Olfactory examination

The study of the olfactory function is of great importance as a very effective method for diagnosing diseases of the PNS and CNS. Many of the so-called essential anosmia or "parosmia" may be associated with certain organic diseases of the intracranial structures, directly or indirectly related to the olfactory centers and their conductors. Often, olfactory disorders, most often unilateral (for example, objective hyposmia or olfactory hallucinations), can manifest themselves among the earliest symptoms of an intracranial disease. In the context of these provisions, the most valuable methods are quantitative assessment of the olfactory function, allowing one to judge the dynamics of the pathological condition and the effectiveness of treatment.

Anamnesis

The patient is questioned according to the generally accepted scheme. They find out the signs of changes in the sense of smell: decrease, absence, heightened perception; whether the smells cause any associations or parosmia (for example, the smell of a certain substance is perceived as the smell of another or unfamiliar substance). They also find out whether certain smells cause bronchospasm, palpitations or any vegetative reactions. They clarify the time of occurrence of olfactory disorders, their periodicity or continuity, dynamics, possible cause. They clarify the nature of diseases remote and immediate before the olfactory disorder, their severity, what signs accompanied these diseases (trauma, acute cerebrovascular accidents, infectious diseases, poisoning), as well as the nature of the profession and the presence of occupational hazards (vapors of aggressive and toxic liquids, aerosols, smoke and dust in the room).

All methods of olfactory examination are divided into subjective, indirectly objective and objective. In everyday clinical practice, mainly subjective methods are used, based on the presentation of a test substance to the subject and his verbal report ("yes", "no", "yes, but I can't determine", a specific smell is called).

Indirect-objective methods are based on the objective recording of the so-called olfactory-vegetative reactions that arise in response to the activation of the projection systems of the subcortical olfactory centers, their connections with the stem structures and the hypothalamus. These reactions may include changes in the heart rate, phase changes in the respiratory cycle, changes in the respiratory rate, olfactonupillary reflexes, changes in the galvanic skin response, etc. When using these methods, the indirect signs of the functioning of the olfactory organ are the indicated vegetative reactions realized by the reflex path: "receptor - olfactory bulb - subcortical olfactory centers". However, the presence of these reactions is not an absolute indicator of the normal functioning of the olfactory analyzer, since isolated disturbances that occur in the cortical zone of the third neutron, while affecting the cortical function of the analyzer (perception, recognition, differentiation), may not affect the occurrence of vegetative reactions, switching to which occurs below the level of damage (before the third neutron).

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ]

Objective methods are based on ECoG and EEG recording.

ECoG is used in animal experiments or during neurosurgery, electrodes for recording biopotentials are placed on the olfactory zone of the cerebral cortex. In EEG, electrodes are placed on the skin projections of the cortical zones of the olfactory analyzer, located in the temporal-basal sections of the hypnocampus. However, the results of these studies should also be treated with a certain degree of distrust. Only when ECoG potentials are synchronized with olfactory stimulation and correspond in form to typical oscillations, can it be stated that the reflex path "receptor - cortex" is functioning. However, even here the question of the qualitative aspect of perception in the last resort remains open, for example, in the phenomenon of parosmia. ECoG and EEG methods for assessing the olfactory function have a certain value in a comprehensive examination of patients with volumetric processes in the parietal-occipital-temporal region.

All methods of olfactory examination are divided into qualitative and quantitative. Qualitative examination is carried out by exposing the PV in close proximity to one, then to the other nostril, during which the patient is asked to actively sniff and answer whether he feels any smell, and if so, what kind of smell it is. To conduct this examination, various authors have proposed sets of different PV. The latter are used in the form of solutions placed in dark bottles with ground stoppers; the bottles are numbered, under which the corresponding PV are designated.

Thus, N.S. Blagoveshchenskaya (1990) reports on the set of W.Bornstein (1929), consisting of eight PV, arranged in sequence from the weakest (No. 1) to the strongest (No. 8): laundry soap, rose water, bitter almond water, tar, turpentine (these substances act mainly on the olfactory nerve), aqueous ammonia solution, acetic acid (act on the olfactory and trigeminal nerves), No. 8 - chloroform (acts on the olfactory and glossopharyngeal nerves). The use of PV that have a differentiated effect on the olfactory, trigeminal and glossopharyngeal nerves has a certain diagnostic value, since with a completely switched off olfactory nerve, the patient will still sense the "smells" that act on the V and IX nerves, but in a significantly weakened and distorted form.

At one time, the odorimetric set of V.I. Voyachek was widely used. In its original version, this set consisted of four PVs of increasing strength: 0.5% acetic acid solution (weak odor); pure ethanol (medium-strength odor); valerian tincture (strong odor); aqueous ammonia solution (super-strong odor). Later, gasoline (for technical personnel unfamiliar with the odor of valerian) and distilled water (control) were added to this set.

