In vitro tests are commonly employed to assess nebulizer performance. Whether the square or sine waveforms employed during in vitro tests could alter the nebulizer performance compared to
that observed when a patient breathes through the nebulizer is debatable. Accordingly, the aim of this in vitro study was to compare the rates of delivery from nebulizers with simulated human breathing
patterns to those obtained with matching sine and square waveforms. Regular human breathing patterns with tidal volumes (VT) of ~40, ~200, ~500, and ~800 mL were selected. Sine and square waveforms that
matched the VT, peak inspiratory flow rate (PIF), breathing frequency (f), and inspiratory duty cycle (ti/ttot) of the human breathing patterns were
created with a breathing simulator. The rate of delivery of nebulized technetium-99m-labeled diethylenetriamine pentaacetic acid (99mTC-DTPA) from two different jet nebulizer brands was determined.
The rate of delivery was defined as the amount of the 99mTC-DTPA deposited during 30 sec of nebulization on a filter placed between the nebulizer and the breathing simulator. The rate of delivery
of 99mTC-DTPA with the human breathing pattern was similar to that measured with the matching sine or square waveforms for either nebulizer. The configuration of the breath (PIF, VT,
f, ti/ttot) did, however, influence the rate of delivery. In conclusion, the shape of the waveform, in other words, one resulting from a human breathing pattern,
or a matching sine or square waveform, did not influence the rate of 99mTC-DTPA delivery from a nebulizer in vitro.
