Physiology to Disease Transmission of Respiratory Tract Infection: A Narrative Review.

INTRODUCTION

In the current scenario of the COVID 19 pandemic, the protective reflexes, namely sneeze and cough, have received great importance. However, it is not in terms of protection but in terms of the spread of infection. The present review tries to bring out the correlation between the physiology of sneeze and cough, taking into consideration the various receptors that initiate the two reflexes, then correlating it with the formation of expelled droplets and the significance of various aspects of droplets that lead to the spread of infection.

MATERIAL AND METHODS

For the compilation of the present review, we searched the terms "Physiology of cough", "Physiology of sneeze", "droplets", "aerosols" and "Aerosols in COVID 19". The above-mentioned terms were extensively searched on PubMed, Google Scholar, and google search engine. After reviewing the various available material, the most significant research has been considered for this review.

CONCLUSION

Through this review, we conclude that there are various factors responsible for the initiation of sneeze and cough, but in the case of infection, it is mainly the inflammatory reaction that directly stimulates the receptors to produce the reflex outburst air. As the flow of air during expiration is turbulent, it causes damage to the Epithelial Lining Fluid present in the respiratory conduit. In addition, it gets admixed with the saliva in the oropharynx and oral cavity and mucus in the nose to form droplets of various sizes. Large droplets settle close and are responsible for droplet and fomite transmission, but the smaller droplets remain suspended in the air and travel farther distances to cause airborne transmission. The spread of droplet cloud in sneezing may range to 6m or more as compared to cough; hence the concept of 1m to 2m of social distancing does not hold reliable if the patient is sneezing.