ABSTRACT
While a broad range of disease processes can lead to interstitial lung disease (ILD), the exercise manifestations of any condition leading to the symptomatic onset of diffuse pulmonary scarring can be identified with a CPET. In addition to a reduction in maximal oxygen uptake, patients with early ILD demonstrate an excessive exercise ventilation demand, best characterized by a high exercise VE/VCO2 and a reduced ETCO2 throughout the exercise effort. Exercise arterial blood gas measurements permit calculation of two exercise gas exchange abnormalities seen in ILD patients: a sustained elevation of exercise physiologic dead space and an abnormally increased alveolar-arterial PO2 difference. Patients with severe progressive ILD ordinarily develop significant pulmonary hypertension in addition to the above noted gas-exchange abnormalities, so that the CPET manifestations of severe ILD cannot be distinguished from the exercise manifestations patients with primary pulmonary hypertension. A second cause of a reduced total lung capacity arises in patients with respiratory muscle weakness or chest wall abnormalities, but normal underlying lung parenchyma. Patients with unilateral diaphragmatic paralysis may demonstrate nearly normal maximal oxygen uptake, but associated with substantial exertional dyspnea as a exercise-limiting symptom. Patients with restrictive abnormalities due to kyphoscoliosis can demonstrate a primary ventilation limitation to maximal exercise performance.
