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Nasal anatomy, physiology, and function
Post-graduate
course
Nasal anatomy,
physiology,
Nathan
Geurkink,
M.D. Hanover,
and function
N.H.
Knowledge of the anatomy and physiology of the nose is a necessary prerequisite for understanding the pathophysiologic characteristics of rhinitis and occupational allergy. The nose and paranasal sinuses have a unique anatomical location, shape, and function in modifying and transforming inhaled air. The anatomy of the nose and paranasal sinuses and their basic physiologic functions are reviewed. (/ALLERGY CUN IMMUNOL 72:123-128, 1983.1
NASAL ANATOMY
AND DEVELOPMENT
The outward protuberance of the external noseencloses osseous,cartilaginous, epithelial, and neuroepithelial structures. Its outward appearancedoesnot necessarily provide any indication of its internal structure. The nasal passageis composed of a horizontally skin-lined vestibule with the passagesbeing directed upward and backward and separatedby a cartilaginous and bony nasal septum. The lateral nasal walls are convoluted with strategically placed air-warmer turbinates that mold the air streamto their configurations and changing dimensions.The accessorysinuses that communicate with the nasal chambers by their respective ostia are situated laterally in the maxilla, superiolaterally in the ethmoid bones, superiorly in the frontal bone, and posteriorly in the sphenoidbone. The olfactory cleft is situated in the superior portion of the nasal chamber. The histology of this mucous membraneof the noseand the paranasalsinusesvaries in its anatomical location. Both nonolfactory and olfactory epithelia are present. The nasal mucous membrane derives its sensory supply from the fifth cranial nerve and has both parasympatheticand symFrom the Hitchcock Clinic, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Hanover, N.H. Presented at the Postgraduate Course-Rhinitis, 39th Annual Meeting American Academy of Allergy, March, 1983, Hollywood, Fla. Received for publication Feb. 16, 1983. Accepted for publication Feb. 16, 1983. Reprint requests: Dr. Nathan Geurkink, Hitchcock Clinic, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Hanover, NH 03756.
pathetic autonomic nervous system fibers. The neuroepithelium for olfaction is derived from the first cranial nerve. The control of the arterial and venous supply to the mucous membrane of the nose by the autonomic nervous system is one of the most important fundamental physiologic phenomenathat will be reviewed. Internal anatomy-gross
and developmental
After about 3 wk of fetal life, olfactory placodes appear in the frontonasal processand within a week they becomenasalpits that are the first indication of a vestibular-like structure. By 5 wk of fetal age, the nasalpits have progressedinto cleftlike structuresand are separatedby a primitive septum. Around the sixth week of embryonic life, both maxillary and ethmoid folds begin to appearand theseare the first evidences of nasalturbinates. The nasalchamber and the primitive stomodeumare not separateduntil approximately 3 mo when palatal fusion is complete. During the third and fourth month of fetal life, the maxillary sinus, ethmoid sinus,and sphenoidsinusoutpouching begins.’ The vestibule of the adult noseis lined with squamousepithelium that contains vibrissae and sweatand sebaceousglands. Within this vestibule are baffles created by the protrusion of the medial crus of the lower lateral cartilage and the lower end of the upper lateral cartilage. Just superior to this is one of the more important areasof the nose. It has been called the nasal valve. It is the areaof the lateral nasal wall and the adjacent septumjust anterior to the tips of the middle and inferior turbinate and the upper border of the vestibule. This mobile portion of the nosehasthe 123
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ability to both open and close and creates a varying amount of air flow resistance. The nasal septum, which was first apparent as a broad, thick structure between the nasal pits, is ultimately composed of two separate supporting tissues. Anteriorly, the septum is composed of skin and cartilage and posteriorly, of thin sheets of bone. The cartilaginous septum is formed by a very large quadrangular cartilage that has a posteriorly directed tail called the sphenoidal process. In early life this sphenoidal process is in continuity with the sphenoid bone and would separate the perpendicular plate from the vomer. The perpendicular plate of the ethmoid forms the superior bony structure of the septum. Inferiorly, the septum is composed of the vomer, which forms the medial portion of the posterior choana. This rests on the nasal crest of the maxilla and the nasal crest of the palatine bone. The other cartilage of the septum is simply the medial crus of the alar cartilage. The quadrangular cartilage articulates with the premaxillary crest and the vomer in a tongue-and-groove fashion. The flared parts of the vomer and the premaxilla form what is known as premaxillary wings. These project into the airstream and act as baffles to air flow. The vomeronasal cartilages are structures associated with the rudimentary vomeronasal organ of Jacobson. In some animals there are olfactory nerves in this area, but in man the organ is very short and is of no apparent significance. Anterior rhinoscopic examination reveals that the septum varies in thickness from anterior to posterior. The septum in the area of the nasal valve and posterior to the anterior margins of the middle and inferior turbinates tends to be thicker so that the airstream is not precisely vertical but tends to curve in two different planes. It is not difficult to understand how deflections or deviations of this structure may cause increased airway resistance to the point of obstruction. The turbinates are located on the lateral nasal walls. The maximal development of the number of ethmoid turbinates occurs in the fetus at around 7 mo. After this, coalescence occurs, so that only two or three turbinates of the ethmoid group will be present at birth. These structures consist of an underlying bony framework. The inferior turbinate is attached to the medial wall of the maxillary bone, the middle turbinate is attached to the roof of the nose just lateral to the cribriform plate and laterally to the ethmoid bone, and the superior turbinate is situated in the sphenoethmoid recess. The bony skeleton shows this arrangement .2 The inferior turbinate is placed more anteriorly than either the middle or the superior, and the
J. ALLERGY
CLIN. IMMUNOL. AUGUST 1983
