Inclusion criteria:  clinically stable, as defined by stable hemodynamic status, optimized medical treatment, no changes in medication dosage or frequency of administration with no hospital admissions in the preceding 6 weeks; Mild or absent mechanical restriction as determined by a total lung capacity (TLC) >70% predicted; male or female non-pregnant adults >40 years of age; ability to perform all study procedures and provide informed consent. A key IPF inclusion criterion includes, in addition to the above, a clinical diagnosis of idiopathic pulmonary fibrosis.  Exclusion criteria:  women of childbearing potential who are pregnant or trying to become pregnant; computed tomography evidence of any (significant) emphysema evidence of airway obstruction (forced expiratory volume in 1 s/forced vital capacity <0.70, active cardiopulmonary disease (other than IPF) or other comorbidities that could contribute to dyspnea and exercise limitation; history/clinical evidence of asthma, atopy and/or nasal polyps; currently taking phosphodiesterase type 5 inhibitors; important contraindications to clinical exercise testing, including inability to exercise because of neuromuscular or musculoskeletal disease(s); body mass index (BMI) <18.5 or ≥35.0 kg/m2; use of daytime oxygen or exercise-induced O2 desaturation (<80% on room air).