Sometimes when interpreting spiromtery, a patient may have what appears to be a mixed obstructive/ restrictive picture. (Reduced FEV1/FVC and Reduced FVC).
Patients with an obstructive process (i.e COPD) may have gas trapping, which will reduce their FVC due to increased residual volume (RV). This may falsely lead a clinician to interpret it as a mixed obstructive/ restrictive process, while it is truly just obstructive.
NOTE: The next step to confirm pseudo-restriction, is to get a TLC. If normal (and therefore not restrictive) it highly suggests this pathology. Also look at the RV and RV/TLC ratio.
Sorino, C et al. Physician’s mistakes in the interpretation of spirometry. European Respiratory Journal 2012 40: P1131
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As-Ashkar, F, Mehra, R, Mazzone, PJ. Interpreting pulmonary function tests: recognize the pattern, and the diagnosis will follow. Cleve Clin J Med. 2003;70:866–881.