Mod IV: Fetal Circulation Flashcards
Pediatric Physiology - Terminology
0-1 mos. old
Neonate
Pediatric Physiology - Terminology
1 mos-12 mos. old
Infant
Pediatric Physiology - Terminology
1-3 years of age
Toddler
Pediatric Physiology - Terminology
4-14 years of age
Smaller Children
Pediatric Physiology - Terminology
A Preterm is defined as “a viable infant born after xxth week, but before yyth week of gestation”?
20th week
37th week
Pediatric Physiology - Terminology
weeks after conception
Postconceptual age
Pediatric Physiology - Terminology
Why is this important to consider Postconceptual age?
For example: a Preterm born 10 weeks ago at 26 weeks gestation is technically how old?
10 weeks old
Pediatric Physiology - Terminology
What’s the Postconceptual age (PCA) of a Preterm born 10 weeks ago at 26 weeks gestation?
36 weeks PCA
Although technically, that infant in 2 mo old
However, their Postconceptual age is only 36 weeks
This should be taken into account when thinking about their plan of care
Pediatric Physiology - Terminology
For mutiple births, how much time could be substracted from the PCA to adequately assess developmental age?
1 week
Pediatric Physiology - Terminology
Conception to 8 weeks:
Embryo
Pediatric Physiology - Terminology
8 weeks after conception to birth:
Featus
Pediatric Physiology - Fetal Circulation
T/F: Fetal lungs are functional
False
Fetal lungs are nonfunctional
Fetal lungs are resistant to blood flow
Pediatric Physiology - Fetal Circulation
Why are fetal lungs resistant to blood flow?
Fluid filled
Pediatric Physiology - Fetal Circulation
How do fetal lungs ensure nourishment for growth?
Receive enough blood flow to ensure nourishment for growth
Pediatric Physiology - Fetal Circulation
What does the fetus depend on for oxygenation and ventilation?
Placental circulation
Pediatric Physiology - Fetal Circulation
The fetal circulation is marquedly different from the adult circulation because. Fetal gas exchange does not occur in the lungs but where?
In the placenta
The placenta must therefore recieve de-oxygenated blood for the fetal systemic organs and return its oxygen rich venous drainage in to the fetus arterial systemic circulation
Pediatric Physiology - Fetal Circulation
In addition, the fetal cardiovascular circulation is designed in such a way that the most highly oxygenated blood is delivered to which fetal organs?
Myocardium and the Brain
Pediatric Physiology - Fetal Circulation
Why is fetal circulation termed “shunt-dependent circulation”?
Circulatory adaptions are achieved in the fetus by both
Preferential streaming of oxygenated blood
Presence of intra and extra cardiac shunts
Pediatric Physiology - Fetal Circulation
Name three structures that are exclusive to fetal circulation:
Ductus Venosus
Foramen Ovale
Ductus Arterious
Pediatric Physiology - Fetal Circulation
Name five important adaptions of fetal circulation:
Umbilical vein (1)
Ductus venosus
Foramen ovale
Ductus arteriosus
Umbilical arteries (2)
Pediatric Physiology - Fetal Circulation
T/F: Clamping of the umbilical cord after delivery is painful to the infant
False
Clamping of the umbilical cord after delivery is not painful because the umbilical cord does not contain nerves
Pediatric Physiology - Fetal Circulation
Temporary organ that connects the developing fetus via the umbilical cord to the uterine wall to allow nutrient uptake, thermo-regulation, waste elimination, and gas exchange via the mother’s blood supply; to fight against internal infection; and to produce hormones which support pregnancy. This organ is also known as:
Placenta
Pediatric Physiology - Fetal Circulation
Vessel that carries oxygenated blood from placenta to fetus
Umbilical vein
(Considered the first adaptation)
Pediatric Physiology - Fetal Circulation
Blood from the umbilical vein can either enter the fetal liver and take a while going throught the liver to reach the fetal IVC or it can bypass the the liver and enter the IVC directly via a second fetal adaptation called:
Ductus venosus
(connects veins)
This is a shortcut from the umbilical vein to the IVC
Pass the Ductus venosus, highly oxygenated blood from the umbilical vein meets up with deoxygenated blood from the IVC and that blood dumps in to the RA
Pediatric Physiology - Fetal Circulation
Blood in the fetal RA is coming from where? How is its oxygen content?
Mixed umbilical and IVC blood
Blood draining from the SVC
Blood in the RA is even more mixed at this point
Pediatric Physiology - Fetal Circulation
Where could blood flow after the RA?
