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Introduction

• The nose contains organ of smell and respiration• It warms, cleans and humidifies the inspired air, cools and

remove the water from the expired air• It also adds quality to speech production• The ENT surgeon should distinguish normal nasal fuction from

pathological symptoms to prevent unnecessary surgery• Although the nose is a paired structure divided coronally into

two chambers, it act as a functional unit

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Function Mechanism

Respiration

Heat exchangeDirection of blood flowLatent heat of evaporationThermoregulation

Humidification

Anterior serous glandsMixed serous and mucus glandsCapillary permaebilityOther body fluids; e.g. tears

Filtration Airflow pattern: laminar/turbulent

Nasal resistanceAnatomical, fixedNeurovascular, variable

Nasal fluids and ciliary fuction

Mucus, mucinsProtein including immunoglobulinsCiliary structure and function

Nasal neurovascular reflexes

ParasympatheticSympatheticSensory: axon reflexesSneezingCentral: pulmonary reflexesNasal cycle

Voice modification Nasal escape 3

Olfaction

StimulusThreshold and suprathresholdAdaptation, discrimination and classification

Pathways Neurones in contact with the external environment

Two neurone peripheral pathway

Higher centresPerceived smell

Trigeminal input Pain

Olfaction and behaviour

Pheromones

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Respiration

• The nose acts as an air conditioning unit • Performs: humidification, heat transfer and filtration• The functions of nose are bypasses during exercise• The nose may be more important in temperature regulation

than in respiration because of its ability to transfer the heat• Inspired gases contain pollutants, domestic dust particles and

pollen, industrial products, bacteria, viruses and tobacco smoke

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I. Heat Exchange

• Temperature of the inspired air can vary from -50 to 50oc

Conduction, convection and radiation• Conduction occurs without flow when heat is transferred by

increased molecular movement• A temperature gradient leads to convection of currents

affect airflow in the nose turbulence• Flow results in forced convection

FH = h(Twall – Tf)FH = heat flux in J/m per s; Tf = bulk temperature; h = heat transfer coefficient

in J/m per s per oC

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• Prandtl number, the heat transfer coefficient

Pr = (CPƞ)KH

CP = heat capacity of gas in J/g per oC; ƞ = viscosity; KH = thermal conductivity in J/m per oC

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II. Humidification

• Vaporization cools the surface and 10 percent of the body heat is lost in this way

Inspiration• Saturation follows the temperature rise rapidly• Energy required for:

raising the temperature of inspired air (1/5) latent heat of evaporation (4/5)1

• The amount of energy is dependent on ambient temperature and relative humidity of an inspired air

• 10% of body heat loss occurs through the nose in humans• Air in post nasal space is approximately 31oC and is 95%

saturated2

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Expiration • The temperature of the expired air at the back of the nose is

slightly below body core temperature and is saturated• Some water condenses into the mucosa as the temperature

drops along the nose• The temperature in the anterior nose at the end of the

expiration is 32oC and approximately 30oC at the end of inspiration

• Approximately 1/3rd of the water required to humidify the inspired air is recovered in this way

• People who breathe in through the nose and out through the mouth will dry the mucosa

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Water production• Water comes from the serous gland, which are extensive

throughout the nose• During nasal cycle, secretions are lower on the more

obstructed side• Additional water comes from the expired air, the nasolacrimal

duct and the oral cavity• Humidification is reduced by atropine probably acting on the

gland rather than the vasculature3

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III. Airflow

• The airflow and the sensation of it are very different• Cold receptors sense airflow• Most of the work of heat and mass transport has been

performed on simple structures with constant cross sections.2

• The flow is turbulent, but is considered laminar at rest• The equations below describe flow, two for laminar and one

for the transition to turbulent flow

Airflow : VA = constantBernoulli’s equation : P + ½ ρV2 = constant

Reynolds number : Re =

ρ = density (g m-1); V = velocity (m sec-1); A = cross-sectional area (m2); P = pressure (N m-2); d = diameter (m); ƞ = viscosity (g sec-1 m-1)

dVρƞ

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• Gases flow faster through the choana4

• The characteristic of air flow were similar in different noses regardless of variety of nasal shape

• The cross-sectional flow is maximal at the centre and is zero at the edge

• Bernoulli equation is not strictly applicable since the energy overcoming the viscosity results in an irreversible drop in pressure

• The nose has variable cross section – the pressure and velocity will alter continuously within the system

• Because of the flow is turbulent in an irregular tube, the resistance is inversely proportional to the square of the flow rate5

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Inspiration• Airflow is directed upwards and backwards from the nasal

valve initially, mainly over the anterior part of the inferior turbinate

• It then splits into two, below and over the middle turbinate, rejoining into posterior choana

