Sniff test
Updates to Article Attributes
The fluoroscopic sniff test, also known as diaphragm fluoroscopy, is a quick and easy real time fluoroscopic assessment of diaphragmatic motor function (excursion). It is used most often to confirm absence of muscular contraction of the diaphragm during expiration in patients with phrenic nerve palsy or breathing difficulties following stroke. Chest radiograph demonstrating a newly elevated hemidiaphragm often precedes a sniff test.
Technique
With the patient either standing (preferred) or supine, frontal fluoroscopy of the diaphragm is performed first with the patient at rest and breathing quietly through an open mouth. Then the patient is asked to take a few quick short breaths in with a closed mouth ('sniffs') causing rapid inspiration. Occasionally repeating this in the lateral projection is required to evaluate the posterior hemidiaphragms.
It is best to ask the patient to practice the sniff before hand.
Findings
-
normal
normaldiaphragm motion- the diaphragm contractsduring inspiration - moves downwards
- the diaphragm relaxes during expiration - moves upwards
- 3-5cm of excursion is normal and up to 8cm can be seen in athletic individuals in deep inspiration
- both hemidiaphragms move together
-
abnormal
abnormaldiaphragm motion- the affected hemidiaphragm does not move upwards during inspiration
Interpretation
Absence of diaphragmatic movement confirms phrenic nerve palsy in the appropriate clinical setting. A mass anyway along the course of the phrenic nerve requires exclusion, usually with neck and chest CT. A hilar mass due to lung cancer is the most common finding on CT and a classic exam case.
Normal diaphragmatic excursion can also be impaired in patients with:
- previous diaphragmatic trauma or surgery
- neuromuscular disorders
- previous stroke
-<li>-<strong>normal </strong>diaphragm motion<ul>- +<li>normal<strong> </strong>diaphragm motion<ul>
-<li>-<strong>abnormal </strong>diaphragm motion<ul><li>the affected hemidiaphragm does not move upwards during inspiration</li></ul>- +<li>abnormal<strong> </strong>diaphragm motion<ul><li>the affected hemidiaphragm does not move upwards during inspiration</li></ul>
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Image ( destroy )
Image 1 Fluoroscopy (Frontal) ( update )
Image 2 Fluoroscopy (Frontal sniffing) ( update )
Image 3 Fluoroscopy ( update )
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