Stethoscopes - Electronic, Cardiology, Nurse, Doctor, Digital, Pediatric
Stethoscopes are diagnostic devices doctors and nurses use to assess the health of patients. In a hospital or clinic environment, it is the most frequently used medical device. In fact, its use is so frequent that health practitioners wear these devices around their necks all day for easy accessibility. These instruments are a healthcare symbol. A photograph of a doctor or nurse is not complete without the device around their neck. Its utility is to listen to the heart, lungs, and digestive system to determine if there are any abnormalities. Stethoscopes are the first line of patient screening devices used in healthcare.
Cardiovascular disease (CVD) is recognized as the leading cause of mortality in countries throughout the world, and thus, timely detection, treatment, and prevention are the cornerstone of the comprehensive care that a physician provides to his/her patients.1
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With multiple sophisticated advancements made in medicine, which aid in clinical diagnosis and management, none of the modalities compare to the simplicity and vitality of a stethoscope.2
The stethoscope is one of the most simple and practical diagnostic tools used in medicine. Presently, two different types of stethoscopes are available on the market: acoustic and electronic. The main advantages of acoustic stethoscopes are their robustness and ergonomic designs. However, they are not ideal because they attenuate sound transmission proportional to frequency, their frequency response shows maxima and minima at very specific frequencies due to tubular resonance effects, and differences in the transmission properties are observed between different models. Because the intensity of heart sounds and murmurs is generally faint with some sounds below the threshold of hearing, amplification of the acoustic signal with a more uniform frequency response has been introduced in electronic stethoscopes to solve the main limitations of acoustic stethoscopes. However, it appears that these advantages are overcome by the sensitivity of the electronic stethoscope to manipulation artifacts, and electronic and ambient noises. Also, they do not take into consideration the sensitivity of the human ear, which varies significantly as a function of frequency. Consequently, the acoustic stethoscope is still the one mostly used today, even if several sophisticated designs have been patented for the construction of electronic stethoscopes during the last 20 years.3
Anatomy of a Stethoscope
What are the parts of a stethoscope?
Ear tips – soft rubber or silicone stubs that go on the end of the binaural and inserted into your ears. They offer a snug fit and a good seal to keep out ambient noise.
Tubing – soft, flexible hose that connects the chestpiece to the binaural. The tubing transmits the sound picked up by the chestpiece to your ears. Dual-lumen tubing is the best choice since it provides two sound paths within the same tube and does not produce the rubbing noise often found in dual-tube devices.
Headset – refers to the section of the stethoscope that includes the binaural, binaural spring, sound conductor, and ear tips.
Chestpiece – contains the sound collection device for auscultation that houses the diaphragm(s), bell, and the drum. This device collects acoustical sound from the body for diagnosis.
Diaphragm – located on the chest piece is larger than the bell and captures high-frequency sounds.
Bell – located on the chestpiece that captures low-frequency sounds for heart assessments. The bell, located on the smaller side of the chestpiece, is a prominent addition on most acoustic stethoscopes. One medical study found the bell side of the stethoscope just as effective as the diaphragm side in measuring blood pressure. "Both sides of the acoustic stethoscope give similar results in the measurement of office blood pressure and either side can be used in the reliable measurement of blood pressure."4
Sound Conductor – is the splitting section of the tubing that transitions sound from a single tube coming from the chestpiece (on non-) into the binaural tubing leading to each ear. On the Sprague Rappaport designs, two separate tubes run from the chestpiece to the binaural.
Binaural – is the main section of the stethoscope headset that connects to the tubing from the acoustic valve stem and connects to the ear tips. The binaural comes with a spring that holds the device in place on the user’s head and keeps the ear tips in place during diagnostic exams.
Acoustic Valve Stem – transitions sound waves from the chestpiece to the tubing. Some manufacturers insert a valve into the stem to open or close a channel for double-headed chestpieces. This valve allows the user to control which side of the dual-headpiece transmits sound.
Single head chestpieces have one diaphragm to listen to heart and lung sounds. The sound collection end is circular with a flat surface. These devices collect a wide frequency of sounds, allowing the user to discern abnormalities.
