A Randomized Trail Protocol to Access Efficacy of Modified Olfactory Training Method for Patients With Post-viral Olfactory Dysfunction

Patients allocated to the COT group are told to expose themselves twice daily to four odors (phenyl ethyl alcohol: rose, menthol: mint, citronellal: lemon, and eugenol: cloves)，which are placed in four brown glass jars (total volume 50 mL) with one of the four odors in each (1 mL each, soaked in cotton pads to prevent spilling). All jars are labeled with the odor name.

Olfactory training includes exposure to odorants twice per day for 5 minutes. Every olfactory session included rotated exposure to each odorant for 10 seconds each, with time intervals of 10 seconds between odors. The resting order of the four odors is mint-rose-lemon-clove.

Patients were advised to sniff the odors in the morning before breakfast and in the evening before bedtime.

The COT group will differ solely with regard to the ingredients contained in the training jars given to the participants. Whereas in the COT group, the training jars will contain the active odors previously selected, in the placebo group, the training jars will be filled with a placebo odorless solvent (propylene glycol). To increase the overall compliance and to ascertain that the placebo (odorless) group remains blinded to the treatment allocation, all patients are told that whereas the odors used during the therapy tend to be less strong, and may be insufficiently intense to produce an odor sensation (i.e., subliminal odors), they are intense enough to be perceived by the brain and may influence mental processes and behavior. The training will last for 12 weeks. After the study completion, all participants will be individually contacted and their group allocations will be revealed. All patients will be offered the possibility of performing or continuing a training with odors.

When the patient is doing olfactory training, he/she selects an odor and installs the corresponding odor bottle on the new olfactory training device. Insert the nose end into one nostril, hold the mouth end in the mouth, take a deep breath through the nose, blow out slowly for about 7 seconds, and carefully experience the changes in the nature and intensity of the nasal odor. Immediately remove the device from the nostril and mouth, take a slow, natural breath through the nose for about 3 seconds; Repeat the above operation for a total of three cycles. The operation steps for the other nostril are the same as those above. When both nostrils have finished sniffing the same odor, stop the training, breathe freely, and rest for 10 seconds. Then continue to sniff the next odor and train in the order and method described above.

Accordingly, all odors used for the application of MOT were identical to the COT method in terms of the duration and application time of each session.