Fast Response Ultrasonic Flowmeter Measures Breathing Dynamics

Questions about the dynamics of respiration following prolonged exposure to hypogravity led to a set of flowmeter requirements that included: ~240 Hz sampling rate, ±0.02 1/s accuracy, 500: 1 bidirectional range (±0.02 to ±10 1/s), sample volume ¿50 cm3, and small pressure drop. In the present laboratory feasibility study, the investigators modified an industrial ultrasonic flowmeter such that 100 kHz pulses, alternately transmitted upstream and downstream at a 300 Hz rate, interrogated inhaled or exhaled air flowing through a 2 ×2 cm square duct or a 1.27 ×2.54 cm rectangular duct. This communication emphasizes the electronic and programming aspects of the ultrasonic flowmeter developed for this study, and includes waveform illustrations and upstream-downstream time difference data obtained in laboratory tests.