Pulmonary Vascular Disease:
Hypertrophy of the smooth muscle lining the pulmonary arterioles produces increased pulmonary vascular resistance (Table 4.18). This may be viewed as a mechanism designed to protect the pulmonary capillaries. As stated above, after about 24 months this process becomes irreversible.
This process progressively increases right ventricular afterload, and eventually reverses shunt flow through the VSD, resulting in cyanosis. The systolic murmur then disappears and S2 becomes loud and narrowly split. Left heart size diminishes, leaving isolated right ventricle enlargement. The peripheral lung vascularity is decreased as seen by X-ray.
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