Reduction of FEV1%FVC ratio together with lowered FVC often is interpreted as "mixed" ventilatory disturbances. The aim of this study was to evaluate the real frequency of the overlapping obstructive and restrictive impairments in patients with FEV1%FVC<0.7 and FVC<80% of predicted, which is often described as "mixed" ventilatory defect.
Material and methods: Retrospective, cross-sectional analysis of pulmonary function data. Only 748 out of 6673 patient's data met inclusion criteria: performed bodypletysmography and FEV1%FVC<0.7 together with FVC<80%pred. in spirometry. In all cases spirometry and whole body pletysmography were performed according to ERS standards by experienced staff using MasterLab-"Jaeger" equipment. Reference values according to ERS guidelines were applied.
Results: We found volume restriction defined as TLC below lower limit of normal in only 17% of the patients. There was also inverse correlation between FEV1%pred. and RV%TLC%pred. ratio. So, the basic mechanism of reduction in VC and FVC in patients with normal TLC is increased RV.
Conclusion: "Mixed" ventilatory impairment in majority cases represents airway obstruction with lung hyperinflation. Such a coincidence of reduced FVC and FEV1%FVC ratio requires further investigations (pletysmography) to clarify the reason for the diminished vital capacity.