All are CVS changes in pregnancy except –
Correct Answer: Increase in peripheral resistance
Description: Ans. is 'a' i.e., Increase in peripheral resistance PregnancyThe major hemodynamic changes induced by pregnancy include an:Increase in cardiac outputBlood volume expansion due to Na+ and water retentionReduced systemic vascular resistanceReduced blood pressureThese changesBegin early in the pregnancyReach their peak during the second trimester and thenRemain relatively constant until deliveryThey contribute to optimal growth and development of the fetus and help to protect mothers from the risk of delivery such as hemorrhage.Changes in blood volumeExpansion of the plasma volume and increase in red cell mass :Begins as early as 4th week of pregnancyPeaks at 28-34 weeksThen plateausTotal body volume expansion is accompanied by retention of 900- 1000 meq of sodium and 6-8 litres of water, distributed among the fetus, amniotic fluid and extracellular and intracellular spaces.Red blood cell massRed blood cell mass begins to increase at 8-10 weeks of gestation and steadily rises in women taking iron supplements by 20-30% above the nonpregnant levels.PIasma volume increases 30-50% above the basal value whereas red cell mass increases only 20-30% above the basal value.A greater increase in intravascular volume compared to the red cell mass results in dilutional or physiological anemia of pregnancy.This is most manifested at 30-34 weeks of pregnancy when plasma volume peaks in relation to red cell volume. Cardiac outputMaternal and fetal metabolic requirements increases as pregnancy progresses:-A change in volume and distribution of cardiac output occurs during the pregnancy to meet this output.The cardiac output rises to 30-50% above baseline during normal pregnancy.The elevation in cardiac output occur due to three factors :-Increased preload due to increase in blood volumeDecreased in afterload due to decrease in peripheral vascular resistance.Increase in heart rate.Cardiac output increases in: Early pregnancy due to - | in stroke volume Late pregnancy due to - | in heart rateThe increase in cardiac output usually peaks at 20-24 weeks.Vascular resistance and blood pressureSystolic and diastolic blood pressure fall during pregnancy.The fall in B.P. in pregnancy is induced by reduction in systemic vascular resistance.The factors responsible for causing vasodilation and decreasing vascular resistance are :-Increased endothelial prostacyclinEnhanced nitric oxide production andReduced aortic stiffness.Uterine blood flowUterine arteries blood flow increases from 50-60 ml/hr to 450-750 ml at term.
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