ABSTRACT
Usual interstitial pneumonia (UIP), the distinct histopathological lesion observed in idiopathic pulmonary fibrosis (IPF) (1), exhibits stereotypic physiological aberrations which include reduced lung volumes; normal or increased expiratory flow rates; increased forced expiratory volume in 1 s/forced vital capacity (FEVI/FVC) ratio; reduced diffusing capacity for carbon monoxide (DLCO) (2-5); hypoxemia or a widened alveolar-arterial PO2 gradient [P(A-aO2)] which is accentuated by exercise (2-4); reduced lung compliance (6) downward and rightward shift of the static expiratory pressurevolume curve (7); and abnormalities on cardiopulmonary exercise tests (CPETs) (3,7-9) (discussed below). Impairment in gas exchange (DLCO) and oxygenation may be evident early in the course of the disease even when spirometry and lung volumes are normal (5). A restrictive defect is characteristic of IPF/UIP, but lung volumes may be normal if emphysema coexists (2,11,74). In this context, DLCO and oxygenation are disproportionately reduced (2,10,11). Cardiopulmonary exercise testing (CPET) demonstrates hypoxemia, widened A-aO2 gradient, reduced oxygen consumption (VO2), high respiratory frequency, low tidal volume (VT) breathing pattern, increased dead space (VD/VT), increased minute ventilation for the level of oxygen consumption, and a low O2 pulse (Table 1) (3,7,9).
