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Health Effects
Published in Wayne T. Davis, Joshua S. Fu, Thad Godish, Air Quality, 2021
Wayne T. Davis, Joshua S. Fu, Thad Godish
The respiratory system is protected from airborne contaminants by a variety of defense mechanisms. In the nasal region, the stiff nasal hairs or impaction on the mucus layer of the winding passages of the turbinates may remove large particles. Cilia sweep the mucus layer and entrapped particles toward the back of the throat where they are swallowed or expectorated. Contaminants may also be removed from upper airways by the sneeze reflex.
Toxicity and Toxins
Published in Gary S. Moore, Kathleen A. Bell, Living with the Earth, 2018
Gary S. Moore, Kathleen A. Bell
The respiratory system is composed of the nose, pharynx, larynx, trachea, bronchi, and lungs (Figure 5.2). Its function is to supply oxygen to the body’s cells and to expel carbon dioxide from the body in a process called respiration. The act of breathing or ventilation brings air into and out of the lungs. The exchange of oxygen and carbon dioxide between the atmosphere and blood is known as external respiration, while the exchange of gases between blood and individual cells is called internal respiration. Air is drawn into the nasopharyngeal area through nasal hairs at the vestibule and then over mucous- membrane-covered bony plates called the nasal conchae. These structures combine to filter, warm, and moisten inhaled air. Additionally, nerve endings in this nasal area may be stimulated to cause a sneeze reflex helping to eliminate the mucous and the trapped particles. The inhaled air then enters the trachea-bronchial area where the bronchi branch into numerous bronchioles with even smaller diameters until they terminate into thin-walled, delicate alveoli where gas exchange takes place. The trachea, bronchi, and bronchioles are lined by a velvety layer of cilia with mucous cells throughout. Particles such as dust and pollen of 10 mm or larger are removed by the constant streaming of mucous propelled from the bronchial and tracheal passages by the cilia beating at over 1300 times per minute in a process known as mucociliary streaming. The tube-like structures of the bronchi and trachea are surrounded by layers of smooth muscle that contract in response to irritating substances and allergens (Figure 5.3). This bronchoconstriction narrows the lumen and restricts the flow of air, other gases, and particles from reaching more delicate tissues deeper in the lung. This process may also be combined with excess mucous secretions or other fluids that make breathing difficult. When prolonged and severe, this process can be life threatening as in asthmatic attacks. A cough reflex may be initiated at the level of the bronchi to eliminate accumulated mucous in which foreign substances have become lodged.3,4,6
A pedestrian-based model for simulating COVID-19 transmission on college campus
Published in Transportmetrica A: Transport Science, 2023
The microscopic person-to-person transmission mechanism of respiratory infection diseases may include three modes: direct contact transmission, droplet transmission, and aerosol transmission (Zhang, Li, and Deng 2020). Droplet transmission and aerosol transmission are closely related to the transmission distance of cough/sneeze droplets and aerosols, which has been explored in many studies (Wells 1934; Duguid 1946; Breese 2007). It seems that the difference among these three modes of transmission is only reflected in the different distances between the infected and healthy people, but the prevention-control measures for these three modes differ a lot. Theoretically speaking, the above three transmission modes should be considered in each indoor scenario. However, to reduce the complexity of simulation and make simulation results more interpretable, direct contact transmission and droplet transmission are regarded as direct transmission in this study. It is assumed that the infection risk of susceptible people in the canteen scenario is caused by direct transmission while the infection risk of susceptible people in the classroom and dormitory scenarios can be attributed to prolonged exposure to infectious aerosols. Given the randomness of infection, we assume that person-to-person transmission follows the Bernoulli distribution.
Transmission characteristics of respiratory droplets aerosol in indoor environment: an experimental study
Published in International Journal of Environmental Health Research, 2022
Yanju Li, Chunbin Wu, Guoqing Cao, Dexing Guan, Chaoguo Zhan
Additionally, in terms of aerosol generating technology, some studies on an unobstructed cough sneeze and breath jet were conducted to examine the performance and dynamic interaction of a cough jet with different indoor airflow distributions, considering the interpersonal transport of coughed particles (Lindsley et al. 2013)(Liu and Novoselac 2014)(Tang et al. 2013)(Wei and Li 2017). Droplet number concentration and size distribution (coughing and talking) were measured by droplet experimentation, which were 9.01 × 107 and 8.23 × 107 droplets per cubic meter, respectively (You et al. 2013). The technique of generating viable bioaerosol was adopted in a previous study on the removal efficiency of uniform bioparticles under ventilation (Li et al. 2009). The literature has shown that the research on the distribution and propagation of droplet aerosol exhaled by human has achieved some results and basic data.
Assessment of environmental and surgical mask contamination at a student health center — 2012–2013 influenza season
Published in Journal of Occupational and Environmental Hygiene, 2018
Steven H. Ahrenholz, Scott E. Brueck, Ana M. Rule, John D. Noti, Bahar Noorbakhsh, Francoise M. Blachere, Marie A. de Perio, William G. Lindsley, Ronald E. Shaffer, Edward M. Fisher
Participants were asked to provide SMs that they wore for each patient exhibiting ILI. At the beginning of each day, prior to seeing any patients, participants donned an SM, wore it for 10 min, and then placed it into a sealable plastic bag to serve as a baseline. After seeing a patient with ILI, the participants placed their SM into a bag, using a separate bag for each new patient. Study participants were instructed to identify collection bags containing SMs that were exposed to a direct sneeze or cough during HCP-ILI patient interactions with a colored adhesive label. All SMs were stored at −20 °C until analysis. A subset of used SMs (15%) were analyzed to determine if influenza virus was present on the SM surface. All SMs that were identified as having been exposed to a direct sneeze or cough, worn during the administration of an aerosol generating procedure, or worn in a room with an influenza positive air sample were analyzed.