Table 3.

Pulmonary function and lung volume alterations accompanying neuromuscular weakness

Pulmonary function/Lung volume	Effect
Residual Volume (RV)	↑ (with expiratory muscle weakness
Vital Capacity (VC)	Initially normal, ↓after max pressures ↓50%
Total lung Capacity(TLC)	↓ (inspiratory weakness)
Functional Residual Capacity (FRC)	↓ (inspiratory weakness)
FEV1/FVC	Normal (proportional ↓ FEV1 & FVC in inspiratory weakness)
Residual Volume (RV)	↑ (with expiratory muscle weakness)
Peak Expiratory Flow (PEF) Maximum Voluntary ventilation (MVV)	↓ (NM weakness or effort)
Diffusing Capacity (DLco)	Normal (unless infiltrative/parenchymal process)
Maximal Inspiratory Pressure MIP	↓ (more than MEP in diaphragmatic weakness, effort)
Maximal Expiratory Pressure MEP	↓ (NM weakness, effort)