[bctt tweet=”ECMO centrifugal pump circuits require ultrasonic sensors to measure blood flow and detect air.”]
The sensors work by by measuring the transit-time of ultrasonic pulses through the blood flow. The flow sensor surrounds the ECMO circuit tubing. Ultrasonic impulses are sent from one piezo crystal to another (either directly in an X-pattern or by a reflector with the crystals acting alternately as transmitters and receivers depending on the manufacturer). The transit time taken by each impulse is determined, and the differences times taken by the impulses flowing upstream and the ones flowing downstream are proportional to the flow rate.
Even though the physical path lengths of the ultrasound beams within the the sensor are the same, the transit time is longer for the beam going upstream is longer because of the Doppler effect. An object moving towards the ultrasonic beam compresses the wave, thereby increasing the signal’s frequency, whereas an object moving away from the beam reduces the signal’s frequency. The change in frequency, which is also termed the Doppler shift, provides information about the object’s speed and direction of motion.
Bubble Detection Sensor
Bubble detection is critical to maintain the steady-flowing circuit and prevent complications from air embolism especially with veno-arterial ECMo circuits. Non-invasive ultrasonic bubble sensor uses an active piezoelectric element as a piezoelectric transmitter to generate a high frequency acoustic wave. This acoustic wave travels through the sensor wall and is