Mod IV: Fetal Circulation Flashcards

Question

_{Pediatric Physiology - Fetal Circulation} Blood in the fetal RA is coming from where? How is its oxygen content?

Answer 1

Mixed umbilical and IVC blood Blood draining from the SVC Blood in the RA is even more mixed at this point

Answer 2

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

Answer 3

**Fluid** And going pass those fluid-filled alveoli are little blood vessels (arterioles) Fluid filled alveoli lack oxygen

Answer 4

**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

Answer 5

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

Answer 6

**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

Answer 7

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

Answer 8

To the **LV** where it gets squeezed into the **aorta**, and the aorta distributes blood througout the **rest of the body**

Answer 9

**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

Answer 10

**Umbilical areteries** They bring blood back to the placenta; and these are very high flow vessels

Answer 11

**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

Answer 12

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

Answer 13

**No** The umbilical cord doesn't have nerves

Answer 14

**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

Answer 15

**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

Answer 16

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

Answer 17

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**

Answer 18

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

Answer 19

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

Answer 20

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

Answer 21

Ductus arteriosus can sense that the placenta is removed via the d**rop in prostaglandins levels**; prostaglandins are made by the placenta When protaglandins levels fall, the Ductus arteriosus is more willing or able to close dowm

Answer 22

The begining of the Ductus arteriosus constricting and closing off happens just **a few hours** after bitrh

Answer 23

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**

Answer 24

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

Answer 25

Placenta → 1 Umbilical Vein → Ductus Venosus → IVC → RA → Foramen Ovale → LA → LV → ascend. Ao → Head & Upper extremity vessels

Answer 26

SVC → RA → RV → pulmonary trunk → Ductus Arteriosus → descending Ao → lower body → exits via 2 Umbilical Arteries to placenta

Answer 27

**25-40%** oxygenated

Answer 28

_Cord Clamped_ =\> **↑ SVR** & ↓ Venous Return =\> LAP \> RAP =\> Functional Closure of the Foramen ovale =\> Blood Flow to Lungs Begins (and the lungs begin gas exchange)

Answer 29

_Cord Clamped_ =\> **↓ Venous Return** (↓ Portal BP) =\> Mechanical Closure (3-7 days) =\> Blood Flow to Liver/Lung

Answer 30

**Liver** & **Lungs**

Answer 31

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)

Answer 32

(few hours after birth)

Answer 33

(1-4 days)

Answer 34

**↑ PaO2** _{(Which leads to decreased PVR + Decreased in the levels of PEG1)}

Answer 35

See picture attached

Answer 36

See picture attached

Answer 37

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

Answer 38

Congenital **heart defects** **Primary** Persistent Fetal Circulation hypertrophy **Secondary** Persistent Fetal Circulation

Answer 39

Allow adequate cardiac output

Answer 40

**R=\>L shunt** The hallmark of at Cyanotic heart defect

Answer 41

**Primary** Persistent Fetal Circulation **hypertrophy** There is a poor prognosis for this etiology

Answer 42

Secondary Persistent Fetal Circulation

Answer 43

Meconium aspiration (most common) Hilum membrane disease Diaphragmatic hernia Sepsis syndrome Pulmonary embolism

Answer 44

Hypoxia Hypercarbia Acidosis Hypothermia *The ultimate reason why PVR will remain elevated is failure of PaO2 to rise and the resulting Hypoxia*

Answer 45

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*

Mod IV: Fetal Circulation Flashcards

(73 cards)