Impact of Salivary Rheology on Expiratory Aerosol Formation in the Vocal Folds during Phonation

更多的人死于下呼吸道疾病，如流感和COVID-19，而不是任何其他类型的传染病。在COVID-19大流行期间经历了许多早期的混乱之后，现在的科学共识是，许多空气传播的疾病是通过“气溶胶”传播的，气溶胶是人类说话或以其他方式呼气时释放的非常微小的液滴。 这些微小的液滴太小了，看不见，但它们足够大，可以携带病毒或其他病原体。虽然人们相信在讲话过程中在声带处形成许多微小的液滴，但迄今为止还没有工作直接验证这一假设。在这个研究项目中，一名训练有素的医生将通过人类研究参与者的鼻子插入一个光纤摄像机，以提供液滴形成期间声带的第一个直接视频观察。 工程师们同时进行的实验将测量液滴排放的总体速率，以及每个参与者唾液的“粘度”或厚度。 因此，这项研究将直接验证这一假设，即负责空气传播疾病传播的液滴排放率与受感染个体的唾液粘度直接相关。液滴形成率被假设为由衬在声门上的唾液中的弹性、毛细血管和惯性效应的平衡所控制，如Deborah和Ohnesorge数所表征的。每次声带分开时（每秒多达数百次），细的流体细丝被拉伸并最终被挤压分开，产生卫星液滴，这些液滴被呼气气流捕获并最终呼出到周围环境中。该研究小组包括一位耳鼻喉科医生，他在使用喉镜（其特征是通过鼻子插入光纤电缆）观察患者声带方面有很多经验。一个频闪视频系统将被用来直接可视化和记录声带在体内的参与者在发声过程中，在系统地改变响度，而呼气气溶胶排放率的同时测量将使用空气动力学粒子大小。将收集每个参与者的唾液样本，以使用双间隙几何流变仪测量唾液的储存和损耗模量，并使用液桥几何中的毛细管破裂流变仪测量拉伸粘度和液滴形成动力学。在统计上显著数量的不同参与者上的这些多个数据流的组合将告知互补的流体力学建模，并提供对呼气液滴形成的前所未有的基本见解，可能提供了一个流体力学的解释，为什么有些人是超级，该奖项反映了NSF的法定使命，并通过使用基金会的学术价值和更广泛的影响评审标准。

More people die from lower respiratory diseases, like influenza and COVID-19, than any other type of infectious disease. After much early confusion during the COVID-19 pandemic, the scientific consensus now is that many airborne diseases are spread via “aerosols,” which are very tiny droplets emitted by humans when they speak or otherwise exhale. These tiny droplets are much too small to see, but they are sufficiently large to carry viruses or other pathogens. Although it is believed that many tiny droplets are formed at the vocal cords during speech, to date no work has directly examined this hypothesis. In this research project, a trained medical doctor will insert a fiber optic camera through the nose of human study participants to provide the first direct video observations of the vocal cords during droplet formation. Simultaneous experiments by engineers will measure the overall rate of droplet emission, as well as the ‘viscosity’ or thickness of the saliva in each participant. The research will thus directly test the hypothesis that the rate of droplet emission responsible for air-borne disease transmission is directly related to the viscosity of the saliva in infected individuals.The droplet formation rate is hypothesized to be governed by a balance of elastic, capillary, and inertial effects in the saliva that lines the glottis, as characterized by the Deborah and Ohnesorge numbers. Each time the vocal folds move apart (up to hundreds of times per second), thin fluid filaments are stretched and eventually pinch apart, yielding satellite droplets that are caught in the expiratory airflow and ultimately exhaled into the surrounding environment. The research team includes an otolaryngologist with much experience visualizing patients’ vocal folds using a laryngoscope (which features a fiber optic cable inserted through the nose). A stroboscopy video system will be used to directly visualize and record the vocal folds in vivo of participants during vocalization at systematically varied loudness, while simultaneous measurements of the expiratory aerosol emission rate will be performed using an aerodynamic particle sizer. Saliva samples from each participant will be collected to measure the storage and loss moduli of the saliva with a double-gap geometry rheometer, and to measure the extensional viscosity and drop formation dynamics using capillary break-up rheometry in a liquid bridge geometry. The combination of these multiple data streams over a statistically significant number of different participants will inform complementary fluid mechanics modeling and provide unprecedented and fundamental insight into expiratory droplet formation, potentially providing a fluid mechanical explanation for why some individuals are super-emitters of expiratory aerosols.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.