Olfactometry

Among the many diagnostic procedures, there are also little-known methods, such as olfactometry. This is a study that evaluates the threshold of sensitivity and identification of various odors. Olfactometry is necessary to determine olfactory disorders, in particular, anosmia, hyposmia, parosmia. The procedure is performed using a series of cylinders filled with special solutions, as well as a device for quantitative delivery of these solutions. The quality of olfaction is assessed by the volume of odorant at which the patient begins to feel the aroma. [ 1 ]

Indications for the procedure

Olfactometry is prescribed to people with insufficient sense of smell, changes in the ability to distinguish smells, or suffering from olfactory hallucinations. Such disorders are discussed when the patient suffers from one of the neurological or ENT pathologies:

• atrophic processes in the nasal cavity;
• congenital disorders of the upper respiratory system;
• tumor processes, polyps;
• rhinitis of drug-induced, allergic, hypertrophic origin;
• craniocerebral injuries with trauma to the olfactory fibers of the ethmoid bone;
• destructive processes affecting the olfactory bulbs;
• inflammatory processes affecting the nasal sinuses;
• brain oncological processes;
• exotoxic reactions;
• senile dementia, Parkinson's disease.

Olfactometry helps not only to determine the disorder, but also to determine the degree of intensity of the pathology, which is necessary:

• to assess professional suitability;
• to conduct a medical examination;
• to evaluate the results of the treatment;
• for the diagnosis of various pathological conditions.

Preparation

The olfactometry procedure does not require any special preparation of the patient. However, in order for the diagnosis to be as accurate as possible, doctors advise adhering to the following rules:

• Stop smoking a few days before the test. Tobacco resins reduce the quality of smell perception, so the results of olfactometry after smoking a cigarette may be distorted. To obtain more objective information, it is recommended to smoke your last cigarette at least 24 hours before the test.
• Use external vasoconstrictors. If the patient suffers from acute rhinitis or other diseases that involve swelling of the mucous tissue of the nose, it is recommended to inject a few drops of vasoconstrictors into the nose before olfactometry. In such a case, the results of the study will be as accurate as possible.
• Conduct anterior rhinoscopy in advance. If organic damage to the external nose is suspected, anterior rhinoscopy must be performed in advance to identify factors that may affect the result (tumor processes, mucosal injuries, etc.). [ 2 ]

Technique olfactometry

Olfactometry is performed using a special device called an olfactometer. The device can be different, but most often it consists of two cylinders of different diameters: the smaller cylinder is inserted into the larger one, filled with an odorant - a smelling solution. When the smaller cylinder is immersed in the larger one, the solution comes out into the outlet tube.

The procedure is carried out in stages:

• The doctor explains the purpose and subtleties of the study, explains what exactly is required of the patient, and what sensations he should tell the specialist about.
• The device's outlet tube is inserted into the patient's nasal cavity, through which the odorant is dosed. Its volume is gradually increased, monitoring the patient's reaction. Usually, several variants of the aromatic solution are used, which also have a taste and irritant effect.
• The results are assessed using objective and subjective criteria. In addition to the patient telling the specialist at what point the aroma begins to be perceived, electroencephalography is used to assess the active phase of olfaction. The result is calculated in centimeters of cylinder indentation (olfactions) or in cubic centimeters. Adequate sensitivity values may vary depending on the specific odorant.

The doctor prepares a special set of odorous substances for olfactometry, the registration certificate of which is carefully checked and certified. In addition, olfactometry can assess the quality and quantity of the olfactory function: the qualitative version of olfactometry is more accessible, but is used to diagnose only anosmia. Quantitative assessment allows you to determine the level of olfaction, depending on the amount of odorant required to begin to perceive the aroma. [ 3 ]

Contraindications to the procedure

Solutions for olfactometry have extremely low toxicity, so there are not many contraindications to the study. Olfactometry is not used if the patient suffers from severe bronchial asthma (a strong aroma can cause an exacerbation of the disease), or if the anamnesis indicates hypersensitivity to the flavors used.

