The nasal cycle is the rhythmic congestion and decongestion of blood vessels in the nasal cavities over a period of 2 to 4 hours, regulated by the autonomic nervous system. This causes alternating airflow between the nostrils, with one nostril more congested than the other at a time. This cycle helps to ensure one side of the nose is always moist to facilitate humidification and warming of inhaled air, while the alternating low and high airflow sides aid in detecting a greater range of smells. Factors like head position, temperature, and medical conditions can modify the nasal cycle.

1. NASAL CYCLE
BY : S . ABIHARINI
ROLL NO 02

2. Nasal mucosa undergoes rhythmic cyclical
congestion and decongestion of venous
sinusoids of inferior turbinates and
anterior nasal septum .
Reflex periodic alteration in nasal airflow
resistance between two nasal cavities .
Regulated by autonomic nervous system .

3.  Each cycle lasts for 2 to 12 hours and at
an average for 2 to 4 hours .
 When one nasal chamber is working ,
total nasal respiration equal to that of
both nasal chambers , carried out by it .

5. Pattern of nasal dominance altered by :
• Pressure of a crutch in axilla due to
reflex reversal of nostril dominance .
• Pressure on thorax while sitting
• Pressure in hemithorax while lying down
on the side leads to reduced patency of
ipsilateral nostril and increased patency
of opposite nostril .

7. • Decreased airflow in ipsilateral nostril
• Increased airflow in contra lateral nostril
• Pattern starts to change in a minute and
equalizes in both nostrils about 4th min
and reaches peak in 17 min .

8.  Can be demonstrated in over 80% of the
adults .
 Difficult to demonstrate in children .
 Nasal secretions are also cyclical with an
increase in secretion in the side with
greater airflow .

9. Factor modifying nasal cycle :
 Temperature and humidity of surrounding
air
 Head position
 Body temperature
 Physical activity
 Emotional and psychological status
 Hypothyroidism and hyperthyroidism
 Nasal decongestants and anti hypertensives

10.  Allergy
 Infection
 Pregnancy

11. Benefits for breathing :
It has been shown that the cilia of the
congested side suspend their motility
until that side decongests. Thus the
cycle ensures that one side of the
nose is always moist, to facilitate
humidification, which is one of the
three functions of the nose, the other
two being filtration and warming of

12. Benefits for olfaction :
Some odor chemicals bind with
olfactory receptors easily, even under
conditions of high airflow, and other
odors need more time, under low airflow
conditions, to bind with receptors. With
high airflow on one side and low airflow
on the other side, the olfactory center
detects a greater range of smells.