Objectives:

1. To evaluate endurance time during cardiopulmonary exercise test (CPET) performance comparing standard oxygen therapy to high-flow nasal cannula (HFNC) oxygen therapy in subjects with idiopathic pulmonary fibrosis (IPF) with exertional desaturation.
2. To assess oxygenation level (peripheral and muscular) as well as dyspnea and fatigue during exercise in IPF subjects with exertional desaturation using oxygen supplementation with HFNC compared with standard oxygen supplementation.

Method: multicenter crossover clinical trial. Patients with IPF presenting oxygen desaturation during the six-minute walking test (6MWT) (SpO2 mean ≤ 85%) will be included consecutively . Each subject evaluated will perform initially an incremental CPET to evaluate the patient's maximum exercise capacity. Supplemental oxygen will be applied to maintain SpO2 >85% with a Venturi mask. Maximum exercise capacity and the appropriate final oxygen inspiratory fraction (FiO2) needed for the following tests will be determined.

Posteriorly each patient will perform two constant load CPET (at 75% of the maximum workload achieved with the incremental CPET); one with standard oxygen therapy and the other one with HFNC oxygen therapy. Endurance time, dyspnea and leg fatigue and oxygen saturation (peripheral and muscular) will be recorded.

Evaluation measures: Endurance time, dyspnea and leg fatigue (Borg scale), and oxygen saturation.

Inclusion Criteria:

• Subjects with IPF diagnosis according to the 2018 international consensus guidelines
• Mean SpO2 ≤ 85% during the 6MWT performed under room air conditions

Exclusion Criteria:

• Fibrotic interstitial lung diseases other than IPF
• Chronic obstructive pulmonary disease (COPD)
• Inability to perform a complete CPET due to osteo-articular or cognitive limitations
• End-stage lung disease
• Severe pulmonary hypertension