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BIOL 1840U
Peter Cheung

Outline of Lecture 61 (06-09 A; Gurewitsch) Maternal Physiologic Adaptations to Pregnancy I. Respiratory System A) Mechanical changes Thorax enlarges and diaphragm elevates ⇒↓TLC, RV, FRC Tidal volume increases at expense of ERV, but constant respiratory rate Small airway closure occurs earlier Increased minute ventilation decreases CO2 levels - Important for CO2 exchange with fetus - Maternal compensation is increased HCO3 renal excretion B) Oxygen uptake Placenta acts as a concurrent exchange system, ∴umbilical vein pO2 ≤ uterine vein pO2 In reality, umbilical pO2 is always less than uterine pO2 Many factors most affect uterine pO2 (pH, blood flow, O2 saturation and capacity and uterine consumption rate) Fetal oxygenation can be enhanced (e.g. in maternal hypoxia) by - Administering IV fluids (↑blood volume, ↑CO, ↑blood flow) - Adminstering 100% O2 (↑Hgb saturation) - Roll mom to left side (decompress IVC, ↑heart preload, ↑CO) II. Circulatory System A) Physiologic anemia of pregnancy - Plasma volume and red blood cell mass both increase, but plasma volume more so, ∴ hematocrit drops B) Cardiac output increases - Result of increased HR and increased SV - CO is less in supine position due to fetus compression of IVC - Increased output is directed mostly to uterus, skin, and breast C) Other - Peripheral vascular resistance drops (progesterone and skin vasodilation for heat dissipation) - Systolic and diastolic blood pressure drop - Gradient between oncotic P and pulm. capillary wedge P is decreased - Increased risk for pulmonary edema - Increased lower extremity venous pressure due to fetal pressure - Edema at ankles D) Labor - Further increase in CO and arterial BP during labor due to pain/anxiety - Immediately post-partum, further 10-20% ↑CO b/c of fetal pressure release - Risk of excessive blood loss III. Urinary Syst
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