Restrictive Lung Disease
| Overview |
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- Restrictive Lung Diseases are pathologies of the lung characterized by a reduced capacity of the lung to expand. A large variety of distinct diseases can result in a restrictive pattern and may affect the lung parenchyma itself, reducing lung compliance, or affect the capacity of extra-pulmonary structures to mechanically expand the lung.
| Diagnosis |
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- Restrictive Lung Diseases are characterized by reductions in both the Forced Expiratory Volume (FEV) and Forced Vital Capacity (FVC) of the lungs. However, the key feature of restrictive disease is that the FEV declines less than the FVC, typically leading to an abnormally high FEV/FVC ratio. The FEV/FVC ratio of a normal lung is roughly 80%; however, in those with a restrictive pattern of lung disease this ratio is typically elevated and can reach 90%.
| Etiologies |
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- Overview
- As mentioned, restrictive lung disease arise from a reduced capacity for expansion of the lung; however, a wide variety of very different etiologies can account for this phenomenon. The etiologies of restrictive lung disease can be conveniently separated based on the anatomical location of the primary defect.
- Parenchymal Disease
- In some cases, the pulmonary parenchyma exhibits pathology which causes decreased lung compliance and thus requirements for greater pressures to expand the lung. Restrictive parenchymal diseases can be sub-categorized into those which develop acutely and are typically accompanied by pulmonary edema and those that develop chronically and are typically accompanied by progressive parenchymal fibrosis. Acute parenchymal restrictive diseases include Acute Respiratory Distress Syndrome and Neonatal Respiratory Distress Syndrome. Chronic parenchymal restrictive diseases include Idiopathic Pulmonary Fibrosis, Sarcoidosis, Hypersensitivity Pneumonitis, Pneumoconioses, Goodpasture Syndrome, Wegener Granulomatosis.
- Diseases of the Pleura
- Gases or liquids in the pleura can derange normal processes of lung expansion and thus result in a restrictive pattern of pulmonary function. Consequently, pneumothorax and pleural effusion will result in restrictive disease.
- Diseases of the Chest Wall
- Expansion of the chest wall is critical for proper breathing and thus diseases which restrict chest wall movement can lead to restrictive pulmonary function. Consequently, deformities of the chest wall as occurs in scoliosis or reduced mobility of vertebral joints as occurs in Ankylosing Spondylitis can yield restrictive disease. Although this is not purely a chest wall issue, morbid obesity can prevent proper mechanical expansion of the lung.
- Neuromuscular Diseases
- Deranged neural control of the muscles which coordinate breathing biomechanics can also result in restrictive disease in a patient with otherwise healthy lungs and chest wall. This might occur in those with Guillain-Barre Syndrome, Amyotrophic Lateral Sclerosis, or those with post-polio syndrome.
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