Dual head stethoscopes employ a two-head diaphragm design, one opposite the other. Often, the smaller side of the chestpiece, called the bell, collects low-frequency sounds from the circulatory system. The larger side, called the diaphragm, recieves high-frequency sounds from the respiratory system. These double-sided stethoscopes are available in many different versions and styles.
A tunable diaphragm on Littmann products is a feature that helps tune in frequencies that are helpful in diagnosis. These tunable diaphragms work by the amount of pressure applied to the skin. Firm pressure with a tunable chestpiece against the skin restricts the diaphragm membrane. The pressure blocks low-frequency sound to allow you to hear higher-frequency sounds more clearly. Light pressure on the chestpiece against the skin suspends the diaphragm membrane allowing the resonation of low-frequency sounds.
Turnable chestpieces allow you to easily tune to the frequency bands just by the amount of pressure you apply to the chestpiece. By using firm pressure against the skin, you can hear the high-frequency sounds or the respiratory system. With light pressure, you can listen to the low-frequency sounds from the heart. The graphic above from Littmann portrays the use of a Tunable Stethoscope.
The Sprague Rappaport chestpiece has a dual-output acoustic valve stem that attaches to separate tubing, connecting to the binaural. Users of this device can easily identify the active sound channel because of the separated channels. "One study of this device found that "Rappaport and Sprague demonstrated that the acoustic efficiency of a stethoscope increases as the length of the tubing decreases...."5
There are four types of stethoscopes for sale—acoustic, electronic, digital, and ultrasound. An Acoustic Stethoscope provides a means to listen to the internal sounds of the body. A small disc shape resonator connects to hollow tubing that splits with two ear tips on the other end. The listener places the resonator against the skin near the part of the body that is under examination. The resonator captures the sound and transmits it to the earbuds.
An Electronic Stethoscope amplifies sounds by converting acoustic sounds into louder audio signals. These devices selectively amplify certain frequency waves associated with the heart or lung functions. They also diminish noise to help the user focus on the right sounds to detect problems. This ambient noise reduction aids doctors and nurses to distinguish abnormal functioning of heart valves and air exchange in the lungs. On study involving extreme ambient noise showed that electronic devices could help users with diagnostic tests.
The ability to auscultate during air medical transport is compromised by high ambient noise levels. The aim of this study was to assess the capabilities of a traditional and an amplified stethoscope (which is expected to reduce background and ambient noise) to assess heart and breath sounds during medical transport in a Falcon 50 plane.... Practicians in Falcon 50 are more able to hear cardiac sounds with an amplified than with a traditional stethoscope, whereas there is no significant difference concerning breath sounds auscultation.6
In this study, we conducted real-ear measurements of heart sounds with one acoustic and two electronic stethoscopes. The results indicated that electronic stethoscopes can offer some advantage over acoustic stethoscopes in increasing the intensity of cardiovascular sounds reaching the user's ears. However, even with the electronic stethoscopes, some of the low-frequency acoustic energy that potentially contains diagnostic information remained below the threshold of audibility.... Our solution to this and other shortcomings of conventional stethoscopes was to develop a PC-based stethoscope that transforms the heart sounds upward to frequencies where the sensitivity of the ear is greater and the dynamic range is broader.7
Digital Stethoscopes are becoming popular because of the additional functions they bring to exams. They also offer the ability to sync with smartphones, store data, and graph findings. Some offer the convenience of cordless functioning with Bluetooth technology. Instead of changing the chestpiece to amplify sound frequencies, all you have to do is press a button.