From the fetal RA, blood can flow
Down the RV. Some of the blood will do this. Blood down this path will get squeezed into the Pulmonary trunk, and to each PA
Remember, as that blood approaches the lungs, we need to remember what’s happening inside the lungs
Pediatric Physiology - Fetal Circulation
Alevoli in the fetal lungs are filled with:
Fluid
And going pass those fluid-filled alveoli are little blood vessels (arterioles)
Fluid filled alveoli lack oxygen
Pediatric Physiology - Fetal Circulation
The process whereby, fluid-filled alveoli lacking oxygen help constrict pulmonary arterioles is called”
Hypoxic pulmonary vasoconstriction (HPV)
Arterioles have smooth muscles
The lack of oxygen in the surrounding alveoli will cause the arterioles smooth muscles to constrict
This increases the resistance of the arterioles
This phenomenom involes millions of alveoli and result in increase resistance in the entire lung
Pediatric Physiology - Fetal Circulation
D/t increaseed lung resistance caused by hypoxic pulmonary vasoconstriction, how are PA pressures? What’s the overall effect on fetal blood flow via this route?
The pressure in the PA will be very high
So, for it to be forward flow of blood via this route, there needs to be a lot of flow in the RV, and therefore the RA
Pediatric Physiology - Fetal Circulation
As a results, pressures on the right heart become quite elvated, to the point where pressures in the RA become higher that pressures in the LA. Consequently, some blood will flow from the RA to the LA across a passage known as
Foramen Ovale
So, from the RA, some blood will go down the RV, and some blood will go across to the LA via the Foramen ovale
Pediatric Physiology - Fetal Circulation
You actually don’t have that much blood coming back through the pulmonary veins, why is that?
b/c of foramen ovale allows high pressures in the RA to go across the LA
This is quite useful b/c as you have blood going across to the LA, you actually don’t have that much blood coming back through the pulmonary veins
In addition it’s hard to get blood flowing through the lungs, d/t the increased resistance there
Still, a litle bit of blood will come through the pulmonary veins, and you have some blood coming from the RA into the LA via the foramen ovale
Pediatric Physiology - Fetal Circulation
Where does blood from the LA flows next?
To the LV where it gets squeezed into the aorta, and
the aorta distributes blood througout the rest of the body
Pediatric Physiology - Fetal Circulation
Going back to the right side of the heart, It’s important to note that some blood will flow from the RV to the PA and directly to the aorta via a vessel or passage called
Ductus arteriosus
Remember that the PA has very high pressures d/t the high resistance in the fluid-filled lungs
Blood will go from high pressures (PA) to low pressures (aorta)
The Ductus arteriosus also explains why we don’t have that much blood coming from the pulmonary veins since much of the blood that’s pumped into the pulmnary trunk by the RV ends up going into the aorta via the Ductus arteriosus, not into the lungs
Pediatric Physiology - Fetal Circulation
Some of the blood that goes down the descending aorta will also flow into the internal iliac arteries, from which, vessels carry de-oxygenated blood back to the placenta. These vessels are called:
Umbilical areteries
They bring blood back to the placenta; and these are very high flow vessels
Pediatric Physiology - Fetal Circulation
What facilitates blood flow from the faetus back to the placenta via the two umbilical arteries?
Very low resistance of the placenta
Just as the lungs have a very high resistance and divert blood away from it, the placenta has a very low resistance and diverts blood towards it
Pediatric Physiology - Fetal Circulation
What are the two initial adaptations to infant circulation after birth?
The placenta is removed from the infant circulation
The lungs get used to bring in air in for the first time
These two events will cause other adaptations
Pediatric Physiology - Fetal Circulation
After delivery, an umbilical clamp is placed to the cord. Is this painful to the infant?
No
The umbilical cord doesn’t have nerves
Pediatric Physiology - Fetal Circulation
Substance that starts contracting around the two umbilical arteries and the umbilical vein as soon as the temperature falls d/t exposure outside the woumb
Wharton’s jelly
Contraction of Wharton’s jelly will squeeze down on all the vessels inside it (the imbilical vein and the two umbilical arteries)
The fetal circulation goes from being exposed to low resistance placental circulation to high resistance from both the mechanical clamp and from Wharton’s jelly contracting the umbilical vessels
Pediatric Physiology - Fetal Circulation
After birth and separation from the placenta, when does blood flow through the umbilical vein ceases?
Over the next few days
Removal of the placenta creates high resistance
The umbilical vein start building clots all the way to the Ductus venosus
Blood flow through the umbilical ceases over the nex few days
De-oxygenated blood flow through the ICV continues
Pediatric Physiology - Fetal Circulation
After birth and separation from the placenta, decribe blood flow on the right side of the infant’s heart?
De-oxygenated blood that flows through the IVC continues
This blood has no new fresh oxygenated blood to mix with
It flows to the RA where it mixes with de-oxygenated blood from the SVC
Flows continues down to the RV, and blood is pumped into the pulmonary trunk, to the PAs and finally to the lungs
Pediatric Physiology - Fetal Circulation
Explain why resistance in the infant’s lungs fall following the first few breaths after birth?
