A Low-Noise-Level Heart Sound System Based on Novel Thorax-Integration Head Design and Wavelet Denoising Algorithm

Abstract

Along with the great performance in diagnosing cardiovascular diseases, current stethoscopes perform unsatisfactorily in controlling undesired noise caused by the surrounding environment and detector operation. In this case, a low-noise-level heart sound system was designed to inhibit noise by a novel thorax-integration head with a flexible electric film. A hardware filter bank and wavelet-based algorithm were employed to enhance the recorded heart sounds from the system. In the experiments, we used the new system and the 3M™ Littmann® Model 3200 Electronic Stethoscope separately to record heart sounds in different noisy environments. The results illustrated that the average estimated noise ratio represented 21.26% and the lowest represented only 12.47% compared to the 3M stethoscope, demonstrating the better performance in denoising ability of this system than state-of-the-art equipment. Furthermore, based on the heart sounds recorded with this system, some diagnosis results were achieved from an expert and compared to echocardiography reports. The diagnoses were correct except for two uncertain items, which greatly confirmed the fact that this system could reserve complete pathological information in the end.

Advances in Microsensors and Wearable Bioelectronics for Digital Stethoscopes in Health Monitoring and Disease Diagnosis

“…[27] Zhang et al utilized lowpass fourth-order Butterworth filter for the active filtering, a parallel-T RC notch filter for the passive filtering and a wavelet-based algorithm for digital filtering. [28] Finally, Malik et al applied a fourth-order Butterworth bandpass filter for active filtering in cardiac auscultation to filter out heart sounds from the designed stethoscope. [1] For pulmonary auscultation, Yilmaz et al used a second-order low pass filter with a 3-dB cutoff frequency at 1.6 kHz with a gain of 10 V V −1 for active filtering, first-order high-pass filter for the passive filter.…”

“…A second MEMS microphone is added to capture ambient sounds to use adaptive filtering to cancel out the ambient noise. Figure 2e [28] illustrates a low-noise level heart sound system on a novel thorax-integration head design for heart sound acquisition. A piezoelectric sensor in this device has a high-output impedance, so a charge amplifier is added to the circuitry with a hardware filter bank to remove ambient noise.…”

Development of a Bed-Based Unconstrained Cardiac Auscultation Method

“…1(a). In addition, the equation of the rotational motion of C is obtained as (2), where I is the moment of inertia.…”

“…Thus, monitoring the cardiac information of a person lying on a bed without any attached sensors on the body would be useful for diagnosis and health care. Under these circumstances, unconstrained PCG measurement methods have been proposed [2,3]. The use of a piezoelectric device attached to the chest of the patients lying on a bed [2] has been proposed as a moderately constrained PCG methods.…”

“…Under these circumstances, unconstrained PCG measurement methods have been proposed [2,3]. The use of a piezoelectric device attached to the chest of the patients lying on a bed [2] has been proposed as a moderately constrained PCG methods. Moreover, an unconstrained PCG method using radar [3] has been proposed.…”