Respiratory Muscle Assessment in Clinical Practice.

Respiratory muscle weakness is relatively rare in clinical practice; therefore, it is seldom a clinician's first thought. However, it should always be considered where a patient has unexplained breathlessness, respiratory failure, or experiences difficulty weaning from mechanical ventilation. Diaphragm weakness can often be ruled out by careful application of history, examination, and noninvasive bedside tests, although more quantitative tests exist. Where the predominant problem is respiratory muscle weakness, these tests convey useful prognostic information, which can be used for the management of an individual patient and to enrich study populations allowing reduced sample size in clinical trials.