Endothelial dysfunction is recognized to be the first step of arteriosclerosis. To estimate vascular endothelial function, the measurement of forearm blood flow (FBF) is well known as one of the most desirable methods. However, in this method, the forearm of the patient is confined using a cuff in order to measure the volumetric change, and this process is considered to increase stress in the patients. In addition, the method does not yield the true mechanical characteristics of the blood vessels because it does not measure the continual change of arterial pressure. This paper proposes a method that evaluates the beat-to-beat vascular conditions without needing to confine the forearm of the patient. It can estimate the mechanical impedance of an arterial wall by simultaneously recording a strain-gauge plethysmogram and measuring continual arterial pressure. First, we compare the impedance model that changed the combination of stiffness, viscosity and inertia as an evaluation of the arterial wall impedance model. From the results, we found that the viscoelastic model can be used to determine vascular characteristics. Next, the stiffness and viscosity responses to acetylcholine and sodium nitroprusside were evaluated. When the dose of the vasorelaxant agent (acetylcholine) is increased from 3.75 to 15 μg/min, the stiffness decreases approximately 0.4-0.8 times, and the viscosity decreases approximately 0.6-0.9 times. It was also confirmed that the proposed method is adequately comprehensive to estimate the vascular endothelial function.
