Respiratory muscle weakness is present in many patients and may represent a
significant problem for several reasons.' It is a common feature of several
neuromuscular diseases (box 1) and is associated with a higher morbidity and
mortality.`5 Recently, there has been increasing awareness that respiratory muscle
weakness can be a compounding factor in many diseases, such as
malnutrition,6 chronic obstructive pulmonary disease,` congestive heart
failure,'0-"2 and sepsis.'3 Furthermore, respiratory muscle weakness is a complication
of many metabolic diseases (box 2),'4 endocrine disorders, and steroid
therapy.'5 Measurement of respiratory muscle strength is useful in order to
detect respiratory muscle weakness and to quantify its severity,'6 and to
determine optimal long-term management. Respiratory muscle testing is useful
in establishing the causes of unexplained dyspnoea, bulbar problems, and
impaired cough, and is also important for the follow-up of patients with respiratory
muscle weakness or those on respiratory muscle training programmes, and
it is currently being used in ventilator weaning protocols."' Indications for evaluation
of respiratory muscle strength are shown in box 3.