middle turbinate is anterior to the superior. The inferior meatus is that space lateral and inferior to the middle turbinate. In the anterior portion of this inferior meatus, the opening of the nasolacrimal duct is found. The middle meatus is that space beneath and lateral to the middle turbinate. The ostia of the frontal maxillary, and anterior and middle ethmoid sinuses, are found here. The middle turbinate is shaped more like a pontoon, whereas the inferior turbinate has no anterior overhanging edge. The superior turbinate is less than half the length of the other two turbinates and its anterior margin begins at about the middle of the middle turbinate. The posterior end of each turbinate ends in the posterior choana. The superior turbinate is located in the sphenoethmoid recess and is in close proximity to the front face of the sphenoid sinus. These bony structures are covered with mucoperiosteum and are very smooth and streamlined in appearance. The paranasal sinuses begin to develop as outpouchings of the mucosa of the nasal chamber during the third and fourth fetal months. The maxillary and ethmoid sinuses are present at birth. The frontal sinus is a very small diverticulum at birth and undergoes almost all of its development after birth. By about the third year of life, the sphenoid sinus invades the sphenoid bone. These sinuses may vary from individual to individual. The maxillary sinus is paired. It is the largest of the paranasal sinuses and is located within the body of the maxillary bone. The opening to the maxillary sinus is located on the highest part of its medial wall. Drainage of the sinus occurs by ciliary activity and it opens into the medial meatus, which is a common place for nasal polyposis. Because of this, it is common to have an obstructive phenomenon creating sinusitis. The number of ethmoid sinuses is more varied. They resemble honeycombs. There may be as few as three or four or as many as 18 or 20 cells and they are located lateral to the middle turbinate and medial to the medial orbital wall. The majority of these sinuses open into the middle meatus. The posterior ethmoid cells open into the superior meatus. The anterior ethmoid cells may invade the perpendicular part of the frontal bone. The size of the frontal sinus varies. The nasofrontal duct communicates with the middle meatus through the ethmoid infundibulum. The sphenoid sinuses are bilateral. They are in the posterior portion of the nose and are situated anteriorly and inferiorly to the sella turcica. The ostium is in the anterior wall and communicates with the sphenoethmoid recess. Its degree of expansion into
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Nasal
the sphenoid bone varies greatly. The capacity of the sinus may range from 1 to 30 mm, the average being approximately 7 mm. Vital structures are related to its lateral walls. The carotid artery, the optic nerve, the maxillary nerve, and the cavernous sinus are in very close proximity to this wall. The anatomic relationships of the sphenoid sinus with the pituitary gland and the nasal septum make it a ready avenue for surgical approaches to the pituitary gland. The olfactory cleft is that area of the nose between the middle turbinate and the septum. It is covered with the neuroepithelium of the olfactory nerve. The olfactory mucous membrane is limited to the upper third of the mucosa on the lateral wall of the nose and the adjacent part of the roof and corresponding parts of the septum. It is yellow in color. Histology of the mucous membrane nose and the paranasal sinuses
of the
The mucous membrane of the nasal cavity can be divided into the nonolfactory epithelium and the olfactory epithelium. The nonolfactory epithelium is a highly vascular tissue that is covered by a pseudostratified, columnar, ciliated epithelium. It is particularly thick in the area over the medial surfaces of the middle and inferior turbinates. It is very tightly attached to either perichondrium or periosteum, depending on its relationship to cartilage or bone in the nose. The thickness and the thermal properties of the mucosa in the nose are regulated by the sympathetic and parasympathetic nerve fibers that are supplied this membrane. Superficial and deep layers of arterioles supply the lamina propria. Between the venules and the capillaries are numerous sinuses or venous lakes that have been likened to erectile tissue because of the rapidity with which they can become engorged. Small muscle bundles are present at the distal ends of these venous lakes and act as sphincters to bring about an engorgement of the sinusoids. This pattern is most marked in the inferior turbinate area but is also present in the middle turbinate and on portions of the septum. The olfactory epithelium is pseudostratified columna in type and consists of specialized olfactory cells, supporting cells, and both serous and mucous glands. The olfactory cells are bipolar neurons and act as peripheral receptors and first-order ganglion cells. It has been estimated that 10 to 20 million cells are in each nasal fossa. Cilium-like rods protrude from these cells into the mucous blanket and the approximately 1000 filaments on the rods of each cell magnify the surface area of the cell itself. The axons of these olfactory cells form bundles to pass through the crib-
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125
riform plate as the olfactory nerves. There are approximately 20 nerves in each nasal fossa. Innervation The general sensation of the nasal cavity is supplied by the first and second divisions of the fifth cranial nerve. The branches of the first division of the fifth nerves supply the anterior superior and anterior portion of the nose. The vestibule of the nose is supplied by the infraorbital nerve. The autonomic nervous system plays a major role in the control of the vascular supply of the nasal mucous membrane. The parasympathetic innervation of the mucous membrane begins in the superior salivatory nucleus of the brainstem. Fibers from this nucleus unite with the fibers of the facial nerve and after leaving the geniculate ganglion join the postganglionic sympathetic fibers of the superior cervical ganglion. These fibers form the nerve of the vidian canal, which enters the sphenopalatine ganglion. The parasympathetic nerve fibers synapse at this ganglion and their postganglionic fibers are distributed to the nose and nasopharynx. Those fibers of sympathetic nervous system origin arise from the first and second thoracic segments of the spinal cord in the lateral horn cells. They exit from the spinal cord with the anterior nerve root and synapse in the superior cervical ganglion high in the neck. The postganglionic sympathetic fibers then form a network around the internal carotid’ artery and join the parasympathetic fibers from the seventh cranial nerve. They are distributed with the parasympathetic nerve fibers as branches of the sphenopalatine nerve. Vascular
supply
The arterial supply to the nose is derived from both the external and the internal carotid arteries. The terminal branch of the maxillary artery, which is a branch of the external carotid, supplies the sphenopalatine artery, which in turn supplies the lateral and medial wall of the nasal chamber. The anterior and posterior ethmoid branches come from the ophthalmic artery, which is a branch of the internal carotid artery. These vessels supply the anterior portion of the nose. In addition, there are twigs from the facial artery that supply the vestibule and the anterior portion of the septum. A few vessels from the greater palatine artery pass through the incisive canal of the palate to reach the anterior part of the nose. The veins of the nose drain into the sphenopalatine foramen and then into the pterygoid plexus, whereas others accompany the ethmoid arteries to join the su-
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perior ophthalmic vein. Those that are anterior in the nose drain into the facial vein. PHYSIOLOGY NOSE
