数字听诊器 — 听诊新时代

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Introduction

auscultation of sound phenomena accompanying the functioning of internal organs is one of the most important stages of the objective examination of a patient. Indirect auscultation has been used for almost 200 years, since the invention of the first stethoscope by Laennec in 1816. The funnel with a membrane he introduced made it possible to amplify the volume of sound signals. In 1940, Rappaport and Sprague improved the design of the stethoscope by proposing a dual-head configuration combining a bell and a diaphragm [1]. For a long time, the stethoscope remained unchanged in form.

The simplicity of use, cost-effectiveness, and wide availability make the classical stethoscope a popular tool among healthcare professionals [2]. It should be noted that, despite the simplicity and reliability of the classical auscultation method, it has a number of limitations. First and foremost are the distortions of transmitted sound signals caused by the acoustic properties of the stethoscope head, the flexibility of the tubing walls, and individual patient characteristics (chest wall thickness). In addition, sound perception is subjective and depends on the age and experience of the examiner [3, 4]. Finally, classical auscultation does not allow other specialists to analyze the detected sounds without direct patient presence, and the resulting data cannot be stored or reviewed [5]. This creates challenges in consulting patients using telemedicine technologies, as well as in remote monitoring and interpretation of physical examination findings in controversial clinical situations or legal proceedings [6].

The COVID-19 pandemic also highlighted the need to develop a new approach to auscultation using stethoscopes that can provide remote monitoring and minimize the risk of infection for healthcare workers during patient examination [7].

Electronic Stethoscope

New opportunities for auscultation emerged with the development of the electronic stethoscope. An electronic stethoscope consists of three modules providing for data acquisition, preprocessing, and signal transformation. The data acquisition module performs filtering, buffering, and amplification of the auscultated sounds, and converts the acoustic signal into a digital one. The preprocessing module filters the signal and removes artifacts. The signal transformation module then clusters the data for clinical decision-making [8].

Several types of electronic stethoscope sensors are distinguished based on the mechanism used to convert sound into an analog electrical signal.

Dual-diaphragm sensor: sound vibrations are captured by the stethoscope diaphragm and transmitted to a diaphragm within the microphone. However, the two diaphragms, separated by an air channel, may lead to excessive amplification of ambient noise and inaccurate transmission of the sound signal.

Piezoelectric sensor: sounds captured by the diaphragm alter the structure of a crystalline substance, converting the sound signal into an electrical signal.

Microelectromechanical system. The diaphragm of the stethoscope is located in a nominal capacitance field, which changes in accordance with the pressure of the sound wave. This change in capacitance converts the sound signal into an electrical one [9, 10].

Environmental noise suppression is also a critical function of the electronic stethoscope. Cain et al. [11] tested electronic stethoscopes in simulated helicopter noise conditions at 70–100 dB to determine the noise threshold for auscultation of heart and lung sounds. The noise threshold was 85 dB for heart tones and 75–80 dB for breath sounds. This implies the need for a signal-to-noise ratio improvement of at least 30 dB, which can be achieved by enhanced noise suppression. This would allow electronic stethoscopes to be used during natural disasters and patient transportation. This problem has been addressed using a digital filter capable of isolating the desired frequency range from the signal [1, 2]. The sound phenomena of internal organ function span different frequency ranges. Existing digital stethoscopes offer adjustable frequency modes for optimal auscultation of specific sounds, such as breath or heart sounds. For instance, the Welch Allyn Elite™ electronic stethoscope (Welch Allyn, USA) uses a 20–420 Hz frequency mode for heart auscultation and a 350–1900 Hz mode for lung auscultation. Thus, electronic stethoscopes enhance both sound quality and volume. The 3M™ Littmann® CORE stethoscope (3M, USA) with a piezoelectric sensor amplifies sound up to 40 times, whereas the Thinklabs One™ stethoscope (Thinklabs, USA) with a MEMS sensor amplifies sound up to 100 times [12, 13].

