Nasal Airway Obstruction

Septum

The septum is composed of several components, both bony and cartilaginous. Maxillary, palatine, vomerine, and ethmoid bones contribute to the bony septum. However, the anterior nasal septum is cartilaginous, which allows for the most protruding portion of the nose to be flexible. The cartilaginous septum is attached superiorly to the perpendicular plate of the ethmoid, the bony groove on the undersurface of the nasal bones, and the upper lateral cartilages; these structures are held together by the continuity of the perichondrium and periosteum. Anteriorly fibrous attachments to the medial crura of the lower lateral cartilages determine the integrity of the tip. Inferiorly, the cartilaginous and bony septum lie in the bony groove of the maxillary crest via dense fibrous connective tissue. Embryologically, the cartilaginous septum develops from the perpendicular plate of the ethmoid, yet it remains nonossified. As such, the overlying perichondrium is contiguous with the periosteum of the perpendicular plate. While the vomer has a different embryologic origin and maintains its own periosteum, it is separated at the transition point with the septum of ethmoid bone origin. This seemingly innocuous fact is an important one in that elevation of the mucoperichondrium at the juncture of the perpendicular plate of ethmoid is rarely met with resistance or perforation. The majority of perforations occur at the junction of the cartilage to the vomer due to the noncontinuous covering.

The flow of air in the nasal passage follows the basic tenets of physics and Ohm's law, whereby gases move when there is a pressure gradient, and this flow can be hampered by friction. In laminar flow in a passageway, the fluid in the center has the greatest motion while that which is in contact with the sidewalls is hampered and moves slowly. Turbulent flow results from random, nonlinear motion. In the nasal cavity, laminar flow is of utmost importance because it allows for appropriate humidification and proper mucociliary flow of mucus, while turbulence creates more friction and impairs both functions. The septum helps ensure a laminar flow pattern.

Turbinates

The three paired turbinates are located on the lateral nasal wall. The superior and middle turbinates arise from the ethmoid bone, whereas the inferior turbinates are made of independent bony structure. Covered by both respiratory and olfactory epithelium, the superior turbinate is located high in the nasal vault and usually arises from the cribriform plate of the ethmoid bone. The middle turbinate has a less consistent site of origin and could arise from the cribriform plate, the lamina papyracea, or the uncinate process in some cases.

The inferior turbinate bone arises on the inferior portion of the lateral nasal walls. The bone itself is penetrated heavily by vascular channels, which supply the overlying respiratory epithelium. The lacrimal duct drains into the nose just lateral to the inferior-anterior portion of the inferior turbinate.

The anterior tip of the turbinates not only directs the air along the passageway to the nasopharynx in a laminar fashion but also acts to deflect some of the air upward towards the olfactory mucosa, thus facilitating olfaction. The nasal cycle , a periodic alternating engorgement and enlargement of the inferior turbinates on one side accompanied by contralateral turbinate shrinkage, occurs in about 85% of people. The cycle takes anywhere between 3 to 4 hours to complete, and the total airflow throughout the cycle remain constant. Often, in the postoperative setting, patients complain of alternating nasal obstruction, which is in effect a heightened awareness of the cycle due to surgery and resultant hypersensitivity.