Respiratory muscle fatigue following exercise in patients with interstitial lung disease

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.

To assess the development of respiratory muscle fatigue in patients with ILD and relate it to the respiratory pattern during exercise.

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.

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).

Abdominal muscle fatigue develops during exercise in some ILD patients in association with increased expiratory muscle activity manifested by reduced EELV.