8. Cardiovascular changes, respiration & renal function Flashcards
as pregnancy advances, how is the fetal-placental unit’s increasing need for nutrition met?
via maternal vascular-neogenesis
how is the maternal vascular-neogenesis accommodated by?
changes in function of the maternal baro- and volume receptors
where else is there increased blood flow to?
growing breasts, kidneys and GI tract (increased metabolism)
what increases during pregnancy? How is this achieved?
plasma volume and cardiac output (CO = HR x SV)
Through increase in stroke volume (rather than HR - don’t want palpitations)
what falls during pregnancy?
peripheral vascular resistance
why do diseases of the respiratory system become more serious during pregnancy?
due to increased oxygen requirement of gestation
what changes in terms of respiration during pregnancy?
resp rate is nearly unchanged, but tidal volume and oxygen uptake increases significantly
what is common in pregnancy? how is it interpreted?
an increased awareness of the desire to breath is common in pregnancy
may be interpreted as dyspnoea
what is dyspnoea?
difficulty breathing
what is the function of increased awareness of desire to breathe in pregnancy?
increase in tidal volume that lowers the pCO2
what induces the respiratory effort and the reduction in pCO2?
progesterone acting directly on the respiratory centre (brain) and sensitising chemoreceptors to CO2 changes
what happens to renal blood flow during pregnancy?
increase in renal blood flow
why does renal blood flow increase during pregnancy?
raises glomerular filtration rate (GFR) to 160% of normal
what happens as a result of GFR increasing to 160% of normal?
increased secretion of renin, aldosterone and angiotensin II
activation of RAAS
why will there be an increased secretion of renin, aldosterone and angiotensin II?
(activation of RAAS)
compensate for the expected sodium (Na+) loss from GFR increasing to 160% of normal
what else contributes to the maternal synthesis of calcitriol (DHCC, active vitamin D) in pregnancy?
the placenta
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?
mean BP remains same, but increased SV raises systolic BP slightly, therefore stroke volume, flowing so rapidly into additional tissue, reduces diastolic BP slightly
what changes to the heart does increase in plasma volume, CO, systolic BP and decrease in diastolic BP upon examination?
upward displacement, hypertrophy
flow murmurs are common
how may mean arterial BP be affected by progesterone? what would the mother feel?
peripheral vasodilation - can cause hyPOtension
feeling heat, east to sweat, nasal congestion (dilated mucus flow)
(possible postural hypotension)
how do you work out mean arterial BP?
total peripheral resistance x cardiac output
(TPR x CO = mean aBP)
takes into account systolic + diastolic (mean)
how do you work out mean arterial BP from systolic and diastolic pressures?
(2 x diastolic BP + systolic BP) / 3
what factors associate with venous distension and engorgement in late pregnancy?
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)
what are the 2 long-term sequelae that are attributed to the period of venous distension in late pregnancy?
varicose veins and haemorrhoids (GI tract)
what mechanism will affect the expanding uterus on the maternal respiratory system?
diaphragm rises
intercostal angle widens (between ribs)
uterus exerting a mechanical limitation to inspiration
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?
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)
why might pregnancy cause increased urinary incontinence?
pressure on bladder from enlarged uterus
engagement of foetal head towards end of pregnancy
why might progesterone dilating SM in nephrons of kidneys (collecting duct, GFR) increase UTI?
dilation slows excretion of urine, making UTI more common
how does active form of vitamin D contribute to foetal growth?
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)
