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Circulatory changes at birth (Congenital defects (Patent ductus arteriosus…
Circulatory changes at birth
Circulatory adaptations in utero
Lungs collapsed, oxygenated blood via umbilical vein, drains into caudal vena cava, foramen ovale open allowing oxygenated blood to pass from right to left atrium, liver largely bypassed due to ductus venosus
Blood supply to brain more oxygenated as ductus arteriousus after brachiocephalic trunk
Changes in circulation at birth
Umbilicus
Umbilical arteries contract
Umbilical veins contract
On rupture, arteries undergo elastic recoil to prevent haemorrhage
Umbilical artery becomes round ligament of bladd
Umbilical veins becomes round ligament of liver
Foramen ovale
First breath leads to large drop in resistance in pulmonary circulation
Reduced right ventricular afterload, so increased pulmonary blood flow
Increased venous return to left atrium = increased left atrial pressure
Closure of foramen ovale as septum primum pushed against septum secundum
Remnant of foramen ovale = fossa ovalis
(fibrosed)
Ductus arteriosus
Pressure in aorta increased
Pressure in pulmonary trunk decreases
Smooth muscle of ductus constrics, stopping flow
Becomes ligamentum arteriosum
Ductus venosus
Smooth muscle contracts
Diverts blood into hepatic circulation
Permanent closure in 2-3 weeks
Effects on blood pressure
Congenital defects
Aortic stenosis
Increased pressure in aorta -> increased afterload
Reduced emptying (increased ESVV)
Heart works harder, beat faster/harder -> hypertrophy -> reduced lumen of ventricle)
Pulmonic stenosis
Increased pressure in pulmonary artery -> increased afterload
Reduced CO
Works harder -> hypertrophy -> reduced lumen of ventricle
Patent ductus arteriosus
More blood to lung
Systemic circulation may be reduced
Returns to left atrium, increased preload. Preload too high, EDVV can no longer increase. High venous pressure -> high capillary pressure -> pulmonary edema
V.Rare
Sometimes causes vasoconstriction in lungs, increased resistance to flow could potentially have reversed flow from pulmonary artery to artery. Diluted blood (in O2)
Machinery murmor: Always murmors as pressure always higher in aorta so blood always moves into ductus
Ventricular septal defect
The greater the defect (the hole) the quieter the murmur. If small hole, fast jet loud murmur
Flow left to right ventricle
Atrial septum defect
Pressures in atrial relatively similar, so flow COULD be in either direction
Small = not much of a problem usually
Vascular ring anomaly
Abnormality in aortic arteries
Wrong aortic arch formed aorta, but ductus arteriosus still tried to join.
Entraps oesophagus, -> cannot swallow. Leads to mega-oesophagus