Fetal Circulation and Changes at Birth PDF

Foetal Circulation and Changes at Birth Dr Panayiotis Avraamides MBBS Lond, BSc, FRCP Lond, FRCP Edin, FESC, FEACVI, FACC, FAHA, FSCAI, FHRS Clinical Professor of Cardiology  Objectiv es Discuss anatomy and physiology of fetal circulation Compare and co...

Foetal Circulation and Changes at Birth Dr Panayiotis Avraamides MBBS Lond, BSc, FRCP Lond, FRCP Edin, FESC, FEACVI, FACC, FAHA, FSCAI, FHRS Clinical Professor of Cardiology  Objectiv es Discuss anatomy and physiology of fetal circulation Compare and contrast fetal circulation to infant circulation Define specialized structures of fetal circulation Full Term Fetus Before Birth Umbilical vein carries Oxygenated blood  Anatomy and Physiology Fetus depends on placenta to meet O2 needs while organs continue formation Oxygenated blood flows from the placenta to the fetus via the umbilical vein After reaching fetus the blood flows through the inferior vena cava  Anatomy and Physiology Fetal Umbilical Circulation cord 2 umbilical arteries: return non- oxygenated blood, fetal waste, CO2 to placenta 1 umbilical vein: brings oxygenated blood and nutrients to the fetus FETAL CIRCULATION  PLACENTA  UMBILICAL VEIN  DUCTUS VENOSUS  INFERIOR VENA CAVA  RIGHT ATRIUM  FORAMEN OVALE  LEFT ATRIUM  LEFT VENTRICLE  ASCENDING AORTA  HEAD & UPPER BODY FIG.  Fetal Circulation Blood continues to travel from the umbilical vein to the Ductus Venosus Small amount of blood routed to growing liver Increased blood flow leads to large liver in newborns A/P = Ante Partum (before birth)  Fetal Circulation Blood continues to travel up the inf. vena cava Empties into the right atrium of the heart The blood then passes to the left atrium through the foramen ovale FETAL CIRCULATION - The Heart  Fetal Circulation Foramen ovale Small opening in the atrial septum of the heart Completely bypasses the non- functioning lungs Blood continues journey to the left ventricle blood is then pumped into the aorta Blood is circulated to the upper extremities  Fetal Circulation From the right atrium, blood goes to the right ventricle then to the pulmonary arteries Pulmonary arteries Small amount goes to the maturing lungs Rest of blood is shunted away from the lungs by the ductus arteriosus to the aorta FETAL CIRCULATION  SUPERIOR VENA CAVA  RIGHT ATRIUM  RIGHT VENTRICLE  PULMONARY TRUNK  DUCTUS ARTERIOSUS  DESCENDING AORTA  INT. ILIAC ARTERIES  UMBILICAL ARTERIES  PLACENTA  Fetal Circulation Blood travels back from the aorta to the two umbilical arteries to the placenta via the internal iliac arteries The placenta will re-supply the blood with oxygen  NB. Fetal circulation is a low-pressure system  Fetal Circulation Low pressure system Lungs are closed Most oxygenated blood flows between the atria of the heart through the foramen ovale This oxygen rich blood flows to the brain through the aortic arch via the left ventricle FETAL CIRCULATION- The Heart  Changes at birth- umbilical cord clamping At birth Clamping the cord shuts down low- pressure system Increased atmospheric pressure (plus increased systemic vascular resistance) causes lungs to inflate with air containing oxygen Lung now becomes a low- pressure vascular system (because the  Conversion of Fetal to Infant Circulation At birth Clamping the cord shuts down low- pressure system Increased atmospheric pressure (plus increased systemic vascular resistance) causes lungs to inflate with air containing oxygen Lung now becomes a low-pressure vascular system (because the pulmonary vessels - mainly small and medium diameter vessels - have increased diameter or “opened up” so offering little resistance to blood flow)  Overview of FirstConversion breath Lungs expand and fluid is expelled Decreased pulmonary vascular resistance Increased pressure in