[Restrictive pattern in spirometry: does FEV(1)/FVC need to be increased?]

Spirometry is an excellent tool in diagnosis of airway obstruction, but is less reliable in restrictive diseases. Diagnosis of lung restriction on the ground of reduced forced vital capacity (FVC) is saddled with a lot of mistakes. According to 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) 〉 85-90%. However, to our knowledge, this recommendation has not been validated. The aim of the study was to check how inclusion of an increased FEV(1)/FVC as a mandatory condition affects value of spirometry in detection of restrictive ventilatory defect.

Material consisted of pulmonary test results obtained from consecutive patients referred to our lab during the year 2009, who had undergone spirometry and lung volumes measurements at the same visit.

Out of 1739 test results, 1402 non-obstructive patients, 679 females (48.4%) and 723 males (51.6%); mean age 49.7 ± 14.5 years were included into analysis. ERS 1993 reference equations were applied to all parameters. Lower limit of normal was set at -1.645 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 restriction could be detected with reduced FVC and increased FEV(1)/FVC condition.

Dual condition of reduced FVC and increased FEV(1)/FVC greatly diminishes sensitivity of the test, and hampers diagnosis of restrictive ventilatory defect in spirometry, especially in mild and moderate stages.