Multimodal assessment of arterial stiffness using photoplethysmography and laser Doppler flowmetry

Age-related deterioration of vascular elasticity contributes to cardiovascular disease (CVD), the leading cause of death worldwide, making early detection in primary care essential. This study investigated the feasibility of photoplethysmography (PPG) and laser Doppler flowmetry (LDF) in an in vitro vascular system, examining independent and combined use. Custom femoral vessel-tissue phantoms replicated healthy (0.82 MPa), intermediate (1.48 MPa) and unhealthy (2.06 MPa) arterial stiffness. Two blood-mimicking fluids (BMFs) with scattering agents (intralipid and LPFS) evaluated modality performance. Extracted features included area, slope ratio and datum-based PPG metrics, plus LDF DC mean flux, statistically analysed using the Kruskal-Wallis test. The intralipid-based BMF produced larger reductions in LDF DC flux. Multiclass classification improved prediction when combining signals, yielding 100% holdout accuracy for red and infra-red (IR) PPG and 95.24% for green PPG with intralipid. These findings demonstrate technical feasibility for stiffness discrimination and motivate in vivo validation against clinical markers.