left atrium* Closure of foramen ovale * From increased venous return from lungs CHANGES IN PULMONARY & SYSTEMIC CIRCULATION at Birth PULMONARY SYSTEMIC  BLOOD FLOW  AORTIC PRESSURE  LEFT VENTRICULAR PRESSURE  LEFT ATRIAL PRESSURE  VASCULAR RESISTANCE  PULM. ARTERY PRESSURE  VASCULAR RESISTAN CE CLOSURE OF FORAMEN OVALE (CONNECTS Right TO Left ATRIUM) REASON: PRESSURE DIFFERENCE BETWEEN LEFT AND RIGHT ATRIUM REVERSES i.e. RIGHT: LOW v LEFT: HIGH) BLOOD PREVENTED FROM FLOWING LEFT TO RIGHT METHOD: VALVE OF OVAL FORAMEN APPOSED WITH SEPTUM SECUNDUM, CREATING FOSSA OVALIS *PATENT FORAMEN OVALE: (ASYMPTOMATIC) ATRIAL SEPTAL DEFECT FIG. Conversion: Fetal to Infant Circulation Increased pressure from increased blood flow in the left side of the heart causes closure of the foramen ovale More richly oxygenated blood passing by the ductus arteriosus causes it to constrict (plus release of bradykinin and reduction in prostaglandins) Functional closure of the foramen ovale and ductus arteriosus occurs soon after birth  CLOSURE OF DUCTUS ARTERIOSUS REASON: (CONNECTS PULMONARY A. TO AORTA) INCREASE IN SYSTEMIC PRESSURE INCREASED PRESSURE IN LEFT SIDE OF HEART AND AORTA DECREASE IN PULMONARY RESISTANCE DECREASED PRESSURE IN PULMONARY ARTERIES BLOOD PREVENTED FROM FLOWING FROM AORTA TO PULMONARY TRUNK METHOD: SMOOTH MUSCLE CONSTRICTION (INDUCED BY INCREASED OXYGEN TENSION, RELEASE OF BRADYKININ & REDUCTION IN CIRCULATING PROSTAGLANDINS) * PATENT DUCTUS ARTERIOSUS: (SYMPTOMATIC)  DECREASED OXYGEN SATURATION OF AORTIC BLOOD.  Overview of Conversion Abdominal Organs Umbilical cord is clamped Loss of placenta Closure of ductus venosus Blood is transported to liver + portal system  Overview of Conversion Thoracic organs Loss of placental circulation also leads to Increased systemic vascular resistance Pressure in right atrium decreased due to lowered pulmonary artery resistance Change from right to left shunting to left to right blood flow Increased O2 levels in pulmonary CLOSURE OF DUCTUS VENOSUS (CONNECTS UMBILICAL V. TO INFERIOR VENA CAVA) REASON: - FULL LIVER FUNCTION REQUIRED - PREVENTION OF ITS BYPASS BY BLOOD METHOD: - CONTRACTION OF SPHINCTER NEAR UMBILICAL VEIN - INCREASES PRESSURE IN PORTAL VEIN - CONVERSION of DUCTUS VENOSUS TO FIBROUS LIGAMENT * PORTOSYSTEMIC SHUNT: (SYMPTOMATIC) - FAILURE TO CLOSE - BLOOD CONTINUES TO BYPASS THE LIVER FIG.  Conversion (cont) What happens to these special structures after birth? Umbilical arteries atrophy Umbilical vein becomes part of the fibrous support ligament for the liver The foramen ovale, ductus arteriosus, ductus venosus atrophy and become fibrous ligaments KEY FUNCTIONAL CHANGES AFTER BIRTH 5 4 2 1 3 1 & 2 – UMBILICAL CORD CLAMPED (CLOSURE OF UMBILICAL ARTERIES AND VEIN) 3 – FORAMEN OVALE CLOSED 4 – DUCTUS ARTERIOSUS CLOSED 5 – DUCTUS VENOSUS CLOSED FET INFA AL NT CIR CIRC. C.  Fetal v Infant Circulation Fetus Infant Low pressure High pressure system system Right to left Left to right blood shunting flow Lungs non- Lungs functional functional Decreased Increased pulmonary pulmonary resistance resistance Increased Decreased systemic  RESULT OF PRESSURE CHANGES AT BIRTH UMBILICAL CORD CLAMPED (Closure of umbilical arteries and vein ) FORAMEN OVALE CLOSED DUCTUS ARTERIOSUS CLOSED DUCTUS VENOSUS CLOSED  STRUCTURAL CHANGES (FOETAL: ADULT) UMBILICAL ARTERIES: MEDIAL UMBILICAL LIGAMENTS SUPERIOR VESICULAR ARTERIES UMBILICAL VEIN: LIGAMENTUM TERES HEPATIS DUCTUS VENOSUM: LIGAMENTUM VENOSUM FORAMEN OVALE: FOSSA OVALIS  Summa ry Reviewed anatomy and physiology of fetal circulation Discussed conversion from fetal to infant circulation Compared fetal to infant circulation Determined outcome of special features associated with fetal circulation after birth  FETAL CIRCULATION and CHANGES at BIRTH Thank You for your Attention !