AND FUNCTION
OF THE
In order to review the functions of the nose, the following factors should be considered: (1) airway, (2) air conditioning, (3) olfaction, (4) effects on speech, (5) reflex functions, and (6) common factors that will affect nasal blood flow. Airway The nose is one of the most important components to airflow resistance. It has been calculated to provide between 30% and 50% of the total resistance to inspiration. The cross-sectional diameter of the anterior nares is much smaller than the posterior choana, so that inspiratory air currents are much different than expiratory air currents. The former are directed upward across the superior surface of the inferior turbinate and the main surfaces of the middle turbinate into the nasopharynx. This upward direction is governed somewhat by the horizontal position of the anterior mu-es and the smooth anterior ends and surfaces of the turbinates and the shape of the septum. These streamlined structures tend to create a minimal resistance in guiding the inflow of air. The cartilaginous framework of the nasal alae prevents total collapse of these structures during negative pressure of inspiration. The nasal value is one of the most important structures governing the rate and volume of air traversing the anterior nares. The baffles created by the shape of the vestibule add to this airway resistance. The expiratory airway is different in that it begins to traverse the nose from a larger posterior choana adjacent to the nasopharynx to a relative constriction of the anterior nares. This creates a large central eddy or recurrent stream through the inferior meatus to finally join the main stream from the nasopharynx. This action conserves some of the heat of the expired air. Deflections of the septum, masses in the nose, or hypertrophy of the mucous membrane obviously will distort and obstruct the air currents through the nose. The pattern of airflow to stimulate olfaction is somewhat different. It is initiated by sniffing. This redirects the air superiorly into the olfactory cleft for stimulation of the neuroepithelial membrane. Air conditioning One of the better known functions of the nose is that of providing humidification and heating of the inspired air. The volume and rate of airflow along with the specialized vascular nasal mucosa are espe-
CLIN. IMMUNOL AUGUST 1983
cially important in maintaining a constant range of temperature of the inspired air from the portal of entry to the alveoli. Cole:’ has stated that air in the nasopharynx will have a relative humidity approaching saturation. The rather rapid change in the process of conditioning this air occurs because the inspiratory air comes into contact with a moist and warm nasal mucous membrane. Its high gradients of temperature and water vapor pressure are responsible for this rapid change. The phase of expiration is in a sense a reverse of inspiration. Some of the least well-conditioned air is expelled from the dead space in the tracheobronchial tree and passes over the mucosa of the pharynx and nose that has been cooled by the previous inspired air. This air gives up its heat and moisture to this membrane. Cole4 has estimated that a third of the heat and water is returned to the mucous membrane during expiration. He also stated that a normal, healthy adult residing in a temperate environment would lose between 300 and 400 ml of water and between 250 and 350 kcal in the expired air in a 24 hr period. Physical activity and living in dry, cold environments will increase these figures. Occurring simultaneously with the heating of inspired air is the humidification of the air. The main supply of moisture is through a physical process of transudation of fluid through the mucosal epithelium. Secretions of the epithelial glands and goblet cells in the nasal membrane provide a smaller volume. The exact volume of fluid necessary to create this high percent of saturation will depend to some degree on the temperature and the relative humidity of the ambient air. A rough calculation of the daily volume of secretion and transudate from the nose is 1000 cc. It has been estimated that three fourths of this is used to saturate the inspired air and the remainder is used in the ciliary mechanisms of cleaning and purifying the inspired air. Protective
mechanism
The vibrissae in the vestibule and nose are responsible for removing particles in the ambient air that are larger than 15 pm in size. Only 5% of those particles smaller than 1 pm are removed by the mucous membrane. Muscociliary
activity
The mucous blanket is another important aspect in the protective function of the nose. It consists of two layers. The outer layer is relatively viscous and rests on a thin layer of serous fluid that tends to facilitate the action of the underlying cilia. The fine particulate
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matter that enters the inspired air is filtered by the process of adhering to the mucous film. This occurs by two mechanisms. One is the impaction of the particles on the surface of the mucous membrane and the other is an electrostatic surface charge. So efficient is this function that the mucous membrane of the posterior choana contain very few bacteria and the sinuses are normally sterile. Both the population and the activity of the cilia in the mucous membrane of the nose have been studied exhaustively.“, - 6 In the front part of the nose there is a paucity of cilia and the movement of the mucous is slow at about 1 to 2 mmihr. However, in the posterior aspect of the nose, the mucus may be propagated at a rate of 10 mm each minute and the mucous blanket in the posterior two thirds of the nose will tend to reconstitute itself every 10 to 1.5 min. The ciliated cells have from 12 to 20 cilia that project from the luminal surface of the cell into the mucus. The beat of the cilia is quick and forceful in a forward, propulsive stroke that is followed by a slower recovery stroke. This cycle may be repeated hundreds of times each minute. The beating appears to pass from one region to another adjacent posterior one in a metachronous fashion. Anything that affects ciliary activity is of clinical importance. Drying of the nasal mucous membrane will cause cessation of ciliary activity while prompt moistening will restore its normal activity. The optimum temperature range for ciliary activity is 28” to 30” C. Hypotonic saline solutions will inhibit ciliary activity; hypertonic saline solutions will cause it to stop. The use of adrenaline and cocaine in the nose will ultimately cause irreversible inhibition of the ciliate cell activity if they are exposed to them for a sufficient length of time. Olfaction The olfactory area in the human nose is confined to the roof of the nasal cavity, the superior part of each superior turbinate in the lateral wall of the nose, and approximately the upper one third of the nasal septum of each side. The histologic appearance of the membrane is that of a thick, pseudostratified, columnar nonciliated epithelium. It contains three types of cells: basal cells, supporting cells, and olfactory receptor cells. The receptor cells are situated among the supporting cells. Their number has been estimated to be between 10 and 20 million. They act as both peripheral sensory receptors and neuronal cell bodies with processes and are oval in shape. The central elongated end of each olfactory cell acts as a continuous strand or thick axon that is enveloped by the basal cells. The
