Developmental Pathophysiology, Develop. Physiol., Dr. D. Penney
Table 4.18. Characteristics in large VSD with pulmonary vascular obstructive disease.
- Hypertrophy of the smooth muscle lining of the pulmonary arterioles produces increase in PVR; hence increase RV afterload progressively reduces L ---> R shunt, eventually reversing it to R --->L; mild cyanosis.
- Systolic murmur disappears and S2 becomes loud and narrowly split.
- Left heart size diminishes, leaving isolated RV enlargement.
- X-ray shows diminished peripheral lung vascularity.
- Pulmonary hypertension seen by catheterization, permitting calculation of blood flows and resistance.
- In the premature baby the muscularis of the pulmonary arterioles is not completely developed, so a patent ductus or VSD produces excessive pulmonary flow and pulmonary congestion.
- In the full term infant mature muscularis provides high Pulmonary Vascular Resistance at birth, limiting lung flow, but also obscuring murmurs due to septa defects. Regression of the muscularis at 3-8 weeks gives higher lung flow and reveals signs of L ---> R shunting for the first time.
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