Question
A 27-year-old woman comes to the physician because of a 1-month history of progressive shortness of breath. She can no longer walk one block without stopping to catch her breath. Her last menstrual period was 3 months ago. Menarche occurred at the age of 12 years, and menses had occurred at regular 28-day intervals. Cardiac examination shows a grade 3/6, rumbling diastolic murmur at the apex. Laboratory studies show an elevated ß-hCG concentration. Which of the following is the most likely explanation for this patient’s worsening dyspnea?
| A. |
Increased peripheral vascular resistance
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| B. |
Decreased right ventricular preload
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| C. |
Decreased minute ventilation
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| D. |
Increased intravascular volume
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Show Answer
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Correct Answer � D
Explanation
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Answer D) Increased intravascular volume
This patient’s cardiac examination shows mitral stenosis. Her amenorrhea and an elevated ß-hCG also indicate pregnancy, which can exacerbate underlying heart valve disorders.
Increased intravascular volume
During pregnancy, the plasma volume increases by 40–50%. This increase leads to greater cardiac output and can cause a harmless physiological systolic murmur. However, the increased blood volume can also exacerbate pre-existing heart valve disease. In the case of mitral stenosis, blood backs up before the mitral valve and increases pressure within the pulmonary circulation, which is the most likely explanation for this patient’s worsening dyspnea.
In contrast to plasma volume, RBC volume only increases by 20–30% during pregnancy. This subsequently leads to dilutional anemia and decreased viscosity.
Increased peripheral vascular resistance
Increased peripheral vascular resistance is not observed during pregnancy. The production of the hormones relaxin and progesterone leads to decreased vascular resistance and vasodilatation in pregnant women.
Decreased right ventricular preload
Decreased right ventricular preload can be observed during the third trimester of pregnancy. The enlarged uterus can compress the vena cava and subsequently decrease backflow into the right atrium when the mother is lying on her back. Because this patient is still within the first trimester of pregnancy, it is unlikely that her worsening dyspnea is due to compression of the vena cava by the uterus.
Decreased minute ventilation
Decreased minute ventilation is not observed during pregnancy. Instead, the diaphragm is displaced upwards, which leads to decreased total lung capacity and decreased functional residual volume. However, the tidal volume increases by about 40%, resulting in increased minute ventilation, which compensates for the increased oxygen consumption during pregnancy.
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