8. Cardiovascular changes, respiration & renal function

Question 1

as pregnancy advances, how is the fetal-placental unit’s increasing need for nutrition met?

Answer 1

via maternal vascular-neogenesis

Question 2

how is the maternal vascular-neogenesis accommodated by?

Answer 2

changes in function of the maternal baro- and volume receptors

Question 3

where else is there increased blood flow to?

Answer 3

growing breasts, kidneys and GI tract (increased metabolism)

Question 4

what increases during pregnancy? How is this achieved?

Answer 4

plasma volume and cardiac output (CO = HR x SV)

Through increase in stroke volume (rather than HR - don’t want palpitations)

Question 5

what falls during pregnancy?

Answer 5

peripheral vascular resistance

Question 6

why do diseases of the respiratory system become more serious during pregnancy?

Answer 6

due to increased oxygen requirement of gestation

Question 7

what changes in terms of respiration during pregnancy?

Answer 7

resp rate is nearly unchanged, but tidal volume and oxygen uptake increases significantly

Question 8

what is common in pregnancy? how is it interpreted?

Answer 8

an increased awareness of the desire to breath is common in pregnancy
may be interpreted as dyspnoea

Question 9

what is dyspnoea?

Answer 9

difficulty breathing

Question 10

what is the function of increased awareness of desire to breathe in pregnancy?

Answer 10

increase in tidal volume that lowers the pCO2

Question 11

what induces the respiratory effort and the reduction in pCO2?

Answer 11

progesterone acting directly on the respiratory centre (brain) and sensitising chemoreceptors to CO2 changes

Question 12

what happens to renal blood flow during pregnancy?

Answer 12

increase in renal blood flow

Question 13

why does renal blood flow increase during pregnancy?

Answer 13

raises glomerular filtration rate (GFR) to 160% of normal

Question 14

what happens as a result of GFR increasing to 160% of normal?

Answer 14

increased secretion of renin, aldosterone and angiotensin II

activation of RAAS

Question 15

why will there be an increased secretion of renin, aldosterone and angiotensin II?
(activation of RAAS)

Answer 15

compensate for the expected sodium (Na+) loss from GFR increasing to 160% of normal

Question 16

what else contributes to the maternal synthesis of calcitriol (DHCC, active vitamin D) in pregnancy?

Answer 16

the placenta

Question 17

from the increase in plasma volume (about 50% - circulating blood) and CO (4.5 to 6L/min), what changes in mother’s BP do these adjustments induce?

Answer 17

mean BP remains same, but increased SV raises systolic BP slightly, therefore stroke volume, flowing so rapidly into additional tissue, reduces diastolic BP slightly

Question 18

what changes to the heart does increase in plasma volume, CO, systolic BP and decrease in diastolic BP upon examination?

Answer 18

upward displacement, hypertrophy

flow murmurs are common

Question 19

how may mean arterial BP be affected by progesterone? what would the mother feel?

Answer 19

peripheral vasodilation - can cause hyPOtension
feeling heat, east to sweat, nasal congestion (dilated mucus flow)
(possible postural hypotension)

Question 20

how do you work out mean arterial BP?

Answer 20

total peripheral resistance x cardiac output
(TPR x CO = mean aBP)
takes into account systolic + diastolic (mean)

Question 21

how do you work out mean arterial BP from systolic and diastolic pressures?

Answer 21

(2 x diastolic BP + systolic BP) / 3

Question 22

what factors associate with venous distension and engorgement in late pregnancy?

Answer 22

SM relaxation - progesterone
mechanical pressure from uterus compressing IVC - may increase LOWER LIMB venous pressure (only when mother is recumbent - lying flat)
(lower limb: femoral artery from EIA, great saphenous vein, medial)
(possibly raised circulating BV, greater venous return)

Question 23

what are the 2 long-term sequelae that are attributed to the period of venous distension in late pregnancy?

Answer 23

varicose veins and haemorrhoids (GI tract)

Question 24

what mechanism will affect the expanding uterus on the maternal respiratory system?

Answer 24

diaphragm rises
intercostal angle widens (between ribs)
uterus exerting a mechanical limitation to inspiration

Question 25

after the gravid uterus rises form the pelvis, it rests upon the ureters compressing them above the pelvic brim, what possible effects might this have?

Answer 25

increase INTRAURETERAL tone (distended)
urethral dilatation
hydro-ureter (dilation of ureters)
hydronephrosis (swollen kidneys from urine buildup within)
(from blockage of urine flow to the bladder within pelvis)

Question 26

why might pregnancy cause increased urinary incontinence?

Answer 26

pressure on bladder from enlarged uterus

engagement of foetal head towards end of pregnancy

Question 27

why might progesterone dilating SM in nephrons of kidneys (collecting duct, GFR) increase UTI?

Answer 27

dilation slows excretion of urine, making UTI more common

Question 28

how does active form of vitamin D contribute to foetal growth?

Answer 28

it increases uptake of calcium from the maternal gut
increased availability of calcium to the foetus facilitates skeletal formation + growth
(PTH also increases in the 3rd trimester, enhancing calcium mobilisation from maternal bone and increasing availability to foetus)