Physiological Changes in Pregnancy
Least likely physiological change in pregnancy (AIIMS Nov. 2011)
|A||increase in intra vascular volume|
|B||increase in cardiac output|
|C||increase in stroke volume|
|D||increase in peripheral vascular resistance|
Increase in peripheral vascular resistance
a. Uteroplacental blood flow increases progressively during pregnancy, with estimates ranging from 450 to 650 mL/min near term (Edman and associates, 1981; Kauppila and co-workers, 1980).
b. hypervolemia associated with normal pregnancy averages 40 to 45 percent above the nonpregnant blood volume after 32 to 34 weeks.Because of great plasma augmentation, hemoglobin concentration and hematocrit decrease slightly during pregnancy (see Appendix). As a result, whole blood viscosity decreases output is increased as early as the fifth week and reflects a reduced systemic vascular resistance and an increased heart rate.
c. Maternal cardiac output is augmented further by another almost 20 percent because of a greater stroke volume (15 percent).
d. Late pregnancy was associated with the expected increases in heart rate, stroke volume, and cardiac output.
e. Systemic vascular and pulmonary vascular resistance both decreased significantly, as did colloid osmotic pressure. Pulmonary capillary wedge pressure and central venous pressure did not change appreciably between late pregnancy and the puerperium. Thus, Although cardiac output is increased, left ventricular function as measured by stroke work index remains similar to the nonpregnant normal range. Put another way, normal pregnancy is not a continuous "high-output" state.