CHAPTER 5 – Ultrasonic flowmeters

Publisher Summary This chapter describes two types of ultrasonic flowmeters. First are those that depend on a difference in the time of arrival when the ultrasound is transmitted in the direction of flow and against the direction of flow. The second type is the Doppler-shift flow velocity meter. The possibility of hazards to the patient when using Doppler instruments has been the subject of much discussion in the past three years. To put the position in perspective, it is necessary to consider the intensity of the ultrasonic field, either the mean intensity or the peak intensity depending on whether the ultrasound is pulsed or continuous. The frequency of the ultrasound also is an important parameter when discussing potential hazard. The thermal interactions are generally regarded as the ones that present themselves as the main potential hazard in the use of Doppler flow-velocity measurements. The calibration is usually carried out in vitro using a flow system with a constant head for steady flow calibration and a pump for pulsatile calibration. The chapter further discusses the factors affecting calibration—such as high-pass filter in the output stage, haematocrit, and signal dropout.