In simpler times, when someone sneezed, the common response from those nearby was a polite “Gesundheit.”
Today, if someone sneezes, the room empties out faster than you can say “pandemic.”
That’s because the COVID-19 virus is mainly spread through respiratory droplets or small particles that are produced when an infected person sneezes, coughs, talks, or breathes — so-called expiratory events. While the aerodynamics of such droplets have been the focus of many studies, little is known about the journey of these expelled droplets and where they come to rest.
Arshad Kudrolli has worked to change that.
The Clark physics professor received a $200,000 grant for Rapid Response Research from the National Science Foundation Division of Materials Research to examine transmission rates, explore ways to mitigate risk, and suggest strategies to avoid another pandemic. Through this research, Kudrolli and his team study not only how respiratory droplets move through the air during normal expiratory events, but also how the virus-laden particles may affect health care providers when exhaled by patients using oxygen delivery devices.
The latter study, which Kudrolli says is the first of its kind, led him to recommend that patients on supplemental oxygen be outfitted with face masks to better protect caregivers.
“The work we’ve done has illuminated how far exhalations travel and can affect people where they’re standing,” he explains.
To better understand how mucosalivary droplets are distributed on surfaces after expiratory events, Kudrolli and students Brian Chang, a postdoctoral researcher in Kudrolli’s lab, Ram Sharma ’19, M.A. ’20, and Trinh Huynh ’21 spent several months tracking how particles travel through the air. That research led Kudrolli to collaborate with Dr. William McGee, MHA ’97, a critical care doctor at Baystate Medical Center in Springfield, Massachusetts, on a second study to investigate how aerosols and droplets are exhaled from patients on breathing devices, such as simple face masks or nasal cannulas.
The team began its research last spring by creating a mechanical spray inside a 3D-printed mannequin face to expel fluorescent-tagged mucosaliva — made from a combination of water and mucin (large, heavily glycosylated proteins that give mucus its slimy feel) — to imitate a human sneeze. They employed a high-speed camera to examine the “puff cloud” dynamics of the droplets, landing times, and spatial distribution on a flat surface.
The mannequin was also outfitted with a standard medical mask to determine how effective face masks are at reducing droplet dispersal.
The researchers found that the six-foot guideline for social distancing is effective, but time guidelines should also be followed because droplets may linger in the air for several seconds or longer after an expiratory event, according to Chang. The team also found that standard medical masks are effective at stopping the spread of droplets — reducing the dispersed mucosaliva by a factor of at least 100 compared to the dispersal when unmasked.
“Masks are effective, even if they aren’t perfect,” Chang says. “That was our most important finding.”
Story continues after video
During the second study, Kudrolli and students Anton Deti ’22 and Jade Consalvi ’22 collaborated with Dr. McGee to study how aerosols and droplets are dispersed by patients on supplemental oxygen. McGee approached Kudrolli about the study after learning of the professor’s COVID-19 transmission research from a newspaper article. “That question had never been fully answered, and I thought he could help us do that,” McGee recalls. “Ultimately, he did.”
The researchers outfitted a medical mannequin with a mechanical lung controlled by a ventilator to simulate human breathing, with fog drawn into the lung and exhaled through the mannequin’s mouth and nose. The team then used green lasers and a flood light with backlighting to illuminate the fog, tracking how aerosols and droplets travel under various conditions, and captured images using a high-speed camera.
The study revealed that health care workers can help control the spread of virus-laden particles by placing a simple medical mask over oxygen delivery devices.
“Typically, what happens is when patients are put on these devices, the exhalations are traveling straight ahead or to the side. This is where a caregiver is located. Our idea was that we would put a simple surgical mask [on the patient], very lightly, so that it would deflect the exhalation backward and away from the faces of these caregivers,” Kudrolli explains. “That was something very concrete that our work has been able to demonstrate for the first time. We not only illustrated the problem, but we came up with a solution that can be carried out everywhere across the world very simply.”
McGee says virtually every patient admitted to the hospital with COVID-19 is given supplemental oxygen, adding that masking the patient will help protect not only hospital workers, but other caregivers including firefighters and EMTs. This same technique can also be applied to help control the spread of other infectious respiratory diseases like tuberculosis, he says.
“In the United States, many of us are getting vaccinated and we feel like we have an adequate supply of PPE. That is not true in most of the world, so there’s a huge opportunity to use these inexpensive surgical masks we’ve all become familiar with,” McGee says. “At this point in the pandemic, we cannot overemphasize, especially in underresourced parts of the world, how this simple strategy will be effective and ultimately save lives.”