This paper proposes an innovative technique to monitor vascular conditions by using the biological signals, such as electrocardiogram, arterial pressure, and pulse oximetric plethysmogram. A second order linear model with damping is used to describe the nonlinear viscoelastic relationship between the blood pressure waveform and the transillumination plethysmographic waveform. The validity of the proposed method is then discussed by monitoring vascular conditions during surgical operations with arterial wall impedance. It has been demonstrated that the estimated impedance properties of arterial wall correspond to events during a surgical operation.
