The short answers

Where the internal valve sits: About 1.5 cm inside the nostrilThe narrowest part of the airway and its point of greatest resistance.
Normal valve angle: Usually cited as 10 to 20 degreesA range reported across populations, not a threshold that predicts symptoms.
Reported average angles: Approximately 15.5 degrees in Caucasian populationsAnd approximately 22.0 degrees in Asian populations.
How it is diagnosed: History and examinationA clinical diagnosis. CT is unreliable, so a normal scan does not rule it out.
Score suggesting real obstruction: Above 30 on the 0 to 100 NOSE scaleA score of 30 best separated obstructed from unobstructed patients in a 345 patient study.
When repair is considered: Obstruction lasting 12 weeks or moreSpecialty society guidance also requires moderate to severe symptoms and prior counselling on non-surgical options.

A blocked nose is usually not surgical. Allergy, infection and inflammation of the lining all cause blockage that medical treatment improves. Valve collapse is different: the framework itself narrows the airway on breathing in.

Two valves are involved, one behind the other. Blocked nasal breathing covers the other causes.

The internal and the external valve

The internal valve is the angle where the septum meets the upper lateral cartilage. It is the narrowest segment of the airway and its point of greatest resistance, roughly 1.5 cm inside the nostril. It is often the cause when the septum looks straight.

The external valve is the nostril rim and the soft side wall above it, which draw inwards on a deep breath in.

A weak side wall. Soft or poorly supported cartilage gives way on a hard breath in.
An old injury. Bones and septum healed off centre after a fracture, so the twist outside and the blockage inside are one injury.
Previous surgery. A hump reduced without rebuilding the middle third lets the upper lateral cartilages drop into an inverted V, tightening the valve.
Over-trimmed tip cartilage. Narrowing a nose can narrow its airway, so a commonly cited minimum of 6 to 8 mm of lateral crural width is preserved.

Treating the septum alone while the valve collapses leaves the person blocked, and more than one cause is usually present. Enlarged turbinates narrow the same airway.

Why valve collapse gets missed

Collapse shows only on inspiration. A nose examined at rest, or judged from a photograph, can look open. The finding depends on watching the side wall as the person breathes in.

What a scan will not settle

In its position statement on nasal valve repair, the American Academy of Otolaryngology-Head and Neck Surgery calls symptomatic valve dysfunction a clinical diagnosis from history and examination. CT is unreliable, so a normal scan does not rule it out.

The septum also takes the blame, because a deviation is easy to see and name, and it can be corrected while the valve is left unsupported. Where an earlier operation caused the narrowing, correction is revision surgery.

The Cottle manoeuvre, and its limits

The Cottle manoeuvre is the part of the examination a reader can picture. The cheek is drawn gently outwards while the person breathes in, and if airflow improves, the valve is implicated.

A modified version supports the side wall directly with a probe or cotton bud inside the nostril, which is meant to localise the problem more precisely.

Neither is proof. Drawing the cheek opens more than the valve, so a positive result points towards the diagnosis rather than settling it.

A speculum or endoscope in each passage, repeated after a decongestant, separates the two possibilities. What improves was swelling. What stays narrow is structural.

Scoring the obstruction

The Nasal Obstruction Symptom Evaluation, or NOSE scale, was validated in 2004. Five items are scored 0 to 4, and the total multiplied by 5. That gives a range of 0 to 100, and a higher score means more blocked.

A severity classification derived from 345 patients grades that total as mild, moderate, severe or extreme. A score of 30 best separated obstructed from unobstructed patients.

The score is subjective and does not show where the narrowing sits, so it never replaces examination. It is a baseline to repeat months later.

How the valve is supported

Repair adds support rather than removing tissue. The manoeuvres follow what the examination found, and the cartilage is usually taken from the septum.

Spreader grafts widen the internal valve angle. They are commonly 1 to 2 mm wide. Height is commonly 3 to 4 mm.
Batten grafts and repositioning of the lower lateral cartilages support a weak side wall.

Specialty society guidance puts repair at 12 weeks or more of persistent obstruction, with symptoms moderate to severe and non-surgical options discussed first.

The nose is commonly blocked on both sides for about 10 to 14 days afterwards, and breathing can take up to three months to settle fully.

What repair does not do

Surgery does not cure allergy, so allergic patients often still need their spray. Breathing difficulty is itself a recognised risk of nasal surgery.

Before committing to a surgeon

A surgeon should watch the side wall on inspiration and record an obstruction score before operating on an airway. Ask whether they do, and ask before you book. Our doctors answer questions sent through the site.

Questions to ask a surgeon

Take these to a consultation. The consultation checklist is built to be printed and written on, and our doctors will answer questions sent through the site before you travel.

Did you watch my side wall while I breathed in, or examine the nose only at rest?
What did the Cottle manoeuvre show, and which valve did it point to?
Is my blockage the septum, the valve, the turbinates, or more than one of them?
What is my NOSE score today, and will you record it again after surgery?
If you narrow my nose for appearance, what will you do to keep the valve open?
Where will the graft cartilage come from, and what happens if the septum has too little?

Sources

Every source below was opened and checked. We link to health authorities, peer-reviewed journals and professional bodies, and to nothing else.

Position statement: nasal valve repairAmerican Academy of Otolaryngology-Head and Neck SurgerySpecialty society position that nasal valve compromise is a distinct, treatable cause of obstruction.
Development and validation of the Nasal Obstruction Symptom Evaluation (NOSE) scaleOtolaryngology-Head and Neck Surgery, via PubMedThe validated instrument used to measure nasal obstruction before and after surgery.
Development of a severity classification system for subjective nasal obstructionJAMA Facial Plastic Surgery, via PubMedHow NOSE scores translate into mild, moderate, severe and extreme obstruction.