Function of the
Paranasal Sinuses
Kyung Shik Suh, M.D.
The possible functions of the sinuses are as follows:
1. air conditioning
2. pressure damping
3. reduction of skull weight
4. heat insulation
5. flotation of skull in water
6. increasing the olfactory area
7. mechanical rigidity
8. vocal resonance and diminution of auditory feedback
On the other hand, the sinuses may have no function at all.
or paranasal sinuses (are)
1. rudimentary in human but of olfactory use in animals
2. give some assistance in olfactory function by evenly distributing the inspired air in the olfactory region
3. lighten the skull for better balance
4. resonators for voice
5. areas for the production of mucus to moisten the nasal chambers and inspired air1923 (Skillern,R.H.)
Nitric Oxide(NO) study - NO is more produced in the paranasal sinuses(for protective function?)
The biologic purpose of the nasal sinuses is largely speculative. It is obvious that the pneumatized cavities of the bone of the skull reduce the weight, at the same time increasing the superficial extent of the bones of the skull.
The existence of the ostia causes particular pathophysiologic problem affecting ventilation and drainage.
Ostial obstruction interrupts the self-cleaning mechanism of the affected sinus; therefore, the secretions stagnate and change in composition. The retained secretions form an ideal medium for saprophgic bacteria which are often present in normal sinuses.
Ostial obstruction often also causes a vicious circle.
The causes of closure of the ostium include:
1. Environmental factors such as relative dryness of the nose, toxic gases, or agents in the air.
2. Local congenital or acquired anomalies, including:
deviation of septum, scars, lesions of the turbinates, infections of the nose or nasal cavities, dental diseases, allergic diseases of the nose or nasal sinuses(particularly in children),vasomotor dysfunctions with a neurogenic hormonal basis, metabolic diseases such as avitaminoses, diabetes, disordered electrolytes, mechanical obstruction due to crusts, polypi, foreign bodies, prolonged use of a nasogastric tube or prolonged nasotracheal intubation, and benign and malignant tumors.
ostial obstruction ---> oxygen tension is impaired ---> ciliary activity is reduced ---> stasis of secretions ---> saprophyte infection ---> thickening of mucosa ---> internal osium obstruction by thickened mucosa ---> ongoing inflammation(vicious cycle)
Ostium size
Blockage of the natural sinus ostium results in a reduction of ventilation and stasis of secretions. If the ostium size is below 2.5 mm, it predisposes to the development of disease (Aust, Drettner and Hemmingsson, 1976).
Pressure changes
The pressure in the maxillary sinus varies with respiration but lags behind by 0.2 s. There is little fluctuation when the nose is patent, and the variation of pressure during quiet respiration and on exercise. If the nose is blocked then the pressure fluctuations are much more marked. Barotrauma is five times less common than in the ear and is most frequently seen in the maxillary sinuses, particularly in divers.
Summary
The volume of the largest sinus is under 50 ml and, therefore,
the sinuses contribute little to air conditioning Similarly, a
damper has to have a large volume to be effective. The reduction
of skull weight is small compared to the overall weight.
Most of the cranial activity is away from the sinuses so they
play little part in insulating the brain. Man has long ceased to
be an amphibian. It is probable that apart from mucus production
and some strengthening of the facial bones, the paranasal sinuses
have little or no physiological function.
go to "Anatomy of Nose and PNS"(click here)
go to "Paranasal Sinuses, Anatomy and Nomenclature" for further study(click here)