L20: Fetal Neonatal Cardiorespiratory Physiology Flashcards
Which artery brings in maternal blood to the placenta
Maternal spiral arteries
Which vessel carries oxygenated blood from the placenta back to the baby by going through the umbilical cord
Umbilical vein
Which vessel does the umbilical vein join to
The inferior vena cava
Which vessel brings deoxygenated blood form the baby to the placenta so blood is oxygenated
Umbilical artery
Where does exchange with the fetal blood and maternal blood occur
Chorionic villus
What is the partial pressure of oxygen at the uterine artery
12.7kpa
What is the partial pressure of oxygen at the uterine vein
5.6kpa
What is the partial pressure of oxygen at the umbilical artery
3.2kpa
What is the partial pressure of oxygen at the umbilical vein when it picks up oxygen
4.2kpa
As the partial pressure of oxygen in the umbilical vein (4.2) is lower than the partial pressure of oxygen in the uterine artery (12.7kpa) is low what does this indicate
The fetal umbilical vein does not reach equilibrium with the maternal blood for oxygen
What is the partial pressure of carbon dioxide in the uterine artery
Pco2=5.3kpa
What is the partial pressure of co2 in the uterine vein
6.1kpa
What is the partial pressure of co2 in the umbilical artery
6.6kpa
What is the partial pressure of co2 in the umbilical vein
5.8kpa
What does the close partial pressure of the uterine vein and umbilical vein suggest
Carbon dioxide has diffused the maternal side i.e uterine vein and almost equilibrium has occurred
Why do we get a close equilibrium with carbon dioxide but not for oxygen
- placental barrier is more permeable to co2 than o2
- not all maternal blood comes in contact with the villi
- placental tissue if highley active and consumes 20% of oxygen so there is less in the fetal blood
What type of haemoglobin does the fetus have
Fetal haemoglobin
When does the fetal haemoglobin reach a peak level
At 10 weeks
What happens to the levels of fetal haemoglobin at term i.e after birth
Declines by 80% and disappears completely after 6 months
What are the features of fetal haemoglobin
Has a higher affinity for oxygen
Which polypeptide chain in the fetal haemoglobin allows for a higher affinity for oxygen
Gamma polypeptide chain that does not interact with 2,3DPG
What does having a higher affinity for oxygen mean
Fetal haemoglobin picks up more oxygen at a lower partial pressure
If the fetal haemoglobin has a higher affinity for oxygen what is the saturation of oxygen for the fetal haemoglobin like
75% saturated with oxygen (more than adult haemoglobin)
What is the fetal haemoglobin saturation further affected/influenced by
The Bohr effect
What is the Bohr shift/effect
The fetal haemoglobin gives off more carbon dioxide to pick up oxygen and the adult haemoglobin releases more oxygen to pick up the fetal carbon dioxide
What is the concentration of fetal haemoglobin like in the Fetal blood compared to the maternal blood
Fetal haemoglobin concentration is higher in the fetal blood
What does a higher concentration of fetal haemoglobin mean
More oxygen is picked up at Po2=4.2kpa compared to the maternal blood
What are the 3 shunts present in the fetal circultion
- ductus venosus
- foramen ovale
- ductus arteriosus
Where is the ductus venosus located
At the liver
Where is the foramen ovale located
At the heart between the right atrium and left atrium
Where is the ductus arteriosus located
Between the pulmonary and systemic circulation
What is the flow of each shunt dependent on
Intravascular pressure gradient i.e from high to low
Describe the flow of the fetal blood from the umbilical vein back to the placenta via umbilical arteries
1) blood from the umbilical vein passes through the ductus venosus at the liver to the inferoir Vena cava
2) the umbilical vein has a higher oxygen concentration than the inferoir vena cava which brings blood back form the feet/legs
3) blood then goes through the foramen ovale from the right atrium to the left atrium as blood pressure from the umbilical vein is greater than the inferior vena cava pressure And right atrial pressure is greater than the left atrium
4) blood from the right ventricle goes through the pulmonary artery through the descending aorta by the ductus arteriosus as the lungs are not working
5) blood from the ascending aorta takes the highest conc of oxygenated blood to the brain.
In a normal adult what are the right and left stroke volumes like
The same because there are no shunts therefore the exact volume of blood from the right ventricle is the same as the left ventricle as the same volume of blood enters to the left ventricle .