Undoubtedly, the electronic stethoscope increases the diagnostic value of auscultation [14]. In 2016, Azimpour et al. [15] investigated the potential of using an electronic stethoscope for acoustic diagnosis of hemodynamically significant (>50%) coronary artery stenosis by detecting intracoronary murmurs caused by turbulent blood flow within the artery in the presence of such stenosis. The coronary anatomy, as well as the presence and severity of atherosclerotic lesions, were verified using coronary angiography. The sensitivity and specificity of coronary artery stenosis detection by auscultation using an electronic stethoscope were 70% and 80%, respectively (p < 0.001). Several electronic auscultation test systems have been proposed for detection of obstructive coronary artery disease: CSA SonoMedica model 3.0™ (SonoMedica, USA), CADence Ironman™ (AUM Cardiovascular, USA), and CADScor System™ (Acarix AB, Sweden). In experimental studies, these test systems showed statistically significant detection of obstructive coronary artery lesions with a sensitivity of 81%–89.5% and specificity of 53%–83% [16].

In general, electronic stethoscope use expands auscultation capabilities by enhancing sound amplification and suppressing background noise.

Digital Stethoscope

The vast majority of modern electronic stethoscopes are equipped with a function to record and transmit sound to a computer or smartphone. By instructing the patient on how to position the stethoscope head, the physician can remotely auscultate and analyze the sounds. This enables remote monitoring of patients under quarantine (e.g., due to COVID-19) or in hard-to-reach areas, as well as the simultaneous interpretation of auscultatory sounds by multiple specialists to improve the quality of telemedicine consultations [17].

Another advantage of the digitalization of auscultation is the improved quality of medical student training. Auscultation simulators reproduce pre-recorded sounds from patients with various heart and lung diseases, allowing an entire audience to listen to the same recording [18]. The ability to display signals graphically as a spectrogram makes auscultation training more visual and facilitates the identification of spectrographic “patterns” associated with specific diseases [19].

The digitization of data has also enabled the use of artificial intelligence (AI) algorithms for sound analysis, opening new possibilities for auscultation. The most common method for sound processing is the Fourier transform, which analyzes the frequency components of the signal. A machine learning algorithm based on an artificial neural network can further process obtained information and correlate different frequencies with specific auscultatory findings. Gurung et al. [20] conducted a meta-analysis of studies to assess the predictive potential of combining digital lung auscultation with computational data analysis algorithms. The sensitivity and specificity of detecting pathological lung sounds using computational algorithms were 85% and 80%, respectively.

The next step in the development of digital auscultation was the ability not only to detect pathological sounds produced by internal organs, but also to diagnose diseases using computational algorithms. For example, Kaddoura et al. [21] analyzed the potential for diagnosing pulmonary hypertension based on heart and lung auscultation. Auscultatory findings obtained with a digital stethoscope were compared between healthy individuals and patients with pulmonary hypertension. The computer algorithm diagnosed pulmonary hypertension based on auscultation data in 74% of cases.

Thus, the modern digital stethoscope offers the following advantages [22]:

High-quality sound signals. Amplification of sounds produced by internal organs and ambient noise suppression facilitate auscultation in high-noise environments, such as in the field, in emergency zones, overcrowded hospital wards, and during patient transportation.

Remote patient examination. The absence of direct contact is essential when patients are geographically remote or when clinicians must use personal protective equipment under radiation, biological, or chemical hazard conditions.

Monitoring of acoustic phenomena in outpatient settings. Continuous auscultation during rest and daily activities, including physical exertion, as well as data collection from multiple sensors placed on different body regions, enable over-time patient assessment.

Auscultation data storage. The ability to reassess recorded data improves the effectiveness of telemedicine consultations and supports resolution of disputes in forensic practice. A database of auscultatory recordings typical of various diseases can be used in the training of medical students.

Disease diagnosis using AI algorithms.

A comparison between traditional and electronic stethoscopes is presented in Table 1.

