Table 3.15 - Perinatal Changes in the Circulation.

Loss of low resistance placental circulation.
Decrease pulmonary vascular resistance in response to rising PO₂.
Rising systemic vascular resistance and pressure.
Transformation of heart from two pumps in parallel to a series arrangement.
Closure of umbilical vessels, ductus venosus, ductus arteriosus and foramen ovale.
Gradual decrease in thickness of RV wall relative to LV, due to more rapid growth of the latter.
Gradual changeover from fetal type to adult type hemoglobin (Hb_F to Hb_A).
Increase in arterial PO₂ & % Hb saturation.
Hemoconcentration if cord is clamped late
Gradual decrease in cardiac output & O₂ consumption on a per g. body wt. basis.
Loss of O₂ carrying capacity (Hb) after birth, "postnatal anemia".
Decrease in ratio of heart weight to body weight (greater in some animals than in others).
Decrease in heart rate to 60 - 70 bpm.

Return to Page 18