Evaluation of Small Airway Involvement in Patients With Chronic Hypersensitivity Pneumonitis and Its Impact on Exercise Limitation

Detailed Summary

Hypersensitivity pneumonitis (HP) is a syndrome with variable clinical presentation in which lung inflammation is caused by inhalation of specific organic antigens or low molecular weight particles in previously sensitized individuals. Systemic symptoms may or may not be present. Chronic HP represents the final stage of the disease, caused by prolonged exposure to a particular antigen, leading to pulmonary fibrosis. In chronic HP, pulmonary function tests (PFTs) commonly present a restrictive ventilatory pattern, with decreased diffusion of carbon monoxide (DLCO). Some patients can also have obstructive disorders with expiratory flow limitation, due to obstruction of the small airways typically caused by bronchiolar involvement in this pathology. However, PFTs are relatively insensitive for detecting small airway involvement when there is concomitant interstitial fibrosis. First, conventional PFTs may be normal in patients with small airway involvement, since they contribute to less than 30% of the total airway resistance. In addition, damage to the small airways in HP is generally occurring parallel to areas of focal fibrosis - even when small airways are involved, these regions can be completely ignored, since they are excluded from ventilation. In summary, traditional PFTs are not sufficiently sensitive to detect diffuse small airway involvement in these diseases. In these cases, other functional tests, such as forced oscillation technique (FOT) and high resolution computer tomography (HRCT) scans of the chest with expired studies, could be used for this purpose. This will be a cross-sectional study, which will include the following evaluations in 28 patients with HP recruited from our clinic: \- Clinical variables: (A) demographic and anthropometric data; (B) Clinical data: Onset of symptoms and time of diagnosis C) Dyspnea score: D) Smoking: \* Current or former smoker \* Smoking history (number of cigarettes smoked per day and for how long); * Spirometry with forced and slow maneuvers before and after bronchodilator (salbutamol); * Plethysmography to measure lung volumes; * Diffusion capacity of carbon monoxide (DLCO); * High-resolution chest CT with expiratory scans; * Six-minute walk test; * Cardio-respiratory test using a maximal incremental treadmill. * Forced oscillation technique (FOT).

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