Gasoline, as the most volatile and most “penetrating” substance from the set, was placed by V.I. Voyachek under number 6. In the absence of its perception, the sense of smell should be considered completely switched off.

Correct conduct of a qualitative olfactory study requires a certain standardization of the experiment: eliminating the possibility of olfactory vapors getting into the non-examined half of the nose; conducting an olfactory assessment on inhalation with breath holding to exclude retrograde olfactory vapors getting into the other half of the nose on exhalation. A piece of filter paper measuring 0.3x1 cm, fixed in a cleft of a splint and moistened in a olfactory solution, is brought to one nostril, closing the other, and the patient is asked to take a light breath through the nose, hold the breath for 3-4 seconds and determine what smell he smells. The results of the study are assessed using a 5-degree system, depending on what smells the subject perceives:

• I degree - the subject identifies the weakest odor - No. 1;
• II degree - smells No. 2, 3, 4, 6 are perceived;
• III degree - smells No. 3, 4, 6 are perceived;
• IV degree - smells No. 4, 6 are perceived;
• Level V - only smell No. 6 is perceived.

If none of the smells are perceived, then a diagnosis of anosmia is made.

In case of hyposmia, its mechanical cause is excluded. To do this, carefully examine the upper parts of the nasal cavity and, if necessary, treat them with a single lubrication of the mucous membrane with a solution of adrenaline chloride 1:1000 (but not anesthetic!) and after 5 minutes, conduct a repeat examination. The appearance or improvement of the sense of smell after this procedure indicates the presence of "mechanical" hyposmia.

Quantitative study of the olfactory function involves determining the threshold of perception and the threshold of recognition. For this purpose, olfactory, trigeminal and mixed action PVs are used. The principle of the method consists in dosing the volume of air containing PV in a constant concentration, or in gradually increasing the concentration of PV until the threshold of perception is obtained.

The method of quantitative study of olfaction is called olfactometry, and the devices by which this method is implemented are called olfactometers. Classic examples of such devices are the olfactometers of Zwaardemaker and Elsberg-Levi. At the end of the 19th century, H. Zwaardemaker designed an olfactometer whose operating principle is that the sampling tube is located inside a cylinder consisting entirely of dense PV, covered with glass on the outside to prevent its sublimation into the environment. When the distal end of the tube extends beyond the cylinder, PV vapors do not enter it.

When the tube is drawn into the cylinder, the amount of PV entering it depends on the distance of the tube to the end of the cylinder, i.e. on the volume of PV that can enter the tube. The disadvantage of the method is the uncontrolled active inhalation of the subject. The "pulse" (injector) method of Elsberg - Levy does not have this disadvantage.

The Elsberg olfactometer is a flask with a solution of polyvinyl alcohol, hermetically sealed with a rubber stopper, into which two glass tubes (short and long) with rubber hoses at the proximal ends are inserted. The hose of the long tube is closed with a tap or clamp. The hose of the short tube branches into two tubes with olives at the ends. Air is introduced into the flask through the long tube using a syringe with a nozzle, which displaces the vapors of polyvinyl alcohol through the short tube and olives. The principle of injector supply of polyvinyl alcohol was used in the olfactometer of N.S. Melnikova and L.B. Daynyak (1959). In subsequent years, various more advanced designs of olfactometers with electromechanical and electronic dosing of PV, with a complex system of conditioning the odorous mixture by temperature, humidity and vapor concentration in different modes of their supply (intermittent, continuous, increasing, decreasing modes) were developed.

A quantitative study of the olfactory function can be carried out in an extremely simple way using filter paper and an increasing concentration of any one substance, for example, in the range of 0.2-0.5% ethyl alcohol solution, 0.2-0.9% acetic acid solution, etc. For this purpose, it is possible to dose the volume of air saturated with olfactory vapors coming from the solution using an injection syringe (a modification of the Elsberg-Levi method) by sucking this air into the injection syringe (10 or 20 ml) and then introducing this air into the nasal cavity at 1, 2, 3 ml, etc. until a sensation of smell appears. The latter method is simple, reliable and requires virtually no material costs. To construct such a device, you need a flask filled 1/3 with a solution of table vinegar; a rubber stopper with two glass tubes on which two rubber hoses with clamps are put on; a syringe tightly inserted into one of the hoses, and a thin rubber catheter for introducing air taken from a flask containing vinegar vapors into the nose. Before the final air intake, two or three suctions are performed with a syringe to fill the outlet tube with vinegar vapors. The glass end of the intake tube, inserted into the cavity of the flask, should be placed significantly lower than the end of the second glass tube, but not touch the liquid. The advantage of this method is that it provides a dosed forced introduction of PV into the nasal cavity to the desired depth, right up to the olfactory slit, which eliminates the uncontrolled force of inhalation in methods that do not provide for the forced introduction of PV.