6. physiologic changes to cardiovascular and respiratory systems in pregnancy

Question 1

What are the first observable changes to occur in pregnancy

Answer 1

Breast enlargement and tenderness

Morning sickness until the 12th week

Frequent urination

Changes in food desires, coffee, smoke aversions.

Question 2

Changes to the blood

Answer 2

Increased Na and Water retention

Increased total body water by about 6-8 Liters

Blood volume increases by 30-50% by the second trimester.

Increased total RBC volume and total hemoglobin, but with Dilutional anemia and mild thrombocytopenia with mild leukocytosis

• from 12-16 g/L normal down to 10-14 g/L
• Hct from 36-46% down to 32-39%
• Leukocytes increased up to a range of 10,000-12,000/uL, up from 4.5-11K.
• platelets drop to around 150,000

Fibrinogen increases by about 50% from normal levels
Other clotting factors also increase

Total serum protein decreases due to hypoalbuminemia. Other proteins increase.

Question 3

Changes to the heart and vessels

Answer 3

• Gradual increase in Cardiac Output up to 20% by the 10th week.
• Further increased by 10-20% by the 26th week.
• Due to increased stroke volume.
• In multiple gestations CO increases farther.

Heart rate slowly increases by about 20%

Blood pressure slowly drops by about 10% until about 30 weeks, then moves back to normal. It should NOT increase beyond normal.
-Drop is due to progesterone which decreases systemic vascular resistance.

The heart physically rotates anterior, upwards, and to the left.

The heart appears enlarged on imaging due to mild hypertrophy.

Soft systolic murmurs near the apex are commonly heard.

Extrasystolic beats are common.

Blood flow to all organs increases, but the largest increases are to the kidneys, skin, and uterus.

Question 4

Changes to the respiratory system

Answer 4

Steady increases in Tidal Volume and Alveolar Ventilation up to about +40%

Minor increase in respiratory rate by 10%

The Functional Residulal Capacity decreases, due to diaphragm elevation by about 4cm.
The ribs also flare outwards by about 2 cm.

Respiratory rate and vital capacity remain unchanged

Pregnancy becomes a state of compensated respiratory alkalosis, CO drops to about 27-32 mmHg, compensated by decreased bicarbonate levels.

• Increased urinary pH increases risk for UTIs.
• Low CO2 levels cause leg pain at night.

About a 20% increase in total oxygen consumption.