Considering Skin Inhomogeneity in Photoplethysmography-Based Local Pulse Transit Time Measurement

The local measurement of pulse transit time in blood vessels can be implemented using photoplethysmography-based sensors. Therefore, at least two sensors must be placed such that the measured signals originate from the same artery. However, results from our previous research suggest that this kind of measurement does not always provide reliable results. We assumed that the inhomogeneous structure of the skin causes this behavior. Based on this theoretical background related experiments $(\mathbf{n}=\mathbf{8})$ were executed. The results suggest a signal distortion that strongly depends on the mounting position of the sensors. It can be shown that this distortion is presumably responsible for erroneous calculations of pulse transit time.