A Wearable Stethoscope for Long-Term Ambulatory Respiratory Health Monitoring

Abstract

Lung sounds acquired by stethoscopes are extensively used in diagnosing and differentiating respiratory diseases. Although an extensive know-how has been built to interpret these sounds and identify diseases associated with certain patterns, its effective use is limited to individual experience of practitioners. This user-dependency manifests itself as a factor impeding the digital transformation of this valuable diagnostic tool, which can improve patient outcomes by continuous long-term respiratory monitoring under real-life conditions. Particularly patients suffering from respiratory diseases with progressive nature, such as chronic obstructive pulmonary diseases, are expected to benefit from long-term monitoring. Recently, the COVID-19 pandemic has also shown the lack of respiratory monitoring systems which are ready to deploy in operational conditions while requiring minimal patient education. To address particularly the latter subject, in this article, we present a sound acquisition module which can be integrated into a dedicated garment; thus, minimizing the role of the patient for positioning the stethoscope and applying the appropriate pressure. We have implemented a diaphragm-less acousto-electric transducer by stacking a silicone rubber and a piezoelectric film to capture thoracic sounds with minimum attenuation. Furthermore, we benchmarked our device with an electronic stethoscope widely used in clinical practice to quantify its performance.

Keywords: COPD; auscultation; digital health; electronic stethoscope; respiratory sound; wearables.

Figure 1

Electronic circuit (impedance converter) interfacing with the high-impedance sound sensor. The piezoelectric sensor (in red) is modelled as a voltage source in series with a capacitance in its linear mode (highlighted with red-dashed lines).

Figure 2

Noise breakdown of the impedance converter.

Figure 3

Simplified schematic of the sound acquisition module composed of impedance converter, gain and filtering stage, and analog-to-digital converter.

Figure 4

(left) Exploded view of the sound acquisition module and (right) images of the assembled sensor with its dimension; from top to bottom: side view of the sensor with 1 euro coin, top view of the sensor with 1 euro coin, and bottom view of the sensor.

Figure 5

Sensor positions on the chest.

Figure 6

Magnitude spectra for position 18.

Figure 7

Magnitude spectra for position 7.