89 Vital capacity of lungs (VC)

Vital capacity: lung volumes, lower limit of normal, restrictive and neuromuscular causes of reduced VC.

Vital capacity (VC) is the largest volume of air a person can breathe out after the deepest possible breath in. It is the sum of the inspiratory reserve volume, the tidal volume and the expiratory reserve volume. VC depends on height, age, sex and ethnicity, and on the size of the lungs, the elasticity of lung tissue and the strength of the breathing muscles. Together with other lung function measurements it helps diagnose lung disease and assess its severity. When measured during a forced, rapid exhalation it is called forced vital capacity (FVC).

SpirometryLung volumesRestrictive disease

Typical adult≈ 3–5 L (depends on body size)

Normalabove the lower limit of normal

Reference equationsGLI-2012

Measured byspirometry

Figure 1. Lung volumes on a spirogram. TV tidal volume, IRV/ERV inspiratory/expiratory reserve volume, RV residual volume, VC vital capacity, FRC functional residual capacity, TLC total lung capacity. Typical adult values: TV ≈ 0.5 L, RV ≈ 1.2 L, FRC ≈ 2.4 L, VC ≈ 4.8 L, TLC ≈ 6 L.

Interpretation

Measured VC is compared with a value predicted for a person of the same age, height, sex and ethnicity. Current ERS/ATS standards recommend using the lower limit of normal (the 5th percentile, z-score −1.645) rather than a fixed percentage such as 80% of predicted. A reduced VC with a normal FEV1/FVC ratio suggests restriction, which must be confirmed by measuring total lung capacity; a reduced VC also occurs in obstruction when air is trapped.

Causes of reduced VC

Lung tissue diseases: pulmonary fibrosis, interstitial lung disease, sarcoidosis, pneumonia, lung resection
Chest wall and pleura: kyphoscoliosis, pleural effusion or thickening, obesity, ascites, pregnancy
Muscle weakness: neuromuscular diseases (motor neurone disease, muscular dystrophy, Guillain–Barré syndrome, myasthenia gravis), diaphragm paralysis; serial VC measurements are used to monitor respiratory muscle failure
Airway obstruction with air trapping (COPD, asthma)
Heart failure with pulmonary congestion

Seek emergency care

for rapidly progressing breathlessness, especially with muscle weakness, difficulty swallowing or a weak cough.

When to see a doctor

Breathlessness on exertion, a persistent dry cough or reduced exercise tolerance should be investigated with spirometry.

References

Graham BL, Steenbruggen I, Miller MR, et al. Standardization of spirometry 2019 update: an official American Thoracic Society and European Respiratory Society technical statement. Am J Respir Crit Care Med. 2019;200(8):e70–e88. doi:10.1164/rccm.201908-1590ST
Stanojevic S, Kaminsky DA, Miller MR, et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur Respir J. 2022;60(1):2101499. doi:10.1183/13993003.01499-2021
Quanjer PH, Stanojevic S, Cole TJ, et al. Multi-ethnic reference values for spirometry for the 3–95-yr age range: the global lung function 2012 equations. Eur Respir J. 2012;40(6):1324–1343. doi:10.1183/09031936.00080312

This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

Published on 1 May 2024