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What is Restrictive lung disease and explain in detail?
Restrictive lung diseases  are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.

Presentation
Due to the chronic nature of this disease, the leading symptom of restrictive lung disease is progressive exertional dyspnea.  For acute on chronic cases, shortness of breath, cough, and respiratory failure are some of the more common signs.

Causes
Restrictive lung diseases may be due to specific causes which can be intrinsic to the parenchyma of the lung, or extrinsic to it.

Intrinsic
Pneumoconiosis caused by long-term exposure to dusts, especially in mining. For example, Asbestosis.
Radiation fibrosis, usually from the radiation given for cancer treatment.
Certain drugs such as amiodarone, bleomycin and methotrexate.
As a consequence of another disease such as rheumatoid arthritis.
Hypersensitivity pneumonitis due to an allergic reaction to inhaled particles.
Acute respiratory distress syndrome (ARDS), a severe lung condition occurring in response to a critical illness or injury.
Infant respiratory distress syndrome due to a deficiency of surfactant in the lungs of a baby born prematurely.
TuberculosisMany cases of restrictive lung disease are idiopathic (have no known cause). Still, there is generally pulmonary fibrosis. Examples are:

Idiopathic pulmonary fibrosis
Idiopathic interstitial pneumonia, of which there are several types
Sarcoidosis
Eosinophilic pneumonia
Lymphangioleiomyomatosis
Pulmonary Langerhans cell histiocytosis
Pulmonary alveolar proteinosisConditions specifically affecting the interstitium are called interstitial lung diseases.

Extrinsic
Nonmuscular diseases of the upper thorax such as kyphosis, pectus carinatum and pectus excavatum.
Diseases restricting lower thoracic/abdominal volume (e.g. obesity, diaphragmatic hernia, or the presence of ascites).
Pleural thickening.

Pathophysiology
In normal respiratory function, the air flows in through the upper airway, down through the bronchi and into the lung parenchyma (the bronchioles down to the alveoli) where gas exchange of carbon dioxide and oxygen occurs