Nasal Inspiratory Flow Measurement Technique

An expiratory pause should not be used when measuring Nasal Inspiratory Flow (NIF). 1

Proper Technique for Measuring Nasal Inspiratory Flow

The standardized procedure for measuring nasal inspiratory flow involves several key components:

The patient should inhale through the mouth to total lung capacity (TLC) or near TLC if full TLC is difficult to achieve 1
The inhalation should take approximately 2-3 seconds 1
The patient should exhale immediately after reaching TLC without any breath holding or pause 1
Breath holding or pausing at the end of expiration should be avoided as it causes NO accumulation in the nasal cavity and airways 1

Expiratory pauses can negatively impact measurement accuracy for several reasons:

Breath holding results in NO accumulation in the nasal cavity, lower airway, and oropharynx 1
This accumulation causes NO peaks in the exhalation profiles that can interfere with accurate measurement 1
The use of breath hold is discouraged in standardized techniques for respiratory flow measurements 1
Pausing can alter the natural airflow dynamics between inspiration and expiration 2

When measuring nasal inspiratory flow, maintaining proper flow rates is essential:

A constant expiratory flow rate should be maintained during the measurement 1
For most standardized measurements, a flow rate of 0.05 L/second (BTPS) is recommended 1
Flow rate should be clearly recorded and reported with any measurements 1
The exhalation is deemed adequate if the mean exhalation flow rate is within 10% of the target flow rate 1

The measurement technique should include these important elements:

The patient should be seated comfortably with the mouthpiece at proper height and position 1
A nose clip should not be used as it may allow nasal NO to accumulate 1
Velum closure during measurement is important to prevent nasal contamination 1
Expiratory resistance should be maintained between 5-20 cm H₂O to ensure proper measurement conditions 1

Research comparing nasal inspiratory and expiratory measurements shows:

Inspiratory peak flow measurements show certain advantages compared to expiratory measurements 3
At low flow rates, airflow is greater during inspiration than expiration 2
Peak inspiratory flow rate correlates better with nasal resistance than peak expiratory flow rate 2
Results are best expressed as the means of three consecutive registrations rather than using only the highest value 3

When interpreting nasal flow measurements, be aware of these limitations:

Distribution of individual values for both PNIF and PNEF can be wide and independent of subject's age, height, or gender 4
Repeatability may be poor and diurnal variation substantial 4
Variability in PNIF measurements is significantly higher than in other respiratory measurements 5
For follow-up assessments, the peak expiratory flow index (PEFI) shows better correlation with nasal obstruction symptoms than absolute PNIF values 6