Optical flow sensor for continuous invasive measurement of blood flow velocity

Continuous monitoring of intrapulse measurement of blood flow in humans is currently not achievable with clinically available instruments. In this paper, we demonstrate a method of measuring the instantaneous variations in flow during pulsatile blood flow with an optical flow sensor comprising a fiber Bragg grating sensor and illumination from a 565 nm Light-Emitting-Diode. The LED illumination heats the blood and fluctuations in temperature, due to variations in flow, are detected by the fiber sensor. A set of experiments at different flow rates (20 to 900 mL/min) are performed in a simulated cardiac circulation setup with pulsatile flow. Data are compared with an in-line time of flight ultrasound flow sensor. Our results show that the optical and ultrasonic signals correlate with Pearson coefficients ranging from -0.83 to -0.98, dependent on the pulsatile frequency. Average flow determined by ultrasound and the optical fiber sensor showed a parabolic relationship with R² = 0.99. An abrupt step change in flow induced by occlusion and release of the circuit tubing demonstrated that the optical fiber and ultrasound sensor had similar response. The method described is capable of intrapulse blood flow measurement under pulsatile flow conditions, with potential applications in medicine where continuous blood flow sensing is desired.