A sneeze simulator reveals the role of the nasal cavity in the dispersion of respiratory aerosols

Researchers at the Universitat Rovira i Virgili have developed a simulator capable of replicating intense respiratory episodes - such as coughing or sneezing - to study the dispersion of particles that carry respiratory diseases. The results of the study demonstrate the impact of the nasal cavity on the delivery and dispersion of aerosols. The new data provide information to improve personal protective equipment, such as masks, and to design ventilation systems that reduce exposure to pathogens in shared environments and the consequent transmission of diseases.

Respiratory aerosols are one of the main mechanisms of transmission of diseases such as influenza, COVID-19 and tuberculosis. They are produced when we cough or sneeze, and are made up of tiny particles that are dispersed in the air. Despite advances in understanding these processes, the anatomical variability of human respiratory systems and the intensity of respiratory episodes have made it difficult to obtain data to understand how aerosols are dispersed and how we can mitigate the transmission of the pathogens they carry.

To overcome these limitations, the ECoMMFiT research group has created a simulator that reproduces in a precise and controlled manner the particulate matter generated by coughing and sneezing. It is a three-dimensional model of the upper respiratory tract, including the nasal cavity, the organ that determines the aerosol evacuation trajectory. The device varies the degree of opening of the nostrils in order to alter air flows and thus reproduce respiratory episodes with different configurations. The device makes it possible to adjust parameters such as speed, air and exhalation duration to achieve an accurate reproduction of respiratory flows in different conditions. In data collection, the research team used high-speed cameras and a laser beam, which allowed them to study particle dispersion in detail in real time.

The results of the research reveal that the nasal cavity has a significant impact on aerosol dynamics. When the nose participates in exhalation - when we exhale with the nose - aerosols tend to disperse more vertically and less horizontally. This may reduce the risk of direct transmission between people in the vicinity, but it also makes it easier for particles to remain in suspension for longer and to be distributed evenly in space. In confined environments with little ventilation, this accumulation increases the concentration of aerosols and, therefore, the risk of long-term exposure by other individuals.

In contrast, in the absence of nasal spray - when we exhale through our mouths - aerosols follow a more horizontal path and cover a greater distance. This pattern increases the risk of transmission in close proximity, as particles are more likely to be directly deposited on people in close proximity, especially in situations such as face-to-face conversations or in shared environments.

"These results help us to understand how particle nuclei are dispersed in indoor spaces and, consequently, how diseases are transmitted through the air," explained Nicolás Catalán, a researcher at the URV's Department of Mechanical Engineering. In this sense, it is crucial knowledge for designing personal protective equipment, such as masks, or for improving ventilation systems in high-risk environments such as hospitals, laboratories or educational centres in order to reduce the risk of contagion.

Moreover, in the process of the research, the team designed an analytical model capable of predicting the evolution of aerosol nuclei according to variables such as the speed of exit, the volume of air exhaled and the conditions of the respiratory system. "It is a tool that we have been able to validate experimentally; it is applicable in different situations and could be a useful resource in future projects," said Catalán, co-author of the research.

By eliminating individual variability and providing more consistent data, the method used in this research represents an improvement on previous studies, which collected data by studying intense respiratory episodes in volunteers. Nevertheless, the researchers stress the need to extend the research to "include environmental factors, such as temperature and humidity, and to explore the long-term dispersion of aerosols"

Reference: Catalán, N., Cito, S., Varela, S., Fabregat, A., Vernet, A., & Pallarès, J. (2024). Effects of nasal cavity and exhalation dynamics on aerosol spread in simulated respiratory events. Physics of Fluids, 36(12). https://doi.org/10.1063/5.0241346

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