The Role of Pulmonary Function Test for Pulmonary Arterial Hypertension in Patients with Connective Tissue Disease

Objective: The study aimed to investigate the value of pulmonary function test (PFT) in evaluating and predicting pulmonary arterial hypertension (PAH) in patients with connective tissue disease (CTD). Methods: This was a prospective observational study recruiting patients diagnosed with CTD-PAH. Patients with interstitial lung disease and pulmonary hypertension induced by other causes were not eligible for enrollment. All patients were assessed for PAH every 1–3 months. A patient was considered to have clinical improvement if the grade of risk stratification declined or at least two parameters improved during follow-up, otherwise no improvement. Results: A total of 31 patients with CTD-PAH were recruited in this study. Nearly 70% of patients had declined forced vital capacity (FVC), 60% had declined total lung capacity and maximum expiratory flow at 50% of vital capacity, and 95% had normal or mild decline in forced expiratory volume in 1 second (FEV1)/FVC. A decline in diffusing capacity of the lung for carbon monoxide (DLCO) was present in 96% of patients, and 60% were moderate to severe. Furthermore, 50% of patients had an FVC/DLCO ratio of less than 1.4. Univariate analysis showed that FEV1/FVC, DLCO, and FVC/DLCO were associated with disease prognosis. After adjusting for age as a confounding factor, multivariate logistic regression analysis revealed that DLCO was an independent predictive factor for the prognosis of CTD-PAH. Conclusion: The pulmonary function of patients with CTD-PAH is abnormal in parameters such as lung volume, small airway, and gas exchange. PFT can reveal complex pathophysiological changes in the lungs of CTD-PAH patients and predict prognosis.