Avaliação da heterogeneidade na distribuição da ventilação e sua correlação com testes de função pulmonar tradicionais e tomografia computadorizada em pacientes com artrite reumatoide

Abstract

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by joint and extra-articular manifestations. The lung is a common site of involvement, contributing to morbidity and mortality. Chest computed tomography (CT) is the method of choice for diagnosing lung lesions and pulmonary function tests (PFTs) are useful for follow-up and assessing the severity of the involvement. Spirometry and carbon monoxide diffusion measurement (DLCO) are normal in many patients with RA, even with alterations in the CT scan. PFTs that assess ventilation distribution are sensitive and detect functional abnormalities early. The nitrogen washout test (TWN2) is a measure of the heterogeneity of ventilation distribution that assesses the function of the small airways. In patients with RA, the involvement of the pulmonary interstitium by inflammation or fibrosis can lead to structural changes in the small airways and alveoli, resulting in loss of airflow and poor ventilation distribution. The general objective was to assess which clinical, serological, functional, and radiological findings were associated with elevated phase III slope (SIII) values measured by TWN2. The specific objectives were to analyze the main findings on chest CT and PFTs, correlating them and evaluating the severity of the different lung involvement; to evaluate SIII with the extent of involvement on CT; to correlate SIII with the findings of spirometry, plethysmography, and DLCO, and with clinical and serological variables and inflammatory markers. Two cross-sectional studies were carried out in patients with RA and, in both, the patients were submitted to the Health Assessment Questionnaire-Disability Index (HAQ-DI), Clinical Disease Activity Index (CDAI), and analysis of autoantibodies and inflammatory markers. All patients underwent PFTs including spirometry, plethysmography, DLCO measurement, TWN2 by the single breath technique, and chest CT. The first study was a preliminary analysis of 21 patients. According to SIII, 11 and 10 patients had values <120% and >120% of those predicted, respectively. The subgroup with SIII >120% had a significantly lower forced expiratory volume in the first second (FEV1). The residual volume/total lung capacity ratio (RV/TLC) and positive RF were significantly higher in the subgroup with SIII >120%. RF and CDAI showed significant results for abnormal chest CT. The main radiological findings were air trapping and bronchiectasis. Five patients with limited involvement in CT had SIII >120%. The second study involved 60 patients, where 65% of them had SIII >120% predicted. There were significant correlations between SIII and age, HAQ-DI, forced vital capacity (FVC), TLC, RV/TLC, and DLCO. On CT scans, the subgroup with moderate/severe disease had a significantly higher SIII than the normal/minimal/mild subgroup. In the regression model, FVC, the extent of moderate/severe involvement, and age were predictive of SIII, explaining 59% of its variability. In those with a predominance of small airway disease (SAD) on CT, TWN2 was able to detect heterogeneity in the distribution of ventilation in approximately half of the cases. Furthermore, the presence of respiratory symptoms and deterioration in physical function were closely related to the distribution of ventilation in these patients.