The emergence of a digital stethoscope has only made this historic tool even more refined. The physician can now hear heart and lung sounds with more accuracy and precision. Through this advancement, there is now potential to auscultate for obstructive coronary artery disease, and other bruits and obstructive vascular diseases such as carotid artery stenosis, and examine multiple frequencies that may comprise pulmonary auscultation. Furthermore, there is also potential to drastically impact patient care by appreciating disease processes earlier and to prevent fatal outcome. Medical care can also be provided in areas that are underserved or which do not have medical facilities by applying digital stethoscope technology to telemedicine to allow remote assessment.8
Another device still in the introductory phase is the ultrasound stethoscope. Instead of merely hearing sounds, doctors with this instrument can see scans of the area under examination. The GE Vscan is the most widely known model, offering a hand-held device that transforms a physical exam into data collection for improved assessments and targeted treatments. Several medical studies proclaim that these devices will ultimately replace the classic stethoscope. Ultrasound adds additional advantages to stethoscopes. For example, ultrasound can identify "hypertrophic cardiomyopathy, pericardial effusion, and abnormalities of valves."9 One study found that "diagnostic sonography truly is the next stethoscope."10
Many small devices, even of pocket size, are now being developed with increasing capabilities and offer ease of use similar to the standard stethoscope (the echocardiograph in your pocket!). These devices will undoubtedly revolutionize our physical cardiac examination.11
Pocket-size imaging devices can be very useful for detecting subclinical cardiac abnormalities in asymptomatic or pauci-symptomatic outpatients.112
As newer generations of clinicians incorporate it as a part of their basic bedside examination and as technological advances make ultrasound less and less prohibitive in terms of cost and size, we argue its time to augment the archaic tools of past centuries and embrace ultrasound as the visual stethoscope of the 21st century.13
[O]ver the past decade machines have become cheaper, more reliable, and highly portable with the result that general practitioners and specialists are increasingly using them to make on the spot diagnoses of many conditions without having to consult an imaging expert.14
How to Select the Best Stethoscopes
Selecting the best stethoscope for your needs first starts with identifying who you will be diagnosing (the patients). Next is to determine the level of quality and accuracy required (technology). Last is the position of the user (student, nurse, doctor, etc.). By identifying these criteria, you will be in a better position to make the best product choice. The continuum above displays the breakdown of the stethoscope types and selection criteria. Below is a brief discussion of the categories and the selection criteria within each group to help you narrow down your specific stethoscope needs.
The size of the patient plays a significant role in this style or characteristic. The smaller the patient, the smaller the diaphragm to isolate the sounds needed for a correct assessment. Device adaptability may be necessary, particularly if only a single instrument will do the assessments. An array of different size chestpieces may help diagnose diverse types of patients. If pets are the patients, a suitable chestpiece will be necessary. For patients with faint sounds, amplification is necessary. Cold metal contact with the skin of sensitive patients may require accommodation. Younger patients may need customized devices to deter fear. A picture of a cute animal on the chestpiece or pattern decorated tubing can help persuade a pediatric patient that this medical device will not harm them. Below is a list of essential selection criteria for patient-oriented characteristics.
- Sound Amplification
- Non-Chill Rim
- Diaphragm Size
- Customization for Patient Acceptance
Neonatal diagnostic tools incorporate a smaller diaphragm and bell to distinguish the appropriate sounds.
The typical design of infant devices includes high acoustic sensitivity, non-chill rims and diaphragms, a floating diaphragm, and an open bell. These devices offer monitoring, diagnosis, and assessment tools for young patients. Some models come with interchangeable chestpieces to assess even smaller patients.
These devices have a 3.3 cm floating diaphragm and an open bell. The rim is non-chill to help keep pediatric patients calm and comfortable. Children are often noisy and restless, which causes additional noise and distractions when making a diagnosis. These devices have greater acoustical clarity to identify sounds. Users also look for durability, a dual-sided chestpiece, and color choices.
Some may wonder why veterinary devices locate under patients instead of users. The design of veterinary scopes focuses on patient size and fur or hide, rather than on the doctor. These scopes are similar to the pediatric versions. The design is adaptable to smaller patients that require more isolated sounds. The tubing is usually longer by at least 5 inches to accommodate working with the animal under assessment. If the animal is tiny, such as a bird or lizard, an infant or neonatal stethoscope may be a better choice. The chestpiece is an essential item for veterinary diagnostics to form a seal to the haircoat or feathers. Note that veterinary models fall under the patient-oriented category instead of user-oriented devices because the selection criteria derive from the patients served and not the user.
