The medical profession is closely associated with stethoscopes. For example, googling ‘doctor’ results in images of stethoscopes, or doctors wearing stethoscopes. A 2012 study showed that physicians are much more likely to be regarded as ‘trustworthy’ if they have a stethoscope with them [1]. However, with rapid technological advancements and the miniaturization of sensors and electronics, stethoscopes might find their way into museums in the near future.The Evolution of Stethoscopes
The concept of a stethoscope was first realized in 1816 by René Théophile Hyacinthe Laënnec. He noticed children amplified sounds by playing with hollow sticks, and this observation gave him the idea of using a tube to auscultate patients. His first stethoscope was a simple paper tube used to listen to heartbeats, but he experimented with different materials and eventually settled on a wooden tube with a plug on the end. Unfortunately, this tube only had listening access for one ear.
By 1843, stethoscopes were upgraded and doctors could now listen with both ears. By 1945, the modern design of the stethoscope was finalized using thin tubing, rubber earpieces, and more features. By 1956, stethoscopes were being made with modern materials such as PVC or latex. By 2019, noise cancellation technology, and microphones had been successfully adapted into stethoscopes [2]. With the new technology also came a price increase. A stethoscope’s cost on average is $100, but there is a range of prices. Disposable ones are as little as $5, good stethoscopes are $75, and high-end gadgetry can push the cost to $300 [3, 4].
From the 1970s onward, electronics have revolutionized medicine, from being able to request medications remotely to genetic sequencing. Even the stethoscope has received upgrades. Recently, Eko [5] designed an add-on to a stethoscope that can detect abnormal pulmonary and heart conditions, has noise-canceling technology and links to Bluetooth. Other possible innovations (which are not widely used) include on-the-spot AI analysis, connecting ECG probes to a stethoscope, and replacing the stethoscope with a listening device and wireless earbuds. Companies, such as Thinklabs [6] are already working on such alterations. These innovations to the stethoscope would allow doctors to obtain additional diagnostic information. Adding ECG probes can also alert to abnormal electrical activity in the heart, and allow better diagnoses for arrhythmia. An example of mobile ECG technology approved by the FDA (which could be integrated into future stethoscopes) is in the KardiaMobile offered by AliveCor [7].
Limitations of Today’s Stethoscopes
The stethoscope works by ‘listening’ to the body sounds when its diaphragm is pressed against the skin. Applying more pressure on the diaphragm would enable the user to hear higher frequencies.[8]. In this case, low-frequency sounds include Korotkoff sounds, arrhythmias, while high-frequency sounds include airflow through the lungs [9].
However, stethoscopes are not without inherent limitations. The stethoscope may indicate if the heart or lungs are diseased, but doesn’t provide any further information for a conclusive diagnosis [10]. Stethoscopes also can’t facilitate virtual diagnosis, which is growing especially important due to the ongoing COVID-19 pandemic. To receive an interpretation from a stethoscope, a doctor has to be physically present and close to the patient, which is a hindrance when doctors are placed in unstable situations or where patients are immobile or in remote locations. Even with the enhancements stated earlier, some of the above limitations would still apply.
Solutions
There are different paths for improvements. One path forward could be to incrementally enhance the stethoscope. Companies such as Eko, Thinklabs, and StethoMe have already commenced such enhancements. These enhancements would slowly transition towards replacing the stethoscope entirely. For such a change to occur, the replacement must have the functionalities of a modern stethoscope, eliminate its limitations, and incorporate additional features.
There have been proposals to replace stethoscopes with handheld ultrasound devices [11], which give images of the internal human body. A stethoscope allows doctors only to hear the sound, while an ultrasound allows doctors to “see the sound” [12]. It poses almost no health risk because it does not use any form of radiation. Instead, it uses high-frequency sound waves between 2-18 megahertz [13]. Although lower frequency sound waves can penetrate farther into the body, they produce blurrier images. Higher frequency sound waves produce good quality images but get absorbed by tissues more easily. Since ultrasounds cannot penetrate through the bone, they are not generally used for brain imaging. An ultrasound can be used to diagnose conditions in the lungs, liver, gallbladder, spleen, pancreas, kidneys, bladder, uterus, ovaries, eyes, thyroid, and testicles [14]. Doppler ultrasounds can even determine the velocity of blood flow thereby enabling detection of clots, heart disease, and other cardiovascular conditions [15]. Doppler ultrasounds work by measuring the magnitude of ‘red’ or ‘blue’ (Doppler) shift of echoed frequencies to determine the velocity of the target [16]. The figure below demonstrates a Doppler ultrasound showing deep vein thrombosis of the subsartorial vein.
