Respiratory Muscle Function in Interstitial Lung Disease

Interstitial lung diseases (ILD) limit daily activities, impair quality of life and result in (exertional) dyspnea. This has mainly been attributed to a decline in lung function and impaired gas exchange. However, the contribution of respiratory muscle dysfunction to these limitations remains to be conclusively investigated. ILD patients and matched controls performed body plethysmography, a standardized 6-minute walking test, volitional (respiratory drive: P0.1, global maximal inspiratory mouth occlusion pressure: PImax, sniff nasal pressure: SnPna, inspiratory muscle load) and non-volitional tests on respiratory muscle function and strength (twitch mouth and transdiaphragmatic pressure during bilateral magnetic phrenic nerve stimulation: TwPmo,TwPdi). 25 patients and 24 controls were included in the study. PImax and SnPna remained unaltered (both p>0.05), whereas P0.1 and the load on the inspiratory muscles were higher (both p<0.05) in ILD patients compared to controls. TwPmo and TwPdi were lower in ILD patients (TwPmo: 0.86SD0.4vs1.32SD0.4,p<0.001; TwPdi 1.34SD0.6vs1.88SD0.5,p=0.022). Diaphragmatic force generation seems to be impaired in this cohort of ILD patients while global respiratory muscle strength remains preserved. Central respiratory drive and the load imposed on the inspiratory muscles are increased. Whether impaired respiratory muscle function impacts morbidity and mortality in ILD patients needs to be investigated in future studies