Use of a Vortex Whistle for Measures of Respiratory Capacity

Abstract

A vortex whistle produces a tone which has a frequency proportional to the inlet air flow rate. The objectives of this study were to replicate previous studies demonstrating the use of a vortex whistle as an accurate flow meter, and to assess the degree of relationship between measures of vital capacity (VC) obtained using low-cost methods (vortex whistle and hand-held spirometry) vs. pneumotach-based spirometry. A vortex whistle was designed using 3D modeling software and manufactured using a 3D printer with non-toxic, biodegradable polylactic acid (PLA). The digitized vortex whistle tone was analyzed using custom software to produce a frequency vs. time contour. As the frequency is proportional to flow, the integral of this curve corresponds to the overall volume by a linear relationship. The accuracy of vortex whistle volume estimates were assessed using (1) controlled flow rates from a consistent volume calibration syringe, and (2) with 66 subjects between the ages of 18-30 yrs. in comparison to hand-held spirometry and two pneumotach systems. Observations from the calibration syringe experiment confirmed that the vortex whistle and software are able to effectively track the flow rate, with a correlation coefficient between the average flow and the average frequency of r2=0.9965. Results from the human VC testing showed that measures obtained using both vortex whistles and hand-held spirometry correlated very strongly (r>0.94) with computerized pneumotach systems, and the strength of correlations obtained via vortex whistles vs. hand-held spirometry were highly comparable. When coupled with the analysis software described herein, valid and reliable frequency/flow curves and volume estimates may be obtained using a vortex whistle that are highly comparable to the hand-held spirometer. The use of the vortex whistle has the potential to bring measures of basic respiratory function to clinicians and patients alike at a fraction of the cost of currently used spirometric methods.