Cardiovascular Adaptations at Birth

Question 1

What supplies the Foetus with Oxygen-rich blood?

How does the Umbilical vein enter the Hepatic circulation?

What is the difference in composition between HbF and HbA?

How does 2,3 Bisphosphoglycerate (2,3 BPG) promote O2 release?

How does 2,3 BPG bind to HbF compared to HbA?
→ What’s the reason for this?

Answer 1

• Umbilical VEIN
• • 50-60% of its blood bypasses Liver via the DUCTUS VENOSUS and enters the IVC
  • Remainder goes into the HPV
• • HbF comprises 2α and 2γ chains
  • HbA comprises 2α and 2β chains
• Has a higher affinity for deoxygenated Hb than oxygenated Hb = Promote O2 release
• Binds less easily to HbF than HbA
  → HbF less affected by the Right Bohr shift effects of 2,3BPG

Question 2

What structures form in the Foetus for the blood to bypass Pulmonary circulation?

How is the Ductus Arteriosus kept open?

What properties of the Pulmonary vessels keep blood away from the foetal lungs?
→ Why does it do this?

Answer 2

• • Foramen Ovale (Right to Left Atrium)
  • Ductus Arteriosus (Pulmonary artery to Aorta)
• BY LOW O2 TENSION
• High Pulmonary Vascular Resistance (PVR), Large
  muscle mass, and Resting tone (Constriction)
  → Lungs are undeveloped

Question 3

SHUNT CLOSURE AT BIRTH:
What’s the reason for clamping down the Umbilical cord?

What occurs when that First Breath is taken?

How does this increase in pulmonary blood flow cause the closure of the Foramen Ovale?

How does this increase in pulmonary blood flow cause the closure of the Ductus Arteriosus?

Answer 3

• To stop Placental circulation, dropping flow in Ductus Venosus
• Lung expansion = Activation of Pulmonary stretch receptors, INCREASED O2 TENSION, and a huge increase in Blood flow (8-10x)
• Fall in PVR = Massive rise in venous return to Left atrium = RA and LA pressure become equal = Flap of Foramen Ovale pushed against Atrial septum
• Increased O2 Tension

Question 4

ABNORMAL CIRCULATION:
What problems can occur with the transition from foetal to adult circulation?

What about the Pulmonary arteries make them susceptible to problems?
→ What does this lead to?

Patent Ductus Arteriosus (PDA):
In what conditions does it commonly occur?

What occurs here?

What are the signs and symptoms?

How is it treated?
→ What do these drugs do? Why does it do this?

Answer 4

• Transition may not be permanent (Reversible)
• Very reactive and CONSTRICT in response to Hypoxia, Hypercapnia, Acidosis, and Cold
  → RISE IN PVR = RIGHT TO LEFT SHUNTING MAINTAINED

• Premature babies, Down syndrome, Rubella, Congenital Heart disease
• Aorta shunts blood into Pulmonary circulation (Left to Right shunt)
• Continuous machinery murmur (Asymptomatic), Fast breathing with increased work, Poor feeding and growth, Tachycardia with bounding pulse
• Indomethacin/Ibuprofen (NSAIDs) and Surgery
  → Block Prostaglandins, which are responsible for shunt not closing

Question 5

THERMOREGULATION:
What are Newborns more at risk of? Why?

Why do Newborns lose heat so easily?

How do Babies lose heat?

Why is Brown Fat in Newborns so important?

What does Hypothermia increase the risk of?

What is Thermal Stress?

Answer 5

• HEAT LOSS due to having a HIGH Surface area : Body weight ratio
• Less Subcutaneous fat = Less insulation, and a Reduced ability to generate heat
• Conduction, Convection, Lack of fat, Evaporation, Radiation
• Carries out Non-shivering thermogenesis, is Highly vascular, has Sympathetic innervation and ↑Mitochondria = Doubled heat production
• Death
• Energy needed to maintain normal body temperature

Question 6

FLUID BALANCE:
How is Fluid lost?

How does Fluid loss change with gestational age?

What are the Nephrons like at birth?

Answer 6

• Stool, Urine, Respiratory tract and Skin
• Reduces
• Complete in number, but FUNCTIONALLY IMMATURE
  o ↓GFR, Limited concentrating ability