Which of the following is used to measure the resistance to small airways

Ans. is 'c' i.e Max. Mid expiratory flow rates. * The following lines from Harrison support the answer.In obstructive lung disease, the hallmark is a decrease in expiratory flow rates. With fully established disease, the ratio of FEV1/FVC in decreased, as is the FEF25-75 %'( Max. mid expiratory flow rate).With early obstructive disease, which originates in the small airways, FEV1/FVC may be normal, the only abnormalities noted on routine testing of pulmonary function may be a depression in FEF25-75% and an abnormal configuration in the terminal portion of the forced expiratory flow-volume curve. "