Introduction: Spirometry is an excellent tool in the diagnostics of airway obstruction, but is less reliable in restrictive diseases. Diagnosis of lung restriction on the grounds of reduced forced vital capacity (FVC) is burdened with many potential errors. According to the American Thoracic Society/European Respiratory Society (ATS/ERS) 2005 guidelines, restrictive pattern in spirometry consists of a reduction in vital capacity and increase in forced expiratory volume in 1 second/vital capacity (FEV
1/VC) of > 85–90%. However, to our knowledge, this recommendation has not been validated. The aim of this study was to check how the inclusion of an increased FEV
1/FVC as a mandatory condition affects the value of spirometry in detecting a restrictive ventilatory defect.
Materials and methods: The material consisted of pulmonary test results obtained from consecutive patients referred to our lab during the year 2009, who had undergone spirometry and lung volume measurements at the same visit.
Results: Out of 1739 test results, there were 1402 non-obstructive cases (679 females [48.4%] and 723 males [51.6%]) with a mean age of 49.7 ± 14.5 years, included in the analysis. ERS 1993 reference equations were applied to all parameters. The lower limit of normal (LLN) was set at –1.645 of the SR level. Restrictive ventilatory defect (TLC < LLN) was found in 283 patients (20.2%). Reduced FVC only, as a condition of restrictive ventilatory defect diagnosis, was found in 202 patients (14.4%) (sensitivity 59%, specificity 97%). Reduced FVC together with increased FEV
1/FVC > 85% was found in only 76 patients (5.4%) (sensitivity 23%, specificity 99%). Only 14% of mild, 26% of moderate, and 64% of severe restrictions could be detected with reduced FVC and increased FEV
1/FVC.
Conclusions: Dual condition, i.e., reduced FVC and increased FEV
1/FVC, significantly diminishes the sensitivity of the test and hampers the diagnosis of restrictive ventilatory defect in spirometry, especially in mild and moderate stages.
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