Restrictive defects are caused by the following: Loss in lung volume (eg, lobectomy) Abnormalities of structures surrounding the lung (eg, pleural disorder, kyphosis, obesity) Weakness of the inspiratory muscles of respiration (eg, neuromuscular disorders) Abnormalities of the lung parenchyma (eg, pulmonary fibrosis) The feature common to all is a decrease in the compliance of the lungs, the chest wall, or both.