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filaments pierce the basement membrane and become directly continuous as a nerve axon of unmyelinated nature. These axons group together to form the fibers of the olfactory nerve, which ultimately terminate in the glomeruli of the olfactory bulbs. Olfactory stimulation, discrimination
sensitivity,
and
The exact mechanism of stimulation and sensitivity of the olfactory system is still unclear.7 It is clear that the odor must reach the olfactory area or, more specifically, the olfactory mucosa. Normal breathing does not necessarily bring the air current into that area of the nasal chamber. Odor detection may bring about reflex sniffing that diverts the air flow into the olfactory cleft. It is not really certain to what extent the perception of odor is influenced by sniffing. Whether the volume of air, the duration of contact with the olfactory membrane, the change in air flow, or pressure is responsible for odor perception is also not known. The perception of an odor that is detected depends on a number of aspects. It would include whether or not the odor is volatile, what its concentration in the inspired air may be, the exact volume of air that reaches the mucosa of the olfactory region, and possibly the force with which it strikes the mucosa. The lipid water solubility and the state of olfactory mucosa at the time of stimulation are also important. Obviously the integrity of the olfactory nervous pathway and cortical centers for perception are also important. Speech The nose provides vocal resonance. It is obvious that a person’s voice can be changed by nasal obstruction for any cause. Rhinolalial clausa is the medical term used to describe nasal resonance due to a nasal obstruction. Rhinolalial aperta occurs when the vibrating air column passes from the larynx to the pharynx, mouth, and into the nose. This is most commonly observed in an individual with a cleft palate. Only the nasal consonants M, N, and NC are made by the vibrating air column of air passing from the larynx through the nose. Nasal reflex functions There are a myriad of reflex functions originating in the nose. They consist of two primary groups: those that originate from the sense of smell and those that are initiated through trigeminal nerve ending terminals. Common examples of olfactory group functions are reflexes related primarily to digestive actions. Salivary, gastric, and pancreatic glands are reflexly
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stimulated by the olfactory centers. Fifth nerve reflexes include changes in the lower respiratory tract, particularly in the larynx, trachea, and tracheobronchial tree, changes in the heart rate, and changes in pulmonary ventilation, and reflex sneezing. Common flow
factors
that may affect
nasal blood
Many different factors, both local and general, will affect the vasomotor reaction of the nose. Local factors include changes in the ambient temperature and humidity, the topical administration of vasoactive drugs, the external compression of large veins in the neck, trauma, and inflammation. The normal mucous membrane of the nose reacts to maintain the homeostatic mechanism in the nasopharynx and tracheobronchial airway. Sympathomimetic drugs that have been applied locally to the mucosa will produce shrinkage with blanching. This action may persist for 1 to 3 hr, depending on the drug used. Common drugs causing this action are adrenaline, Neo-Synephrine, and ephedrine. Parasympathomimetic drugs will produce congestion in the nasal mucous membrane and decreased airflow and will increase the volume of nasal secretions. Atropine causes constriction of the capillaries and contraction of the cavernous tissue in the nose and cocaine produces marked contraction of these erectile spaces. General factors that affect nasal blood flow have been known for some time. Holmes et al. ,H in their monograph on the nose, describe the emotional factors that are characteristic of nasal symptoms. Fear was found to create a “sympathetic ” type of response of the nasal mucous membrane, whereas frustration, humiliation, and anxiety engorged the nasal mucous membrane and caused a “parasympathetic” type of response. They demonstrated these effects by comparing the emotional tone with biopsies of the inferior turbinate mucosa from subjects undergoing different periods of emotional conflict. The nasal vessels may react to other sympathetic vasomotor responses of the body. Auditory stimuli, deep breathing, and breath holding may produce vasoconstriction in the nasal mucosa. Painful stimulation may cause marked vasoconstriction. Overventilation may produce dilatation of the nasal vessels. SUMMARY The nose in man, despite its unusual external apoearance. has a varietv of functions that are related to
CLIN. IMMUNOL. AUGUST 1983
its unique internal anatomy and the vascular tone of its mucous membrane. In addition, it houses the receptor side of the first cranial nerve. This receptor is relatively primitive in man and probably less effective in monitoring his environment than that of other mammals. The nose is the portal by which the ambient air first enters the body. The nose functions as a “guard dog” or “watch dog” for the lungs. It conditions air to a specific range of temperature and humidity. Its protective filtration and ciliary mechanisms are abundant. Nasal reflex functions affect the lower respiratory tract and cardiopulmonary functions and respond to intense emotional situations. Since the time of Proetz’ original essays on the physiology of the nose,” a great deal of study has been done on the various and myriad functions of the nose. A working understanding of its peculiar anatomy and unusual functions are important for understanding the pathophysiology of nasal disease. REFERENCES 1. Fairbanks DNF: Embryology and anatomy. In Bluestone CD, Stool SE, editors: Pediatric otolaryngology. Philadelphia, 1983, W. B. Saunders Co., vol. II, pp 647-648. 2. Hollingshead WH: Anatomy for surgeons-the head and neck, ed. 3. Philadelphia, 1982, Harper & Row Publishers, vol. I., chap. 4. 3. Cole P: Upper respiratory airflow. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam. 1982, Elsevier Biomedical Press BV, p. 166. 4. Cole P: Modification of inspired air. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, pp. 370-371. 5. Mygind N, Pederson M, Nielsen MH: Morphology of the upper airway epithelium. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, p. 81. 6. Proctor DF: The mucociliary system. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, pp. 245-278. 7. Berglund B, Lindval T: Olfaction. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, p. 283. 8. Holmes TH, Goode11 H, Wolf S, Wolff HG: The nose. Springfield, Ill., 1950, Charles C Thomas, Publisher. 9. Proetz AW: Essays on the applied physiology of the nose, ed. 2. St. Louis, 1953, Annals Publishing Co., p. 153.
course
Nasal anatomy,
physiology,
Nathan
Geurkink,
M.D. Hanover,
and function
N.H.
