Restrictive Ventilatory Defects (RVD) are a group of respiratory disorders characterized by a reduction in Total Lung Capacity (TLC). The classification of RVD plays a crucial role in patient management, yet various international interpretive strategies, including the ATS 1991, ATS/ERS 2005, and ATS/ERS 2022 systems, define severity differently. This study aimed to compare these three classification systems and assess their association with clinical severity, including dyspnea and hospitalization during the previous year.

A retrospective analysis was conducted on 238 patients diagnosed with RVD based on plethysmographic measurements, with each patient classified according to the 1991, 2005, and 2022 systems. Dyspnea severity was measured by the modified Medical Research Council (mMRC) scale. Hospitalization during the previous year was also recorded.

The comparison of classification systems revealed that the 2022 ATS/ERS system, based on TLC z-scores, classified a higher proportion of patients as severe compared to the 1991 (VC%) and 2005 (FEV1%) systems. Significant associations were observed between all classification systems and both dyspnea severity and hospitalization during the previous year. The ATS/ERS2005 classification showed the strongest association with dyspnea severity (cc=0.569), whereas the ATS/ERS2022 classification demonstrated the strongest association with hospitalization (cc=0.290).

Our findings highlight the challenges associated with the interpretation and classification of RVD severity. The significant associations observed between RVD classifications, dyspnea severity, and hospitalization support the clinical relevance of functional severity assessment in restrictive disorders. Further studies are needed to determine which classification approach best reflects the clinical burden of disease.