 

Table 1. Comparative characteristics of traditional and electronic stethoscopes
Feature	Traditional stethoscope	Electronic stethoscope
Sound amplification	No	Yes
Noise reduction	No	Yes
Versatility for auscultation of internal organs	Yes	Not all models
Data recording and transmission	No	Yes
Use of AI algorithms	No	Yes
Dependence on power supply	No	Yes
Cost of the device and replaceable parts	Low	High
Note. AI, artificial intelligence.

 

All digital stethoscope models currently available on the market are equipped with sound amplification and noise reduction functions, as well as the ability to record and transmit acquired data to a personal computer or smartphone via Bluetooth. The 3M™ Littmann® 3200 stethoscope (3M Littmann, USA) is one of the most widely used tools for digital auscultation (Fig. 1a). This device amplifies the sound signal 24-fold and features two auscultation modes (for low- and high-frequency sounds). A backlit liquid crystal display shows heart rate (HR), auscultation mode, volume level, and battery status. The device records data in 30-second tracks, which are saved as audio files. The recorded sounds can be visualized as phonocardiograms using StethAssist™ software [23]. Digital stethoscopes manufactured by 3M™ are the most commonly used tools for evaluating the advantages of digital auscultation [24]. The Stethee Pro™ stethoscope (M3DICINE, Australia) amplifies sound 24-fold during direct auscultation and 96-fold when used with the Stethee Pro™ application. It captures and analyzes sounds in the frequency range from 20 Hz to 2 kHz, followed by AI-based interpretation using the AIDA™ algorithm (Fig. 1b). Like the previous device, it features the ability to visualize sound as a phonocardiogram on the screen of the receiving device. It is also equipped with a lithium battery with fast USB charging. Another advantage is the compact size of the model [25].

 

Fig. 1. Appearance of the most popular electronic stethoscopes currently on the market: a, 3M™ Littmann 3200 stethoscope (USA), http://stetoskopy.ru/shop/3m-littmann/3200_BK_27.html; b, M3DICINE Stethee Pro™ stethoscope (Australia), https://m3dicine.com/#deeper_level; c, Thinklabs One™ stethoscope (USA), https://www.thinklabs.com/stethoscopes; d, eKuore Pro™ cardiology stethoscope (Spain), https://www.deal-med.ru/stetoskop_elektronniy_ekuore_pro.html; e, StethoMe™ stethoscope (Poland), https://www.stethome.com/en-gb/; f, Sensors of the CADence™ system for cardiac disease diagnostics (USA), https://evercare.ru/cadence; g, Ekoscope™ stethoscope with ECG recording capability (USA), https://ekoscope.com/ekoscope; h, Healthy Networks Lung Passport™ stethoscope (Belarus), https://cetez.ru/lungpass/; i, Laeneco™ stethoscope (Russia), https://laenecocom.tmweb.ru/.

 