Knowledge of the anatomy and physiology of the nose is a necessary prerequisite for understanding the pathophysiologic characteristics of rhinitis and occupational allergy. The nose and paranasal sinuses have a unique anatomical location, shape, and function in modifying and transforming inhaled air. The anatomy of the nose and paranasal sinuses and their basic physiologic functions are reviewed. (/ALLERGY CUN IMMUNOL 72:123-128, 1983.1
NASAL ANATOMY
AND DEVELOPMENT
The outward protuberance of the external noseencloses osseous,cartilaginous, epithelial, and neuroepithelial structures. Its outward appearancedoesnot necessarily provide any indication of its internal structure. The nasal passageis composed of a horizontally skin-lined vestibule with the passagesbeing directed upward and backward and separatedby a cartilaginous and bony nasal septum. The lateral nasal walls are convoluted with strategically placed air-warmer turbinates that mold the air streamto their configurations and changing dimensions.The accessorysinuses that communicate with the nasal chambers by their respective ostia are situated laterally in the maxilla, superiolaterally in the ethmoid bones, superiorly in the frontal bone, and posteriorly in the sphenoidbone. The olfactory cleft is situated in the superior portion of the nasal chamber. The histology of this mucous membraneof the noseand the paranasalsinusesvaries in its anatomical location. Both nonolfactory and olfactory epithelia are present. The nasal mucous membrane derives its sensory supply from the fifth cranial nerve and has both parasympatheticand symFrom the Hitchcock Clinic, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Hanover, N.H. Presented at the Postgraduate Course-Rhinitis, 39th Annual Meeting American Academy of Allergy, March, 1983, Hollywood, Fla. Received for publication Feb. 16, 1983. Accepted for publication Feb. 16, 1983. Reprint requests: Dr. Nathan Geurkink, Hitchcock Clinic, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Hanover, NH 03756.
pathetic autonomic nervous system fibers. The neuroepithelium for olfaction is derived from the first cranial nerve. The control of the arterial and venous supply to the mucous membrane of the nose by the autonomic nervous system is one of the most important fundamental physiologic phenomenathat will be reviewed. Internal anatomy-gross
and developmental
After about 3 wk of fetal life, olfactory placodes appear in the frontonasal processand within a week they becomenasalpits that are the first indication of a vestibular-like structure. By 5 wk of fetal age, the nasalpits have progressedinto cleftlike structuresand are separatedby a primitive septum. Around the sixth week of embryonic life, both maxillary and ethmoid folds begin to appearand theseare the first evidences of nasalturbinates. The nasalchamber and the primitive stomodeumare not separateduntil approximately 3 mo when palatal fusion is complete. During the third and fourth month of fetal life, the maxillary sinus, ethmoid sinus,and sphenoidsinusoutpouching begins.’ The vestibule of the adult noseis lined with squamousepithelium that contains vibrissae and sweatand sebaceousglands. Within this vestibule are baffles created by the protrusion of the medial crus of the lower lateral cartilage and the lower end of the upper lateral cartilage. Just superior to this is one of the more important areasof the nose. It has been called the nasal valve. It is the areaof the lateral nasal wall and the adjacent septumjust anterior to the tips of the middle and inferior turbinate and the upper border of the vestibule. This mobile portion of the nosehasthe 123
124
Geurkink
ability to both open and close and creates a varying amount of air flow resistance. The nasal septum, which was first apparent as a broad, thick structure between the nasal pits, is ultimately composed of two separate supporting tissues. Anteriorly, the septum is composed of skin and cartilage and posteriorly, of thin sheets of bone. The cartilaginous septum is formed by a very large quadrangular cartilage that has a posteriorly directed tail called the sphenoidal process. In early life this sphenoidal process is in continuity with the sphenoid bone and would separate the perpendicular plate from the vomer. The perpendicular plate of the ethmoid forms the superior bony structure of the septum. Inferiorly, the septum is composed of the vomer, which forms the medial portion of the posterior choana. This rests on the nasal crest of the maxilla and the nasal crest of the palatine bone. The other cartilage of the septum is simply the medial crus of the alar cartilage. The quadrangular cartilage articulates with the premaxillary crest and the vomer in a tongue-and-groove fashion. The flared parts of the vomer and the premaxilla form what is known as premaxillary wings. These project into the airstream and act as baffles to air flow. The vomeronasal cartilages are structures associated with the rudimentary vomeronasal organ of Jacobson. In some animals there are olfactory nerves in this area, but in man the organ is very short and is of no apparent significance. Anterior rhinoscopic examination reveals that the septum varies in thickness from anterior to posterior. The septum in the area of the nasal valve and posterior to the anterior margins of the middle and inferior turbinates tends to be thicker so that the airstream is not precisely vertical but tends to curve in two different planes. It is not difficult to understand how deflections or deviations of this structure may cause increased airway resistance to the point of obstruction. The turbinates are located on the lateral nasal walls. The maximal development of the number of ethmoid turbinates occurs in the fetus at around 7 mo. After this, coalescence occurs, so that only two or three turbinates of the ethmoid group will be present at birth. These structures consist of an underlying bony framework. The inferior turbinate is attached to the medial wall of the maxillary bone, the middle turbinate is attached to the roof of the nose just lateral to the cribriform plate and laterally to the ethmoid bone, and the superior turbinate is situated in the sphenoethmoid recess. The bony skeleton shows this arrangement .2 The inferior turbinate is placed more anteriorly than either the middle or the superior, and the
