Vital capacity <60% predicted | Children generally need to be over 6 years of age to produce reliable spirometry. In boys with DMD, a vital capacity of over 1.8 litres indicates that nocturnal hypoventilation is very unlikely to be present |
Loss of ambulation because of progressive weakness, or children who never attain the ability to walk | Inability to walk is a measure of moderate to severe muscle weakness |
Infants with weakness | Infantile onset is often associated with more severe weakness |
Children with symptoms of obstructive sleep apnoea or hypoventilation | See section on clinical assessment |
Children with diaphragmatic weakness | Sleep-associated hypoventilation can occur even if general muscle strength is preserved |
Children with rigid spine syndrome | These children are at particular risk of nocturnal hypoventilation despite relatively preservation of general muscle strength, ambulation and near normal vital capacity |