Physiology of the lung in idiopathic pulmonary fibrosis

Abstract

The clinical expression of idiopathic pulmonary fibrosis (IPF) is directly related to multiple alterations in lung function. These alterations derive from a complex disease process affecting all compartments of the lower respiratory system, from the conducting airways to the lung vasculature. In this article we review the profound alterations in lung mechanics (reduced lung compliance and lung volumes), pulmonary gas exchange (reduced diffusing capacity, increased dead space ventilation, chronic arterial hypoxaemia) and airway physiology (increased cough reflex and increased airway volume), as well as pulmonary haemodynamics related to IPF. The relative contribution of these alterations to exertional limitation and dyspnoea in IPF is discussed.

FIGURE 1

Pathological alterations in idiopathic pulmonary fibrosis (IPF). Lung biopsy of a patient with IPF showing the usual interstitial pneumonia pattern (haematoxylin–eosin–saffron stain; ×10 magnification; scale bar=500 µm). Fibrotic lung with microscopic honeycomb change (^#) and remodelled arteries (arrows) is visible on the right, adjacent to preserved alveolar parenchyma on the left. Fibroblastic foci (arrowheads) are visible in between. A bronchiole is visible in the upper left corner of the micrograph.

FIGURE 2

Model for the association between pathological features, physiological alterations and their association with pathological and clinical features. Filled arrows represent strong and/or demonstrated associations; dotted arrows represent associations seen in end-stage disease. V′/Q′: ventilation/perfusion ratio; PH: pulmonary hypertension.