• Air reaches the other parts of the nose to a lesser degree• The velocity at the anterior valve is 12 - 18 m per sec during

quiet respiration

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Expiration• Expiration lasts longer than inspiration and is more turbulent• Extrapulmonary airflow is turbulent because of the direction

changes, the calibre varies markedly and walls are not smooth. The surface area is enlarged by the turbinates and the microanatomy of the epithelium

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Nasal resistance• Differs between races• Negroes and Caucasians are similar, but it is difficult to obtain

the sampling pressure for rhinometry in Japanese6,7

• The nose accounts for up to half of the total airway resistance• Produced by two resistors in parallel and each cavity has a

variable value produced by the nasal cycle fixed: bone, cartilage and muscle variable: mucosa

• High in infants (obligatory nose breathers)• Adult breath preferentially through the nose at rest even

though there is a significant resistance

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• During expiration, the positive pressure is transmitted to the alveoli

• Removal of this resistance by tracheostomy reduces dead space but results in a degree of alveolar collapse

• Reduced alveolar ventilation gives a degree of right to left shunting of the pulmonary blood

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The anterior nasal valve• Narrowest part of the nose and less well defined

physilogically then anatomically• Greatest resistor – produces the most turbulent airflow8

• Formed by the lower edge of the upper lateral cartilages, the anterior end of inferior turbinate, the adjacent nasal septum and with the surrounding soft tissues

• EMG – shows contraction of the dilator naris alone during inspiration9 which increases during exercise and can be mimicked by voluntary dilatation10

• Alar collapse occurs after denervation, even in quiet respiration

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Nasal cycle• Consists of alternate nasal blockage between passages• First physiological description by Kayser in 189511

• The changes are produced by vascular activity particularly the volume of blood on the venous sinusoids (capasitance vessels)

• Cyclical changes occurs between 4 to 12 hours, they are constant for each person

• Can be demonstrated in over 80% of adults• Difficult to demonstrate in children and it is present in early

childhood12

• Nasal secretions are also cyclical with an increase in secretions in the side with the greatest airflow3

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• Factors modify the nasal cycle: allergy, infection, exercise, hormones, pregnancy, fear and emotions, sexual activity

• Vagal overactivity may cause nasal congestion• High levels of CO2 in the inspired air produced by rebreathing

may also reduce the nasal resistance – this reverses following hyperventilation

• Drugs which block the action of noradrenaline cause nasal congestion

• Antihistamine has anticholinergic effects block the parasympathetic activity increase the sympathetic tone improve airway

• Puberty and pregnancy – affect nasal mucosa – mediated directly on the blood vessels

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IV. Protection of Lower Airway: Mechanical and Chemical

• The nose protects the lower airway by removing particles down to approximately 30 μm, including the most pollens from the inspired air

• The shape and roughness of smaller particles may cause them to be deposited in the nose

• Inspired air travels through 180o and velocity drops markedly just after the nasal valve

• Turbulence increases deposition of particles• Particles in motion will tend to carry on in the same direction• Resistance to change in velocity is greater in irregular particles

because of larger surface area and the number of facets• Vibrissae will only stop the largest particles

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Nasal secretions• Composed of two elements – mucus and water• Glycoprotein – produced by mucus glands• Water and ions – produced mainly from the serous glands

and indirectly from transudation from the capillary network• 2 secretory cell types – mucus and serous cells• Glycoprotein found in mucous are produced in goblet cells

(within the epithelium) and the glandular mucus cells• Submucosal glands are mixed and are arranged around ducts• The anterior part of the nose contains serous glands only in

the vestibular region – produce a copious watery secretion when stimulated

• Sinuses has fewer goblet cells and mixed glands 22

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Composition of mucus• Water and ions from transudation• Glycoprotein: sialomucins, fucomucins, sulphomucins• Enzymes: lactoferrin, lysozymes• Circulatory proteins: complement, α2-macroglobulin, C

reactive protein• Immunoglobulins: IgA, IgE, IgG, IgM, IgD• Cells: surface epithelium, basophils, eosinophils, leukocytes

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Rheology of mucus• Glycoproteins give mucus viscosity and elasticity• Viscosity is lowered by reducing the ionic content• The temperature of nasal cavity is relatively constant and is

lower than tracheobronchial tree• Movement of the cilia produce shearing effects that the

elasticity counteracts - if it is the right consistency – viscosity and elasticity complement each other and mucus moves

• Techniques to measure the rheology: microspherometry and controlled stress technique

• Mucus viscosity can be measured by drawing up mucus into a capillary tube under negative pressure and measuring the flow relative to the pressure

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Proteins in nasal secretion

1. Lactoferrin Produced by glandular epithelium, mainly the serous gland Its action is to bind divalent metal ions – like transferrin in the

circulation Lactoferrin and transferrin both bind two divalent metal ions,

particularly irons prevent growth of certain bacteria, particularly staphylococcus and pseudomonas

2. Lysozymes Comes from serous glands and tears Also produced from leukocytes and microphages found in nasal

secretion and mucosa Act only on non capsulated bacteria

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3. Antiproteases Produced by leukocytes Increase with infection Example: α-antirypsin, α1-antichemotrypsin, α2-antimicroglobulin,

etc.

