All of the following are characteristic feature of obstructive pulmonary disease, except:

Answer is A (Residual volume Normal): Lung disease is typically associated with an Increased Residual volume Taken from Harrison 17th/1588 The hallmark of obstructive Lung Disease is decreased expiratory flow rate such the FEF25_75 is reduced and FEVI is typically reduced out of propoion to the Forced Vital Capacity ('FEV1/FVC). The Residual volume is typically increased. The vital capacity (FVC) may be normal or decreased while Total Lung capacity may be normal or increased. The hallmark of Restrictive Lung Disease is a decrease in lung volume typically TLC and vital capacity. Flow rates are preserved and hence FEF25_75 is generally normal. Also, when FEV1 is considered as a percentage of FVC, (FEV1/ FVC), the flow rates are often supranormal i.e. disporopoionately high relative to the size of lungs. Residual volume is also generally decreased.