Oscillatory Capillary Extensional Rheometer (OsCER) to Probe Expiratory Aerosol Generation in the Human Larynx

Some airborne lower respiratory infections responsible for millions of deaths each year are transmitted by respiratory droplets formed within the larynx and emitted during speech. A small subset of the human population known as " super emitters" expel one order of magnitude more particulates than the average person, however the underlying fluid mechanical cause has not been identified. Direct droplet formation is difficult to visualize due to severe lighting constraints within the larynx making it desirable to construct an artificial model that mimics the rapid (100 to 200 Hz) open and close motion of the vocal folds with large (millimeter scale) amplitudes. Using a powerful subwoofer, the type commonly used in 'monster trucks', as the basis of OsCER we can control the frequency and amplitude independently. Using a high-speed camera, we visualize the stretching of salivary films into beads-on-a-string structures that break up into droplets. We complement these videos with rheological characterization and particle size distribution measurements to determine the influence of frequency, amplitude, and rheology on aerosol emission.