Olfactometry

Among the many diagnostic procedures, there are also little-known methods - for example, olfactometry. It is a study that evaluates the threshold of susceptibility 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 the quantitative supply of these solutions. The quality of smell is assessed by the volume of the odorant at which the patient begins to smell the scent. [1]

Indications for the procedure

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

• atrophic processes in the nasal cavity;
• congenital developmental disorders of the upper respiratory system;
• tumor processes, polyps;
• rhinitis of drug, 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 sinuses;
• brain oncological processes;
• exotoxic reactions;
• senile dementia, Parkinson's disease.

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

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

Preparation

The olfactometry procedure does not require 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 diagnosis. Tobacco tar reduces the perception of odors, so the olfactometry results after smoking a cigarette may be distorted. For more objective information, it is recommended to smoke the last cigarette at least 24 hours before the study.
• Use external vasoconstrictors. If the patient suffers from an acute form of a cold or other diseases in which there is swelling of the nasal mucosa, then before olfactometry, it is recommended to inject a few drops of vasoconstrictor agents into the nose. In this case, the results of the study will be as accurate as possible.
• Perform anterior rhinoscopy in advance. If you suspect an organic lesion of the external nose, you must first perform an anterior rhinoscopy to identify factors that can affect the result (tumor processes, mucosal injuries, etc.). [2]

Technique of the olfactometry

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

The procedure is performed in stages:

• The doctor explains the purpose and subtleties of the study, explains what exactly is required of the patient, what sensations he should tell the specialist about.
• An outgoing tube of the device is inserted into the patient's nasal cavity, through which the odorant is dosed. Its volume is gradually increased, monitoring the patient's response. Usually, several versions of the aromatic solution are used, which also have a taste and irritation effect.
• Evaluation of the results is carried out according to objective and subjective criteria. In addition to the fact that the patient tells the specialist at what moment the aroma begins to be perceived, electroencephalography is used to assess the active phase of smell. The result is calculated in centimeters of cylinder indentation (olfactia), or in cubic centimeters. Adequate sensitivities may vary depending on the particular 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 olfactory function: a high-quality version of olfactometry is more affordable, but is used to diagnose only anosmia. Quantification allows you to determine the level of smell, depending on the amount of odorant required to start smelling. [3]

Contraindications to the procedure

Solutions for olfactometry have extremely low toxicity, so there are not so many contraindications for conducting a study. Olfactometry is not used if the patient suffers from a severe course of bronchial asthma (a bright aroma can exacerbate the disease), or if a history of hypersensitivity to the flavors used is indicated.

The child's age of the subject is considered a relative contraindication: not because the study can somehow harm a person. The fact is that in most cases the child cannot adequately assess the manipulations carried out with him, is not always able to clearly articulate the sensations. The question of olfactometry in children is decided with the doctor individually. [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 goes home immediately after the procedure. In rare cases, the patient is left for observation for another 2 hours. This is true, for example, if a person is allergic to substances used in the course of olfactometry. In addition, patients who experienced discomfort and noted a deterioration in well-being during the study need additional supervision by an otolaryngologist and therapist.

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

• Normosmia - olfactory function within normal limits.
• Hyposmia  is a decreased olfactory function.
• Anosmia  - lack of smell.
• Cocosmia is a perverse olfactory function.

If any violations of the olfactory function are detected in the process of olfactometry, the possibility of their mechanical cause is investigated. For this purpose, the specialist conducts a thorough examination of the nasal cavity. If necessary, he treats some areas with adrenaline solution. If the olfactory ability is not restored within five minutes, then they talk about the mechanical origin of hyposmia. 

Olfactometry is generally considered a safe, non-invasive procedure with no complications. There were only isolated cases of worsening of the condition:

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

It should be noted that olfactometry causes the development of complications only in 0.1% of patients - in particular, in people susceptible to disorders of the vestibular system, or with increased allergic sensitivity of the body. In general, olfactometry refers to a highly effective and safe manipulation for assessing the presence and level of olfactory sensory disorders.

Care after the procedure

There are no measures for the care and recovery after olfactometry. The patient can return to the usual rhythm of life immediately after the examination.

Positive aspects of olfactometry include:

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

Reviews

According to numerous reviews, olfactometry refers to informative diagnostic procedures that are completely safe for patients. The study allows the doctor to obtain information about the functional ability of the olfactory organ, which helps him in making a diagnosis and the correct prescription of treatment.

If the doctor prescribes olfactometry, then the study should definitely be carried out, since there is practically no alternative to this method of diagnosis. In a sense, the olfactory function can be assessed by using methods that register vegetative-olfactory reactions - in particular, the heart rate and respiratory movements, the size of the pupils. 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 autonomic reactions, but provoke disturbances on the part of the olfactory analyzer. In some cases, the fixation of bioelectric brain activity after exposure to odorous stimuli is used to determine the ability to perceive aromas.

Olfactometry evaluates olfactory sensitivity by determining a person's response 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 scents, and others not. It is important to consider that certain scents can irritate the endings of the trigeminal nerve. For example, a "mint" smell gives a cool sensation, and alcohols give a warm sensation; ammonia, formalin, bitterness can provoke unpleasant and even painful sensations. In this regard, olfactometry should include a set 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 flavoring component.