope for your program.


When thinking about quantitative testing related to electronic stethoscopes, you need to be thinking about testing to obtain objective factual data. Qualitative/subjective tests designed to evaluate sound quality are very hard to do because the results are about as variable as each evaluator. Some of the variables are the users’ hearing ability, their diagnostic skills and their neurological functioning related to how they process sound in their brain. This makes you realize it would be much more ideal to be able to design some quantitative/objective tests to evaluate sound quality as well. The best testing design for electronic stethoscope testing is a comprehensive combination of both qualitative and quantitative tests.

The concept of sound quality is hard to evaluate, but certain components can be broken out and evaluated with some reliability and a good design. Purely lab based quantitative studies that utilize artificially generated waveforms do not represent true heart and lung sounds, and may introduce artificial sound elements. While the results might be more consistent and repeatable, the results might not be as close to human sounds because the elements of resonance and sound transmission through tissue will be lacking. Obtaining exact replications of internal human sounds is very difficult in the laboratory. Also, Testing of the audio signals does not take into account the intricacies and complexities of the human ear, and how humans perceive human sounds. While these tests may not always yield specifically clinically relevant information, the data gathered can help to provide a more robust picture of the overall performance of the stethoscope. All of these variables associated with quantitative testing show the importance of having good test designs and having an equal pairing of quantitative test designs with robust qualitative test designs as discussed above.

When it comes down to it, the quantitative tests that you are going to perform on the electronic stethoscopes might have something to do with sound, but will also be related to electricity, engineering, and circuitry components. Some of the aspects that you might want to design tests for would be related to:

  • Frequency Response
  • Amplification
  • Noise Reduction
  • LEQ

Self vs. Experienced 3rd Party

Quantitative testing is often very labor intensive and can be cost prohibitive, so you depending on your budgeting resources and what you intend to obtain from testing, you may want to consider a third party to complete the testing for you. There are multiple independent engineering firms that are willing to work with your program to design and complete quantitative testing measures. It is hard to technically know what you want to know, but essential to have an informed idea before approaching these firms is the best plan. Also, knowing your budget and being prepared to get multiple quotes before making a decision is a very wise approach to third party testing. If you desire to complete the testing yourself, again it is very important to have a specific plan in place and know exactly what you plan on determining by conducting the testing. This will most certainly require in-house engineering knowledge and a significant investment in equipment. If you are lucky enough to have a plan and have figured out exactly what you equipment you need for your testing, you may be able to work with the equipment vendors to try and borrow some equipment or do a lease to decrease the cost involved. Also, don’t rule out the possibility of partnering with a local engineering or biomedical engineering educational program on the project.


Selecting an electronic stethoscope that best meets the needs of your Telehealth program can be a labor intensive process, but with some planning up front can be well worth it in the end. Selecting a technology that is most appropriate to your program’s needs and desires, which can be supported and will best meet the clinicians’ needs, can be invaluable to the success of a program. One does not have to ponder far to think of the alternatives. Selecting a technology that is not the best for your program can lead to unnecessary cost in purchasing the wrong equipment, technology that is not supported by the clinicians expected to use it, and worse yet equipment that is never utilized and patients or customers that are not served.

We try to present many options because each program will have a unique set of needs when considering an electronic stethoscope. The technology assessment that each program will be able to complete is also very closely connected to the budgetary possibilities of the program. This process will also remain closely tied to your program development objectives and deployment and support plan. We encourage you to utilize your industry connections, communicate with your peers, utilize available resources, and form partnerships when at all possible to make technology assessment a reality for your program. Hopefully your program sees the success where this process will become cyclical, and the more times you complete this process the better you will get at it. Remember to be a resource to others in your field as you complete more and more technology assessments and learn valuable lessons along the way.

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