Abstract
This paper proposes a novel technique to monitor peripheral vascular conditions by using biological signals, such as electrocardiogram, arterial pressure, and pulse oximetric plethysmogram. A second-order log-linearized model (called the log-linearized peripheral arterial viscoelastic model) is used to describe the nonlinear viscoelastic relationship between the blood pressure waveform and the transillumination plethysmographic waveform. The proposed index is able to estimate the changes of stiffness of peripheral arterial wall induced by sympathetic nervous activity, and the validity of the proposed method is then discussed by monitoring peripheral vascular conditions during arm position tests and during endoscopic thoracic sympathectomies (ETSs). As results of the arm position tests, the stiffness was arm position-independent (Up: 4.0 [%], Down: 5.5 [%]). Then, as results of the ETSs, the variation of the stiffness was significantly changed between before and during the ETS procedure (p < 0.01), and between during and after the ETS procedure (p < 0.01). The above experimental results clearly show that the proposed method can assess changes in the sympathetic nervous activity during ETSs.
