Resting physiological and perceptual responses to nasal high-flow O2 therapy in naïve patients with fibrotic interstitial lung disease.

Fibrotic interstitial lung disease (f-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 f-ILD. 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 ([Formula: see text]) = 0.5 or 1.0]; nasal high-flow without O2-enriched air (NHFair; 30 L·min-1, [Formula: see text] = 0.21); and nasal high-flow O2 ([Formula: see text]; 30 L·min-1, [Formula: see text] = 0.3 or 0.5). Breathing pattern (respiratory plethysmography), O2 saturation ([Formula: see text]), dyspnea intensity (Borg CR-10), and qualitative descriptors were compared across conditions. [Formula: see text] improved in O2-enriched conditions (≥98%) versus air and NHFair (∼92%; P < 0.001). NHFair and [Formula: see text] with [Formula: see text] = 0.3 and [Formula: see text] = 0.5 lessened ventilation versus room air (7.8 ± 3.0, 7.1 ± 3.3, 7.0 ± 2.5, and 9.3 ± 3.0 L·min-1, respectively; all P ≤ 0.044), but conventional O2 had no significant effect. Respiratory rate only decreased with [Formula: see text] with [Formula: see text] = 0.3 versus air (20 ± 6 vs. 23 ± 5 breaths·min-1; P = 0.008). Dyspnea intensity was greater with NHF modalities versus conventional O2 (∼1 Borg unit; all P ≤ 0.030); qualitative descriptors did not differ across conditions. In moderately hypoxemic patients with f-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 [Formula: see text] in naïve patients with f-ILD.NEW & NOTEWORTHY In moderately hypoxemic, naive individuals with fibrotic interstitial lung disease, nasal high flow (regardless of O2 enrichment) lessened resting ventilatory requirements versus room air but increased dyspnea intensity versus conventional O2 therapy, suggesting dissociation between physiological and perceptual responses in this population. Our findings thus highlight the need for individualized strategies when implementing nasal high flow O2 therapy in these patients.