Chronic Bronchitis Reid Index

A 62-year-old male with a 45-pack-year smoking history and occupational coal dust exposure presents with a 6-year history of daily productive cough with thick mucopurulent sputum, progressive dyspnea on exertion, and recurrent winter exacerbations. Clinical examination reveals cyanosis at rest, plethoric face, peripheral edema, and cor pulmonale. Arterial blood gas shows PaO₂ 55 mmHg and PaCO₂ 55 mmHg. Pulmonary function testing confirms an obstructive ventilatory defect. Histopathologic examination of the resected lung reveals the structure marked **A** with marked hyperplasia and hypertrophy. Which of the following best describes the pathologic hallmark that distinguishes this condition from emphysema?