Oxygen supplementation during exercise improves leg muscle fatigue in chronic fibrotic interstitial lung disease

Background Exercise-induced hypoxaemia is a hallmark of chronic fibrotic interstitial lung disease (f-ILD). It remains unclear whether patients' severe hypoxaemia may exaggerate locomotor muscle fatigue and, if so, to what extent oxygen (O-2) supplementation can ameliorate these abnormalities. Methods Fifteen patients (12 males, 9 with idiopathic pulmonary fibrosis) performed a constant-load (60% peak work rate) cycle test to symptom limitation (Tlim) while breathing medical air. Fifteen age-matched and sex-matched controls cycled up to patients' Tlim. Patients repeated the exercise test on supplemental O-2 (42%+/- 7%) for the same duration. Near-infrared spectroscopy assessed vastus lateralis oxyhaemoglobin concentration ((HbO(2))). Pre-exercise to postexercise variation in twitch force (Delta Tw) induced by femoral nerve magnetic stimulation quantified muscle fatigue. Results Patients showed severe hypoxaemia (lowest O-2 saturation by pulse oximetry=80.0%+/- 7.6%) which was associated with a blunted increase in muscle (HbO(2)) during exercise vs controls (+1.3 +/- 0.3 mu mol vs +4.4 +/- 0.4 mu mol, respectively; p<0.001). Despite exercising at work rates similar to one-third lower than controls (42 +/- 13 W vs 66 +/- 13 W), Delta Tw was greater in patients (Delta Tw/external work performed by the leg muscles=-0.59 +/- 0.21 %/kJ vs -0.25 +/- 0.19 %/kJ; p<0.001). Reversal of exertional hypoxaemia with supplemental O-2 was associated with a significant increase in muscle (HbO(2)), leading to a reduced decrease in Delta Tw in patients (-0.33 +/- 0.19 %/kJ; p<0.001 vs air). Supplemental O-2 significantly improved leg discomfort (p=0.005). Conclusion O-2 supplementation during exercise improves leg muscle oxygenation and fatigue in f-ILD. Lessening peripheral muscle fatigue to enhance exercise tolerance is a neglected therapeutic target that deserves clinical attention in this patient population.

Automated summary

Exercise-induced hypoxaemia is common in patients with f-ILD, leading to increased muscle fatigue. Oxygen supplementation during exercise can significantly improve muscle oxygenation and fatigue in these patients.