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middle turbinate is anterior to the superior. The inferior meatus is that space lateral and inferior to the middle turbinate. In the anterior portion of this inferior meatus, the opening of the nasolacrimal duct is found. The middle meatus is that space beneath and lateral to the middle turbinate. The ostia of the frontal maxillary, and anterior and middle ethmoid sinuses, are found here. The middle turbinate is shaped more like a pontoon, whereas the inferior turbinate has no anterior overhanging edge. The superior turbinate is less than half the length of the other two turbinates and its anterior margin begins at about the middle of the middle turbinate. The posterior end of each turbinate ends in the posterior choana. The superior turbinate is located in the sphenoethmoid recess and is in close proximity to the front face of the sphenoid sinus. These bony structures are covered with mucoperiosteum and are very smooth and streamlined in appearance. The paranasal sinuses begin to develop as outpouchings of the mucosa of the nasal chamber during the third and fourth fetal months. The maxillary and ethmoid sinuses are present at birth. The frontal sinus is a very small diverticulum at birth and undergoes almost all of its development after birth. By about the third year of life, the sphenoid sinus invades the sphenoid bone. These sinuses may vary from individual to individual. The maxillary sinus is paired. It is the largest of the paranasal sinuses and is located within the body of the maxillary bone. The opening to the maxillary sinus is located on the highest part of its medial wall. Drainage of the sinus occurs by ciliary activity and it opens into the medial meatus, which is a common place for nasal polyposis. Because of this, it is common to have an obstructive phenomenon creating sinusitis. The number of ethmoid sinuses is more varied. They resemble honeycombs. There may be as few as three or four or as many as 18 or 20 cells and they are located lateral to the middle turbinate and medial to the medial orbital wall. The majority of these sinuses open into the middle meatus. The posterior ethmoid cells open into the superior meatus. The anterior ethmoid cells may invade the perpendicular part of the frontal bone. The size of the frontal sinus varies. The nasofrontal duct communicates with the middle meatus through the ethmoid infundibulum. The sphenoid sinuses are bilateral. They are in the posterior portion of the nose and are situated anteriorly and inferiorly to the sella turcica. The ostium is in the anterior wall and communicates with the sphenoethmoid recess. Its degree of expansion into
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the sphenoid bone varies greatly. The capacity of the sinus may range from 1 to 30 mm, the average being approximately 7 mm. Vital structures are related to its lateral walls. The carotid artery, the optic nerve, the maxillary nerve, and the cavernous sinus are in very close proximity to this wall. The anatomic relationships of the sphenoid sinus with the pituitary gland and the nasal septum make it a ready avenue for surgical approaches to the pituitary gland. The olfactory cleft is that area of the nose between the middle turbinate and the septum. It is covered with the neuroepithelium of the olfactory nerve. The olfactory mucous membrane is limited to the upper third of the mucosa on the lateral wall of the nose and the adjacent part of the roof and corresponding parts of the septum. It is yellow in color. Histology of the mucous membrane nose and the paranasal sinuses
of the
The mucous membrane of the nasal cavity can be divided into the nonolfactory epithelium and the olfactory epithelium. The nonolfactory epithelium is a highly vascular tissue that is covered by a pseudostratified, columnar, ciliated epithelium. It is particularly thick in the area over the medial surfaces of the middle and inferior turbinates. It is very tightly attached to either perichondrium or periosteum, depending on its relationship to cartilage or bone in the nose. The thickness and the thermal properties of the mucosa in the nose are regulated by the sympathetic and parasympathetic nerve fibers that are supplied this membrane. Superficial and deep layers of arterioles supply the lamina propria. Between the venules and the capillaries are numerous sinuses or venous lakes that have been likened to erectile tissue because of the rapidity with which they can become engorged. Small muscle bundles are present at the distal ends of these venous lakes and act as sphincters to bring about an engorgement of the sinusoids. This pattern is most marked in the inferior turbinate area but is also present in the middle turbinate and on portions of the septum. The olfactory epithelium is pseudostratified columna in type and consists of specialized olfactory cells, supporting cells, and both serous and mucous glands. The olfactory cells are bipolar neurons and act as peripheral receptors and first-order ganglion cells. It has been estimated that 10 to 20 million cells are in each nasal fossa. Cilium-like rods protrude from these cells into the mucous blanket and the approximately 1000 filaments on the rods of each cell magnify the surface area of the cell itself. The axons of these olfactory cells form bundles to pass through the crib-
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riform plate as the olfactory nerves. There are approximately 20 nerves in each nasal fossa. Innervation The general sensation of the nasal cavity is supplied by the first and second divisions of the fifth cranial nerve. The branches of the first division of the fifth nerves supply the anterior superior and anterior portion of the nose. The vestibule of the nose is supplied by the infraorbital nerve. The autonomic nervous system plays a major role in the control of the vascular supply of the nasal mucous membrane. The parasympathetic innervation of the mucous membrane begins in the superior salivatory nucleus of the brainstem. Fibers from this nucleus unite with the fibers of the facial nerve and after leaving the geniculate ganglion join the postganglionic sympathetic fibers of the superior cervical ganglion. These fibers form the nerve of the vidian canal, which enters the sphenopalatine ganglion. The parasympathetic nerve fibers synapse at this ganglion and their postganglionic fibers are distributed to the nose and nasopharynx. Those fibers of sympathetic nervous system origin arise from the first and second thoracic segments of the spinal cord in the lateral horn cells. They exit from the spinal cord with the anterior nerve root and synapse in the superior cervical ganglion high in the neck. The postganglionic sympathetic fibers then form a network around the internal carotid’ artery and join the parasympathetic fibers from the seventh cranial nerve. They are distributed with the parasympathetic nerve fibers as branches of the sphenopalatine nerve. Vascular
supply
The arterial supply to the nose is derived from both the external and the internal carotid arteries. The terminal branch of the maxillary artery, which is a branch of the external carotid, supplies the sphenopalatine artery, which in turn supplies the lateral and medial wall of the nasal chamber. The anterior and posterior ethmoid branches come from the ophthalmic artery, which is a branch of the internal carotid artery. These vessels supply the anterior portion of the nose. In addition, there are twigs from the facial artery that supply the vestibule and the anterior portion of the septum. A few vessels from the greater palatine artery pass through the incisive canal of the palate to reach the anterior part of the nose. The veins of the nose drain into the sphenopalatine foramen and then into the pterygoid plexus, whereas others accompany the ethmoid arteries to join the su-
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perior ophthalmic vein. Those that are anterior in the nose drain into the facial vein. PHYSIOLOGY NOSE
AND FUNCTION
OF THE
