Prone positioning is not an airway clearance technique. It is used to correct ventilation to perfusion matching which is impaired in acute respiratory distress syndrome (ARDS).

Thread. #physiology #COVID2019 #cvpPT

Acute respiratory distress syndrome (ARDS) due to a viral infection (ex. COVID) is not an “airway clearance” problem. It’s a ventilation to perfusion problem due to changes in the epithelial layers of the type 1 alveolar cells and pulmonary capillary.

Normally those epithelial layers create a barrier that only permits at most a trace amount of fluid into the alveoli and the space between the layers. The space between the two layers is incredibly small, it is about 1 cell thick.

If the amount of fluid increases, ion pumps in the type 1 and type 2 alveolar cells (which produce surfactant that reduce surface tension to keep the alveoli inflated or reinflate if they get compressed) are able to mobilize it out & into the lung microvasculature and lymphatics.

This is necessary because if the size of that space between the capillary and alveoli increases or if excessive fluid enters into the space, it will impair the ability for gases to exchange in and out of your lungs.

This means your body won’t be able to take in enough oxygen or expel carbon dioxide. This means you will have problems fueling the cells in your body through oxidative respiration and keeping your blood PH normal.

When you have widespread inflammation in the lungs which can occur with a viral infection, the epithelial layers separate. This permits a large amount of fluid into the alveolar space and alveoli from the capillaries.

If the amount of fluid becomes too high it will overtax the fluid regulatory systems and if severe enough can fill the alveoli. This causes major impairments to gas exchange.

A large amount of fluid in the lungs can also make it hard for the lung to expand. If the amount of fluid gets too high, it can even leech into the pleural space causing pleural effusion making it even harder for the lungs to expand.

Early reports suggest that COVID also damages the type 2 alveolar cells, resulting in less surfactant; making it hard for the alveoli to stay inflated or reinflate if they get compressed (ie fluid) & increases the surface tension in the lungs..

Taken together COVID impairs has exchange, impairs lung expansion (restrictive defect) and also significantly increases the work of breathing. This is why positive pressure or mechanical ventilators are needed in severe cases to keep people alive.

This is also why chest physiotherapy and airway clearance techniques aren’t really indicated for these cases of COVID because it’s not really what’a causing the problems.