[Respiratory muscle testing: state of the art]

Assessing respiratory muscle function has become more and more essential both in clinical research and in the broad field of respiratory and intensive care medicine. In clinical practice, the assessment of respiratory muscle function is useful for differential diagnosis, for the quantification of respiratory muscle impairment and for follow-up assessments, for example, following respiratory muscle training or mechanical ventilation. Both volitional tests on respiratory muscle function, which are dependent on the patient making a truly maximal effort, and non-volitional tests exist. Non-invasive, less complex and most often volitional tests are suitable for screening. However, in case of pathological results these tests need to be complemented by the application of more complex, non-volitional and finally invasive techniques. This is particularly true if the cut-off value indicating no impairment is not achieved by the patient. In this case non-volitional tests are required in order to exclude pathological values resulting from sub-maximal efforts during volitional tests. In addition, isolated respiratory muscle impairments (e. g., solely diaphragmatic) might escape notice in certain tests on respiratory muscle function. For this reason, a diagnostic approach with the application of a combination of different tests should be chosen in those cases where respiratory muscle impairment is suspected. This current "state of the art" article gives a detailed description and comparative evaluation of the different volitional and non-volitional tests that are used for the assessment of respiratory muscle function.