Respiratory muscle testing.

Respiratory muscles are a vital component of the respiratory system. Compromise in the function of respiratory muscles is assessed with a careful history, determination of the breathing frequency, and observation of the pattern of thoracoabdominal movements in the upright and supine positions. The most important diagnostic tools include measurement of lung volumes, FVC, oximetry, Pi(max) and Pe(max), and SNIP. Measurement of Pes and Pga pressures, Tw Pmo, phrenic nerve stimulation, magnetic stimulation, and EMG add new dimensions to the study of these muscles. These tools are helpful in understanding patients with acute and chronic disease that affects the respiratory muscles.