Olfactometry (synonyms: olfactory test, olfactory test, olfactory test) is a diagnostic procedure used in ear, nose and throat medicine to check for a possible restriction of the sense of smell.The olfactory test is performed on various odorants, so that an accurate determination of the olfactory restriction can be guaranteed. With the help of olfactometry, it is possible to diagnose both subjectively and objectively the functional limitations of the olfactory organ. The examinations are carried out in the case of a wide range of diseases, such as damage to the peripheral and central olfactory pathways (the olfactory pathways are structures of the central nervous system through which information from the olfactory sensory cells is transmitted to a specific area of the brain). Moreover, it should be mentioned that the application of olfactory examinations is standardized.
Indications (areas of application)
- In the presence of Parkinson’s disease and Alzheimer’s disease, approximately 80 percent of sufferers suffer from olfactory dysfunction (dysosmia) because the areas of the brain required for smelling are damaged. Since this damage can occur early in the course of the disease, it consolidates the diagnosis in the presence of other symptoms or indicates the diseases as a single symptom.
- A deteriorated ability to smell can also be seen as a sign of diabetes mellitus type 1 and 2, because here, too, anosmia or hyposmia (decreased sense of smell) can arise due to neuropathy (nerve damage).
- In the presence of nasal polyps, olfactometry may be indicated (indicated), as these can also be noticeable through the mucosal swelling via a reduction in olfactory performance.
The procedure
The principle of olfactometry is based on the use of diverse odorants from different odor classes. The basic odorants are the following:
- Pure olfactory substances: this form of odorants exclusively irritates the olfactory nerve (olfactory nerve) – examples include coffee, vanilla, lavender and cinnamon.
- Combination odorants: these odorants are able not only to irritate the olfactory nerve and thus initiate the transmission of stimuli, but also to achieve an additional stimulation of the trigeminal nerve (a cranial nerve that supplies both the muscles and the skin on the face).
- Olfactory substances with a taste component: this present form of odorants irritates the olfactory nerve on the one hand, but on the other hand still additionally various taste nerves such as the facial nerve (mixed nerve with a motor (supplying a muscle) and a sensitive (supplying an area of the skin) portion). As an example of this genus is chloroform.
Due to the fact that pure olfactory substances can be perceived exclusively through the olfactory nerve, there is no perception of odor in anosmia (complete loss of smell). In the other forms, however, the substances can be perceived via the sense of taste, for example. The olfactometers required for olfactometry are divided into two different systems. Static and dynamic olfactometers can be distinguished from each other, which are distinguished by different dilution methods:
- Static olfactometry: in this method, two different gases are used, each in a different volume. One gas is completely odorless, while the other gas has an olfactory effect. From the ratio of the two gas volumes can now calculate the dilution.
- Dynamic olfactometry: in this method, an odorous gas is also used as an odor sample and mixed with a gas. However, the advantage of this method is the lower requirement of the olfactory substance.
To the procedure of olfactometry:
- When testing for an olfactory disorder present, the patient is offered an odor sample in a dilution of varying strength. In order to obtain a meaningful result, the patient must not be under the influence of any medication that may affect the sense of smell. Furthermore, it is important that he does not suffer from any disease that can affect smelling (example: rhinitis – viral rhinitis).
- To determine the odor threshold (lowest concentration of an odorous substance that can be perceived by the patient), different odor samples in different dilutions are presented to the patient for measurement.
- If possible, the different samples are not only presented in a descending intensity, but are varied during the administration. Another variant for scrambling the order of the samples is the forced-choice method, in which the patient is offered two tubes each and must identify which one contains the diluted odor sample. To be distinguished from this is the yes-no mode, in which the patient is to evaluate whether the tube offered contains an odorous substance.
- In both variants, the odorant may only act on the patient for a maximum of 15 seconds, until the patient must have recognized the presence of an odor. Furthermore, it requires a pause of half a minute after each administration of an odorant, so that an adaptation (habituation) to the odorant can be prevented.
In addition to the separation of the two olfactometry procedures, it is also possible to differentiate the olfactory test itself in two different procedures:
- Subjective olfactory testing, as a qualitative test procedure, relies on the patient’s verbally expressed response as to whether they perceived the odor with one nostril occluded at a time.
- Objective olfactory testing, on the other hand, allows patients who are unable to express themselves (for example, in the presence of mental retardation or young children) whether they have perceived the smell. The test is performed by measuring the patient’s brain waves with an EEG device. The currents triggered when detecting an odor can be displayed by the EEG meter.
In many cases, the patient recovers from the olfactory disorder even without treatment. However, if it is present as a symptom of an underlying disease, olfactometry can help diagnose the underlying disease. Thus, the decisive factor for the patient is not the detection of the olfactory disorder, but rather the identification of the cause.
