Assessment of diaphragm function.

Assessment of diaphragm function begins with the physical examination, but neither the physical examination nor radiography is sensitive enough to detect subtle abnormalities of diaphragm function. Maximal static transdiaphragmatic pressure and maximal static inspiratory mouth pressure have been widely used as measures of diaphragm and inspiratory muscle strength, respectively. Both are useful as rough indications of muscle strength, but, because they are highly effort dependent, they should not be relied upon for absolute accuracy. Objective measurement of diaphragm function requires phrenic nerve stimulation.