Rhinomanometry

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Rhinomanometry

Definition

Rhinomanometry (RM) is the simultaneous measurement of nasal airflow and the trans-nasal pressure gradient, from which nasal airway resistance (NAR) is calculated. The name derives from "manometry" (pressure measurement) applied to the "rhino" (nose). It is the primary objective method of assessing nasal patency.

Nasal Resistance Formula:

$$R = \frac{\Delta P}{\dot{V}}$$

Where:

R = resistance (Pa/cm³/s, or cmH₂O/L/s)
ΔP = trans-nasal pressure (Pa or cmH₂O)
V̇ = nasal airflow (cm³/s or L/s)

How It Works

Two parameters are measured using differential pressure transducers (manometers):

Nasal airflow - via a flow head (mesh resistance inside a tube); pressure difference across the mesh is proportional to airflow.
Trans-nasal pressure - the pressure at the posterior nares relative to atmospheric pressure (or nasal mask pressure) at the nostril entrance.

The relationship between trans-nasal pressure and airflow is curvilinear (sigmoid), not linear, because at higher pressures turbulent flow increases frictional resistance. This means resistance cannot be read from the slope alone - it is measured at a fixed sample pressure point along the curve.

Classification of Methods

Feature	Type	Description
Airflow source	Active	Patient breathes normally
	Passive	External fan/pump drives air through the nose
Pressure sensor location	Anterior	Tube taped to one nostril; measures one side at a time
	Posterior	Tube in the mouth; measures both nostrils simultaneously

Active Anterior Rhinomanometry (AAR) - Most Common

A face mask is applied over the nose.
The pressure-sensing tube is taped into one nostril (occluding it), so the sealed passage acts as an extension of the tube to detect posterior nares pressure.
Airflow is measured from the contralateral (open) nostril.
The tube is then switched to measure the other side.
Resistance is measured for each side separately, then combined to give total resistance.
Cannot be used in nasal septal perforation (pressure equalization prevents measurement).

Active Posterior Rhinomanometry

The pressure-sensing tube is placed in the mouth, detecting posterior nares pressure when the soft palate allows oral communication.
Both nasal passages can be measured simultaneously.
Advantage: total nasal airflow is measured directly.
Disadvantage: not all subjects can maintain soft palate opening; successful in ~90% with training.

Posterior rhinomanometry technique diagram - face mask, flow head, and pressure sensing tube in mouth

Posterior rhinomanometry: the pressure-sensing tube in the mouth detects posterior nares pressure, while the flow head measures total nasal airflow. (Scott-Brown's Otorhinolaryngology, Vol 1)

The Pressure-Flow Curve

Pressure is plotted on the x-axis and flow on the y-axis. Key features:

The curve has a sigmoid shape.
A more obstructed airway produces a curve shifted closer to the pressure axis (lower flow for the same pressure).
Flattening of the curve distally at a single flow rate may represent nasal valve collapse.
During inspiration, the accelerating and decelerating limbs trace slightly different paths (hysteresis), which is the basis of 4-phase rhinomanometry.

Rhinomanometry pressure-flow curves showing less vs more obstructed airways

The pressure-flow curve: curve "b" (patent airway) rises steeply; curve "a" (obstructed) lies closer to the pressure axis. (Cummings Otolaryngology)

Standardized Reporting Points

The International Standards Committee designates:

Unilateral NAR: measured at 150 Pa (classic RM, anterior method)
Bilateral NAR: measured at 75 Pa (posterior method)
Units: Pa/cm³/s (0.1 Pa/cm³/s = 1 cmH₂O/L/s)
Results from inspiration are most commonly reported in classic RM.

Note: The Asian population may not reach 150 Pa during quiet breathing; lower sample pressures (100 and 50 Pa) may be used.

4-Phase Rhinomanometry (4PR)

Introduced by Vogt et al. (2010), 4PR recognizes that inspiration has distinct accelerating and decelerating phases. Parameters include:

Vertex Resistance (VR) - resistance at the highest point of the flow curve during quiet breathing; best correlates with the subjective symptom of nasal obstruction.
Effective Resistance (Reff) - resistance across the entire breathing cycle (area under the curve of hundreds of resistances).
ReffIn / ReffEx - effective resistance during inspiration/expiration separately.
Logarithmic values (LVR, LReff) are used for normal distribution.

Advantage: a result can always be obtained because reaching a fixed pressure target is not required. Classic RM and 4PR do not significantly differ in outcomes, though comparisons have largely been done using in vitro models.

4-phase rhinomanometry output: pressure-flow curve with table of Log Reff, Log VR, and ISOANA flow values

4PR output showing Log Reff, Log VR (at inspiration/expiration), and ISOANA flow values at 75 and 150 Pa. (Cummings Otolaryngology)

Normal Values

Population	Total NAR (congested)
Adults (mean)	~0.23 Pa/cm³/s
Adults (normal range)	0.15-0.39 Pa/cm³/s
Upper limit of normal (clinical screen)	0.30 Pa/cm³/s
Obstructed (Cole's criterion)	>0.25 Pa/cm³/s
Infants	~1.2 Pa/cm³/s
Children 5-12 yr (males)	~0.6 Pa/cm³/s
Adolescents 13-19 yr	~0.29 Pa/cm³/s
Adults >20 yr	~0.22 Pa/cm³/s

NAR is higher in infants, declines to adult values at age 16-18 years.
Females have lower resistance than males on average.
Unilateral NAR is highly variable due to the nasal cycle (can vary 4-fold over 6-8 hours); total NAR is more stable due to reciprocal congestion/decongestion.

Technical Considerations

Multiple measurements with mask repositioning between each are required - a single measurement is unreliable.
The computerized simultaneous display of the pressure-flow curve allows detection of mask leaks during testing.
Decongestion (exercise or topical decongestant) before measurement eliminates physiological variation from the nasal cycle and isolates anatomical factors - particularly useful when assessing nasal skeletal stenosis.
RM can be performed in supine, right-side lying, and left-side lying positions to evaluate positional nasal obstruction.
Can be performed in children as young as 2 years old using a smaller facemask.
Reference values should ideally be established in each department, as population differences exist.

Clinical Applications

Indication	Notes
Nasal obstruction assessment	Objective measurement before/after septoplasty, turbinate surgery
Allergic rhinitis	RM is useful for diagnosis; shown to be sensitive to mucosal changes
Nasal challenge testing	Documents response to allergen or pharmacological challenge
Decongestant response	Demonstrates physiological vs anatomical component of obstruction
Positional nasal obstruction	RM in different body positions
Preoperative/postoperative rhinological assessment	Objective outcome measure
Pediatric nasal airway assessment	From age 2 years

RM has been validated for monitoring decongestant effects - e.g., mean nasal conductance shows significant increase over 10 hours after xylometazoline treatment.

Comparison with Peak Nasal Inspiratory Flow (PNIF)

PNIF is a simpler, cheaper alternative to rhinomanometry. For nasal challenge and decongestant response studies, PNIF compares well with rhinomanometry in assessing nasal patency. However, rhinomanometry provides more detailed pressure-flow data and is the reference standard for objective nasal airway assessment.

Sources:

Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Vol 1, Chapter 90 (p. 1039-1040)
Cummings Otolaryngology Head and Neck Surgery, Chapter 37 (p. 767-768)

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