Dr. T. Balasubramanian M.S.
Introduction: Airway resistance is a very important
factor which prevents total collapse of the lung. A totally
collapsed lung causes intense difficulties during respiration. In
adults 2/3 of the total airway resistance is provided by the nose.
Infact this can even be considered as one of the functions of the
nose in addition to olfaction, and airconditioning.
The components of nasal resistance are:
1. Nasal vestibule
2. Nasal valve area
3. Turbianted nasal passages
Nasal vestibule - has compliant walls, hence it has a
tendency to collapse in response to the negative pressure caused
during inspiration. This collapse of the compliant walls limits the
nasal airflow in this segment. This area can hence be considered as
a flow limiting segment of the nose (starling resistor). This
resistance occur only during inspiration as expiratory flow causes
positive pressure within the vestibule.
Nasal valve - This area is the narrowest portion of the
whole of the nasal cavity and offers the maximum resistance to the
nasal airway. This area is referred to as the nasal valve area.
Anatomically this area lies just anterior to the inferior turbinate.
The dimensions of the nasal valve area is maintained by the inferior
turbinate and the corresponding portion of the nasal septum. The
inferior turbinate is made up of venous erectile tissue, which
determines the size of the turbinate. Any treatment aimed at
reducing the swelling of the inferior turbiante will have major
effects on nasal resistance, whereas any corrective surgery like
trimming of septal spurs posterior to the nasal valve region will
have very little effect on nasal resistance.
Turbinated nasal passages: The turbinates of the nose can
change their shape thereby reducing the dimensions of the nasal
cavity contributing to nasal airway resistance..
showing the contributions of various areas of nose to nasal
How is the nasal resistance controlled?
In normal healthy subjects the nasal airway resistance is
determined by the degree of engorgement of venous erectile tissue,
as well as the accessory muscles of respiration which keep the nasal
airway patent. The venous erectile tissue of nasal mucosa has dense
adrenergic innervation which when stimulated cause intense
vasoconstriction thereby decreasing the nasal airway resistance.
Normally there is a continuous sympathetic vasoconstrictor tone to
the nasal erectile tissue keeping the nasal airway resistance under
check. Reduction in this sympathetic tone increases the nasal airway
resistance. The parasympathetic tone in the nose controls nasal
secretion, but has little role in nasal resistance.
showing the various factors influencing nasal
Nasal air flow receptors are present in the nasal
vestibule, these receptors are supplied by infra orbital branch of
trigeminal nerve. The sensation of nasal air flow is greatly
enhanced by stimulation of these receptors. Menthol is one such
stimulant. When balm containing menthol is applied outside the nasal
cavity it stimulates these receptors increasing their sensation to
nasal airway causing symptomatic improvement.
Methods of measuring nasal airway resistance:
1. Rhinomanometry is used to assess the patency of the
nose. There are two types of rhinomanometry, active and passive
rhinomanometry. Active rhinomanometry involves the generation of
nasal airflow and pressure with normal breathing. Passive
rhinomanometry involves the generation of nasal airflow and pressure
from an external source, such as fan or pump which drives air
through the nose.
Active rhinomanometry: can be divided into anterior and
posterior methods according to the siting of the sensor tube. In
active anterior rhinomanometry, the pressure sensing tube is taped
to one nasal passage. This method measures resistance of one nasal
cavity at a time and must be repeated on the other side. The total
air flow through the nose is measured with the help of the sensor
tube. In active posterior rhinomanometry, the pressure sensing tube
is held within the mouth and it detects the post nasal pressure. Air
flow through each nose can be measured by taping the opposite nose.
Precautions taken while performing
a. The use of face mask is desirable than a nasal
cannula. The face mask should form a soft air tight seal and must
not effect pull on the cheek.
b. Calibration of the equipment must be performed
c. Series of readings must be taken as a single reading
2. Acoustic rhinometry: is performed by generating an
acoustic pulse from a speaker which is transmitted along a tube into
the nose. The sound from the pulse wave is reflected back from
inside the nose and is related to the cross sectional area of the
nasal cavity. The reflected sound is recorded by a microphone and
calculations are made accordingly. It gives a precise estimation of
the nasal cross sectional area.
3. Nasometry: During speech sound is transmitted through
both the oral and nasal cavities. Nasal obstruction causes a
reduction in the amount of sound transmitted through the nose. By
measuring the nasal components of speech the patency of the nasal
airway can be assessed. This is known as nasalance. It is the ratio
of sound energy from the nasal and oral passages and can be measured
by placing two microphones one over the nose and the other over the
mouth. Infact the measure of nasalance has been proposed as a useful
method of selecting children for adenoidectomy. It is also useful in
measuring the nasal airway patency.
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