Auscultation System for Acquisition of Vascular Sounds – Towards Sound-Based Monitoring of the Carotid Artery

Figures

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  Figure 1. Overview of the auscultation system comprising a handheld auscultation device and a desktop application as user interface. Battery and sensing unit (dashed line) can be exchanged to customize the device or to meet hygienic requirements.

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  Figure 2. Propagation path of vascular sounds originating from the blood flow inside the vessel and the propagated intrinsic heart sounds S1 and S2 of the circulatory system. It transmits to the diaphragm* of the microphone via an air-coupled interface and the port hole** of the PCB where it is converted into an electrical signal.

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  Figure 3. Design of the skin-transducer-interface comprising two MEMS microphones, air-coupling via bell-shaped structures with and without acoustic membrane and gasket and insulation layers in a custom-built housing.

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  Figure 4. Control states of the auscultation process and respective control elements (button switches B1, B2) and feedback interface (LED: 0 = off, 1 = on, 1-0-1 = blinking).

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  Figure 5. Auscultation of the carotid vascular sound of a voluntary subject with the final CAAS.

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  Figure 6. Time-domain representation of the acquired vascular sounds. A 7 second segment (top) of each measurement was used for the segment-based stability analysis and one full heart cycle representing one event (bottom) for the event-based analysis.

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  Figure 7. 3D-model (right) and manufactured and assembled prototype of the handheld auscultation device ready to use (here: skin-transducer-interface without acoustic membrane).

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  Figure 8. Proprietary desktop application with (A) current state, duration and date of the auscultation, (B) real-time visualization with integrated scaling functionality and (C) input fields for supplementary information regarding patient, experiment and comorbidities or related medication.

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  Figure 9. Exemplary recordings of (A) vascular sound with intrinsic heart sounds S1 and S2, (B) during deep breath and (C) during swallowing of the subject as common artifacts. The recordings were acquired in one measurement. The upper graph depicts the acquired signal with added membrane (Ch 1) and the lower graph without membrane (Ch 2).

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  Figure 10. Segment-based analysis of the spectral characteristics computed as the wavelet-based and normalized stationary spectral energy. For subject S1 … S5 the first 5 measurements represent the left carotid while subsequent measurements represent the right carotid respectively. The associated frequency of the scale with highest contribution to the overall energy of the spectrum is indicated.

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  Figure 11. Event-based analysis of the spectral characteristics for subject S1 … S5, computed as the wavelet-based and normalized stationary spectral energy. The first 40 events represent the left carotid and 8 events belong to one measurement each. The second 40 events represent the right carotid respectively.

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  Figure 12. Cumulated and normalized PSD representing the accumulation of spectral energy with respect to the frequency. 10 vascular sound recordings of one subject simultaneously acquired with and without acoustic membrane as part of the skin-transducer-interface are shown.