Pda Part 3 Anatomy PhysiologyPresentation Transcript
PATENT DUCTUS ARTERIOSUS
Dr. Sarabon Tahura
Dhaka Shishu Hospital
Anatomical background & pathophysiology
The ductus arteriosus is a vascular structure that connects the main pulmonary artery near the origin of the left branch to the proximal descending aorta.
It is a normal and very essential fetal structure that becomes abnormal if it remains patent after the neonatal period.
In normal cardiovascular development -
The proximal portions of the sixth pair of embryonic aortic arches persist as the proximal branch pulmonary arteries.
The distal portion of the left sixth arch persists as the ductus arteriosus , connecting the left pulmonary artery with the left dorsal aorta.
This transformation completes by 8 weeks of fetal life.
Importance of DA during fetal life
Due to high resistance of fetal pulmonary circulation, only 5-10% of the right ventricular output of the fetal heart passes through the lungs.
Through DA most of the RV output passes to the descending aorta.
Thus the ductus arteriosus is necessary to divert blood flow from the high-resistance pulmonary vascular bed to the systemic circulation.
Factors for maintain Patency of duct In fetal life Low PaO 2
High PGE 2 & PGI 2 level
production by placenta & DA
in fetal lung]
Interaction with ductal Prostanoid receptors Relaxation of DA
Within the first few hours after birth Decreased circulating PGE2 &PGI2 levels due to elimination of placental source & increased metabolism in lung Abrupt increased arterial PaO2 Medial smooth muscle fibers in the ductus contract The inner muscle wall of the ductus arteriosus develops profound ischemic hypoxia Formation of vascular endothelial growth factor, transforming growth factor beta and other inflammatory mediators and growth factors Transform the ductus arteriosus into a non-contractile ligament How ductus close after birth Inhibite ductal smooth muscle voltage dependant K channel Influx of Ca
In normal newborns, the DA is substantially closed within 24-72 hours after birth.
completely sealed within 2-3 weeks.
Fetal Circulation After 8 Hours After 24-72 hrs
Failure of closure of DA IN PRETERM NEONATE PATENT DUCTUS ARTERIOSUS Poor PG metabolism by immature lung High sensitivity to prostaglandin (premature ductus) Reduced Ca sensitivity to O2 in ductal musculature
The absence of DA contraction in full-term neonates might be due to failed prostaglandin metabolism most likely caused by-
Increased pulmonary blood flow &
In Term neonate
The hemodynamic impact of
Patent Ductus Arteriosus
Structural Defects and Cardiac Circulation with PDA Where does the blood shunt to? Is the shunted blood oxygenated or deoxygenated? What happens to the blood flow in the aorta?
Due to pressure gradient between the aorta(110/60) and the pulmonary artery(30/10) Left-to-right shunting occur through the ductus arteriosus.
The magnitude of shunting depends on The flow resistance of the ductus arteriosus Pressure gradient between the aorta and the pulmonary artery
Which depends on -
The constricted diameter
The overall shape
The length of the
This pressure gradient is -
With systolic and diastolic
Depends largely on
pulmonary and systemic
vascular resistances and
Oxygenated blood passes from the aorta to the pulmonary artery Pulmonary Overcirculation Left heart volume overload Increased left atrial and left ventricular end-diastolic pressures The left ventricle compensates by increasing stroke volume Hypertrophy Effect of shunting
Effect of long standing Left-to-right shunting Progressive morphological changes in the pulmonary vasculature Arteriolar medial hypertrophy, intimal proliferation and fibrosis Obliteration of pulmonary arterioles and capillaries Progressive increase in pulmonary vascular resistance Pulmonary vascular resistance exceeds systemic vascular resistance Shunting reverses & becomes right-to-left [ Eisenmenger’s Syndrome ]