In-utero, the fetal lungs are a fluid-filled high resistance environment
After the infant takes their first breath, fluid in the lungs is replaced with air. Air pushes the fluid out
Fluid will enter the capillaries. Before the capillaries you have the arterioles that were constricted d/t HPV
But now that air can enter the alveoli, O2 levels are rising in the alveoli
O2 levels are rising sends a signal to the arterioles to dilate
As a result, resistance in the lungs will fall
Pediatric Physiology - Fetal Circulation
Explain how pressures on the right side of the infant’s heart fall following the first few breaths after birth?
After lung resistance falls following the first few breaths after birth, de-oxygenated blood can now flow into the lungs, from the PAs
Remember that not that much blood was flowing into the lungs in-utero from the PAs because of the fluid-filled high resistant lungs
Blood flowing into low resistance lungs from the PAs will cause RV and RA pressures to fall as well
The entire right side of the heart is now working under lower pressures
Pediatric Physiology - Fetal Circulation
Explain the physiological changes that lead to closure of the Foramen ovale after birth. How soon does this happen after the infant if out of the uterus?
Lower resistance in the lungs allows more blood enter the lungs from the PAs
Blood is now oxygenated in the lungs and returned back to the LA via the pulmonary veins
This is different from before birth where there was not that much blood flowing into the LA from the pulmonary veins
The combination of pressures falling on the right side and more blood coming in through the pulmonary veins will cause increased LA pressures, which in turn will cause the Foramen ovale to close off
Closure of the Foramen ovale happens within minutes after birth
Blood from the LA goes down the LV, and gets pumped into the aorta
Pediatric Physiology - Fetal Circulation
Now remember that blood was moving from the PA to the aorta via the Ductus arteriosus because pressure in the PAs were higher that pressure in the aorta. What happens now that pressures in the lungs and PAs are lower?
In the first few hours of life, smooth muscles in the walls of the Ductus arteriosus will sense that O2 levels are higher and will start to constrict
In addition, the Ductus arteriosus can sense that the placenta is removed via the drop in prostaglandins levels; prostaglandins are made by the placenta
When protaglandins levels fall, the Ductus arteriosus is more willing or able to close dowm
Smooth muscles in the walls of the Ductus arteriosus will sense that O2 levels are higher and that prostaglandins levels are down, and these smooth muscles will start to constrict closing the Ductus arteriosus off
The begining of the Ductus arteriosus constricting and closing off happens just a few hours after bitrh
Pediatric Physiology - Fetal Circulation
How does the Ductus arteriosus senses that placenta has been removed?
Ductus arteriosus can sense that the placenta is removed via the drop in prostaglandins levels; prostaglandins are made by the placenta
When protaglandins levels fall, the Ductus arteriosus is more willing or able to close dowm
Pediatric Physiology - Fetal Circulation
When does the Ductus arteriosus begins to constrict?
The begining of the Ductus arteriosus constricting and closing off happens just a few hours after bitrh
Pediatric Physiology - Fetal Circulation
What happens to blood flow to the umbilical arteries after birth?
Blood flows from the aorta down the descending aorta, to the internal iliac branches from which the umbilical arteries branch off
Blood flow continues to the vessels branching off the internal iliac arteries, but there will be no blood flow to the umbilical aretery remnants
Pediatric Physiology - Fetal Circulation
Blood flow continues to the vessels branching off the internal iliac arteries, but there will be no blood flow to the umbilical aretery remnants, why?
b/c the resistance there is so high
In addition, the umbilical arteries, just like the ductus arteriosus, have smooth muscles in them, which will respond to the very high O2 levels and to low prostaglandins levels and will start constricting
This process happens over the course of a few hours
Pediatric Physiology - Fetal Circulation
How does the high oxygenated blood travels around and through the fetal heart from the placenta?
Placenta → 1 Umbilical Vein → Ductus Venosus → IVC → RA → Foramen Ovale → LA → LV → ascend. Ao → Head & Upper extremity vessels
Pediatric Physiology - Fetal Circulation
What’s the O2 saturation level of blood in the umbilical vein?
80-90%
Pediatric Physiology - Fetal Circulation
How does the low oxygenated blood travels around and through the fetal heart from the SVC?
SVC → RA → RV → pulmonary trunk → Ductus Arteriosus → descending Ao → lower body → exits via 2 Umbilical Arteries to placenta
Pediatric Physiology - Fetal Circulation
What’s the O2 saturation of blood returning to the placenta via the umbilical arteries?
25-40% oxygenated
Pediatric Physiology - Transitional Circulation at Birth
Which events lead to the functional closure of the Foramen Ovale after birth?
