Rhinomanometry

Rhinomanometry is a test that measures nasal airway resistance, which is how hard it is for air to pass through the nose. It records the pressure difference between the front and back of the nose and the airflow at the same time, and from them calculates the resistance. It gives an objective measure of nasal blockage, which is a symptom that patients and doctors often cannot judge well, because the feeling of blockage correlates poorly with measured resistance.

Anterior rhinomanometry is the most common form. A mask covers the nose and a pressure sensor is placed in one nostril, sealed with a tube. The patient breathes quietly through the nose while the airflow through the open nostril and the pressure in the closed nostril (reflecting the pressure at the back of the nose) are recorded.

The resistance is calculated from the pressure and flow (resistance equals pressure divided by flow), usually at a fixed pressure of 150 pascals. Posterior rhinomanometry places a sensor at the back of the mouth to measure the pressure behind the nose, and is used when both sides are tested at once. Active methods require breathing through the nose, and passive methods use an air pump.

The test takes 5 to 15 minutes, and a decongestant can be applied to test the contribution of mucosal swelling. Normal total nasal resistance in adults is about 0.15 to 0.3 pascals per cubic centimetre per second. A resistance over about 0.3 is regarded as obstruction, though cut-offs vary. The related method, acoustic rhinometry, measures the cross-sectional area of the nasal cavity with sound waves.

Indications.

• Nasal blockage with discordance between symptoms and examination, to give an objective measurement.
• Assessment before and after septal surgery, turbinate surgery, or rhinoplasty, to document change.
• Evaluation of the effect of treatment: nasal steroids, decongestants, and allergen immunotherapy.
• Nasal provocation tests, in which resistance is measured after allergen or irritant exposure.
• Occupational and environmental research on nasal effects of dust and chemicals.
• Evaluation of nasal causes in snoring and obstructive sleep apnoea, before surgery on the nose.
• Medico-legal assessment of nasal injury and of the nasal valve.
• Research on nasal cycle and nasal physiology. Not a test to diagnose the cause of nasal obstruction, and not routine in everyone with a blocked nose.

Contraindications and precautions.

• Perforated nasal septum: pressure is not transmitted correctly in anterior rhinomanometry, and a posterior method is used.
• Complete blockage of one nostril: the test cannot be done by the anterior method on that side, and the resistance is recorded as infinite.
• Acute nasal infection, nosebleed, or recent nasal surgery or trauma: the test is delayed.
• Severe anxiety, claustrophobia (with a mask), or inability to breathe quietly through the nose.
• Patients should be rested for 15 to 30 minutes in the room, to adapt to the temperature and humidity. Exercise, hot drinks, smoking, and nasal drugs (decongestants, steroids) before the test alter results.
• Nasal cycle: the right and left sides alternate in resistance over hours, so total resistance (both sides) is more reliable than one side.
• The equipment is calibrated, and masks and tubes are disinfected or single-use.

Preparation and technique.

The patient sits at rest in a room at a stable temperature for at least 15 to 30 minutes. The nose is examined to exclude a septal perforation or severe pathology. For anterior rhinomanometry, a nasal adaptor with a pressure tube is fixed to one nostril with an airtight seal, using tape or a nasal olive, while the mask covers the nose and the other nostril is open.

The patient breathes quietly through the nose, with the mouth closed, for several breaths, and a plot of pressure against flow is drawn for the breath cycle. The other side is tested in the same way, and the total resistance is calculated from the two sides in parallel. The test is repeated after a topical decongestant to measure the reversible component. At least three technically good recordings are made for each side.

Normal appearances.

The pressure-flow curve (a loop) is smooth and nearly straight or gently curved at normal breathing. The total nasal resistance is about 0.15 to 0.3 pascals per cubic centimetre per second at a pressure of 150 pascals, with each side about 0.3 to 0.6 and the two sides different because of the nasal cycle. After a decongestant, resistance falls by only a small amount.

Interpretation.

• Raised total resistance (over about 0.3 pascals per cubic centimetre per second): nasal obstruction. Values of 0.3 to 0.5 are mild, and higher values are more severe.
• Resistance that falls markedly after a decongestant: a large mucosal component (rhinitis, turbinate swelling), which suggests a good response to medical treatment or turbinate reduction.
• Resistance that remains high after a decongestant: a fixed structural cause, such as septal deviation, nasal valve collapse, polyps, a mass, or a bony problem.
• Asymmetry between the sides: septal deviation or unilateral disease, taking the nasal cycle into account.
• Normal resistance with severe symptoms: suggests that the symptom is not due to measurable obstruction (empty nose syndrome, central or psychological causes, or mucosal dryness and altered airflow sensation).
• High resistance on inspiration only: nasal valve collapse.
• After surgery: a fall in resistance shows improvement, though the correlation with symptom relief is modest.
• Results are combined with the history, symptom scores, and endoscopy.

Critical values and findings needing immediate action.

• There are no emergency values on rhinomanometry itself.
• Unilateral complete blockage with a mass seen on endoscopy, blood-stained discharge, or facial swelling: urgent examination and imaging.
• Unilateral obstruction that is progressive with cranial nerve signs or visual symptoms: urgent imaging.
• Nasal obstruction with a pulsatile mass or clear watery leak: no biopsy, and urgent imaging.
• Marked obstruction in a newborn: assessment for choanal atresia, which is an airway emergency in the obligate nose-breathing neonate.

Limitations and artefacts.

• Results are influenced by room temperature, humidity, posture, exercise, time of day, the nasal cycle, drugs, and smoking, and repeat tests at different times may vary by 20% or more.
• Poor seal, leaks, mouth breathing, and turbulent airflow cause errors. The method needs a cooperative patient who breathes steadily.
• There is a poor correlation between the sensation of blockage and measured resistance, so the test does not fully reflect the patient experience, and it does not replace symptom scores.
• Anterior rhinomanometry cannot be done on a blocked or perforated side, and the nostril position changes the airflow.
• Different devices, pressure points, and methods give different values, and normal ranges are not universal.
• The test gives no information on the site or cause of obstruction, and acoustic rhinometry or endoscopy is needed.
• The test is not widely available, and is mostly used in research and in specialist centres.

Special groups.

• Children: difficult to do and requires cooperation. Adenoid enlargement is the main cause of blockage, and is assessed by endoscopy or imaging of the nasopharynx.
• Patients before rhinoplasty and septoplasty: baseline and follow-up measures inform surgical planning and show outcomes.
• Patients with allergic rhinitis: measurements before and after allergen challenge or treatment.
• Patients with snoring and sleep apnoea: nasal resistance contributes to mouth breathing, and its treatment may help continuous positive airway pressure tolerance.
• Pregnant women: nasal congestion from hormonal changes.
• Regions: the equipment is expensive, and not commonly available. In practice, nasal examination, endoscopy, a simple mirror or cold spatula test of nasal airflow, and symptom questionnaires are used. Nasal blockage is very common from allergic rhinitis, infection, and dust and smoke exposure, and septal deviation after trauma is frequent.

Follow-up tests.

• Nasal endoscopy.
• Acoustic rhinometry for cross-sectional area.
• CT of the sinuses and nasal cavity in suspected structural or sinus disease.
• Allergy testing (skin prick, specific immunoglobulin E).
• Symptom scores and nasal peak inspiratory flow.
• Sleep study in suspected sleep-disordered breathing.
• Repeat rhinomanometry after treatment or surgery.