3. Physiology
        3.8. Maternal and foetal
3.8.1. Changes to CVS at birth

Changes to CVS that occurs at birth

Step 1 - Umbilical cord clamped

Loss of umbilical circulation

--> Increase in systemic vascular resistance (SVR)

Step 2 - First breath

First breath causes

--> Both leads to decrease in pulmonary vascular resistance (PVR)
* Reduced to about 1/10th

Step 3 - Reversal in atrial pressure gradient

Increased SVR and venous return to LA

--> Increase in LA pressure

Decreased PVR and venous return to RA

--> Decrease in RA pressure

Therefore,

Pressure in LA>RA

--> Foramen ovale closes

Step 4 - Closure of other shunts

Closure of ductus arteriosus
Closure of ductus venosus

 

Summary

  1. Loss of umbilical circulation
  2. Large increase in pulmonary circulation
  3. Closure of forman ovale
  4. Closure of ductus arteriosus
  5. Closure of ductus venosus


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