Department of Laboratory Medicine, National University of Singapore, Singapore.
J R Soc Interface. 2009 Dec 6;6 Suppl 6(Suppl 6):S727-36. doi: 10.1098/rsif.2009.0295.focus. Epub 2009 Oct 8.
Various infectious agents are known to be transmitted naturally via respiratory aerosols produced by infected patients. Such aerosols may be produced during normal activities by breathing, talking, coughing and sneezing. The schlieren optical method, previously applied mostly in engineering and physics, can be effectively used here to visualize airflows around human subjects in such indoor situations, non-intrusively and without the need for either tracer gas or airborne particles. It accomplishes this by rendering visible the optical phase gradients owing to real-time changes in air temperature. In this study, schlieren video records are obtained of human volunteers coughing with and without wearing standard surgical and N95 masks. The object is to characterize the exhaled airflows and evaluate the effect of these commonly used masks on the fluid-dynamic mechanisms that spread infection by coughing. Further, a high-speed schlieren video of a single cough is analysed by a computerized method of tracking individual turbulent eddies, demonstrating the non-intrusive velocimetry of the expelled airflow. Results show that human coughing projects a rapid turbulent jet into the surrounding air, but that wearing a surgical or N95 mask thwarts this natural mechanism of transmitting airborne infection, either by blocking the formation of the jet (N95 mask), or by redirecting it in a less harmful direction (surgical mask).
已知各种传染性病原体可通过感染患者产生的呼吸道飞沫自然传播。这些飞沫可能是患者在正常呼吸、说话、咳嗽和打喷嚏时产生的。纹影光学方法以前主要应用于工程和物理领域，但在这里可以有效地用于非侵入性地可视化室内环境中人体周围的气流，而无需示踪气体或空气传播颗粒。它通过显示由于空气温度实时变化而产生的光学相位梯度来实现这一点。在这项研究中，对戴和不戴标准手术口罩和 N95 口罩的志愿者咳嗽进行纹影视频记录。目的是描述呼出气流，并评估这些常用口罩对通过咳嗽传播感染的流体动力学机制的影响。此外，还通过计算机跟踪单个湍流涡的方法对单次咳嗽的高速纹影视频进行了分析，证明了对呼出气流的非侵入式测速。结果表明，人咳嗽会将快速的湍流射流喷射到周围的空气中，但戴手术口罩或 N95 口罩会阻止射流的形成（N95 口罩），或者将其引导到危害较小的方向（手术口罩），从而破坏这种自然的空气传播感染机制。
