important to realize, however, that restrictive lung disease cannot be diagnosed by
spirometry alone. With severe airways obstruction the lung volume remaining in the thorax
after expiration (the functional residual capacity) may be increased to such a degree that
it limits inspiratory capacity and, hence, reduces vital capacity. A reduced FEV1 and FVC
are therefore only suggestive of true restrictive disease, but it is necessary to measure
lung volumes to accurately diagnose restrictive physiology.