Olfactometry is a diagnostic procedure for testing the sense of smell. An olfactometer is used for this olfactory test. Different odorants can be used to accurately determine the extent of olfactory impairment or loss.
What is olfactometry?
Olfactometry is a diagnostic procedure used to test the sense of smell. Molecules of odorants attach to receptors in the olfactory mucosa of the nose when inhaled. This excites the olfactory nerve, which transmits these stimuli to the brain. The olfactory system is not solely responsible for the perception of smell. It consists of an interplay between the sense of smell, the sense of taste and sensory perception, which takes place via the trigeminal nerve of the nose. Functional impairments of the olfactory system are divided into several categories: hyposmia, which is a diminished sense of smell. Anosmia is a very greatly reduced perception of odor or a complete loss of smell. Excessive perception of odors is referred to as hyperosmia. Olfactory disorders with neurological disease value are cacosmia and parosmia, in which scents are mistakenly perceived as good or bad. In the psychiatric field, there is phantosmia, which is an olfactory hallucination. In this case, scents are perceived that do not exist. Causes of olfactory reduction, loss, or misperception are varied and range from congenital, so-called olfactory-genital syndrome, to craniocerebral trauma, viral infections, Alzheimer’s disease, tumors, diabetes, and medications such as interferon and certain antibiotics that can cause olfactory impairment. A loss of smell is also an early symptom of the onset of Parkinson’s disease. The so-called Weber-Fechner law serves as the basis for olfactometry: odor intensity, concentration of the odor stimulus and the concentration of the reference stimulus are placed in a context and calculated according to a mathematical formula.
Function, effect and objectives
An odor perception is based on two levels: Recognition of the odor on one side, and the strength of the odor on the other. The limitation of odor perception is based on insufficient contact of the odorant to the olfactory cells in the nose. This can occur due to restricted nasal breathing from a cold or inflammation of the sinuses. As soon as these conditions have subsided, the ability to smell also resumes. Therefore, no further examination is required. However, if the sense of smell is impaired due to disturbed transmission of information from the olfactory cells to the brain, or if the processing of olfactory information in the brain itself is disturbed, detailed examinations are necessary. Olfactometry provides several procedures for this purpose. These include subjective and objective olfactometry. In the subjective examination method, the patient is presented with several odorants. The physician tests the patient’s ability to identify different odors and distinguish them from each other. In another test, the olfactory threshold is determined: At what concentration of an odorant does the patient perceive the scent? The physician notes the sensations that are triggered in the patient as a result. Paper strips with microencapsulated odorants act as odor carriers. Tests with sniffing sticks, which the patient smells for three seconds, are particularly successful. The patient then has to choose the correct answer from four possible answers. Sometimes fragrances are also used, which are sprayed into the patient’s mouth. In addition to this subjective procedure, there is objective olfactometry, in which an electroolfactogram, or EOG, is used. A kind of olfactory EEG is created by recording olfactory-derived potentials. The odorant is passed into a nostril through a thin tube. The electrical excitation produced by the olfactory stimulus is displayed and analyzed via the excitation curves of the EEG. This method of olfactometry is, however, very complex and is not yet generally used as a systematic measurement method in patients, but only for medical reports. In addition, there is reflexolfactometry, in which affection reactions or aversion mechanisms are determined. Here, movements and the mimic musculature are observed on contact with the odorant.In toddlers, affinity or aversion of the odors are evident by turning the head. Certain taste tests and nasal flow tests also serve as further examinations. Magnetic resonance imaging is also sometimes necessary, which often necessitates collaboration with neurologists. In order to initiate therapy, the underlying disease that has led to the olfactory disorder must be determined. For example, there is no therapy for congenital and age-related loss of smell. In sinus surgery, the first goal is to improve breathing. In the course of this, the ability to smell often returns. If the olfactory disorder was caused by medication, it recedes after the substances are discontinued. A similar situation can be observed in the case of brain–skull trauma and viral diseases, where the ability to smell returns after the symptoms of the disease have subsided. Younger people have an advantage over older people. Moreover, the longer an olfactory disorder lasts, the less likely it is that it will be cured, since too many olfactory cells have already been destroyed. Targeted olfactory training can help improve the sense of smell. Over six months, the patient must smell four different sniffin-sticks in the morning and evening. Studies have shown that the sense of smell can be completely restored in some patients.
Risks, side effects and dangers
Unlike people with hearing and vision loss, loss of the sense of smell may be a relatively minor disability. However, patients with olfactory disorders are at risk from spoiled food or gas leaks, for example. Therefore, research into the cause is useful. Especially since the various measurement procedures of an olfactometry are harmless for the patient and are not associated with any discomfort or disadvantages. He only has to be willing to accept a certain expenditure of time.
