Functions of paranasal sinuses

Functions of paranasal sinuses

The following are the possible functions of paranasal sinuses:

Imparting resonance to the voice: Bartholinus in 17th century proposed that the paranasal sinuses played a viral role in resonation of spoken words. Howell studied Maori people of New Zealand and attributed their dead voices to their poorly developed paranasal sinuses. Proetz questioned this theory saying that Lions which had huge roars had small sinuses. He also went on to suggest that Guinea pig and Giraffes which had feeble voices had well developed sinus cavities.

Negus demonstrated through his comparative study that presence or absence of sinuses had no role to play in determining the quality of voice.

Humidification & warming of inspired air: Air exchange is known to take place inside paranasal sinuses during respiration. The quantum of exchange is of course negligible. Since the quantum of air exchange has found to be negligible, it is unlikely for significant amount of humidification occurring inside the sinuses. It has been experimentally demonstrated that even after full 5 mins of respiration, air inside the maxillary sinus cavities are not exchanged at all.

Increasing the olfactory area of nose: Cloquet in 1930 proposed that human maxillary sinus mucosa is of olfactory sensory epithelium type. He also presumed that the mucosal lining of paranasal sinuses increased the surface area of olfactory epithelium. This surmise of course is false given the type of epithelial lining of maxillary sinuses.

Providing thermal insulation to vital parts of head: It was proposed by Proetz that sinuses functioned as thermal insulators much like the water jacket of internal combustion engine. It has been observed that Eskimos don’t have frontal sinuses while Africans have large frontal sinuses. These facts go on to prove that thermal insulation could not be the only function of paranasal sinuses.

Shock absorber function: Negus proposed that paranasal sinuses could play a role in absorbing shock and protecting the sense organs from the effects of shock. Blaney showed that species more prone to injuries to critical sense organs had relatively small paranasal sinuses thus making this theory redundant.

Aiding facial growth: Proetz proposed that the human frontal and maxillary sinuses were designed to assist forward and downward growth of the face. To substantiate this theory he pointed out that frontal sinuses develop along with advancement of the face, while the maxillary sinuses develop with the growth of jaw and sphenoid. Negus rejected this theory pointing out patients with deficient / poorly developed frontal sinuses had normal facial skeletal growth.

Eckel’s theory: Eckel surmised that it was bite and chewing functions that determined the size of maxillary sinuses.

Evolutionary remnants: Negus concluded that there is no functional reason to account for the presence of paranasal sinuses. He stated that “we possess the paranasal sinuses because our ancestors did”.

Lightening the skull bones to maintain head position: This theory suggests that paranasal sinuses reduced the weight of the skull. Studies involving the neck musculature suggest that the presence of sinuses don’t reduce the weight of skull significantly.

Floatation device: Hardy and Evan’s suggested that paranasal sinuses could act like a floatation device. This helps in maintaining the nose above the level of water while swimming.

Secreting mucous to moisten the nasal cavity: Haller suggested that paranasal sinuses played an important role by moistening the nasal cavity mucosa. This has however been found to be untrue since the mucosal glands in the maxillary sinus is very little when compared to that of nasal mucosa.

Aiding nasal cavity immune defense and production of nitric oxide: Sinuses play a vital role in aiding the immunological function of the nasal mucosa. Nitric oxide has been found to be generated by mucosa of paranasal sinuses in very large quantities. Nitric oxide has been postulated to have an antiviral and bacteriostatic function. It also upregulates the ciliary beat frequency.