Technology improvements add more capabilities and ease of operation. Instead of having to switch chestpieces from one patient to another, it is easier to simply activate a button. The enhancement of certain sound frequencies while diminishing distracting frequencies is a big advantage. More detailed data leads to better diagnosis. However, there can be some tradeoffs. Some advanced technologies require additional training to read and interpret new data. Storing, retrieving, and organizing data takes more time. Physicians accustomed to a quick sound check on their patient may not readily accept the additional training and time it takes to use new tools. The design of these types of screening tools targets the following selection criteria:
- Sound Quality
- Construction Materials
- Additional Functions
Users of these devices interested in bringing technology into their assessments will be looking for adjustable acoustics to screen out unwanted frequencies. They want higher sound quality and amplification. Instruments that detect faint sounds with high resonance and a host of added electronic functions like data storage, data transmission, Bluetooth technology, detection AI algorithms, and visual displays of audio waveforms help health practitioners accurately diagnose patients. The use of durable, high-quality materials in the construction of diagnostic tools is another important selection criteria. Stainless steel is the default material for quality and durable devices.
For cardiology, a tool that offers superior low-frequency acoustic performance is critical. The cardiology devices allow for an easier differentiation of the sounds associated with heart valves. These instruments come with enhanced, thicker tubing to reduce distracting noise. The tubing is shorter to improve the transmission of sounds. This assessment tool becomes the doctor’s most important tool during the initial diagnosis.
Sprague Rappaport Stethoscopes
This type uses a separate tube from the chestpiece to each ear tip. The chestpiece is double-barrelled to produce better sound quality. It offers the utility of detecting faint heart sounds.
The heaviest part of these medical tools is the chestpiece, stem, and binaural. Usually, these three parts are metal-based. Construction for durability takes place with stainless steel, while construction for lightweight materials may include chrome-plated brass or plastic. When less weight is essential, most manufacturers turn to aluminum. Some chestpieces outweigh the entire weight of a lightweight model. For instance, the Littman Cardiology STC chestpiece weighs 95 grams, while the Littmann Lightweight II SE weighs 90 grams. Many healthcare practitioners wear their monitoring devices around their neck all day, so many choose a lightweight model for less stress.
These diagnostic tools offer noise cancellation of sounds that are unrelated to the acoustic sounds of the heart and lungs. This noise cancellation takes place by softening unrelated frequencies. It improves listening performance by blocking wavelengths that are unrelated to the sounds physicians and nurses seek. Digital options look very similar to acoustic models but provide advanced functionality. Some digital models include the opportunity to record and playback, as well as connect to a computer to chart results visually. If an LCD screen is available, it may display the level of amplification, remaining battery life, and current heart rate.
Still, under development and acceptance by healthcare practitioners, these diagnostic tools are a significant step forward in technology and diagnosis. The main hurdle for healthcare practitioners is training and experience in interpreting the diagnostic screens. Another deterrent to acceptance is the additional time required to set up these devices for scanning.
These devices are for single patient use. Single patient applications occur when cross-contamination between patients may become an issue. They are essential for patient cases requiring isolation, HIV infection, viral infection, and heavy fluid cases. The construction of disposable models consists of aluminum, plastic, polyvinyl chloride (PVC), or Acrylonitrile Butadiene Styrene (ABS). These instruments are inexpensive and often sold for less than $10.
For user-oriented considerations, stethoscope users look at four key elements to determine which instrument they will choose. Sound amplification is particularly crucial for medical practitioners that have hearing loss. Raises the decibels of the sound helps many with difficulty hearing.
- Sound Amplification
- Noise Reduction
- Construction and Durability
- Customization for Prestige or Personality
Doctor’s have a wide range of selection criteria based on the area of medicine they practice, their technical savvy, and their need for prestige. Cost is not a concern.
Durability is the primary concern for nurses. Hustling from room to room and from patient to patient takes its toll. Nurses want their instruments to be able to withstand the rigors of their job. Nurses have many routines and basic healthcare functions that they provide throughout their busy schedules. The device will need to offer sufficient amplification to meet their hearing needs and meet diagnostic objectives. Lastly, the cost should not be outside of their budget.
Cost is a primary concern of students. They need an instrument that will perform well enough to meet their course objectives and still fall in a limited budget.
Students transitioning from a school environment to an intern position often find themselves upgrading their medical instruments to meet the new challenges they face, including the need for increased diagnostic accuracy. They may also perceive higher quality and better functioning instruments as a badge of arriving.
Also known as training stethoscopes, these devices have one or more additional headsets connected by tubing to the chestpiece. These redundant headsets allow the teacher to listen to the same sounds as the student(s), allowing the instructor to elaborate on the sounds they are hearing. Typically these devices have adjustable tuning and longer tubing.
