Research On Wearable Heart Rate Monitoring Equipment Based On Photoplethaysmography

Photoplethaysmography(PPG)is a noninvasive technique which reflects the blood volume changes in the vessels and plays a vital role in diagnosis cardiovascular diseases.In recent years,PPG has been widely used with the development and popularization of the wearable devices.Nevertheless,it is extremely susceptive to motion artifact caused by the objects' intentional or unintentional movements and then affects the accuracy of the diagnosis results.Therefore,the signal processing is necessary to remove the noises before the signal analysis in the next step.To solve this problem,this paper based on the Compressed Sensing theory,and employed the Gradient Projection for Sparse Recovery algorithm in noise filtering and recovery.For the non-sparse signals,the Compressed Sensing theory mainly consist two steps: sparse and recovery.First,in order to ensure the significant information not be destroyed,using the Haar wavelet base to find the best sparse field.After that the motion artifact can be removed from the contaminated PPG signals while recover the sparse signals.The PPG signal is acquired by the signal acquisition system with the DS-100 A pulse oximeter probe.The system mainly consists of a LED drive circuit and current to voltage conversion circuit.The collected signals are converted to digital signals and saved in the computer by DT9816 data acquisition system.For the signal processing,firstly,in order to find the best sparse field,signals are sparsed by each level wavelet transform.Calculate the mean square error of the sparse reconstruction signals by each level of the Wavelet transform,and many experiments prove that it is more than sufficient to recover the 4 level wavelet transform.During the experiment,three types of noise were measured,and then the proposed algorithm was used to process the noisy signals,the results show that the algorithm can significantly reduce the movement interference in the signals.Other 50 healthy adults with vertical movement of motion artifact were measured,calculate the heart rate and mean square error of the original and reconstruct PPG signals.Compare the obtained heart rates with the noiseless PPG signals' heart rates,the results show that the range of the differences between the noisy and noiseless PPG signals are about ±23 bpm,and the reconstructed PPG signals are about ±2.7 bpm.The mean square error of the reconstructed signals is reduced about 50% compare with the noisy signals.