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Will we soon be able to use an app as an at-home stethoscope? Image credit: Sergey Narevskih/Stocksy.
  • Researchers assessed the feasibility of using a smartphone’s inbuilt microphone to record heart sounds by investigating the quality of smartphone-recorded heart sounds and the factors influencing the quality of the recordings.
  • Overall, three out of four recordings were of good quality, meaning that they could be processed further to obtain medically relevant data.
  • The results indicate that heart sound quality is not influenced by phone version or by the user’s biological sex, but users aged over 60 seemed to have lower-quality recordings.
  • This study paves the way for a future where individuals, particularly those with heart problems, can easily record their own heart sounds at home, thus improving the diagnostic process.

Everyone is familiar with the “lub-dub… lub-dub” sounds the heart makes. The reason that the heart makes these sounds is related to its function of circulating blood throughout the body.

The heart muscle pumps blood by continuously contracting and relaxing. During contraction of the heart, we hear the “lub” sound, known as the first heart sound, S1, and during relaxation of the heart, we hear the “dub” sound —the second heart sound, S2.

The traditional tool used by doctors to listen to heart sounds is the stethoscope.

Heart sounds may be a useful marker in heart failure, but currently, they are only assessed in a clinical setting. It would be useful for patients to be able to record their own heart sounds when they are at home.

One possible way in which heart sounds may be easily captured by individuals in the comfort of their own homes is by using a smartphone with an inbuilt high-quality microphone. To date, several mobile app prototypes for recording heart sounds have been developed and made available to the public, including iStethoscope and CPstethoscope.

Now, researchers at King’s College London in the United Kingdom and Maastricht University in the Netherlands have conducted a study to investigate the feasibility of using a smartphone as a stethoscope and to assess the potential factors that influence the quality of heart sound recordings.

“This research proves that mobile technologies are a viable way of recording heart sounds and that in the future, cardiac patients and doctors could use at-home recordings to check for [the] existence or progression of heart conditions,” says Dr. Pablo Lamata, study co-author and professor of biomedical engineering at King’s College London.

The results of this study appeared in the European Heart Journal – Digital Health.

An app ‘collecting’ heartbeats

In collaboration with cardiac patients through the British Heart Foundation (BHF) and Evelina Children’s Heart Organization (ECHO), and with experts at Cellule Design Studio, the researchers developed a smartphone application that measures heart sound.

To use the Echoes app, the user only needs to place their smartphone on their chest and press “record.” The application has a signal processing algorithm that filters the heart sound recordings to remove any background noise.

The Echoes app asks users to voluntarily provide anonymous basic demographics including age, sex, height, weight, and, if applicable, any heart conditions.

Between May 21 and October 4, 2021, 1,148 individuals downloaded the Echoes app and contributed 7,597 heart sound recordings, which were uploaded to a Google Firebase database.

Is sound quality an issue?

The researchers found that eight out of 10 (80%) users were able to make a good quality heart sound recording. A “good quality” recording is one that can be interpreted for analysis.

Overall, three out of four (75%) recordings could be processed further to obtain medically relevant data.

The researchers then looked at the factors affecting the quality of the heart sound recordings among these users. They found that the following factors do not impact the quality of the recordings:

  • phone version
  • user’s biological sex.

However, the researchers observed that users aged over 60 had lower-quality recordings.

During his doctoral thesis defense, Dr. Hongxing Luo, study co-author and postdoctoral researcher at Maastricht University argued that the issue of low-quality heart sound recordings by older users can be overcome.

One of the easiest solutions, he said, is to instruct the users to use an earpiece to listen to their heart sounds while they search for the position with the loudest heart sounds.

Easy heart health monitoring

Since hospitals already have several tools to evaluate the heart conditions of patients, such as an echocardiogram (ECG) and magnetic resonance imaging (MRI) scans, Dr. Luo believes that the most promising direction for technology like Echoes is remote heart monitoring, especially for the following patient categories:

  • heart failure patients
  • post-operative follow-up of patients with valvular heart disease
  • post-operative follow-up of arrhythmia patients.

Dr. Lamata described the Echoes app as “a tool to empower patient[s] to manage their own conditions.”

Dr. James Leiper, professor of molecular medicine at the University of Glasgow and Associate Medical Director at the British Heart Foundation, notes:

“As we enter the age of digital medicine, technology like Echoes could revolutionize the diagnosis and at-home monitoring of heart conditions. Further research is needed to test how the app can be used in tandem with existing heart monitoring techniques. However, if successful, this development could mark an important step towards having heart monitoring tools at your fingertips.”

Dr. Dominik Linz, professor in the physiology of circulation, kidney, and lung at the University of Copenhagen, pointed out that it is important for researchers to identify “specific thresholds for [heart sound measurements] which should result in action” by the cardiologist assessing the patient’s data via the Echoes app.

Study limitations and next steps

One study limitation is that the Echoes app was only available for iPhone users, thus excluding Android users — who account for more than half of overall smartphone users — from the study.

When asked if the Echoes app would become available to the wider public, Dr. Pablo Lamata, told Medical News Today: “We are now planning our next release, to also include an Android version, hopefully by May next year.”

The Echoes app currently only detects the S1 and S2 heart sounds, and the researchers commented that “the usefulness of recognizing pathological heart sounds including S3, S4, and murmurs, has to be investigated in a future study involving patients.”

The researchers also noted that the study population may not reflect a truly general population “because smartphone users are likely younger and more educated.” Further research is needed to assess the reproducibility of these results.