Physiology of Nose P N S Dr Vishal

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

Functions of nose 1. 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 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 mm 2 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 & n. G • De-nasal voice is seen in nose block. Nasal consonants M, N & n. G 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; 6 - 15 total anosmia; 16 - 35 partial 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