Respiratory Muscle Fatigue following Exercise in Patients with Interstitial Lung Disease

BACKGROUND: It is not known whether respiratory muscle fatigue occurs as a consequence of exercise in patients with interstitial lung disease (ILD) and, if so, to what extent it is related to changes in dynamic lung volumes. OBJECTIVES: To assess the development of respiratory muscle fatigue in patients with ILD and relate it to the respiratory pattern during exercise. METHODS: Sixteen ILD patients (11 women) performed incremental, symptom-limited cycle ergometry with inspiratory capacity manoeuvres used to measure changes in end-expiratory lung volume (EELV). Twitch transdia-phragmatic pressure (TwPdi) and twitch gastric pressure (TwT10Pga), in response to magnetic stimulation, were used to assess the development of fatigue. RESULTS: TwPdi did not differ significantly before and after exercise (21.8 ± 8 vs. 20.2 ± 8 cm H2O; p = 0.10), while TwT10Pga fell from 28.6 ± 18 to 25.2 ± 14 cm H2O (p = 0.02). EELV fell from 2.18 ± 0.65 to 1.91 ± 0.59 liters following exercise (p = 0.04). The fall in TwT10Pga correlated with peak oxygen uptake at peak of exercise (r = -0.52, p = 0.041), increase in heart rate (r = 0.53, p = 0.032) and with the decrease of EELV during exercise (r = 0.57, p = 0.021). Abdominal muscle fatiguers (n = 9, 56%), defined as having a ≥10% fall in TwT10Pga, had a fall in EELV of 22 ± 22% compared to 0.7 ± 8% in non-fatiguers (p = 0.016). CONCLUSION: Abdominal muscle fatigue develops during exercise in some ILD patients in association with increased expiratory muscle activity manifested by reduced EELV.