The second derivative analysis has been used to characterize the changes in forehead photoplethysmographic (PPG) signal, which are caused by the stiffness of blood vessels. Before the distinctive wave amplitudes were measured the forehead PPG signals from healthy volunteers and diabetes patients were filtered, two times differentiated, normalized in length, and averaged. The correlation relationships between normalized amplitudes and age were found. The values of normalized amplitudes b/a and d/a were found to be influenced by the stiffness of the blood vessels.
- second derivative method
- arterial stiffness