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.