In some cases of cystic fibrosis, which primarily affects the airways, temporary decreases in TLC have been described, possibly due to partial atelectasis. Hence the vital capacity alone is of little use in discriminating between restrictive, obstructive and mixed ventilatory defects. However, in small airways disease the RV is increased with no change in TLC accordingly the VC is reduced (with a proportionate decrease in FEV 1 ). the volume change between RV and TLC, may be diminished by both restrictive and obstructive ventilatory defects in the latter case it is due to an increase in residual volume due to (premature) airways closure (gas trapping) and airflow limitation at low lung volumes, leading to incomplete lung emptying. Static lung volumes may be diminished by disorders which restrict lung expansion (restrictive ventilatory defects), such as neuromuscular disorders, diseases of the chest wall and abdomen, disorders of the pleural space, increase in lung stiffness, and decrease in the number of available alveolar units (lung resection, atelectasis, scars).Ī restrictive ventilatory defect is best described on the basis of a reduced TLC rather than from vital capacity measurements. Measurements of lung volumes are also essential in interpreting data on lung elastic recoil pressure, instantaneous ventilatory flows, airways resistance, and the transfer factor of the lung, since these are all volume dependent. emphysema) and by the mechanical properties of lung and thorax (disorders include diffuse fibrosis, kyphoscoliosis).Īssessing the total lung capacity is indispensable in establishing a restrictive ventilatory defect or in diagnosing abnormal lung distensibility, as may occur in patients with emphysema.

muscle paralysis), obstruction, occlusion and compression of small airways (disorders include e.g. The level of maximal expiration (residual volume, RV) is determined by the force exerted by respiratory muscles (disorders include e.g. pulmonary fibrosis and emphysema) and the elastic properties of the thorax and adjacent structures (disorders include e.g. muscular dystrophy), the elastic recoil of the lung (disorders include e.g. The level of maximal inspiration (total lung capacity, TLC) is influenced by the force developed by the inspiratory muscles (disorders include e.g. Factors which determine the size of the normal lung include stature, age, sex, body mass, posture, habitus, ethnic group, reflex factors and daily activity pattern.

Tidal volume chart copd fev