The **forced vital capacity** is usually slightly less than the vital capacity measured on a slow exhalation. Used to predict risk of resp failure in: - [[Guillain-Barré syndrome|GBS]] - [[myasthena gravis]] - ALS (Amyotrophic lateral sclerosis) For ALS: decrease of vital capacity (VC) to 50% of predicted is associated with respiratory symptoms. A VC of <25 to 30% of predicted is associated with respiratory failure or sudden death. For GBS and myasthenia gravis: - FVC <15mL/kg (<30% predicted) suggests need for ventilatory support/ intubation - 15-20 mL/kg needs close monitoring in HDU *Restrictive lung disease:* FEV1 and FVC are reduced and the FEV1/FVC is normal or increased. *Obstructive lung disease:* The FEV1 is reduced much more than is the FVC giving a low FEV1/FVC ![[Pasted image 20241109164304.jpg]] total lung capacity: ~ 7000 mL vital capacity: 5000 mL tital volume: 500mL residual volume ~1200 mL