Exercise intolerance, including dyspnea, is the most common report among patients with ILD. Both exercise intolerance and dyspnea tend to worsen with disease progression, and pulmonary rehabilitation is critical to slowing progression in those with IIPs. Obtaining a baseline assessment of the patient’s capacity for exercise is critical, as many individuals will be symptomatic at presentation. This assessment includes an interview, during which patients are asked about their abilities to walk on flat ground and to climb stairs, among other tasks. A 6-minute walk distance (6MWD) test should also be performed to provide a more objective measure of exercise capacity, including the presence of desaturation hypoxemia. Repeated at 6-month intervals, such assessments can be used to track disease progression. Several analyses have attempted to characterize a “minimal clinically important difference” in 6MWD in patients with ILD, and clinical trials for idiopathic pulmonary fibrosis will often use the 6MWD as part of an assessment of outcomes.

A number of comorbidities associated with ILD may undermine exercise tolerance. For example, group 3 PH is common in patients with fibrotic IIPs, particularly idiopathic pulmonary fibrosis, and has a significant and negative impact on patient survival. Yoo et al measured the direct impact of PH on morbidity as manifested through functional impairment, demonstrating that hemodynamic parameters of PH in patients with fibrosing interstitial pneumonias are independent, significant contributors to exercise capacity, irrespective of the extent of pulmonary fibrosis on high-resolution chest computed tomography. Other comorbidities that contribute to worsening exercise tolerance include heart disease, concurrent emphysema, smoking, sleep apnea, and gastroesophageal reflux or silent aspiration.

In addition to implementing treatment of the ILD and the comorbidities, enrollment in a pulmonary rehabilitation program can help to improve functional capacity and may impact outcomes. Home-based pulmonary rehabilitation provides long-term benefits in exercise tolerance, anxiety, and quality of life for patients with fibrotic IIPs. An oxygen needs assessment may also prove helpful, as supplemental oxygen to maintain saturation may improve exercise tolerance. Pulmonary rehabilitation generally should be recommended to all patients with IIP, although it may not be as useful for those who are already active. For patients who are not active, especially those requiring supplemental oxygen, pulmonary rehabilitation is an effective way to improve exercise capacity, and, perhaps, to reduce mortality.