Post created by: Matheus
A subject that has gain notoriety in all sources of communication (media) is the sars-covid-2. One of the most common symptoms is a dry cough. So, I began to wonder how does a cough happens and what are the mechanisms behind it. Interesting enough, physics play a major role in this process.
First of all, there are three main stages in the physiology of cough: the inspiratory phase, compression phase, and expiratory phase. Physics comes into play in the pressure-volume dynamics/interaction in the respiratory process.
In the inspiratory phase, both the atmospheric and intrapulmonary pressures are initially at 760mmHg. However, when the intercostal muscles and the diaphragm contract, they expand the thoracic cavity, allowing the intrapulmonary volume to increase. As consequence, the intrapulmonary pressure decrease 1mmHg (760 to 759mmHg). Following, Boyle's Law (P1V1=P2V2), atmospheric gases come into the lungs due to the decrease in intrapulmonary pressure.
In the compression phase, the glottis closes although the respiratory muscles continue to contract, increasing even more the pressure in the lungs.
Finally, in the expiratory phase, the glottis open, and the respiratory muscles relax decreasing the thoracic cavity volume. At this point there is a lot of pressure built up (761+ mmHg). Since the intrapulmonary pressure is greater than the atmospheric pressure, the air is pushed out of the lungs in the form of a cough.
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