In order to review the functions of the nose, the following factors should be considered: (1) airway, (2) air conditioning, (3) olfaction, (4) effects on speech, (5) reflex functions, and (6) common factors that will affect nasal blood flow. Airway The nose is one of the most important components to airflow resistance. It has been calculated to provide between 30% and 50% of the total resistance to inspiration. The cross-sectional diameter of the anterior nares is much smaller than the posterior choana, so that inspiratory air currents are much different than expiratory air currents. The former are directed upward across the superior surface of the inferior turbinate and the main surfaces of the middle turbinate into the nasopharynx. This upward direction is governed somewhat by the horizontal position of the anterior mu-es and the smooth anterior ends and surfaces of the turbinates and the shape of the septum. These streamlined structures tend to create a minimal resistance in guiding the inflow of air. The cartilaginous framework of the nasal alae prevents total collapse of these structures during negative pressure of inspiration. The nasal value is one of the most important structures governing the rate and volume of air traversing the anterior nares. The baffles created by the shape of the vestibule add to this airway resistance. The expiratory airway is different in that it begins to traverse the nose from a larger posterior choana adjacent to the nasopharynx to a relative constriction of the anterior nares. This creates a large central eddy or recurrent stream through the inferior meatus to finally join the main stream from the nasopharynx. This action conserves some of the heat of the expired air. Deflections of the septum, masses in the nose, or hypertrophy of the mucous membrane obviously will distort and obstruct the air currents through the nose. The pattern of airflow to stimulate olfaction is somewhat different. It is initiated by sniffing. This redirects the air superiorly into the olfactory cleft for stimulation of the neuroepithelial membrane. Air conditioning One of the better known functions of the nose is that of providing humidification and heating of the inspired air. The volume and rate of airflow along with the specialized vascular nasal mucosa are espe-
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cially important in maintaining a constant range of temperature of the inspired air from the portal of entry to the alveoli. Cole:’ has stated that air in the nasopharynx will have a relative humidity approaching saturation. The rather rapid change in the process of conditioning this air occurs because the inspiratory air comes into contact with a moist and warm nasal mucous membrane. Its high gradients of temperature and water vapor pressure are responsible for this rapid change. The phase of expiration is in a sense a reverse of inspiration. Some of the least well-conditioned air is expelled from the dead space in the tracheobronchial tree and passes over the mucosa of the pharynx and nose that has been cooled by the previous inspired air. This air gives up its heat and moisture to this membrane. Cole4 has estimated that a third of the heat and water is returned to the mucous membrane during expiration. He also stated that a normal, healthy adult residing in a temperate environment would lose between 300 and 400 ml of water and between 250 and 350 kcal in the expired air in a 24 hr period. Physical activity and living in dry, cold environments will increase these figures. Occurring simultaneously with the heating of inspired air is the humidification of the air. The main supply of moisture is through a physical process of transudation of fluid through the mucosal epithelium. Secretions of the epithelial glands and goblet cells in the nasal membrane provide a smaller volume. The exact volume of fluid necessary to create this high percent of saturation will depend to some degree on the temperature and the relative humidity of the ambient air. A rough calculation of the daily volume of secretion and transudate from the nose is 1000 cc. It has been estimated that three fourths of this is used to saturate the inspired air and the remainder is used in the ciliary mechanisms of cleaning and purifying the inspired air. Protective
mechanism
The vibrissae in the vestibule and nose are responsible for removing particles in the ambient air that are larger than 15 pm in size. Only 5% of those particles smaller than 1 pm are removed by the mucous membrane. Muscociliary
activity
The mucous blanket is another important aspect in the protective function of the nose. It consists of two layers. The outer layer is relatively viscous and rests on a thin layer of serous fluid that tends to facilitate the action of the underlying cilia. The fine particulate
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matter that enters the inspired air is filtered by the process of adhering to the mucous film. This occurs by two mechanisms. One is the impaction of the particles on the surface of the mucous membrane and the other is an electrostatic surface charge. So efficient is this function that the mucous membrane of the posterior choana contain very few bacteria and the sinuses are normally sterile. Both the population and the activity of the cilia in the mucous membrane of the nose have been studied exhaustively.“, - 6 In the front part of the nose there is a paucity of cilia and the movement of the mucous is slow at about 1 to 2 mmihr. However, in the posterior aspect of the nose, the mucus may be propagated at a rate of 10 mm each minute and the mucous blanket in the posterior two thirds of the nose will tend to reconstitute itself every 10 to 1.5 min. The ciliated cells have from 12 to 20 cilia that project from the luminal surface of the cell into the mucus. The beat of the cilia is quick and forceful in a forward, propulsive stroke that is followed by a slower recovery stroke. This cycle may be repeated hundreds of times each minute. The beating appears to pass from one region to another adjacent posterior one in a metachronous fashion. Anything that affects ciliary activity is of clinical importance. Drying of the nasal mucous membrane will cause cessation of ciliary activity while prompt moistening will restore its normal activity. The optimum temperature range for ciliary activity is 28” to 30” C. Hypotonic saline solutions will inhibit ciliary activity; hypertonic saline solutions will cause it to stop. The use of adrenaline and cocaine in the nose will ultimately cause irreversible inhibition of the ciliate cell activity if they are exposed to them for a sufficient length of time. Olfaction The olfactory area in the human nose is confined to the roof of the nasal cavity, the superior part of each superior turbinate in the lateral wall of the nose, and approximately the upper one third of the nasal septum of each side. The histologic appearance of the membrane is that of a thick, pseudostratified, columnar nonciliated epithelium. It contains three types of cells: basal cells, supporting cells, and olfactory receptor cells. The receptor cells are situated among the supporting cells. Their number has been estimated to be between 10 and 20 million. They act as both peripheral sensory receptors and neuronal cell bodies with processes and are oval in shape. The central elongated end of each olfactory cell acts as a continuous strand or thick axon that is enveloped by the basal cells. The
