MULTIWAVELENGTH PHOTOPLETHYSMOGRAPHY SYSTEM

Photoplethysmography (PPG) is a promising technology for assessing the cardiovascular system's condition due to its ability to analyze changes in blood volume within the microvascular bed. Beyond standard parameters such as heart rate and blood oxygen saturation, the pulse wave shape in PPG signals contains additional valuable information that can be utilized for assessing heart rate variability, arterial stiffness, and blood pressure. However, the successful use of PPG in everyday activities requires reliable acquisition of signals free from saturation, motion artifacts, and other interferences. This study presents a multiwavelength photoplethysmography (MW-PPG) sensor system capable of continuous real-time signal recording. Two types of sensors were developed: a three-wavelength finger PPG sensor utilizing backscattered light and a three-wavelength ear PPG sensor using transmitted light. The system can record up to eight independent signals, and its operation is controlled by a microcontroller managing the power and signal processing subsystems. The software allows for customizable operation settings, including signal amplification modes and LED activation sequences. To evaluate the system's performance, signal quality was analyzed using the Pearson correlation coefficient (PCC). The average PCC values for the finger and ear sensors ranged from 0.973 to 0.995, indicating the high accuracy and reliability of the developed system. The highest PCC values were obtained for the wavelength pair of 660 nm and 940 nm, while lower values were observed for the 568 nm and 660 nm pair due to stronger light absorption by tissues at 568 nm. The results confirm the effectiveness of the proposed MW-PPG system for measuring high-quality physiological signals.