Role of spirometry in pulmonary function assessment
Pulmonary function testing plays a crucial role in the objective diagnosis of respiratory disorders. The clinical presentation of bronchial obstruction includes harsh vesicular breathing, prolonged expiration phase, and wheezing, yet instrumental methods provide precise quantitative assessment.
The main instrumental tests are:
- Spirometry: detects a drop in the Tiffeneau index below 60% and a decrease in forced expiratory volume in the first second (FEV1).
- Pneumotachometry: records a drop in airflow velocity parameters.
In cases of critical acute obstruction, the "silent lung" phenomenon develops, where breath sounds completely disappear due to severe airway patency impairment.
Differential diagnosis of obstruction and restriction
Comparing spirometric data allows for the differentiation of various types of ventilatory disorders:
- In obstructive processes (e.g., emphysema or chronic obstructive pulmonary disease), the leading sign is a drop in FEV1 and the Tiffeneau index (FEV1/FVC).
- In emphysematous changes, total lung capacity and residual volume increase due to hyperinflation, which is associated with the development of a barrel-shaped chest.
- In purely restrictive processes, velocity parameters and the Tiffeneau index remain within normal limits, while exclusively volume parameters—total capacity or VC—are decreased.
Functional changes in bronchial asthma
Spirometric evaluation is essential for assessing the condition of patients with bronchial asthma. During the intercritical period, patients may have clinically clear breathing, yet spirometry often reveals mild chronic bronchial patency disorders.
Such changes are due to airway remodeling, which involves persistent structural alterations of the bronchial wall driven by chronic Th2-mediated inflammation. Key components of remodeling include:
- Thickening of the epithelial basement membrane and subepithelial fibrosis (collagen deposition).
- Mucosal edema and inflammatory infiltration involving eosinophils and mast cells.
- Hypertrophy of submucosal glands and smooth muscle cells (SMC).
The presence of remodeling explains why obstruction eventually becomes partially irreversible and pulmonary function parameters gradually decline even with maintenance therapy.
Tiffeneau index below sixty — bronchi gripped by obstruction.
Class and exam questions
What are the main parameters evaluated in spirometry for the diagnosis of obstruction?
The main parameters are the Tiffeneau index (its decrease below 60%) and forced expiratory volume in the first second (FEV1).
How do spirometric parameters differ between obstruction and pure restriction?
In obstruction, velocity parameters and the Tiffeneau index drop, whereas in pure restriction they remain normal, and only the volume parameter (VC) decreases.
Why can spirometry detect abnormalities during the intercritical period in bronchial asthma?
This is due to airway remodeling — persistent structural changes in the bronchial wall caused by chronic inflammation, leading to chronic lumen narrowing.
What else to study on this topic
- Air trapping syndrome and its association with pulmonary emphysema
- Genetic mechanisms of airway remodeling and the role of the ADAM33 gene
- Clinical manifestations and auscultation findings in bronchial obstruction syndrome
- Features of restrictive respiratory failure
- Morphological characteristics of bronchial asthma during an attack
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