Non-invasive assessment of exercise performance in children with cystic fibrosis (CF) and non-cystic fibrosis bronchiectasis: is there a CF specific muscle defect?

INTRODUCTION: Peripheral muscle dysfunction is increasingly recognized as complicating respiratory disease, but this is difficult to measure non-invasively. RESEARCH QUESTION: Can skeletal muscle function and efficiency be measured during exercise non-invasively using respiratory mass spectrometry (RMS); and is the known exercise dysfunction in cystic fibrosis (CF) children related in part to a disease specific defect of skeletal muscle, or a non-specific manifestation of chronic airway infection and inflammation. METHODS: Calculations of effective pulmonary blood flow and stroke volume, blood oxygen content and oxygen dispatch from the lungs, skeletal muscle oxygen extraction and consumption, anerobic threshold and capacity, and gross, net and work efficiency in 106 controls and 36 children (18 CF) with bronchiectasis, all aged from 8 to 17 years. RESULTS: Normal values for control subjects are tabulated. CF and non-CF bronchiectatic subjects had similar physiology, and skeletal muscle abnormalities could not be detected. Reduced oxygen dispatch from the lungs, due to an inability to raise stroke volume, without an increase in functional residual capacity was the major factor in reduced exercise ability. CONCLUSIONS: Non-invasive RMS can be used to determine skeletal muscle function in children. The changes observed in CF subjects were very similar to non-CF bronchiectatic subjects and thus a CF specific defect was not demonstrated.