Naris
Naris
User’s
Manual V14 14/02/20 Page 22 of 52
b)
POSTERIOR METHOD
The posterior method allows direct measurement of total nasal resistance from a single
manoeuvre without any direct contact with the nose, and as such is perhaps the preferred
technique.
The mask assembly comprises an anti-viral filter, a pneumotachograph (to measure flow), and
a black nozzle onto which can be added disposable posterior tubes (to measure pressure). The
subject should be asked to put the disposable tube in their mouth and close their lips around it
while breathing through their nose. Under ideal conditions the pressure developed in the
mouth will equal that behind the nasal passages and by dividing this pressure by the passing
flow, a measure of resistance can be obtained:
This technique does not interfere in any way with the nasal passages, but it does have the
disadvantage that it depends on the mouth area having an uninterrupted connection to the
respiratory tract. It is therefore essential that:
a) the subject does not bite the mouth tube
b) the end of the tube is not blocked by the tongue, cheek, or saliva
c) the soft palate is relaxed and the back of the tongue is held down in the mouth
Difficulty may be experienced in training
some subjects to perform satisfactorily -
success figures of around 80% for adults
and 50-70% for children may be typical.
Two techniques have been found useful in
training subjects.
1. Allow the subject to obtain
visual feedback by watching the
screen. By
looking at the trace the clinician can tell
the patient when a valid test
has been obtained (it will pass through
the origin) and within
a short time the patient will
associate a successful test
with a certain posture, meaning tests can
now be made
Resistance = Pressure
Flow
