Optical measurement of cardiac parameters based on the Iso-Path-Length Point

Accurate and continuous monitoring of blood pressure (BP) is essential for cardiovascular health assessment and early detection of potential health issues. Traditional BP measurement methods, such as the inflatable arm cuff, are often inconvenient and do not allow continuous tracking. This study introduces a new optical biosensor for non-invasive BP measurement based on the Iso-Pathlength (IPL) phenomenon, which isolates the scattering effects of light intensity to focus on absorption coefficients, providing a more accurate representation of blood volume changes. The biosensor consists of a single light source and five photodetectors, with one positioned at the IPL point. The sensor was tested on 44 subjects, with measurements taken on the upper arm and compared to reference BP readings from a traditional inflatable cuff monitor. The obtained light intensity was converted into absorption coefficients, from which the photoplethysmogram (PPG) signal was derived. Analysis of the PPG signal identified key points corresponding to systolic, diastolic, and mean arterial pressures, which were found to exhibit a strong linear correlation (R² = 83-84%) with the reference BP values. This correlation outperforms current methods, which generally show a maximum of 78% accuracy. With further research, this non-invasive optical biosensor could provide an effective, continuous BP monitoring tool for clinical and personal health applications.