Cord Clamped => ↑ SVR & ↓ Venous Return
=> LAP > RAP => Functional Closure of the Foramen ovale
=> Blood Flow to Lungs Begins
(and the lungs begin gas exchange)
Pediatric Physiology - Transitional Circulation at Birth
Which events lead to the Ductus venosus Closure after birth?
Cord Clamped => ↓ Venous Return (↓ Portal BP)
=> Mechanical Closure (3-7 days)
=> Blood Flow to Liver/Lung
Pediatric Physiology - Transitional Circulation at Birth
Over what period of time does Ductus venosus closure happens?
3-7 days
Pediatric Physiology - Transitional Circulation at Birth
Ductus venosus closure allows blood to flow to which organs?
Liver & Lungs
Pediatric Physiology - Transitional Circulation at Birth
Which events lead to the Ductus Arteriosus Closure after birth?
PVR (lung expansion) + ↑ SVR (cord clamp)
=>L – R shunting Blood from Ao → PA => ↑ PaO2
=> Initial Constriction (few hours after birth)
=> Functional Closure (1-4 days)
=> Anatomical Closure (2-3wks)
Pediatric Physiology - Transitional Circulation at Birth
When does Initial Constriction of the Ductus Arteriosus happens?
(few hours after birth)
Pediatric Physiology - Transitional Circulation at Birth
When does the Functional Closure of the Ductus Arteriosus happens?
(1-4 days)
Pediatric Physiology - Transitional Circulation at Birth
When does the Anatomical Closure of the Ductus Arteriosus happens?
(2-3wks)
Pediatric Physiology - Transitional Circulation at Birth
What’s the main physiologic change responsible for the Closure of the Ductus Arteriosus?
↑ PaO2
(Which leads to decreased PVR + Decreased in the levels of PEG1)
Pediatric Physiology - Fetal Circulation
Overview of fetal circulation before birth
See picture attached
Pediatric Physiology - Fetal Circulation
Overview of infant circulation after birth
See picture attached
Persistent Fetal Circulation
What happens if the fetus just after birth and as they become a neonate, fail to convert to the adult circulatory pattern, and remains in Persistent Fetal Circulation?
The infant will remain in persistent fetal circulation
A high PVR is responsible for shunting blood away from the lungs and out the ductus arteriosus
I high PVR causes a high RA backward, which is responsible for shunting blood from the RA to the LA via the foramen ovale
As the alveoli are first exposed to O2 after birth, the PVR decreases, resulting in an increase flow in the adult circulatory pattern and eventual closure of the foramen ovale and the ductus aretriosus
When neither of this happens, the neonate remains in
persistent fetal circulation
There are three main categories of etiologies of persistent fetal circulation that would cause the infant to remain in this circulatory pattern
Persistent Fetal Circulation
There are three main categories of etiologies of persistent fetal circulation that would cause the infant to remain in this circulatory pattern
Congenital heart defects
Primary Persistent Fetal Circulation hypertrophy
Secondary Persistent Fetal Circulation
Persistent Fetal Circulation
Any congenital heart defect that results in elevated PA or RA pressures will have a Persistent Fetal Circulation in order to
Allow adequate cardiac output
Persistent Fetal Circulation
Any congenital heart defect that results in elevated PA or RA pressures will have a Persistent Fetal Circulation. The effect of this will be which type of shunt?
R=>L shunt
The hallmark of at Cyanotic heart defect
Persistent Fetal Circulation
PFC characterized by an increase in the muscularization of the walls of the pulmonary vessels, which results in persistently elevated PVR. This is also known as:
Primary Persistent Fetal Circulation hypertrophy
There is a poor prognosis for this etiology
Persistent Fetal Circulation
PFC commonly seen in infants with lung disease, where the hypoxia and acidosis lead to pulmonary vasoconstriction and persistently elevated PVR, is aldo known as:
Secondary Persistent Fetal Circulation
Persistent Fetal Circulation
Some of the causes of these lung-disease types that would lead to secondary PFCs are:
Meconium aspiration (most common)
Hilum membrane disease
Diaphragmatic hernia
Sepsis syndrome
Pulmonary embolism
Persistent Fetal Circulation
In general Persistent Fetal Circulation result from failure of which hemodynamic parameter to decrease after birth?
PVR
Persistent Fetal Circulation
Which could be reponsible for PVR failure to decrease after birth?
Hypoxia
Hypercarbia
Acidosis
Hypothermia
The ultimate reason why PVR will remain elevated is failure of PaO2 to rise and the resulting Hypoxia
Persistent Fetal Circulation
Besides PVR failing to decrease after birth, what are other general causes of Persistent Fetal Circulation?
Anesthetic changes in peripheral vascular tone
High positive airway pressures
R-L extrapulmonary shunting of blood
The ultimate reason of keeping PVR elevated is failure of PaO2 to rise and the resulting Hypoxia
