Neural network based real-time heart sound monitor using a wireless wearable wrist sensor
A new method is presented using a wearable wrist sensor to estimate acoustic parameters S1 and S2 of the heart sounds based on the neural network technique. Using the signal processing method, the heart conditions can be analyzed and monitored in real time and potentially in a long term with a wrist device. The velocities and time delays of the cardiac pulse waves in blood vessels were experimentally acquired and calculated at different artery locations on the human body. Signal attenuation of the pulses from the heart to the wrist radial artery was analyzed and a pulse-waveform travel model in blood vessels was proposed. A band-pass filter is applied to the pulse waves at various artery locations to reveal the heart sound features S1 and S2 existed in the pulse waves. In order to obtain accurate acoustic parameters, a neural network with two layers and 500 nonlinear tansig neurons was employed to estimate the heart sounds using the pulse waveforms from the wrist radial artery. It is encouraging to find that the acoustic parameters of estimated heart sounds by the trained neural network have only 1% average errors compared with the original heart sounds. The effects of various analog-to-digital conversion resolutions and sample rates were empirically analyzed. When the maximum value of errors is allowed within 2.15%, a 10,000-Hz sample rate and 12-bit resolution should be an appropriate selection for lower power consumption. Using the trained neural network, the new estimation method has been verified by a sensor with Bluetooth communication strapped on the wrist, thus mobility is not limited for the person whose heart sounds need to be monitored.
KeywordsWireless sensor networks Stethoscope Digital signal processing Neural network
Authors sincerely thank the technical support by NeoScBio Limited.
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