The Effect of Sleep Disordered Breathing on Olfactory Functions: Analysis by Apnea-Hypopnea Index

One hypothesis of obstructive sleep apnea syndrome (OSAS) is that long-standing snoring vibrations and hypoxia of the nerves cause a local neuropathy in the upper airway during sleep. The aim of this study was to investigate olfactory function in subjects comprising snorers and untreated subjects with OSAS, and to correlate data with polysomnographic parameters.

Sixty-nine patients were evaluated for snoring from January 2010 to December 2013. The mild group (apneahypopnea index [AHI]<15) consisted of 19 subjects, and the moderate-severe group (AHI≥15) consisted of 50 subjects. Exclusion criteria were conductive olfactory dysfunction, previous tonsil or soft palatal surgery, central sleep apnea, and medications that are known to affect peripheral nerves. Nocturnal polysomnography and olfactory function test such as Korean version of Sniffin's stick test I, II (KVSS I, II) were performed.

There was a significant difference in body mass index, average oxygen saturation (SaO2), lowest SaO2, average snoring duration, and KVSS I, II between the two groups. AHI was related to odor threshold score, and average SaO2 was related to odor discrimination score. But, odor identification score showed no relation with AHI and average SaO2 except for age. Average SaO2 and AHI were closely related to the function of smell.

Hypoxia and low nasal airflow caused by OSAS may have an effect on the olfactory function. On comparison between the two groups, patients with a high AHI, especially those with OSAS, had an olfactory dysfunction. Also, low average oxygen is the main risk factor in determining the olfactory function. In people with OSAS, the possibility of olfactory dysfunction should be considered and an olfactory function test should be performed.