4. Complement C3 – produced by liver and locally by macrophages Functions: lysis of microorganism, enhancing neutrophil function

(leukotaxis)

5. Lipids

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6. Ions and Water Na+ and Cl- are hyperosmolar in mucus Hyperosmolarity caused by evaporation and active ion transport This mainly occurs within serous gland which produce the major

proportion of the fluids in nasal secretion

7. Immunoglobulins All classes of immunoglobulins heve been found in nasal secretions IgA2 and IgE involved in mucosal defense and present in greater

quantities than serum (IgA = 50% of the total protein content)

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Cilia

ULTRASTRUCTURE• Found on the surface of cells in the respiratory tract• Function: to propel mucus backwards in the nose towards the

nasopharynx• All cilia have the same ultrastructure although nasal cilia are

relatively short at 5 μm, with up to 200 per cell• A cilium has a surface membrane• 9 paired outer microtubules surround a single inner pair of

microtubules• Outer-paired microtubules are linked together by nexins and

to the inner pair by central spokes29

• Outer pair also have inner and outer dynein arms, which consists of an ATPase, which is lost in Kartagener’s syndrome

• Microtubules become the basal body in the cell – the outer body become triplets and the inner pair disappear

• Nasal mucus film is in two layers, one upper more viscous layer and a lower more watery layer in which cilia can move freely

• There are small hooks at the tips of the cilia where they enter the viscous layer to remove it

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CILIARY ACTION• Best frequency is between 7 and 16 Hz at body temperature13

• Beat frequency remains constant between 32 and 40oC• Beat consists of a rapid propulsive stroke and a slow recovery

phase• Propulsive phase: the cilium is straight and the tip points into

the viscous layer of the mucous blanket• Recovery phase: the cilium is bent over in the aqueous layer• Energy is produced by conversion of ATP to ADP by ATPase of

the dynein arms – dependent of Mg2+ ions• Motions is produced by the pair of outer microtubules sliding

with respect to each other

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• ATP is generated by the mitochondria near the cell surface next to the basal bodies of the cilia

• The mucus blanket is propelled backwards by metachronous movement of cilia – only those at right angles to the direction of flow are in phase

• Mucus flows from the front of the nose posteriorly• Mucus from the sinuses joins that flowing on the lateral wall –

most going through middle meatus pass around the Eustachian orifice swallowed

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FACTORS AFFECTING CILIARY ACTION• Drying stops the cilia• Temperature below 10oC and above 45oC• Solutions above 5 % and below 0.2%• pH below 6.4 and above 8.5• Upper respiratory tract infection – damage the epithelium• Ageing

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DRUGS• Acetylcholine - increases the rate• Adrenaline - reduces the rate• Propanolol – reduces the rate• Cocaine hydrochloride (>10%) – causes immediate paralysis• Corticosteroids – reduces the rate

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V. Protection of Lower Airway: Immunological

• IgA and IgE are mainly present on the surface of the mucosa• IgM and IgG act if the mucosa if breached• Certain bacterial allergens are neutralized but several

bacteria and viruses require the activation of the cell-mediated immune response

• The T and some B cells interact with microphages, which have specific and non specific immunological properties

• Dendritic cells are important in the allergic response• 2 groups of cytokines act on CD4+ T cells and give rise to two

main responses – the Th1 and Th2• Local lymphatic system:

mucosal-associated lymhoid tissue (MALT) – tonsils, adenoid lymph nodes

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Non specific immunity• Lactoferrin, lysozymes, complement, antiproteases

Acquired immunity• IgA

Divided into IgA1 and IgA2

• IgA1 – more frequent in the serum; monomer

• IgA2 – more frequent in the nasal secretion; dimer Accounts for up to 70% of the total protein in nasal secretion Transferred passively through interstitial fluid actively taken up by

seromucinous glands and surface epithelium• Forms insoluble complex when reacts with antigen swallowed

and destroyed by stomach acid

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• IgE main Ig involved in allergic reaction Produced mainly in lymphoid aggregates such as tonsils and adenoids

and within the mucosa

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VI. Vocal Resonance• Nose form resonating chamber for certain consonants in

speech• Phonating nasal consonants (M/N/NG) – sound passes

through the nasopharyngeal isthmus and is emitted through the nose

• Many nasal condition affect the quality of voice by blocking the passage of air in expiration

• When nasopharynx is blocked, speech becomes denasal, i.e. M/N/NG are uttered as B/D/G respectively