The bulky ultrasound machines driven into cramped hospital wards are transitioning to handheld devices whose images can be displayed on cellphones and laptops thanks to advancements and miniaturization of electronics [17]. Handheld ultrasounds can diagnose a larger variety of conditions than stethoscopes can [18]. For example, stethoscopes cannot detect small tumors in the lungs [19], while ultrasounds are able to locate them, as shown in the figure below.
Ultrasounds are more sensitive (97%) & specific (98%) in diagnosing heart failure than stethoscopes (46% and 67%, respectively) [20]. Imaging enables better medical interpretation than simply listening to sounds in a patient’s body. In a study, medical students with 18 hours of cardiac ultrasound training and board-certified cardiologists diagnosed 61 patients with clinically significant cardiac disease. The medical students correctly identified 75% of pathologies, compared to just 49% for the cardiologists [21]. Stethoscopes, on the other hand, are useful for quickly diagnosing conditions that produce sound in a patient’s body, like abnormal heart valves, pneumonia, arrhythmia, heart failure, bronchitis, COPD, or asthma [22, 23, 24]. Stethoscopes are still crucial in pediatrics [25].
During an ultrasound, a probe is pressed into the skin. An ultrasound gel may be applied beforehand to ensure there are no trapped air bubbles between the probe and skin [27]. The probe is connected to a computer, which can display images or real-time video [28]. Handheld ultrasound devices can also be connected to a tablet or cellphone instead of a computer, so they could be almost as portable as stethoscopes. Two major developments need to converge before handheld point-of-care ultrasound is likely to replace the stethoscope. The first is technological: these devices will need to be even smaller, less expensive, more ergonomic, and gain additional functionality, such as the ability to amplify sounds. Secondly, the future generation of physicians will need to be trained to adopt this technology, just as many generations have used the stethoscope. That development will require the medical education community to incorporate this technology throughout the curriculum, and this is already underway at the Icahn School of medicine at Mt. Sinai, Harvard Medical School, UC Irvine, and the University of South Carolina [29].
Even with the previously mentioned developments in place, the point of care and data gathering for a medical diagnosis still remain at the doctor’s office. The point of data gathering could be transferred to the patient by incorporating the above technologies using advanced sensors or transducers which could also enable continuous monitoring of a patient’s biometrics. The patient’s data could then be transferred to a point of diagnosis. One possible device to facilitate such continuous monitoring is a skin-tight vest (a SHIL vest) which contains embedded sensors measuring various biometrics. These sensor arrays could be controlled by a low-powered microcontroller or a microprocessor. Some of these sensors could be MEMS (Micro-Electro-Mechanical Structures) based since they are advantageous in their low power consumption, small size, programmable sensitivity, and good signal-to-noise (SNR) ratio [30]. Currently, commercially available MEMS microphones are used widely in cellphones, and recent advances have enabled using ultrasound for fingerprint detection [31, 32]. Although in its infancy, it is encouraging to note that research is already ongoing to modify MEMS structures for medical-grade ultrasound [33]. It may take some time for commercial availability. Another possible sensor that could be used in the vest would be to borrow the concept of a Holter monitor for continuous monitoring of cardiac electrical activity [34]. Other sensors could be added to this futuristic SHIL vest for the ultimate goal of a ‘complete’ biometric movie.
In summary, stethoscopes are slowly giving way to handheld ultrasounds [35]. While stethoscopes have saved many lives, handheld ultrasounds have been shown to have greater diagnostic accuracy than stethoscopes. For ultrasound devices to become available as a stethoscope replacement, technological advances, as well as a widespread training curriculum, must occur. These ultrasounds would eventually then become commonplace in a doctor’s office, and enable greater accuracy of diagnoses. Even then, handheld ultrasounds do not grant the ability to continuously monitor a patient. However, this ability could be achieved by embedding ultrasound transducers along with other sensors into the SHIL vest of the future for a more complete biometric profile.
References:
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Shourish Mukherjee is a junior at Monta Vista High School in Cupertino, California. He is fascinated with biology because of how applicable the concepts are to our everyday lives and because there is still so much to discover. As a biology enthusiast wanting to pursue a career in medicine, Shourish was excited to participate in a summer workshop at the Stanford Healthcare Innovation Lab, which allowed him to “get a glimpse into the future of medicine.”
Outside of being passionate about biology, Shourish plays the trumpet. He hopes to try llapingachos (stuffed potato patties) from Ecuador in the future. You can also check out his YouTube channel here.
