Pathophysiology
Summary
In restrictive lung disease, core characteristics include decreased lung compliance, an increase in the elasticity of the pulmonary interstitium, and a reduction in total lung capacity (TLC), which hinders the ability to take deep breaths. Functionally, this results in a decrease in forced expiratory volume (FVC) and functional residual capacity (FRC). A notable diagnostic metric is the FEV1/FVC ratio, which is elevated (>80%) due to airway widening and decreased resistance to expiratory flow.
Intrinsic restrictive lung diseases, such as idiopathic pulmonary fibrosis, pneumoconioses, and sarcoidosis, exhibit a low DLCO, indicating the destruction of the alveolar-capillary interface. Intrinsic forms like interstitial lung disease often start with dyspnea on exertion, progressing to dyspnea at rest, and manifest with symptoms like a non-productive cough and unique 'velcro rales' audible primarily at the lung bases. Imaging often reveals diffuse reticulo-nodular opacities, described as 'ground glass,' and chronic stages may precipitate pulmonary hypertension due to the destruction of lung parenchyma and a reduction in alveolar capillaries, leading to increased pulmonary arterial resistance and consequent right heart failure.
Extrinsic restrictive lung diseases arise from factors outside the lungs and may be induced by pleural diseases like mesothelioma and pleural effusions, neuromuscular impairments such as polio or myasthenia gravis, or skeletal deformities like kyphoscoliosis and ankylosing spondylitis. Specifically, obesity-related restrictive lung disease features faster, shallower breaths due to extrathoracic restriction, often resulting in carbon dioxide retention. The most common indicator of this form is a reduction in expiratory reserve volume (ERV). This may escalate into obesity hypoventilation syndrome, characterized by high levels of PaCO2 and low levels of PaO2, leading to chronic hypoxia, chronic pulmonary vascular constriction, pulmonary hypertension, and ultimately cor pulmonale.
Lesson Outline
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FAQs
In restrictive lung disease, total lung capacity (TLC) is reduced, limiting the ability to take deep breaths. Lung compliance also decreases, indicating compromised lung elasticity and making lung expansion difficult. This is often attributed to increased elasticity of the pulmonary interstitium (interstitial lung disease) which results in airway widening and decreased resistance to expiratory flow.
Interstitial lung disease, a type of intrinsic restrictive lung disease, typically manifests with a non-productive cough and ‘velcro rales,’ characterized by dry crackling sounds best heard at the lung bases. Dyspnea initially occurs with exertion and can progress to resting dyspnea. Radiologically, diffuse reticulo-nodular opacities are often observed on x-ray, serving as a hallmark of the disease.
Extrinsic causes of restrictive lung disease include pleural diseases like mesothelioma, neuromuscular diseases such as polio or myasthenia gravis, spinal deformities like kyphoscoliosis, and obesity. These conditions can affect the diaphragmatic and intercostal muscles or restrict chest wall expansion, leading to decreased lung compliance and reduced lung capacity.
Obesity can restrict the expansion of the chest wall expansion, leading to faster and more shallower breaths due to extrathoracic restriction. This can progress to chronic restrictive lung disease, characterized by obesity hypoventilation syndrome, which results in elevated PaCO2 and reduced PaO2 levels. The most prevalent indicator of obesity-related restrictive lung disease is a decrease in expiratory reserve volume (ERV).
Examples of intrinsic restrictive lung diseases include idiopathic pulmonary fibrosis, pneumoconioses, and sarcoidosis. These conditions are characterized by damage to lung tissue, leading to reduced lung compliance and capacity. Specifically, the diffusing capacity of the lung for carbon monoxide (DLCO) is notably low in these diseases. This is due to the destruction of the diffusion surface within the lungs, impairing the ability to exchange gases effectively.
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