A relative contraindication is the child age of the subject: not because the study can somehow harm a person. The fact is that a child in most cases cannot adequately assess the manipulations carried out on him, and is not always able to clearly express his feelings. The question of conducting olfactometry in children is decided individually with a doctor. [ 4 ]

Complications after the procedure

Olfactometry is performed in an outpatient setting and does not require further observation of the patient by a doctor. The patient is sent home immediately after the procedure. In rare cases, the patient is left for observation for another 2 hours. This is relevant, for example, if a person suffers from an allergy to substances used during olfactometry. In addition, patients who experienced discomfort and noted a deterioration in their health during the study need additional observation by an otolaryngologist and therapist.

Upon completion of olfactometry, the following conclusion can be obtained:

• Normosmia – olfactory function within normal limits.
• Hyposmia is a decreased olfactory function.
• Anosmia is the lack of sense of smell.
• Cocosmia is a perverted olfactory function.

If any olfactory dysfunction is detected during olfactometry, the possibility of its mechanical cause is determined. For this purpose, the specialist conducts a thorough examination of the nasal cavity. If necessary, some areas are treated with an adrenaline solution. If the olfactory ability is not restored within five minutes, then the hyposmia is said to be of mechanical origin.

Olfactometry is generally considered a safe, non-invasive procedure that is not associated with complications. Only isolated cases of deterioration have been reported:

• Headache, dizziness, slight nausea appeared as a reflex response to the influence of irritants: ethanol, menthol, acid mixtures. Such a side reaction usually disappears on its own, without outside medical intervention, within a few minutes after the end of the study.
• Anaphylactic shock is the maximum manifestation of allergy, affecting the respiratory system. The complication develops as mechanical respiratory failure, and the patient needs immediate medical care. The pathology is eliminated by intravenous infusion of antihistamines and corticosteroids.

It is worth noting that olfactometry causes complications in only 0.1% of patients, in particular, in people prone to disorders of the vestibular system or having increased allergic sensitivity of the body. In general, olfactometry is a highly effective and safe manipulation for assessing the presence and level of olfactory sensitivity disorders.

Care after the procedure

There are no post-olfactometry care or recovery procedures. The patient can return to their normal routine immediately after the examination.

The benefits of olfactometry include:

• simplicity and ease of use;
• accessibility and portability of the device;
• the ability to record indicators and subsequently observe them in dynamics;
• no need for preliminary special preparation and rehabilitation of the patient after olfactometry.

Reviews

According to numerous reviews, olfactometry is an informative diagnostic procedure that is completely safe for patients. The study allows the doctor to obtain information about the functional capacity of the olfactory organ, which helps him in making a diagnosis and prescribing the correct treatment.

If the doctor prescribes olfactometry, the study must be carried out, since there is virtually no alternative to this diagnostic method. In a sense, the olfactory function can be assessed using methods that record vegetative-olfactory reactions - in particular, heart rate and respiratory movements, pupil size. But such reactions do not fully illuminate the quality of the patient's sense of smell, since there are isolated disorders that do not affect vegetative reactions, but provoke disturbances in the olfactory analyzer. In some cases, to determine the ability to perceive aromas, fixation of bioelectric brain activity after exposure to odorous irritants is used.

Olfactometry evaluates olfactory sensitivity by determining a person's reaction to a special set of solutions with characteristic aromas - usually the smell of vinegar, ethanol, valerian, ammonia. For a complete study, it is advisable to use different smells, since sometimes the patient perceives some aromas, but not others. It is important to consider that certain aromas can irritate the endings of the trigeminal nerve. For example, the "mint" smell gives a feeling of coolness, and alcohols give a feeling of warmth; ammonia, formalin, bitters can provoke unpleasant and even painful sensations. In this regard, olfactometry should include sets of various test solutions, among which there should be substances that irritate the endings of the trigeminal nerve, as well as those that have a taste component.