Measurement of tidal flow using a transit-time ultrasonic breath analyser

The ability of the Transit-time Ultrasonic Breath Analyser (TUBA, GHG Medical Electronics GMBH, Zurich, Switzerland) to measure peak flow and tidal volume in the laboratory was tested using a variety of flow and pressure conditions, chosen to simulate the respiratory patterns of patients receiving mechanical ventilatory support. A stable zero baseline was achieved by acoustic damping of the TUBA flow sensor head. A piston pump was used to generate sinusoidal-flow pattern, with a peak flow range from 0.1 to 1.5 l.s-1. The calculated peak flow matched the peak flow measured by the TUBA. The TUBA accurately measured tidal volumes (±10%) delivered using three different flow patterns over a range of volumes from 0.25 to 1 l. We conclude, that once modified, the TUBA can provide an accurate measurement of peak flow and tidal volume over a range of values likely to be encountered during mechanical ventilation of the lungs.