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.