Spirometry is a functional study of the lungs, including the measurement of volumetric indicators of external respiration using a spirometer device. During the diagnosis, the lung volume (LV), minute ventilation (MV), reserve volumes of inhalation and exhalation (RO vd., RO vd.), inhalation capacity (E vd.), vital lung capacity (VC), forced vital lung capacity (FVC), maximal voluntary ventilation (MVV) are determined. Spirometry is performed for COPD, bronchial asthma, before surgical interventions on the respiratory tract, etc. The cost of spirometry depends on the number of respiratory tests, medication and exercise tests.
Spirometry indicators are recorded when the patient is in a stable condition in the morning on an empty stomach. A day before spirometry, it is advisable to cancel taking bronchodilators. For calculation and comparison with the norm of spirometry indicators, the patient’s gender, age, weight and height are recorded. The study is performed in a sitting position. A mouthpiece connected to the breathing tube of the spirometer is inserted into the patient’s mouth, a clamp is put on the nose, excluding nasal breathing during spirometry. At the command of a specialist, a number of breathing tests are carried out, which can be repeated several times to obtain an average value of indicators.
During spirometry, the following main characteristics are measured and calculated:
- Lung volume (LV) – the amount of inhaled air at rest in one breath (normally 500-800 ml).
- Vital capacity (VC) – the maximum volume of air exhaled from the lungs after maximum inhalation.
- Forced vital capacity (FVC) is a volumetric indicator similar to the FVC when breathing with extreme speed and force.
- Volume of forced exhalation in 1 second (FEV1) is the part of the FVC exhaled in 1 second, expressed as a percentage of the VC (normally FEV1 is 75% of the VC).
- Tiffno index is the ratio of FEV1 to FVC (norm ≥70%).
- Functional residual capacity (FRC) is the amount of air remaining in the lungs after normal exhalation at rest.
- Residual volume (RV) is the amount of air remaining in the lungs after the maximum exhalation produced.
- Total lung capacity – (TLC) is the sum of VC and LV.
- Peak volumetric velocity (PVV) is the maximum flow achieved during exhalation.
- Minute ventilation (MV).
- Maximal voluntary ventilation (MVV).
Sometimes in the process of spirometry, tests are carried out with bronchodilators, bronchoconstrictors or a load to assess the reaction of the airways. When interpreting the results of spirometry, they are guided by the average statistical indicators of a healthy person of the corresponding gender, age and anthropometric characteristics. A decrease in most of the values of spirometry by 20% or more from the norm is regarded as a violation of lung function. Spirometry with samples is carried out with the obligatory participation of a doctor for timely relief of sudden complications.
The inaccuracy of the spirometry results may be due to a violation of the research technique or the condition of the device. The patient’s errors in spirometry can be caused by inadequate or incomplete inhalation, additional exhalations made during the maneuver; loose pressing of the lips to the mouthpiece; early cessation of exhalation; exhalation through the nose. During spirometry, the patient may have a cough or bronchospasm, requiring termination of the study. To ensure the accuracy of spirometry, it is necessary to keep the spirometer in good order, clean, and use the recommendations of the device manufacturer.