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