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filaments pierce the basement membrane and become directly continuous as a nerve axon of unmyelinated nature. These axons group together to form the fibers of the olfactory nerve, which ultimately terminate in the glomeruli of the olfactory bulbs. Olfactory stimulation, discrimination
sensitivity,
and
The exact mechanism of stimulation and sensitivity of the olfactory system is still unclear.7 It is clear that the odor must reach the olfactory area or, more specifically, the olfactory mucosa. Normal breathing does not necessarily bring the air current into that area of the nasal chamber. Odor detection may bring about reflex sniffing that diverts the air flow into the olfactory cleft. It is not really certain to what extent the perception of odor is influenced by sniffing. Whether the volume of air, the duration of contact with the olfactory membrane, the change in air flow, or pressure is responsible for odor perception is also not known. The perception of an odor that is detected depends on a number of aspects. It would include whether or not the odor is volatile, what its concentration in the inspired air may be, the exact volume of air that reaches the mucosa of the olfactory region, and possibly the force with which it strikes the mucosa. The lipid water solubility and the state of olfactory mucosa at the time of stimulation are also important. Obviously the integrity of the olfactory nervous pathway and cortical centers for perception are also important. Speech The nose provides vocal resonance. It is obvious that a person’s voice can be changed by nasal obstruction for any cause. Rhinolalial clausa is the medical term used to describe nasal resonance due to a nasal obstruction. Rhinolalial aperta occurs when the vibrating air column passes from the larynx to the pharynx, mouth, and into the nose. This is most commonly observed in an individual with a cleft palate. Only the nasal consonants M, N, and NC are made by the vibrating air column of air passing from the larynx through the nose. Nasal reflex functions There are a myriad of reflex functions originating in the nose. They consist of two primary groups: those that originate from the sense of smell and those that are initiated through trigeminal nerve ending terminals. Common examples of olfactory group functions are reflexes related primarily to digestive actions. Salivary, gastric, and pancreatic glands are reflexly
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stimulated by the olfactory centers. Fifth nerve reflexes include changes in the lower respiratory tract, particularly in the larynx, trachea, and tracheobronchial tree, changes in the heart rate, and changes in pulmonary ventilation, and reflex sneezing. Common flow
factors
that may affect
nasal blood
Many different factors, both local and general, will affect the vasomotor reaction of the nose. Local factors include changes in the ambient temperature and humidity, the topical administration of vasoactive drugs, the external compression of large veins in the neck, trauma, and inflammation. The normal mucous membrane of the nose reacts to maintain the homeostatic mechanism in the nasopharynx and tracheobronchial airway. Sympathomimetic drugs that have been applied locally to the mucosa will produce shrinkage with blanching. This action may persist for 1 to 3 hr, depending on the drug used. Common drugs causing this action are adrenaline, Neo-Synephrine, and ephedrine. Parasympathomimetic drugs will produce congestion in the nasal mucous membrane and decreased airflow and will increase the volume of nasal secretions. Atropine causes constriction of the capillaries and contraction of the cavernous tissue in the nose and cocaine produces marked contraction of these erectile spaces. General factors that affect nasal blood flow have been known for some time. Holmes et al. ,H in their monograph on the nose, describe the emotional factors that are characteristic of nasal symptoms. Fear was found to create a “sympathetic ” type of response of the nasal mucous membrane, whereas frustration, humiliation, and anxiety engorged the nasal mucous membrane and caused a “parasympathetic” type of response. They demonstrated these effects by comparing the emotional tone with biopsies of the inferior turbinate mucosa from subjects undergoing different periods of emotional conflict. The nasal vessels may react to other sympathetic vasomotor responses of the body. Auditory stimuli, deep breathing, and breath holding may produce vasoconstriction in the nasal mucosa. Painful stimulation may cause marked vasoconstriction. Overventilation may produce dilatation of the nasal vessels. SUMMARY The nose in man, despite its unusual external apoearance. has a varietv of functions that are related to
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its unique internal anatomy and the vascular tone of its mucous membrane. In addition, it houses the receptor side of the first cranial nerve. This receptor is relatively primitive in man and probably less effective in monitoring his environment than that of other mammals. The nose is the portal by which the ambient air first enters the body. The nose functions as a “guard dog” or “watch dog” for the lungs. It conditions air to a specific range of temperature and humidity. Its protective filtration and ciliary mechanisms are abundant. Nasal reflex functions affect the lower respiratory tract and cardiopulmonary functions and respond to intense emotional situations. Since the time of Proetz’ original essays on the physiology of the nose,” a great deal of study has been done on the various and myriad functions of the nose. A working understanding of its peculiar anatomy and unusual functions are important for understanding the pathophysiology of nasal disease. REFERENCES 1. Fairbanks DNF: Embryology and anatomy. In Bluestone CD, Stool SE, editors: Pediatric otolaryngology. Philadelphia, 1983, W. B. Saunders Co., vol. II, pp 647-648. 2. Hollingshead WH: Anatomy for surgeons-the head and neck, ed. 3. Philadelphia, 1982, Harper & Row Publishers, vol. I., chap. 4. 3. Cole P: Upper respiratory airflow. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam. 1982, Elsevier Biomedical Press BV, p. 166. 4. Cole P: Modification of inspired air. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, pp. 370-371. 5. Mygind N, Pederson M, Nielsen MH: Morphology of the upper airway epithelium. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, p. 81. 6. Proctor DF: The mucociliary system. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, pp. 245-278. 7. Berglund B, Lindval T: Olfaction. In Proctor DF, Anderson IB, editors: The nose: upper airway physiology and the atmospheric environment. Amsterdam, 1982, Elsevier Biomedical Press BV, p. 283. 8. Holmes TH, Goode11 H, Wolf S, Wolff HG: The nose. Springfield, Ill., 1950, Charles C Thomas, Publisher. 9. Proetz AW: Essays on the applied physiology of the nose, ed. 2. St. Louis, 1953, Annals Publishing Co., p. 153.