Ultrasonic Measurement of Respiratory Flow

We review ultrasonic measurement of fluid flow with emphasis on ultrasonic pneumotachometers (UPTM´s). For PTM´s we discuss specifications such as dynamic range, resistance, and frequency response. We review fluid flow principles and point out the problems of nonultrasonic PTM´s For UPTM´s we describe transducer construction, attenuation versus frequency, reflection at interfaces, and acoustic field patterns. We present four principle types: 1) time of flight, 2) sing around, 3) phase shift, and 4) phase-locked frequency shift. For each, we detail principles, advantages, disadvantages, and potential for future development.