The use of freeze‐dried retronasal stimuli to assess olfactory function

Pooja Pal, Daniel Shepherd, Nazimah Hamid, Michael J. Hautus

Abstract
Objectives
To evaluate a test of olfactory perception that uses freeze‐dried stimuli developed to rapidly release aromas capable of migrating to the olfactory mucosa retronasally.

Design
Validation study.

Setting
Psychology and Chemistry Departments.

Participants
First, 15 participants provided data for psychometric functions. Second, 70 participants made perceptual judgments of retronasal stimuli. Inclusion criterion included informed consent and a satisfactory Nasal Obstruction Symptom Evaluation result.

Main outcome measures
First, psychometric functions were generated for two types of freeze‐dried stimuli (coffee and orange) using the Single‐Interval Adjustment Matrix method. Second, participants provided ratings of pleasantness, intensity, and familiarity and performed a standardised identification test using seven retronasally presented aromas alongside the previously validated Sniffin’ Sticks orthonasal olfactory test.

Results
Psychometric functions indicated a dose‐response relationship between aroma concentration and probability of detection. Test‐retest reliability of the retronasal stimuli was acceptable (r70 = 0.72, P < 0.001), and identification scores were not dependent on testing method (ie, retronasal vs Sniffin’ Sticks). Stimuli delivered using the Sniffin’ Sticks test were rated more pleasant than their retronasal counterparts.

Conclusions
Freeze‐dried retronasal stimuli offer an easy‐to‐use and rapid means to test olfaction function and are arguably well suited for clinical practice, but require further development and trialing prior to the adoption in the clinical context.