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The speed of sneezing is shown for four different types of nose and mouth. A) is the open nasal passage with teeth, B) is the open nasal passage without teeth, C) is the blocked nasal passage without teeth and D) is the nasal passage blocked with teeth. Credit: University of Central Florida
According to a new study, sneezing from people who have a congested nose and a full set of teeth travel about 60 percent more than people who don’t.
New research from the University of Central Florida has identified physiological characteristics that could make people super-spread of viruses like COVID-19.
In a study that appeared this month in the journal Fluid physics, researchers from UCF’s Department of Mechanical and Aerospace Engineering used computer-generated models to numerically simulate sneezing in different types of people and determine associations between people’s physiological characteristics and the distance traveled by sneezing droplets and their permanence in the air.
They found that people’s characteristics, such as a stuffy nose or a full set of teeth, could increase their potential to spread viruses by affecting the distance the droplets travel when they sneeze.
According to the U.S. Centers for Disease Control and Prevention, the primary way people become infected with the virus that causes COVID-19 is through exposure to respiratory droplets, such as sneezing and coughing, that carry infectious viruses.
Knowing more about the factors that influence the travel distance of these droplets can inform efforts to control their spread, says Michael Kinzel, assistant professor in UCF’s Department of Mechanical Engineering and co-author of the study.
“This is the first study that aims to understand the ‘why’ behind how far sneezing travel,” Kinzel says. “We show that the human body has influencers, such as a complex system of ducts associated with the nasal flow that actually stops the jet from the mouth and prevents it from dispersing droplets over great distances.”
For example, when people have a clean nose, such as blowing it into a handkerchief, the speed and distance of sneezing droplets decrease, according to the study.
This is because a clear nose provides a path beyond the mouth for the sneeze to exit. But when people’s noses are congested, the area from which the sneeze can come out is narrowed, thus causing an increase in the speed of the sneeze droplets expelled from the mouth.
Likewise, the teeth also narrow the sneeze exit area and increase the speed of the droplets.
“The teeth create a shrinking effect in the casting which makes it stronger and more turbulent,” says Kinzel. “They actually seem to lead the broadcast. So, if you see someone with no teeth, you can actually expect a weaker sneeze jet from them. “
To perform the study, the researchers used 3D modeling and numerical simulations to recreate four types of mouth and nose: a person with clean teeth and nose; a person without teeth and a clean nose; a person without teeth and a congested nose; and a person with congested teeth and nose.
When they simulated sneezing in the different models, they found that the spray distance of the droplets expelled when a person has a congested nose and a full set of teeth is about 60 percent greater than when they don’t.
The results indicate that when someone keeps their nose clean, for example by blowing it into a handkerchief, it could reduce the distance their germs travel.
The researchers also simulated three types of saliva: thin, medium and thick.
They found that thinner saliva resulted in sneezing consisting of smaller droplets, which created a spray and stayed in the air longer than average, thick saliva.
For example, three seconds after a sneeze, when thick saliva reached the ground and thereby lessened its threat, the thinner saliva still floated in the air as a potential transmitter of disease.
The work ties into the researchers’ project to create a COVID-19 cough pill that would give people thicker saliva to reduce the distance that droplets from a sneeze or cough would travel, thereby reducing the likelihood of disease transmission. .
The findings provide new insight into the variability of exposure distance and indicate how physiological factors affect transmissibility rates, says Kareem Ahmed, associate professor in UCF’s Department of Mechanical and Aerospace Engineering and co-author of the study.
“The results show that exposure levels are highly dependent on fluid dynamics which can vary according to different human characteristics,” says Ahmed. “Such characteristics may be factors behind superspreading events in the COVID-19 pandemic.”
The researchers say they hope to shift work to clinical trials to compare their simulation results with those of real people from different backgrounds.
Co-authors of the study were Douglas Fontes, postdoctoral researcher at the Florida Space Institute and lead author of the study, and Jonathan Reyes, postdoctoral researcher at UCF’s Department of Mechanical and Aerospace Engineering.
Fontes says that to advance the study results, the research team wants to investigate the interactions between gas flow, mucus film, and tissue structures within the upper respiratory tract during respiratory events.
“Numerical models and experimental techniques should work side by side to provide accurate predictions of the primary rupture within the upper respiratory tract during those events,” he says.
“This research will potentially provide information for more accurate safety measures and solutions to reduce the transmission of pathogens, offering better conditions for dealing with normal diseases or pandemics in the future,” he says.
Reference: “A Study of Fluid Dynamics and Human Physiology Factors Driving Droplet Dispersion from a Human Sneeze” by D. Fontes, J. Reyes, K. Ahmed and M. Kinzel, November 12, 2020, Fluid physics.
DOI: 10.1063 / 5.0032006
The work was funded by the National Science Foundation.
Kinzel received his doctorate in aerospace engineering from Pennsylvania State University and joined UCF in 2018. In addition to being a member of the UCF Department of Mechanical and Aerospace Engineering, part of UCF’s College of Engineering and Computer Science, he works also with the Center for Advanced Turbomachines and Energy Research.
Ahmed is an associate professor in the UCF Department of Mechanical and Aerospace Engineering, a faculty member of the Center for Advanced Turbomachinery and Energy Research and the Florida Center for Advanced Aero-Propulsion. He worked for more than three years as a senior aeronautical / thermal engineer at Pratt & Whitney military engines working on advanced engine programs and technologies. He also served as a faculty member at Old Dominion University and Florida State University. At UCF, he leads research in the field of propulsion and energy with power generation applications and gas turbine engines, jet propulsion engines, hypersonic and fire safety, as well as research related to supernova science and to control COVID-19 transmission. He received his doctorate in mechanical engineering from the State University of New York at Buffalo. He is an associate member of the American Institute of Aeronautics and Astronautics and a faculty member of the US Air Force Research Laboratory and the Office of Naval Research.
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