Pathophysiology of sinusitis

Commonly the sinus cavity is not sterile. They contain micro organisms (commensals).

Pathogens causing sinus infections: Pneumococci, H. Influenza, and anaerobes.

Viral infections cause damage to the lining mucous membrane of the sinus cavity ie maxillary sinus. This damage leads to formation of exudate. The mucosal glands start to secrete. Since the mucosal oedema has blocked the drainage ostium, the secretions are pent up within the sinus cavity forming a nidus for infections.

The oxygen levels within the maxillary sinus is dependent on the patency of the natural ostium, and mucosal absorption. In this case the ostium is blocked, no oxygen is coming from the atmosphere into the sinus cavity. On top of it the inflamed sinus mucosa tends to absorb excessive amounts of oxygen from the sinus cavity. This leads to low partial pressure of oxygen inside the sinus cavity. The increasing levels of carbon dioxide causes a raise in antral pH. This elevated pH affects the mucociliary clearance mechanism adding to the woe.

The impaired ventilation causes to change the antral environment making it conducive overgrowth of anaerobes. The serous sinusitis becomes converted to purulent sinusitis now.

Factors influencing mucociliary clearance mechanism:

1. Temperature: The cilia optimally beats in temperature ranging from between 30 - 40 degrees centigrade. Any temperature above and below this level slows down the ciliary beat causing stasis within the sinus cavity.

2. Normal oxygen tension within the sinus cavity is a must for optimal ciliar motility. Reduced oxygen levels within the sinus cavity also hampers ciliary motility

3. Humidity: Excessive drying hampers ciliary motility. The humidity within the sinus cavity should be at least 90%.