Pneumotachography

Pneumotachography is a method of continuous functional diagnostics of the degree of bronchial patency. The term “pneumotachography” is of Greek origin: “pneumo” – air, “tacho” – speed, “grapho” – write. It is a graphic fixation of the speed of movement and volume of air during increased exhalation. These studies are recorded on a special tape. The curve obtained during the examination on this tape is called a pneumotachogram. The method makes it possible at an early stage to detect such broncho-obstructive diseases as obstructive bronchitis, pneumosclerosis, bronchial asthma.

The essence of the method

For the study, a pneumotachograph or spirograph is required. The simplest of them consists of an apparatus-converter of inhalation-exhalation parameters and a graphic recorder. The principle of the method is to graphically record the pressure indicators that air flows have on the bronchopulmonary structures, depending on the phase of respiration.

The first indicator, which is determined using pneumotachography, is the maximum air velocity (MOS). Normally, in an average adult healthy man, it ranges from 5 to 8 l / s, and in a woman – from 4 to 6 l / s.

To take into account the individual characteristics of the patient, during the procedure, an individual indicator of MOS is calculated according to the formula – FVC × 1,25, where FVC is the forced vital capacity of the lungs.

The obtained MOS indicator is compared with the actual air velocity, which is determined using a pneumotachograph. Normally, the actual MOS should be equal to the calculated one (with a deviation of 10-15%).

The method allows to estimate the resistance of air paths to air flow. The airflow interruption technique is used to assess bronchial resistance. This technique is based on periodically blocking the tube of the apparatus with a special valve at the time when the patient breathes into it.

When the air flow is blocked, the pressure in the alveoli of the lungs and the breathing tube of the apparatus equalizes for a short time. The pneumotachogram records emissions that correspond to alveolar respiration.

Based on the pneumotachogram data, the alveolar resistance is calculated by the formula: R = (PA – P1) / V, where R is the resistance, PA is the alveolar pressure, P1 is the pressure needed to overcome the resistance, V is the airflow velocity.

This indicator shows the degree of bronchial conduction. It is measured in l / s (ml / s). The larger the lumen of the bronchi, the less time will be spent by the body on breathing.

Indications and contraindications

The study is prescribed by a general practitioner, pulmonologist, allergist, infectious disease specialist or phthisiatrician.

Pneumotachography is indicated to determine the cause of frequent shortness of breath or painful cough in patients, to determine the degree of bronchial obstruction in diseases of the respiratory system (bronchial asthma, atopic bronchitis, chronic obstructive pathologies, pneumosclerosis).

The method is also used before surgical interventions on the lungs and bronchi, to assess the effectiveness of the therapy, to conduct an examination of the degree of working capacity of patients with severe respiratory diseases.

Pneumotachography is also a valuable diagnostic method for determining the cause of bronchial obstruction in patients with a prosthetic heart valve. The pneumotachography procedure is contraindicated during pregnancy, with severe respiratory disorders, epilepsy, aneurysm of cerebral vessels, hemoptysis, after lung infections, strokes, myocardial infarction, hypertensive crisis.

Indicators pneumotachography

With the help of this diagnostic method, many indicators characterizing the function of external respiration and the degree of airway patency are determined. The main indicators determined in the study are:

• forced vital capacity (FVC) – this is the volume of exhaled air, the maximum possible after a forced breath (normal – 3500-3700 ml);
• forced expiratory volume in the first second (FEV1) is the volume of air in the first second of forced exhalation (normally at least 70%);
• the Tiffno index is the percentage of FEV1 and FVC (normally at least 70%);
• the maximum speed of air movement (MOS) is the maximum speed with which air passes through the airways with increased exhalation after a full breath (normally – from 4 to 8 l / s);
• airway resistance (normally from 2 to 8 cm of water column), extensibility of lung tissue (normally from 0,15 to 0,35 l / cm of water column), work of breathing at rest (normally – up to 0,5 kgm/min).

Comparison of the obtained results with normative indicators allows to detect obstructive pathology of the respiratory tract and determine its degree.

Advantages and disadvantages

Pneumotachography has many advantages over other functional methods that determine the degree of bronchial obstruction.

The method is non-invasive, therefore absolutely painless for the patient. The duration of the study is no longer than 10-15 minutes, the procedure can be performed on an outpatient basis, in a polyclinic.

Pneumotachography is suitable for diagnosing a large number of people, does not require special training and has a low cost of the procedure.

The disadvantages of this diagnostic technique include the difficulty of interpreting the results. During the procedure, the patient is forced to breathe heavily, which can provoke fainting from hyperventilation.

Preparation for research

To properly prepare for the procedure, you need to stop smoking and drinking alcohol at least a day before it. In the case of taking short-acting bronchodilators, in agreement with the doctor who prescribed them, it is advisable to stop taking them at least 4 hours before the manipulation. Patients using inhalers should definitely take it with them.

Clothing on the person being examined should be spacious so as not to hamper the movements of the chest. The belt also needs to be removed or unfastened. It is necessary to come to the study in advance in order to catch your breath, calm down, bring your breathing to a calm state.

On the day of the procedure, any physical activity is prohibited: they knock down the rhythm of breathing and can distort the result.

Method of conducting

Pneumotachography is performed on an empty stomach. Before the procedure, the patient’s anthropometric data (height, weight, level of physical fitness) are recorded, which affect the interpretation of the study results.

To conduct the examination, the patient sits in a chair, a disposable mouthpiece is put on the tube of the device, and the nose is closed with a special clip.

The subject takes a few quiet breaths. After that, without holding the breath, the patient successively takes several forced breaths and exhalations.

If forced breaths provoke a cough in the patient, you need to interrupt the examination for a few minutes, and then try again.

If, after a second attempt, the cough reappears, the study is postponed for several days. If chest pain or hemoptysis occurs, the study should be stopped immediately, and the subject should be given the necessary assistance.

Pneumotachography as a method of functional study of bronchial patency and the resistance of the airways to air flow is practically not used independently in practice.

Modern pneumotachographic equipment is usually combined with a spirograph in order to combine the maximum number of possible examinations of respiratory functions in one diagnostic procedure.

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