• Rhinolalia clausa – too little air escapes from the nose• Rhinolalia aperta – too much air escapes• The sinuses have no effect on modifying voice• The most affective resonance occurs at lower laryngeal

frequencies 40

VII. Olfaction

• Olfactory compound need high water and lipid solubility• The solute in the mucus is presented to the sensory mucosa

Olfactory area • Area: 200-400mm2 with a density of approximately 5x104

receptor cells/mm2

• Receptor cells have modified cilia, which increase surface area and project like normal cilia into the mucus

Stimulus• Odours react with lipid bilayer of the receptor cells at

specific sites causes outflow of K+ and Cl- Cells depolarization14

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Receptors• Olfaction is mediated by G-protein coupled receptors in the

cells which interact with a specific adenyl cyclase within neuroepithelium15

• Adrenergic and muscarinic antagonists – blocks some odour

Threshold• Threshold concentrations can vary by 1010 depending on the

chemical nature of the stimuli• Thresholds depend on levels of inhibitory activity which

generated by higher centres

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Adaptation• Olfactoy responses show marked adaptation and thresholds

increase with exposure• Adaptation is a peripheral and central phenomenon• Cross adaptations are present between odours at high

concentrations• Other factors affecting threshold:

changes in nasal mucus and its pH Age – decreases the threshold Hormones (sex hormones) – increases the threshold

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Olfactory pathways• Smell is perceived in the olfactory region (high up in nasal

cavity)• Peripheral process of each olfactory cells reaches the mucosal

surface and is expended into a ventricle with several cilia on it• Central process are grouped into olfactory nerves which pass

through the cribriform plate of ethmoid and end in the mitral cells of the olfactory bulb

• Axons of mitral cells from olfactory tract and carry smell to the prepyriform cortex and amygdaloid nucleus where it reaches consciousness

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Disorders of smell• Anosmia: total loss of smell• Hyposmia: partial loss• Parosmia: Perversion of smell – the person interprets the

odour incorrectly seen in recovery phase of post influenzal anosmia, intracranial tumour

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Conclusion

• An understanding of the physiology of the nose is required to: Evaluate nasal symptoms Know its protective role in health and disease Determine the role of investigations in the assessment of airway

function and mucociliary clearence Understand the action of drugs on the nasal mucosa Assess the smell and taste

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Reference1. Cole P. Modification of inspired air. In: Proctor D, Andersen I (eds). The nose: upper

airway physiology and the atmospheric environment, 1st edn. Amsterdam: Elsevier, 1982: 351-73.

2. Swift DL. Physical principles of airflow and transport phenomena influencing air modification. In: Proctor D, Andersen I (eds). The nose: upper airway physiology and the atmospheric environment. Amsterdam: Elsevier, 1982: 337-49.

3. Inglestedt S, Ivskern B. The source of nasal secretions in normal conditions. Acta Oto-Laryngologica. 1949; 37: 446-50.

4. Proetz AW. Applied physiology of the nose, 2nd edn. Vol. 1. Mosby 19535. Otis A, Fenn W, Rhyn H. The mechanics of breathing in man. Journal of Applied

Physiology. 1950; 2: 597-607.6. Calhoun K, House W, Hokanson JA, Quinn FB. Normal nasal airway resistance in

noses of different sizes and shapes. Otolaryngology-Head and Neck Surgery. 1990; 103: 605-9.

7. Babotola F. Nasal resistance values in the adult negroid Nigerian. Rhinology. 1990; 28: 269-73

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8. Bridger GP, Proctor DP. Maximum nasal inspiratory flow and nasal resistance. Annals of Otology. 1970; 79: 481-88.

9. Van Dishoek HAG. The part of the valve and turbinate in total nasal resistance. Rhinology. 1965; 3: 19-26.

10. Rivron R, Sanderson R. The voluntary control of nasal resistance. Rhinology. 1991; 29: 181-84.

11. Kayser R. Die exacte messung der luftdurchangiklit der nase. Archives of Laryngology. 1985; 3: 101-210.

12. Van Cauwenberge PB, Delaye L. Nasal cycle in children. Archives of Otolaryngology – Head and Neck Surgery. 1984; 110: 108-10.

13. Widdicombe J, Wells UK. Airway secretion. In: Proctor D, Andersen I (eds). The nose: upper airway physiology and the atmospheric environment. Amsterdam: Elsevier, 1982: 215-44.

14. Takagi S, Wyse GA, Kitamura H, Ito K. The roles of sodium and potassium ion in the generation of the electro-olfactogram. Journal of General Physiology. 1968; 51: 552-61.

15. Bakayla H, Reed R. Identification of a specialized adenylyl cyclase that may mediate odorant detection. Science. 1990; 250: 1403-6.

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