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Physiology of Nose & P.N.S.
Dr. Vishal Sharma
Functions of nose1. Respiration
2. Air conditioning of inspired air
3. Protection of lower airway
4. Ventilation & drainage of P.N.S.
5. Olfaction: increased on sniffing
6. Nasal resistance
7. Vocal resonance
8. Nasal reflexes
Functions of P.N.S. (?)
1. Air conditioning of inspired air
2. Vocal resonance
3. Thermal insulators for orbit & cranium from
fluctuating nasal temperature
4. 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 disorders1. 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
Thank You