Combination of ECG And PPG Signals For Smart HealthCare Systems: Techniques, Applications, and Challenges

Electrocardiogram (ECG) is preserved as the procedure of the electrical activity recording, while the photoplethysmogram (PPG) is defined as a non-invasive measurement of the volumetric variances in the circulation of the blood. There are several applications in which the ECG combined with PPG can be used in the field of medical health care. This survey illustrates the various applications that use features combined from both signals. The review manifests the techniques, methodologies used in the data acquisition, pre-processing of the signals. The feature extraction and classification phases for both ECG and PPG are explained. The limitations, challenges, and future directions for the combined applications of ECG and PPG are clarified to solve the medical problems that existed, presented, and feasible. This study aims to increase the interest in applying the combination of ECG and PPG signals in more applications and to obtain optimal measurements related to cardiac activity.