Vital capacity

Output of a spirometer

Vital capacity is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.

A person's vital capacity can be measured by a wet or regular spirometer. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease. Furthermore, the vital capacity is used to determine the severity of respiratory muscle involvement in neuromuscular disease, and can guide treatment decisions in Guillain-Barré syndrome and myasthenic crisis.

A normal adult has a vital capacity between 3 and 5 litres.^[1] A human's vital capacity depends on age, sex, height, mass, and ethnicity.^[2]

Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle. Lung volumes are directly measured, whereas lung capacities are inferred from volumes.

Role in Diagnosis

The vital capacity can be used to help differentiate causes of lung disease. In restrictive lung disease the vital capacity is decreased. In obstructive lung disease it is usually normal or only slightly decreased.^[3]

Estimated vital capacities

Males by height^[4]:182

Height	150–155 cm (5'–5'2")	155–160 cm (5'2"–5'4")	160–165 cm (5'4"–5'6")	165–170 cm (5'6"–5'8")	170–175 cm (5'8"–5'10")	175–180 cm (5'10"–6')
Vital capacity (cm^3)	2900	3150	3400	3720	3950	4300

Males by age^[4]:183

Age	15–25	25–35	35–45	45–55	55–65
Vital capacity (cm^3)	3425	3500	3225	3050	2850

Formulas

Vital capacity increases with height and decreases with age. Formulas to estimate vital capacity are:^[1]

$\begin{align} vc_{female} = (21.78 - 0.101 a ) \cdot h \\ vc_{male} = (27.63 - 0.112 a ) \cdot h \\ \end{align}$

where $vc$ is approximate vital capacity in cm³, $a$ is age in years, and $h$ is height in cm.

Several studies have been made to measure and predict vital capacity.^{[5][6][7][8][9]} An online calculator exists that will compute the predicted vital capacity based on these references given a patient's, age, height and sex.

References

1. "Vital Capacity". Family Practice Notebook. Retrieved 19 February 2015.
2. Hutchinson, J (1846). "On the capacity of the lungs, and on the respiratory functions, with a view of establishing a precise and easy method of detecting disease by the spirometer". Med Chir Trans 29: 137–252. PMC 2116876. PMID 20895846.
3. "Pulmonary Function Tests". UCSD. Retrieved 19 February 2015.
4. Pratt, Joseph H. (1922). "Long-continued observations on the vital capacity in health and in heart disease". Transactions of the Association of American Physicians (W. J. Dornan, Incorporated) 37: 182–197.
5. E. Berglund, G. Birath, J. Bjure, G. Grimby, I. Kjellmer, L. Sandqvist, B. Söderholm. Spirometric Studies in Normal Subjects. Acta Medica Scandinavica, Vol. 173, fasc. 2, pp. 185-206, 1963.
6. G. Forche, K. Harnoncourt, E. Stadlober. Neue spirometrische Bezugswerte für Kinder, Jugendliche und Erwachsene. Öst. Ärzteztg. 43/15/16, p.40, 1988.
7. A. Gulsvik. Spirometri (Korrespondanse). Tidsskr Nor Loegeforen nr. 31, 105, pp.2240-2, 1985.
8. H. Hedenström, P. Malmberg, K. Agarwal. Reference Values for Lung Function tests in Females. Bull. Eur. Physiopathol. Respir. 21, pp. 551-557, 1985.
9. A. Langhammer, R. Johnsen, A. Gulsvik, T.L. Holmen, L. Bjermer, Forced spirometry reference values for Norwegian adults: the Bronchial Obstruction in North Trøndelag study. Eur. Respir. J. Volume 18, pp. 1-10. 2001.

External links

• Vital capacity at GPnotebook