The most compact and lightweight digital stethoscope on the market with the highest sound amplification (up to 100-fold) is the Thinklabs One™ (Thinklabs, USA) (Fig. 1c). It supports multiple auscultation modes and features customizable noise filtering with the option to disable it entirely. This stethoscope allows clinicians to examine patients using personal protective equipment, such as in infectious disease units treating COVID-19 patients, and integrates with most videoconferencing and telemedicine systems [12]. The eKuore Pro™ stethoscope (eKuore, Spain) is another device suitable for both in-person and remote auscultation (Fig. 1d). The device analyzes data using AI and easily integrates with any computer or smartphone software. Its distinctive features include the ability to replace the part that contacts the patient’s body and data transmission via Wi-Fi [26]. The StethoMe™ stethoscope (StethoMe, Poland) is designed for home care services and patient self-monitoring in cases of cardiac and respiratory diseases, such as bronchial asthma (Fig. 1e). This stethoscope detects pathological breath sounds using the StethoMe AI™ system and automatically transmits the data to a physician, enabling remote monitoring of disease changes in the patient. A unique feature of this stethoscope is its capability to measure body temperature [27]. The CADence™ diagnostic system (AUM Cardiovascular, USA) combines a stethoscope and an electrocardiograph, with built-in sensors for recording electrocardiogram data (Fig. 1f). This system operates with the CADence Software™ application for clinical decision support, which assists clinicians in analyzing auscultatory findings in combination with ECG results. Data collection takes approximately 8 minutes, after which a report is automatically sent via email within 12 minutes [28]. The Ekoscope™ device (Ekoscope, USA) is another multifunctional medical tool that enables simultaneous cardiac auscultation and six-lead ECG recording (Fig. 1g). It is equipped with a microUSB port for battery charging and data transfer [29]. The Lung Passport™ stethoscope (Healthy Networks, Republic of Belarus) is intended for home-based diagnosis of respiratory diseases (Fig. 1h). The device is equipped with a mobile application that uses AI algorithms to analyze the recorded sounds, compares them with those characteristic of pneumonia, chronic obstructive pulmonary disease, bronchial asthma, and several types of bronchitis, and then generates a preliminary diagnosis. To improve diagnostic accuracy, the application also includes a patient questionnaire [30]. The Russian Laeneco™ stethoscope (Laeneco, Russia) is designed for both self-diagnosis and remote physician assessment based on audio recordings (Fig. 1i). AI-based data analysis takes 2 minutes, after which the device provides a conclusion regarding the presence or absence of pathological sounds, without issuing a diagnosis [31]. A comparative overview of various digital stethoscope models is presented in Table 2.

 

Table 2. Comparative characteristics of the most popular digital stethoscope models on the market
Stethoscope model (manufacturer, country)	Advantages	Disadvantages
3M™ Littmann 3200 (Littmann, USA)	Heart rate (HR) recording Phonocardiogram visualization Auscultation of the heart and lungs	No AI-based data analysis Not suitable for patient self-diagnosis Not compatible with PPE use No rechargeable battery (powered by AA batteries)
Stethee Pro™ (M3DICINE, Australia)	Respiratory rate, heart rate, systole and diastole duration monitoring Phonocardiogram visualization Auscultation of the heart and lungs Use of AI-based data analysis Compatible with PPE use Lithium battery	Not suitable for patient self-diagnosis
Thinklabs One™ (Thinklabs, USA)	Auscultation of the heart and lungs Compatible with PPE use Lithium battery	No AI-based data analysis Not suitable for patient self-diagnosis
eKuore Pro™ (eKuore, Spain)	Auscultation of the heart and lungs Compatible with PPE use Wi-Fi connectivity Remote monitoring capability Lithium battery	No AI-based data analysis Not suitable for patient self-diagnosis
StethoMe™ (StethoMe, Poland)	Auscultation of the heart and lungs Use of AI-based data analysis Compatible with PPE use Remote monitoring capability Suitable for patient self-diagnosis Body temperature measurement Lithium battery	No headphones
CADence™ (CADence, USA)	ECG recording Lithium battery	No lung auscultation Not suitable for patient self-diagnosis
Ekoscope™ (Ekoscope, USA)	ECG recording Use of AI-based data analysis Lithium battery	No lung auscultation Not suitable for patient self-diagnosis Not compatible with PPE use
Lung Passport™ (Healthy Networks, Belarus)	Use of AI-based data analysis Suitable for patient self-diagnosis Lithium battery	No heart auscultation
Laeneco™ (Laeneco, Russia)	Use of AI-based data analysis Suitable for patient self-diagnosis Lithium battery	No heart auscultation
Note. HR, heart rate; AI, artificial intelligence; PPE, personal protective equipment; RR, respiratory rate; ECG, electrocardiogram.

