6.Physiologic changes in pregnancy (cardiovasular-, respiratory system) Flashcards
what occurs to the cardiac output during pregnancy?
increases by 30%-50% (mostly during the 1st semester)
first due to increased plasma volume+ enhanced RAAS activity–> ↑ stroke volume
then end of 3rd trimester: ↑ HR and ↓ SV
What occurs to the systemic vascular resistance during pregnancy?
decreases.
resulting in fall in arterial blood pressure
due to elevated progesterone–> smooth muscle relaxation
what does the uteroplacental circulation cause during pregnancy?
forms an arterio-venous shunt, reducing the peripheral resistance (↓ SVR)
What occurs to the systolic BP during pregnancy?
decreases by 5-10 mmHg, whereas the diastolic BP decreases by 10-15 mmHg with lowest values recorded at around week 24.
what occurs to the BP during 24 weeks of pregnancy to term?
blood pressure slowly returns to pre-pregnancy levels but should never exceed them
why does pregnancy induce a state of dilutional anemia?
Greater increase of intravascular volume (by 40-50%) compared to increased RBC mass (by 20-30%); most apparent at 30-34 weeks gestation.
↓ Hgb
when does blood volume return to pre-pregnancy values?
by 8 weeks postpartum.
Hgb begins to increase from the 3rd postpartum day.
*assuming normal renal function
what is supine hypotensive syndrome?
IVC compression by the gravid uterus;
may result in impaired venous return, decreased pulse pressure with compensatory tachycardia.
*If acutely hypotensive, turn the patient on the left side, allowing gravity to relieve the compression
what cardiac normal and common finding is seen during pregnancy?
systolic ejection murmur
as a result of high flow state
what occurs in Peripartum dilated cardiomyopathy?
ventricular dilatation and decreased contractility
when does Peripartum dilated cardiomyopathy develop?
in < 0.1% of pregnancies during the last month of pregnancy to 5 months postpartum.
Risk is associated with increased maternal age and multiparity.
what occurs to the tidal volume and respiratory rate during pregnancy?
TV increases by 30-40%, with no change of respiratory rate.
Thus, minute ventilation increases as well by 30-40% → arterial O2 (PaO2) increases, arterial CO2 (PaCO2) decreases
what occurs to the Total lung capacity (TLC) during pregnancy?
decreases by 5% due to the elevation of the diaphragm by the gravid uterus
how is O2 delivery to the fetus and CO2 removal from the fetus facilitated during pregnancy?
decrease in PaCO2 from 40mmHg (pre-pregnancy) to 30mmHg (~20 weeks of gestation) mimics a respiratory alkalosis state –> increased gradient between mother to fetus.
why is shortness of breath a common complaint during the late stages of pregnancy?
Caused by the growing uterus which restricts normal lung expansion; commonly seen with macrosomic fetuses, multiple gestations, polyhydramnios, or in patients with preexisting pulmonary disease
