Decreased lung compliance

• Interstitial lung disease
• Pneumonia
• Sarcoidosis
• Acute respiratory distress syndrome (ARDS)

Decreased muscle strength

• Neuromuscular disease (eg, myasthenia gravis, Guillain-Barré)
• Diaphragm dysfunction
• Phrenic nerve injury

Extrapulmonic disease

• Pleural effusion
• Pleural thickening
• Obesity
• Kyphoscoliosis