[Physiology of the sinuses. Physiopathology of sinusitis].

Ventilation and drainage are the two essential intrinsic functions of the sinus. Both of them are dependent upon the permeability of the ostium, whose caliber is extremely variable with respect to anatomical factors, and dynamic factors associated with the vasomotricity of the mucous membrane. In many subjects the ostial permeability is precarious, thus explaining the frequency of inflammatory sinus reactions. These are due, as the level of the middle ear, either to a transostial inoculation of pathogenic germs creating a microbial sinusitis, or to an ostial obstruction responsible for a hypoxia, a hypercapnia, and a local depression creating a a vacuo sinusitis. The second situation leads to conditions that are favorable for the development of the first and vice versa.