Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 79

Vital capacity is the volume of air expelled by a full expiration from a position of full inspiration. The patient is usually encouraged to exhale with maximum effort, referred to as forced vital capacity (FVC). VC may also be measured by a slow exhalation, sometimes referred to as ‘slow’ VC. In normal individuals, slow VC and FVC are very similar, but in patients with airway obstruction, air trapping occurs during forced expiration, so that the FVC may be significantly smaller than the slow VC. VC may be reduced by any condition that limits the lung’s ability to achieve a ‘full’ inspiration, such as:

 reduced lung compliance (e.g. lung fibrosis, loss of lung volume)

 chest deformity (e.g. kyphoscoliosis, ankylosing spondylitis)

 muscle weakness (e.g. myopathy, myasthenia gravis).

It may also be reduced in chronic obstructive pulmonary disease (COPD), when air trapping causes increased residual volume.