Respiratory Muscle Evaluation of the Patient with Neuromuscular Disease

This review presents clinically relevant issues regarding the assessment of respiratory muscles in individuals with neuromuscular disorders, and discusses the advantages and disadvantages of methods generally available to the clinician. Vital capacity (VC) and total lung capacity (TLC) are routinely measured in pulmonary function laboratories and are typically reduced in the context of severe respiratory muscle weakness, but the sensitivity and specificity of these measures are limited. Better measures of respiratory muscle weakness are maximal static inspiratory and expiratory pressures (PI max and PE max). PI max is reduced even with mild or moderate degrees of inspiratory muscle weakness, but low values also may be related to submaximal effort. To circumvent this problem, pressures can be measured using simpler maneuvers such as a maximal sniff. Specific tests of diaphragm function such as measurements of maximal transdiaphragmatic pressure are invasive and not routinely available to the clinician. Recently, noninvasive methods that specifically assess diaphragm function, such as diaphragm ultrasound of the zone of apposition and magnetic or electrophrenic nerve stimulation, have shown promise as new techniques for clinical use.