March 2, 2022

Coughing downward can reduce spread of droplets, study finds

A new study has found that coughing towards the ground can reduce the spread of droplets and aerosols, thus potentially reducing the spread of respiratory illnesses such as COVID-19.

Researchers published their findings in the journal AIP Advances on Tuesday. They put a mannequin model in a water tunnel and illuminated the tunnel with lasers to visualize how the particles would flow. They also inclined the mannequin at different angles to simulate a person going up and down stairs.

As the mannequin would move, it would create a flow field, or a wake, in its path. The researchers found that particles higher than the head were easily able to ride the wake flows.

On the other hand, when the mannequin was angled forward to simulate a person walking upstairs, the researchers found that the wake would cause particles positioned lower than the head to be angled downward and unable to move long distances.

Lead author Hongping Wang calls this the “most surprising” finding.

“Two different patterns of droplets dispersion are observed due to the different wake flows,” Wang said in a news release. “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.”

The study isn’t without its limitations. The researchers used lasers in a water-filled environment to simulate and visualize the flow of air, rather than using an air-filled environment. Wang hopes to follow up on his experience with another study looking into the effects of real people coughing.

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

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