Beyond the lungs in fibrotic interstitial lung disease: does supplemental O2 improve skeletal muscle oxygenation and fatigue?

Background: The severity of exertional hypoxaemia in fibrotic interstitial lung disease (f-ILD) finds no parallel in respiratory medicine. The prevailing view is that supplemental oxygen (O2) may improve exercise tolerance in f-ILD by lessening the hypoxic ventilatory drive and dyspnoea. However, it is conceivable that part of the ergogenic effects of O2 are secondary to improved muscle O2 delivery and fatigue. Methods: Sixteen f-ILD patients (13 males, 73±8 years) performed a constant-load (60% peak) cycle test to symptom limitation on normoxia (Tlimnorm). Fourteen controls cycled up to patients’ Tlimnorm. Later on, patients exercised up to Tlimnorm under supplemental O2 (0.41±0.07). Changes in quadriceps oxyhaemoglobin concentration ([HbO2]) were assessed by near-infrared spectroscopy. A >15% post-cycling fall in quadriceps force response to magnetic nerve stimulation (twitch, Twquad) indicated the presence of muscle fatigue. Results: Patients showed severe exertional hypoxaemia (O2 saturation= 80.7±7.4% after 17±4 min). Fatigue was found in 13/16 patients (Twquad fall= 21.5±8.0%) and was larger than in controls (13.5±9.1%; p Conclusion: The beneficial effects of exertional O2 supplementation in patients with f-ILD are not limited to “the lungs”: lessening peripheral muscle fatigue to improve exercise tolerance is a relevant therapeutic target that deserves clinical attention.