Resting physiological and perceptual responses to nasal high-flow O ₂ therapy in naïve patients with fibrotic interstitial lung disease

<b>Background.</b> Fibrotic interstitial lung disease (<i>f</i>-ILD) is characterized by impaired pulmonary gas exchange, increased ventilatory demand and disabling dyspnea. Conventional O₂ therapy at rest improves patients' oxygenation but not ventilatory requirements. Nasal high-flow (NHF) with or without supplemental O₂ may reduce ventilatory demand but its acute physiological and perceptual benefits remain unclear in <i>f</i>-ILD. <b>Methods.</b> Fifteen naïve patients (partial pressure of arterial O₂= 57±12 mmHg) underwent, in a randomized, single-blind, cross-over trial, six bouts of 7-min exposure: room air; conventional O₂ [fraction of inspired O₂ (FiO₂)=0.5 or 1.0]; NHF_air (30 L·min-1, FiO₂=0.21); and NHFO₂ (30 L·min⁻¹, FiO₂=0.3 or 0.5). Breathing pattern (respiratory plethysmography), O₂ saturation (SpO₂) and dyspnea intensity (Borg CR-10) and qualitative descriptors were compared across conditions. <b>Results.</b> SpO₂ improved in O₂-enriched conditions (≥98%) vs air and NHF_air (~92%; p<0.001). NHF_air, NHFO₂ with FiO₂=0.3 and FiO₂=0.5 lessened ventilation vs room air (7.8±3.0, 7.1±3.3, 7.0±2.5 and 9.3±3.0 L·min^-1, respectively; all <i>p</i>≤0.044), but conventional O₂ had no significant effect. Respiratory rate only decreased with NHFO₂ with FiO₂=0.3 vs air (20±6 vs 23±5 breaths·min-1; p=0.008). Dyspnea intensity was greater with NHF modalities vs conventional O₂ (~1 Borg unit; all p≤0.030); qualitative descriptors did not differ across conditions. <b>Conclusion.</b> In moderately-hypoxemic patients with <i>f</i>-ILD, NHF (regardless of O₂ enrichment) but not conventional O₂ therapy lessened resting ventilatory requirements. Concurrently, NHF increased dyspnea intensity despite preserved qualitative dimensions, suggesting dissociation between physiological and perceptual responses in this population. These findings highlight the need for individualized strategies when implementing NHFO₂ in naïve patients with <i>f</i>-ILD.