Respiratory Muscle Strength
Respiratory muscle strength can be assessed by measuring the maximal inspiratory pressure (MIP or PImax), and the maximal expiratory pressure (MEP or PEmax). The MIP reflects the strength of the diaphragm and other inspiratory muscles, while the MEP reflects the strength of the abdominal muscles and other expiratory muscles. A well validated alternative or additional test of inspiratory muscle strength is maximal sniff nasal inspiratory pressure (SNIP). Common indications for measurement of the MIP, SNIP, and MEP include:
- Respiratory muscle weakness is suspected, such as in a patient with known neuromuscular disease, a weak cough, or unexplained dyspnea (particularly orthopnea)
- Lung function tests show reduced vital capacity (VC) or an increased diffusion capacity of unknown etiology
- Evaluation of whether known respiratory muscle weakness has improved, remained stable, or worsened. These measurements are useful for assessing and following patients with respiratory muscle weakness due to neuromuscular problems, such as spinal cord injury, Guillain-Barre syndrome, diaphragmatic paralysis, muscular dystrophy, myasthenia gravis, amyotrophic lateral sclerosis (ALS) and steroid myopathy.