What is the cardiac output
The total volume of blood the heart pumps in one minute
Co= SV x HR
As the fetal heart contains shunts what is the stroke volume of the left and right
Not equal
Which ventricle contains the least stroke volume
The left ventricle
Why does the left ventricle in the fetus have a lower stroke volume
Because less blood passes to the lungs to return back to the left ventricle due to the ductus arteriosus passing blood from the right ventricle to the aorta
What is the fetal cardiac output
The combined ventricles output
Which hormones play a role in the fetal circulation control
Catecholamines
Which receptors does catecholamines act on
Alpha and beta adrenoceptors
What influence does the circulating catecholamines have on the fetal circulation
Tonic adrenergic vasoconstrictor influence
Which other hormone also produce a vasoconstriction influence on the fetal circulation
Vasopressin
Angiotensin
What is the heart rate of the fetus at the 11 week of gestation
160 beats per min
From 28 weeks onwards what develops
Autonomic control from nerves
When the autonomic control has developed what happens to the heart beat of 160bpm
Decreases to 140bpm due to the vagus nerve
At the 11 week of gestation what is the arterial blood pressure (ABP) at
70/45 mmHG
What happens to the ABP when the sympathetic nervous system begins to develop
Increases to 80/55mg at term
When the sympathetic NS is beginning to develop what reflex is also being developed
The baroreceptor reflex
What type of chemoreceptors are also beginning to develop
Peripheral chemoreceptors
What can peripheral chemoreceptors detect
Hypoxia
When there is hypoxia what adjustment does the peripheral chemoreceptors cause
Bradycardia
Vasoconstriction
Why does the peripheral chemoreceptors produce bradycardia and vasoconstriction
So the blood flow to the brain is preserved
What is the fetal breasting movement
When the baby uses the diaphragm and intercostal muscles to develop the strength of the thorax
What are the 2 types of fetal breathing movement
- regular breathing
- irregular breathing in REM sleep
What type of fetal breathing movement indicates hypoxia
Decreased fetal breathing movement
What are the lungs filled with in a fetus
Fluid
What happens to the fluid in the lungs during vaginal childbirth
Become squeezed out
What is the first breath of the baby triggered by
Cooling, sensory stimulation and chemoreceptor stimulation due it increases carbon dioxide and low oxygen
What structure allows the first breath to be possible
Surfactant
Which cells in the lungs secrete surfactant
Type 2 cells
Which hormone allows for the secretion of surfactant
Fetal cortisol
What is the role of surfactant
Decrease surface tension that opposes lung inflation
When can surfactant be decreased
In pre-term mature babies
What happens to the fluid in the lungs when air moves in
The fluid gets pushed back into the lungs across the alveoli by the air that moves in
Fluid it then taken away from the lymphatics
What happens to the compliance and functional residual capacity as the fetus breaths
Increases
At the first breath what happens to the pulmonary vascular resistance
Decreases
Why does the pulmonary vascular resistance decrease
The lungs expand as the air fills them and the pulmonary circulation open (increase in diameter that decreases resistance)
If the pulmonary vascular resistance decreases what happens to the blood flow to the lungs
Increases
When there is more blood flow through the pulmonary circulation what happens to the volume returning back to the left atrium
Increases
What happens when the left artial pressure is greater than the right atrium
The foramen ovale closes as it gets pushed to close
What happens to the systemic ABP when the umbilical cord is clamped
Increases
Why does the abp increase after clamping the umbilical cord
Because the systemic TPR increases
As a result of the systemic pressure increasing and the pulmonary abp decreasing due to the pulmonary circulation opening what happens
Th ductus arteriosus closes as blood flow reverses from the aorta to the pulmonary artery
In addition to the umbilical cord being clamped what happens to the flow in the umbilical vein
Decreases
What happens as a result of decreased flow from the umbilical vein
Ductus venosus collapses and constricts to close
What other factors contribute to the close of the ductus arteriosus
A decrease in prostaglandin
Why do we get a decrease in prostaglandin synthesis
Due to a higher po2 in the lungs
Which drugs can be used to block the synthesis of prostaglandins and hence facilitate the closure of the ductus arteriosus
NSAID
How doe NSAID work to block the production of prostaglandins
Block the COX enzyme that are required for prostaglandins production
Which other hormone is involved in the closure of the ductus arteriosus
Bradykinin
What happens the thickness of the wall of the pulmonary arteries and right ventricle
Decreases
Why does the thickness of the wall of the right ventricle and pulmonary arteries decrease
Because there is a decreased pulmonary vascular resistance so less work is required to pump blood to the lungs
What happens the wall thickens off the left ventricle
Increases
Why does the ventricle wall thicken
Due to increases peripheral resistance so more work is required
What happens to the peripheral chemoreceptors during the neonatal period (over the 2 weeks after birth)
Reset
Why does the peripheral chemoreceptors need to re-set after birth
So they stop firing at a lower po2 i.e 4.2kpa which they were used to and start firing below po2= 12.5kpa
What is the baby vulnerable to during this re-set period
Hypoxia as the response to hypoxia is going to be weak
If the foramen ovale doesn’t close after birth what can this create
Left to right shunt
What can a left to right shunt present with
Pulmonary remodelling
Pulmonary hypertension
Why do we get a pulmonary hypertension
Because there is too much blood going from the left atrium to the right ventricle that pumps blood to the lungs
If a left to right shunt occurs what can happen to the right ventricles
Hypertrophy instead of thinning due to the big overload of blood
If this continues and the right ventricular pressure becomes greater than the left ventricular pressure what can happen to the shunt
Reverse
What happens to oxygenation if there is a right to left shunt due to a reversal
Compromised
Why is oxygenation compromised in a right to left shunt
Because blood doesn’t go to the lung to become oxygenated as instead is passes from the right ventricle into the left ventricle
What is the syndrome of called when the foramen ovale doesn’t close and you have a reversal of the shunts
Eisemenger syndrome
When there is a right to left shunt what is the baby called
Blue baby
What can happen if the ductus arteriosus doesn’t close after birth
The left ventricular output from the aorta enters back to the pulmonary circulation
What does blood entering from the aorta back to the pulmonary circulation present as
Pulmonary hypertension
Right ventricular afterload (high pressure the right ventricle needs to create to overcome the pressure in the pulmonary circulations blood can flow)
What is pre-eclampsia due to
Poor remodelling of the maternal spiral arteries that results in high resistance due to a smaller lumen and therefore a decreased blood flow to the fetus
What can pre-eclampsia present as in the mother
High ABP
Proteinuria (protein in the urine)
What is the treatment for pre-eclampsia
Delivery of the baby
What is intra-uterine growth retardation/restriction (IUGR)
When the fetus develops in a retarded way i.e doesn’t grow as expected
What is IUGR associated with
Increased blood pressure
Advanced diabetes
Maternal malnutrition
Maternal smoking
What can IUGR lead to
Fetal programming
What is fetal programming
Where the in uterine condition leads to adverse afffects that continue into adulthood life
What conditions can the baby get in adult hood due to Fetal programming
Diabetes
Obesity
Metabolic syndrome
What is fetal programming associated with
Increased cortisol
Oxidative stress
Epigenetics process