 

Thus, the devices described above offer varying functionalities. Some are suitable for patient self-diagnosis, whereas others are intended exclusively for physician use. Additional features of these stethoscopes—such as ECG recording, sound visualization, and body temperature measurement—are particularly noteworthy. Undoubtedly, a significant limitation of several digital stethoscope models is their specialization in auscultation of either the lungs or the heart only. Another obstacle to the widespread adoption of digital stethoscopes is the relatively high cost of the devices and their replaceable components, as well as the complexity and expense of repairs due to the low geographic density of service centers. Nevertheless, the rapid development of clinical decision support systems and AI algorithms, along with the growing need for technologies that enable remote monitoring and telemedicine, position these devices as a promising segment in the medical device industry and market.

Over the past few decades, the development of AI has profoundly transformed key areas of everyday life, including healthcare. It has been shown that healthcare digitalization improves the quality of medical care, enhances treatment adherence, and enables early detection of diseases or their exacerbations [32]. The use of a digital stethoscope allows auscultation findings to be recorded and stored, thereby eliminating subjectivity in data interpretation. Market analysis indicates that an increasing number of medical devices are patient-centered, enabling self-diagnosis at home. Digital stethoscopes are no exception: home-use digital stethoscopes equipped with AI-based diagnostic algorithms represent a distinct market niche. Furthermore, the use of such devices by patients in outpatient settings may help reduce the burden on primary healthcare services. For instance, preliminary assessments suggest that the use of the Lung Passport device may reduce the number of doctor visits by 35% [7]. Remote patient monitoring and examination using personal protective equipment contributes to reducing contact between the patient and the healthcare professional, making the examination process as comfortable as possible for both parties. The use of fast-charging, high-capacity batteries and additional functions (ECG and thermometry) may further enhance the competitive advantages of these devices.

Conclusion

Enhancing the functionality and versatility of digital stethoscopes (including the ability to analyze sounds from the heart, lungs, intestines, and other organs) as well as improving noise reduction and signal filtering, make these devices increasingly attractive for clinical use. As these challenges are addressed, the digital stethoscope is set to become an indispensable tool for the diagnosis, monitoring, and treatment of diseases, as well as for patient self-monitoring. A particularly promising area of application for modern digital stethoscope models is telemonitoring of patients with cardiovascular and respiratory diseases. Of particular importance is the changes assessment of auscultatory findings over time, which may enable the early detection of complications and decompensation in various chronic non-infectious diseases, such as chronic obstructive pulmonary disease, bronchial asthma, myocardial infarction, and others.

Additional information

Funding source. This article was not supported by any external sources of funding.

Competing interests. The authors declare that they have no competing interests.

Authors’ contribution. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work. A.A. Garanin — literature review, collection and analysis of literary sources, writing the text and editing the article, final approval for publication; O.Yu. Aydumova — literature review, collection and analysis of literary sources, preparation and writing the text of the article; A.O. Rubanenko — collection and analysis of literary sources, writing and of the text and editing the article; E.G. Bibikova — literature review, collection and analysis of literary sources and writing the text of the article.

作者简介

Andrey A. Garanin

Samara State Medical University

编辑信件的主要联系方式.
Email: a.a.garanin@samsmu.ru
ORCID iD: 0000-0001-6665-1533
SPIN 代码: 9976-3085
Scopus 作者 ID: 56700078400

MD, Cand. Sci. (Medicine)

俄罗斯联邦, Samara

Olesya Y. Aydumova

Samara State Medical University

Email: o.yu.ajdumova@samsmu.ru
ORCID iD: 0000-0001-5673-7958
SPIN 代码: 6330-2186

MD

俄罗斯联邦, Samara

Anatoly O. Rubanenko

Samara State Medical University

Email: a.o.rubanenko@samsmu.ru
ORCID iD: 0000-0002-3996-4689
SPIN 代码: 6947-1028

кафедра пропедевтической терапии с курсом кардиологии, доцент, к.м.н.

俄罗斯联邦, Samara

Elena G. Bibikova

Samara State Medical University

Email: e.g.bibikova@samsmu.ru
ORCID iD: 0009-0005-9392-1101
SPIN 代码: 1578-1620
俄罗斯联邦, Samara

参考

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