Spirometer Based on Vortex Whistle to Monitor Lung Disorders

This paper describes a method to monitor lung disorders such as the sequelae of the novel coronavirus (SARS-CoV2) and asthma. A battery-less spirometer sensor element used in microphone-equipped devices such as smartphones was adopted. A vortex whistle was employed to measure the blowing flow rate and pressure. The physical characteristics of the vortex whistle sound frequency, blowing flow rate, blowing pressure, and sound pressure were theoretically clarified. Moreover, the structural conditions necessary to ensure a high performance of the whistle were experimentally derived, and the theoretically derived characteristics were experimentally validated using an actual whistle. The experimental results and theoretically derived characteristics were in agreement, and the sound frequency was noted to be linearly proportional to the flow rate. Furthermore, the sound pressure increased to +40 dB / decade as the frequency increased, and the outlet pressure was proportional to the square of the frequency. On the basis of these results, the signal processing conditions to acquire the information pertaining to the spirometer from the vortex sound were clarified.