Coughing downwards decreases the spread of droplets

A team of researchers has found that cough-generated droplets can spread less if you cough downwards.

The study has been published in the 'AIP Advances'.

Researchers described the dispersion of cough-generated droplets that came from people as they walked up and downstairs. Hongping Wang and his team showed models driving how respiratory droplets fell from a mannequin inside a water tunnel, which was inclined at different angles to mimic a person going up and downstairs.

"Two different patterns of droplets dispersion are observed due to the different wake flows," said Wang.

"These results suggest that we should cough with the head down toward the ground to ensure that most of the droplets enter the wake region," Wang added

The group 3D-printed mannequins using white resin, each with a different inclination angle to represent the leaning in that we naturally do when going upstairs and the leaning back when we walk down.

After placing each mannequin in the water tunnel, they introduced hollow glass microspheres into the tunnel. When illuminated by lasers, the glass microspheres provided a way to visualize the flow motion behind the mannequins. This flow field, often called a wake, was studied using a technique called particle image velocimetry.

In computer simulations, particles lower than the head and moving toward the ground became caught in each mannequin's wake and moved downward. It appeared particles above the head were able to move relatively far distances horizontally as if they were emitted from the top of the head.

For the mannequins whose inclines reflected going upstairs, particles concentrated below the shoulder and moved downward with a short travel distance. For simulating going down, particles dispersing over the person's head were carried for a long distance.

"The major challenge is how to use particles in water to simulate the droplets in the air," Wang said.

"The most surprising part was that the particles higher than the head can travel a much longer distance than those particles lower than the head due to the induction of the wake flow," Wang added.

Wang wants to study the 3D effects of what happens when real people cough while walking in experimental conditions.