Analysis of Pulmonary Function in Thymoma Subjects: A 20-Year Retrospective Cohort Study

Abstract

Background: Thymoma is the most common tumor of the anterior mediastinum. However, the correlation between thymoma stage and pulmonary function was not assessed. Our objective in this study was to describe the pulmonary function in thymoma subjects stratified with different staging systems.

Methods: A total of 143 subjects with a diagnosis of thymoma who underwent extended thymectomy for thymoma between January 2001 and December 2019 were reviewed retrospectively. All the subjects experienced pulmonary function tests (PFTs) using Master Screen PFT system and total respiratory resistance measurement.

Results: We evaluated 143 subjects with a diagnosis of thymoma; the significant differences were observed in mean values of vital capacity, inspiratory volume (IC), total lung capacity (TLC), ratio of residual volume to total lung capacity (RV/TLC), forced vital capacity, forced expiratory volume in 1 second, ratio of forced expiratory volume in 1 second to forced vital capacity, peak expiratory flow, peak inspiratory flow, maximum ventilation volume, total airway resistance, and diffusing capacity for carbon monoxide (DLCO) across upper airway obstruction classification. PFTs of subjects with varying Masaoka stages are different. RV and RV/TLC of subjects in stages III and IV were higher than those of normal level, while DLCO of subjects in stage IV was lower than the normal level, and the mean level of IC showed significant difference between stage II and stage III.

Discussion: The pulmonary function patterns of thymoma subjects significantly correlate with tumor location and size rather than clinical Masaoka stage.

Fig. 1

Flow–volume curve ( F – V curve), the dotted line is the normal velocity volume curve. Variable extrathoracic UAO: the obstruction site is outside the thoracic inlet. During inhalation, the airway pressure is lower than the atmospheric pressure, the tracheal wall tends to collapse and close, and the inspiratory resistance increases, resulting in obvious restriction of inspiratory flow. When exhaling, the airway tends to expand because the airway pressure is higher than the atmospheric pressure, and the airflow restriction may not be obvious. The F – V curve is characterized by inspiratory phase platform and FEF _50% /FIF _50% >1 (A) . Variable intrathoracic UAO (VI-UAO): the obstruction site is within the thoracic inlet. During inhalation, the thoracic negative pressure increases, the airway expands, the airway resistance decreases, and the airflow restriction in the inspiratory phase is not obvious. During exhalation, the negative pressure in the thoracic cavity decreased significantly, the trachea retracted, and the airway resistance increased, aggravating the original obstruction, which showed that the expiratory flow was significantly limited, especially in the early and middle stages of force-dependent exhalation, which was reflected in the significant decrease of PEF, FEF _25% , and FEF _50% . The F – V curve is characterized by expiratory phase platform and FEF _50% /FIF _50% <1 (B) . Fixed UAO: the lesion site is more extensive or rigid and airflow restriction is no longer affected by the respiratory phase. It was characterized by lack of changes in caliber during inhalation or exhalation, the inspiratory and expiratory flows were significantly limited and showed a plateau FEF _50% /FIF _50% is close to 1 (C) . Unilateral mainstem bronchial obstruction type (UMBO): the bronchial resistance of the healthy side is normal, and the early respiratory flow rises rapidly to the peak, so the initial flow is large. The bronchial resistance of the affected side increases and the respiratory flow slows down, so the terminal flow decreases significantly. The F – V curve changes in a double butterfly shape (D) . FEF _50% , forced expiratory flow at 50% of FVC; FIF _50% , forced inspiratory flow at 50% of FVC; FVC, forced vital capacity; PEF, peak expiratory flow.