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.
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.
Estimated vital capacities
|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 (cm3)||2900||3150||3400||3720||3950||4300|
|Vital capacity (cm3)||3425||3500||3225||3050||2850|
Vital capacity increases with height and decreases with age. Formulas to estimate vital capacity are:
where is approximate vital capacity in cm3, is age in years, and is height in cm.
Several studies have been made to measure and predict vital capacity . An online calculator exists that will compute the predicted vital capacity based on these references given a patient's, age, height and sex.
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