Ultrasonic TrueFlow Measurement

Cross sectional view of the flow sensor with the disposable spirette installed
Cross sectional view of the flow sensor with the disposable spirette installed

Ultrasound transit-time flow measurement was developed by Dr. Ch Buess at ETH Zurich in 1986 and has since then been evaluated and applied in countless research projects. After much success, the term TrueFlow was coined. The EasyOne product line is now the exclusive choice for the Platino studies, is actively recommended by the National Lung Health Education Program NLHEP and has been repeatedly used in space projects with NASA.

All ndd instruments incorporate the TrueFlow technology to measure the flow of air in and out of the patients' lungs. This technology eliminates problems associated with traditional methods of flow measurement and helps make the ndd products extraordinarily fast, reliable, accurate and error free.

There are no moving parts, no codes to enter, no screens to catch sputum, and no disposables to calibrate. The ultrasonic flow measurement is independent of gas composition, pressure, temperature, and humidity thus eliminating errors due to these variables.

Transducers located on either side of the breathing tube (spiretteTM) cavity emit and receive sound in alternating directions. When gas flow is present in the tube, a pulse that travels against the flow (traveling upstream) is slowed down and takes a longer time to reach the opposite transducer. Conversely, a pulse traveling with the slow (traveling downstream) is sped up and takes a shorter time to reach the opposite transducer.

The transit-time of each sound pulse is precisely measured with a digital clock. The gas flow through the spiretteTM is then calculated from the upstream and downstream transit-times.

The disposable spiretteTM acts only as a hygienic shield and is transparent to the ultrasonic pulses traveling between the ultrasonic transducers. Since the spiretteTM has no sensor elements, it does not perform a measurement function and does not need to be calibrated.