Muscular weakness and respiratory failure

Respiratory muscle weakness is associated with abnormalities of lung volume, compliance, and gas exchange, although the mechanisms are not entirely clear, and that RMS should be assessed directly because VC is affected by other factors. We also conclude that VC in patients with myopathy is lower, at any level of RMS, than would be predicted on the basis of normal respiratory system recoil, and that abnormal chest wall compliance and parenchymal disturbances appear to be responsible. Respiratory muscle weakness is common in myopathy, but repiratory failure is not likely to occur until respiratory muscle strength is less than 30 per cent of predicted. Severe respiratory muscle weakness is an especially grave event in the presence of associated lung disease.