DESIGN AND PRELIMINARY ANALYSES OF A PPG BASED PULSE TRANSIT TIME (PTT) MEASUREMENT SCHEME
Aryalekshmi R Vijayadharan, Lokharan M, Lokesh Kumar K C, Harish Kumar V, Kayalvizhi N
Amrita Vishwa Vidhyapeetham, India
An experimental prototype for measuring the pulse transit time (PTT) using two inline Photoplethysmographic (PPG) signals is presented in this paper. The measured PTT is employed to calculate the pulse wave velocity, which gives the proposed system an extensive utilization in monitoring arterial stiffness and continuous arterial blood pressure. The PPG sensors are placed in-line, 1.5 cm apart, over the digital artery. The time difference between PPG signals obtained from the two sensors is used to calculate the PTT. The signals from the sensors are band limited and amplified, which are then made TTL compatible to generate a rectangular pulse of width equal to the PTT. A phase-shifted sinusoid generated using an all-pass filter is used to validate the prototype. Measurements were done on 11 volunteers (4 Female and 7 Male volunteers in age group from 21 years to 52 years) for four consecutive cycles. The maximum relative error percentage of the experimental setup, when tested with phase shifted sinusoids was found to be 2.5% .The maximum deviation (standard deviation) in the measured PTT is 2.5 and the minimum deviation is 0.38.