Physiology of Nose & P.N.S. Dr. Vishal Sharma

Functions of nose Respiration Air conditioning of inspired air Protection of lower airway Ventilation & drainage of P.N.S. Olfaction: increased on sniffing Nasal resistance Vocal resonance Nasal reflexes

Functions of P.N.S. (?) Air conditioning of inspired air Vocal resonance Thermal insulators for orbit & cranium from fluctuating nasal temperature Lightens weight of skull

Respiration Inspiration: air current passes along mid-portion of nasal cavity in lamellar flow. Expiration: resistance of nasal valve & turbinates leads to formation of eddy current in expired air. This results in awareness of breathing & ventilation of paranasal sinus.

Respiration

Air conditioning Filtration: particles > 3 μm in inspired air are trapped by nasal vibrissae Temperature control: Heat exchange b/w blood in cavernous venous sinusoids of turbinates & inspired air, by radiation Humidification: by secretions of nasal & P.N.S. mucosa; for better ciliary function

Protection of lower airway 1. Muco-ciliary blanket: traps pathogens in inspired air > 0.5 μm & transports them to nasopharynx for swallowing 2. Sneezing: protects against irritants 3. Lysozyme: kills bacteria & viruses 4. Immunoglobulins A & E: for bacteria 5. Interferon: for protection against virus

Muco-ciliary blanket Goblet cells in nasal mucosa secrete a mucous blanket; moved backwards like a conveyer belt into nasopharynx. Consists of:  Superficial mucous or gel layer  Deep serous or sol layer

Muco-ciliary blanket

Muco-ciliary blanket

Ciliary cycle

Factors decreasing mucociliary function Dry atmosphere (absence of humidity) Smoking, air pollutants & nasal irritants Infection Extremes of temperature Hypoxia Drugs: anaesthetics, sedatives, topical nasal decongestants, beta blockers

Ventilation of P.N.S. Inspiration: negative pressure created in nasal cavity  sucks out air from paranasal sinuses via their ostium. Expiration: eddies within nasal cavity create positive pressure  ventilates paranasal sinuses via their ostium.

Ventilation of P.N.S.

Drainage of sinuses

Drainage of sinuses Anterior sinuses drain in lateral pharyngeal gutter Posterior sinuses drain over posterior pharyngeal wall

Drainage of sinuses

Nasal resistance Nasal resistance to expired air keeps positive pressure in respiratory tract & prevents alveolar collapse

Nasal Resistance Nose provides 50-60 % of total airway resistance Nasal resistance is provided by 3 areas: Nasal vestibule Nasal valve (maximum contribution) Nasal turbinates

Nasal valve Anterior nasal valve (ostium internum) is located at limen nasi, 1.5 cm posterior to anterior nares. Consists of inferior margin of upper lateral nasal cartilage + anterior end of inferior turbinate + adjacent nasal septum. Cross-section of airway here is 20-40 mm2 on each side. It is narrowest part of upper respiratory tract. Cottle’s test checks valve patency.

Vocal resonance Nasal cavity & paranasal sinus cavity provide vocal resonance for nasal consonants M, N & nG De-nasal voice is seen in nose block. Nasal consonants M, N & nG are uttered as B, D & G respectively

Nasal reflexes 1. Smell reflex: increases secretions of saliva & gastric juice 2. Naso-pulmonary reflex: Chronic, severe nasal obstruction  increased pulmonary resistance  pulmonary hypertension 3. Sneeze reflex: protection against F.B.

