This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstructive Lung Diseases, Subject name: Pathology
Reid index in increased in - 
Select and explain. 
A. Chronic bronchitis, B. Emphysema, C. Bronchieactasis, D. ARDS
A: Chronic bronchitis
Answer: A: Chronic bronchitis 
Explanation: Ans. is 'a' i.e., Chronic bronchitis o The Reid Index is a mathematical relationship that exists in a human bronchus section observed under the microscope.o It is defined as ratio between the thickness of the submucosal mucus secreting glands and the thickness between the epithelium and cartilage that covers the bronchi.o A normal Reid Index should be smaller than 0.4, the thickness of the wall is always more than double the thickness of the glands it contains.o Chronic smoking causes submucosal gland hypertrophy and hyperplasia, leading to a Reid Index of >0.5 indicating chronic bronchitis