Rationale: In the United States (U.S.), ambulatory oxygen is recommended for patients with idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD) who experience symptomatic exertional hypoxemia. Ambulatory oxygen need is often determined by submaximal hall walk testing; however, this may fail to accurately characterize exertional hypoxemia in some patients.
Objectives: Assess for differences in ambulatory oxygen needs between IPF and COPD patients who completed a ramped treadmill protocol exercise test (RTPET) and correlate oxygen flow rates determined at highest level exertion with lung function and exercise parameters. Oxygen "need" is defined as flow rate needed to maintain oxygen saturation >90% in patients who desaturate to <88%.
Methods: We conducted a retrospective review of RTPET results for IPF and COPD patients who also recently completed spirometry. The RTPET has three phases: rest, submaximal usual pace walking at 0% treadmill grade for 3 minutes, and highest level walking at the UP walk speed with increasing treadmill grade by 2% every 2 minutes. IPF patients were part of a clinical registry while COPD patients were identified based on diagnosis coding and spirometry (FEV1/FVC <0.70). The RTPET for both groups was completed based on a pulmonologist's referral.
Measurements and main results: We included 329 IPF and 2,343 COPD patients. A greater proportion of IPF patients required ambulatory oxygen to maintain saturation >90%. After adjusting for demographic covariates and exercise parameters, IPF patients required higher ambulatory oxygen flow rates compared to COPD subjects with similar DLCO values. Of patients who did not require oxygen with submaximal usual pace testing, 49% with IPF and 24% with COPD required oxygen at highest level exertion.
Conclusions: The RTPET identified higher oxygen flow needs at highest level exertion in IPF versus COPD patients; however, in both diseases, there was a significant proportion of patients who were only found to have exertional desaturation at highest level exertion. Current oxygen policies and reliance on submaximal testing may fail to meet the needs of patients with IPF and COPD. Further studies are needed to determine if oxygen prescriptions targeting highest level desaturation improve clinical outcomes, symptoms, or quality-of-life.