This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
For the diagnosis of obstructive airway disease which of the following is preferred 
Select and explain. 
A. Vital capacity, B. Timed vital capacity, C. Tidal volume, D. Blood gas analysis
B: Timed vital capacity
Answer: B: Timed vital capacity 
Explanation: In obstructive airway diseases fev1 is markedly reduced than FVC. Maximum mid expiratory flow rate(fev 25 -75 %) is the more sensitive measure of small airway obstruction.