Fetal and Neonatal Circulation Flashcards
1
Q
four shunts
A
- placenta
- ductus venosus
- foramen ovale
- ductus arteriosus
2
Q
fetal blood flow
A
- oxygenated blood returning from the placenta via the umbilical vein passes through the ductus venosus, bypassing the liver, then passes into the inferior vena cava
- about 40% of the inferior vena cava flow passes through the foramen ovale into the left atrium
- the rest of the flow passes into the right atrium
- blood also enters the right atrium from the superior vena cava and is directed through the tricuspid valve into the right ventricle
- the blood from the superior vena cava is deoxygenated blood from the forequarters
- about 3/4 or more of the blood from the right ventricle is pumped through the ductus arteriosus into the descending aorta, bypassing the lung
- right and left ventricles both pump blood into the aorta, parallel, not series
- sum of both ventricles is the combined cardiac output
- blood in the descending aorta passes primarily through the hypogastric arteries into the two umbilical arteries and into the placenta
- small portion of the blood flows to the hindquarters and the mesentery
3
Q
cardiopulmonary adjustments at/after birth
A
- loss of placental circulation requires the newborn to breath on its own
- dramatic increase in pulmonary blood flow
- closure of the ductus venosus, foramen ovale, and ductus arteriosus
4
Q
first breath
A
- triggered by mild hypoxia, hypercapnia, tactile stimuli, and cold skin
- first inspiratory effort requires a transpulmonary pressure of 60 cm water to increase lung volume by 40 mk
- breathing becomes easier once the alveoli are open and the type II pneumocytes deliver surfactant to the air-water interface
- respiratory distress syndrome is caused by deficiency of surfactant and often found in premature births
5
Q
fetal to neonatal circulation
A
- accompanied by a dramatic drop in pulmonary vascular resistance, increase in blood flow
- also comes with a decrease in mean pulmonary arterial pressure
6
Q
placenta
A
- four essential functions of adult organs
- the lungs: gas exchange
- GI- nutrition
- liver- nutrition and waste removal
- kidneys-fluid and electrolyte balance, waste removal
- insufficiency causes type II IUGR
- any insult that interferes with gas exchange may lead to fetal asphyxia
- heartbeat one month after fert, increases from 65-140
- at one month all organs formed and details established over 2-3 months
- nervous, kidneys, liver need more than 9 mo for full development
7
Q
intervillous space
A
- contains a pool of maternal blood for gas exchange
- covered with a thin layer of syncytiotrophoblast
- under that are cytotrophoblasts, mesenchyme, and fetal blood vessels
- maternal blood is trapped in the intervillous space bewtween the endometrium on the maternal side and the villi on the fetal side
- spiral arteries from the mother empty directly into the intervillous space, which is drained by maternal veins
- the villi look like a thick forest of trees arising from the chorionic plate (soil)
8
Q
maternal and fetal oxygen levels
A
- uterine artery 100 mm, 97.5 % sat, 40 mm co2
- intervillous space 30-35 mm, 57-67%, 43 mm co2
- uterine vein 30 mm, 57 %,
- umbilical arteries 23 mm, 60%, 48 mm co2
- umbilical vein 30 mm, 85%
- higher Co2, hb concentration 50% or higher, CO2 to mom
9
Q
closure of the placental circulation
A
- increases the pressure in the aorta
- placenta receives 50% of the CO2 in the fetal circulation
- closure causes peripheral resistance to double causing an increase in aortic and left ventricle pressure
- increase in Po2, umbilicus contracts
- decrease prostaglandins, close umbilical cord
10
Q
closure of the foramen ovale
A
- caused by reversal of right/left atrial pressure
- increased pulmonary circulation causes increased venous return to the left atrium
- there is a decrease in the right atrial pressure
- the reversal of pressure closes the foramen ovale’s valve
- permanent seal forms in a few months or years- fossa ovalis
11
Q
closure of the ductus venosus
A
- forces portal blood to perfuse liver
- in the fetus, large portion of blood in the portal vein enters the ductus venosus bypassing the liver
- within 3 hours after birth, constriction of the vascular smooth muscle within the ductus venosus completely occlude this shunt, becomes ligamentum venosum
- mech-increased PO2 and reduced prostaglandins
- failure of closure: portosystemic shunt
12
Q
closure of the ductus ateriosus
A
- mediated by changes in the Po2 and prostaglandins
- within a few hrs, the ductus arteriosus closes because of constriction of the wall
- thrombosis obliterate the lumen in a month
- becomes ligamentum arteriosum
- mechaniscm-increase Po2 and decreased circulating prostaglandins cause constriction
- bradykinin from lung involved
- failure of closure- patent ductus arteriosus, leads to pulm hypertension and possible CHF and cardiac arrythmias
13
Q
neonatal circulation summary
A
- characterized by a reversed flow through the ductus arteriosus to the lung, enhances O2 uptake by the blood as it passes through the lung
- pulm circulation absorbs majority of fluid that fills the alveoli during labor and birth
1. loss of blood flow through the placenta produces a doubling of the systemic vascular resistance-increase in aortic pressure as well as increased pressures in the left ventricle and atrium
2. as a result of resp activity the pulm vascular resistance decreases- lung expansion, no longer compressed; higher o2 levels produce pulm arteriolar vasodilation, as does the release of prostaglandins
3. these lung effects reduce the pulm arterial pressure and right vent and atrium pressures
4. following lung inflation, a large amt of blood is now directed to the left atrium from the lungs, increases left atrial pressure
5. increase in left atrial and dec in right atrial pressure close foramen ovale and flow from IVC now only into R atrium
6. within 1-3 hours the muscular wall of th ductus venosus contracts and closes this avenue of flow
7. with increased aortic pressure and decreased pulm arterial pressure the blood flow through the ductus arteriosus is reversed. increases flow to lung and o2 uptake
8. after a few hours of increased plasma o2 and decreased prostaglandins, the ductus arteriosus constricts markedly
9. closure of ductus arteriosus means adult circulation
14
Q
patent ductus arteriosus
A
- 1/ 2000 newborns
- murmur with small openings
- with larger openings:
- feeding is poor, HR and sweating are elevated and weight is low
- endocarditis risk is life threatening-bacteria like valves
- need surgical intervention
15
Q
coarctation of aorta
A
- smooth muscle of ductus arteriosus that invaded the descending aorta constricts following birth
- associated with high BP in regions perfused by the aorta above constriction
