45 Restrictive Lung Disease: Idiopathic Pulmonary Fibrosis, A A 68-year-old man presents to the clinic with a complaint of shortness of breath. He states that he has become progressively more short of breath for the last 2 months, such that he is now short of breath after ft walking one block. In addition, he has noted a nonproductive cough. He denies fever, chills, night sweats, chest pain, orthopnea, or
paroxysmal nocturnal dyspnea. He has noted no lower extremity edema. His medical history is unremarkable. Physical examination is remarkable for a respiratory rate of 19/min and fi fine dry inspiratory crackles heard throughout both lung fields. Digital clubbing is present. A diagnosis of idiopathic pulmonary fibrosis fi is made.
1. Name six mechanisms by which interstitial lung disease affects ff lung function. • Decreased lung compliance (lungs that are stiff ffer and more resistant to expansion) increases static recoil pressure and increases the work of breathing • Proportional reductions of lung volumes • Alveolar ventilation is maintained by an increased respiratory rate • Decreased pulmonary diffusing ff capacity (DLCO) due to loss of pulmonary capillaries, reduction in pulmonary
capillary surface area, and sometimes an increase in diffusion ff path length due to fibrosis • Patchy nature of fi fibrosis leads to severe inhomogeneity in ventilation and mismatching of ventilation and perfusion including areas of absent ventilation • Pulmonary hypertension from decreased pulmonary capillary surface area, increased pulmonary vascular resistance, and regional alveolar hypoxia