Nasal Cycle

Nasal Cycle Reflex, periodic alternation in nasal airflow resistance b/w two nasal cavities Regulated by autonomic nervous system Due to congestion & decongestion of venous sinusoids of inferior turbinates & anterior nasal septum Each cycle lasts for 2-12 hrs (average 2-4 hrs)

Factors modifying nasal cycle  Temperature & humidity of surrounding air Head position Body temperature Physical activity Emotional & psychological status Hypothyroidism & hyperthyroidism Nasal decongestants & anti-hypertensives

Olfactory area of nose

Olfactory neural pathway Olfactory receptors on nasal mucosa  20 Olfactory nerve bundles  synapse with Mitral & Tufted cells in Olfactory bulb  Axons unite to form Olfactory tract  flattens distally to form Olfactory trigone  trifurcates into Olfactory striae  synapse with 10 & 20 Olfactory cortex + hypothalamus + hippocampus + amygdala.

Olfactory neural pathway

Olfactory neural pathway

Olfactory neural pathway Olfaction is the only sensation to reach cerebral cortex directly without first relaying at thalamus Olfactory pathway incorporates limbic system & is concerned with emotional behaviour, mood & recent memory

Olfactory dysfunction causes 1. Upper respiratory viral infection (30 %) 2. Idiopathic (25 %) 3. Head trauma (20 %) 4. Obstructive sino-nasal disease (15 %)  Rhino-sinusitis  Nasal polyp / neoplasm 5. Neurologic & Psychiatric diseases 6. Intra-cranial neoplasm 7. Toxic chemicals & surgical trauma

Classification Conductive loss: obstruction of nasal passages chronic nasal inflammation, polyposis Sensorineural loss: damage to neuroepithelium viral infection, airborne toxin Central olfactory neural loss: C.N.S. damage tumors, neurodegenerative disorders

Olfactory dysfunction types 1. Anosmia: absence of olfactory sensation 2. Hyposmia: decreased olfactory sensation 3. Parosmia / cachosmia: perception of a pleasant odour as unpleasant odour 4. Phantosmia: perception of odour in absence of olfactory stimulus 5. Hyperosmia: increased olfactory sensation 6. Olfactory agnosia: unable to identify odour

Tests for olfactory disorders 1. Tests for nasal airflow a. Simple Rhino-manometry: anterior & posterior b. Acoustic Rhino-manometry: uses sound waves 2. Tests for ciliary function a. Saccharine test 3. Tests for olfaction 4. CT scan & MRI of PNS & brain

Rhino-manometry Test of nasal function, measures air pressure & rate of nasal airflow during respiration. These are used to calculate nasal airway resistance. anterior rhino-manometry: pressure sensor placed at tip of each nostril in turn. posterior rhino-manometry: pressure sensor (small plastic tube) placed behind nasal cavity.

Anterior Rhino-manometry

Posterior Rhino-manometry

Rhinogram

Acoustic rhino-manometry

Saccharin Test Evaluates ciliary function by measuring time taken for a drop of saccharin to be tasted in throat when applied to inferior turbinate (anterior tip). Normal speed = 5-10 mm / min. Normal time = 10-20 min.

Olfactory function tests 1. Supra-threshold test: only identifies odour  Smell bottles  Smell Identification Test (S.I.T.) 2. Threshold Olfactometry: measures weakest perceptible odour with help of serial dilution  Manual  Dynamic (automatic)

University of Pennsylvania Smell Identification Test U.P.S.I.T. consists of 4 test booklets, each containing 10 stimuli for smell. All 40 stimuli are presented in rectangular areas. Subjects scratch & then sniff them. They are required to pick 1 from 5 multiple choices present for each stimuli.

36 - 40  normal; 16 - 35  partial anosmia 6 - 15  total anosmia; 0 - 5  malingering

Hyposmia or anosmia Nasal block  treat nasal disease Upper respiratory tract infection  medical tx Old age  counseling Head trauma  Neurosurgical referral Smoking  quit smoking Toxin exposure  avoid exposure Congenital  Endocrine referral Parosmia with seizures  Neurology referral psychiatry symptoms  Psychiatry referral

Counseling & Precautions 1. Beware of the following: Spoiled food Explosive gases: use electric stoves Smoke & fire: use detectors with visual alarms Socially unacceptable odors 2. Food enjoyment: flavor additives

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