Many doctors and nurses like to customize their instruments with color, an ID tag, or interchangeable chestpieces. Color choices range from standard black to gold plating to leopard skin. Choosing a specific color that is somewhat unique to you is a big plus for many healthcare providers. Some will personalize their diagnostic tools with imprinting their name on the tubing, while others add an ID tag with their name and position. Custom choices add additional costs to your selection, but it allows you to personalize your instrument. Some models also allow you to change the chestpiece based upon the needs of the patient you are serving. The chestpiece slides off the tubing and another chestpiece inserts in its place.
The Top Stethoscope Brands
Medical studies for stethoscope brands drew the following conclusions:
"This study compared six best selling stethoscopes, which include the Littmann Classic II, Littmann Cardiology II, Littmann Master Cardiology, Hewlett‐Packard Rappaport‐Sprague, Tycos Harvey Triple Head, and Allen Medical Series 5A RPS Binaural.... Tycos Harvey Triple Head ribbed diaphragm attenuated sound transmission to a significantly greater extent than the other diaphragms.... [T]he Littmann Cardiology II, bell and diaphragm, appears to possess the best overall performance."15
How are Stethoscopes Used?
Stethoscopes are diagnostic instruments used to auscultate for sounds from the body. The primary application is to listen to the heart, lungs, and intestines to detect abnormal functioning. The chestpiece containing the diaphragm collects sound from the body and transmits the sound through tubing to the user’s ears. Certain parts of the body provide the best locations for auscultation. These auscultation sites display below.
Auscultation Sites For the Heart
The four traditional heart valve auscultation areas display above on the left. The expanded auscultatory heart monitoring sites show on the right. These are not the actual anatomical locations of the valves, but where they are heard the best since sounds project in the direction of the blood flow.
Heart Auscultation Sites to Detect Heart Valve Functioning
- Aortic – second right intercostal space
- Pulmonic - second left intercostal space
- Tricuspid – fifth right intercostal space, left sternal border
- Mitral – fifth left intercostal space over heart apex16 17 18
Auscultation Sites For the Lungs
Heart and Lung Sound Frequencies
Low heart sounds (presystolic and some systolic murmurs; basal and mitral diastolic murmurs; auricular and first, second, and third heart sounds; gallop rhythms)
Medium and high heart sounds (systolic and
Breath sounds heard in trachea, bronchi,
Fetal heart sounds
Source: Dawson, J. B. (1964). Practitioner, 193, 315.
"The normal classification of lung sounds in frequency bands involves low (100 to 300 Hz)-, middle (300 to 600 Hz)-, and high (600 to 1,200 Hz)- frequency bands (10). In the range of lower frequencies (< 100 Hz), heart and muscle sound overlap. Correct assessment of lung sounds requires filtering out the lower frequency sounds associated with the heart."20
Auscultation Sites For the Intestines
Use the bell side of the chestpiece to listen to the intestines
- Aortic - heard in the epigastrium for signs of abdominal aortic aneurysm
- Renal arteries – listen to sites located in each upper quadrant for symptoms of renal artery stenosis, which is a potentially treatable cause of hypertension.
- Iliac/femoral arteries – sounds emanate from the lower quadrants to detect signs of peripheral atherosclerosis
Some cautions about stethoscope use
The Korotkoff sounds were heard better with the bell of the stethoscope placed over the brachial artery pulse (BB) than with the diaphragm placed over the cubital fossa (DC). The former combination (BB) gave significantly higher blood pressure estimates for systolic blood pressure and fourth phase diastolic blood pressure than the latter combination (DC)20
All results showed a tendency toward higher [blood pressure] BP values with the bell in comparison with the diaphragm, and this was statistically significant for [diastolic blood pressure] DBP…. All results showed a tendency toward higher BP values with the short tube in comparison with the standard length tube, and this was statistically significant for [systolic blood pressure] SBP.21
MDF Stethoscope Review Video (3:16 minutes)
MDF Designed For Life Video (0:24 minutes)
Littmann Review Video (1:24 minutes)
How to Choose Video (0:52 minutes)
Patient Exams Video (2:15 minutes)
Care and Use Video (2:05 minutes)
American Diagnostic ADC Adscope Review Video (0:44 minutes)