Week 4: Cardiovascular Flashcards
Fetal circulation
- The placenta provides the fetus with ______ oxygenated blood.
- PO2 in umbilical vein is _____mmHg.
- poorly
- ~30
Fetal circulation
- Fetal lungs receive _______% of cardiac output
- Oxygenated blood from the placenta returns via the UV to the portal venous system where 30-50% is shunted across the ________ to the _________.
- 10-15
- ductus venosus; IVC
Cardiovascular physiology
Blood from the IVC enters the RA and then the blood with greater oxygen content is directed across the _________ to the LA.
This blood mixes with pulmonary venous circulation and is ejected out to the ascending aorta to the growing heart and brain.
O2 saturation is ___ - ____% at this point.
- foramen ovale
- 65-70%
- Venous return from the SVC and _____% of IVC blood flow reaches the RV and is pumped into the PA.
- The high pressure in the pulmonary vasculature redirects blood flow across the _______ _______into the descending aorta.
- Blood O2 saturation is ___ - ____% at this point
- _______ of this blood is returned to the placenta, the rest perfuses the intestines, kidneys and lower parts of the body.
- 20%
- ductus arteriosus
- 55-60%
- 2/3
Cardiovascular Physiology
- Blood supplied to the heart and upper body has a greater oxygen content [SaO2 = _____%; pO2 = ___-____ mm Hg]
- than that supplied to the abdominal organs, lower limbs and placenta [SaO2 = _____%; pO2 = _____-_____ mm Hg].
- 65% ; 26 – 28
- 55%; 20 – 22
Cardiovascular Physiology
- In utero, the ______ ventricle pumps about 60% of the combined ventricular output, and the ______ ventricle pumps the remainder.
- Fetal circulation is reliant on a high _____ _______ state, greater ______ concentrations and alterations in oxygen binding (think 2,3 DPG) in order to properly oxygenate the fetus.
- right ; left
- cardiac output, hemoglobin
Fetal circulation consists of 3 shunts, which are holes or small passages, which moves, or allows movement of fluid, from one part of the body to another:
– Ductus arteriosus
– Foramen ovale
– Ductus venosus
Ductus arteriosus functions and is associated with:
– Protects the lungs against circulatory overload
– Allows the right ventricle to strengthen
– Associated with high pulmonary vascular resistance and
low pulmonary blood flow
like a “pop-off” valve
Foramen ovale function
- Shunts highly oxygenated blood from the right atrium to the left atrium
Ductus venosus
– Fetal blood vessel connecting the ____ to the _____ and bypassing the liver.
– Blood flow is regulated by a _____ (any ring-like muscle that normally maintains constriction of a body passage or orifice and that relaxes as required by normal physiological functioning)
– Carries _______ blood from the placenta
- umbilical vein; inferior vena cava
- sphincter
- oxygenated
Three dramatic events that change circulation occur immediately after birth:
and most importantly:
- Cessation of the umbilical-placental circulation shortly after the lungs expand (umbilical vessels are reactive to mechanical stimulation esp. stretch)
- Expansion of the lungs to a normal FRC and pulmonary vasculature
- Alveolar PCO2 falls, alveolar PO2 rises
PULMONARY VASCULAR RESISTANCE FALLS
The ductus arteriosus
- Functionally closes in 58% of full-term infants by _______ after birth and in 98% by ______.
- This is in response to ______ oxygen tension and the reduction in circulating ________ that occurs once the placenta separates.
- Within ___ - ___ weeks ductal fibrosis occurs and the ligamentum arteriosum forms.
- 2 days; day 4
- increased; prostaglandins
- 2-3
Closure of the foramen ovale
In the fetus, over half of inferior vena caval blood comes from umbilical venous return.
- Removal of the placental circulation markedly decreases the amount of inferior vena caval blood returning to the heart and causes a small drop in right atrial pressure, whereas the increase in ____________ increases pulmonary venous return and elevates left atrial pressure.
– This combination of pressure changes closes the valve- like flap of the foramen ovale.
- pulmonary blood flow
The foramen ovale functionally closes when the LA pressure exceeds the RA pressure. But, it remains anatomically patent in 50% of children less than ____ years of age and in 25-30% of _______.
This explains why a healthy child can desaturate under anesthesia when _______ to ______ shunting occurs despite ventilation with 100% oxygen.
- 5; adults.
- right to left
Up to 1/3 of patients will have an unclosed patent foramen ovale!!!!
Cardiovascular Physiology
As the umbilical vein is ligated, ________ pressure falls and the ductus venosus functionally closes.
This will take _____-____ and by ______ only fibrous tissue, the ligamentum venosum is left.
portal;
1-2 weeks; 3 months
Neonatal Cardiovascular System
- Neonates have ____ muscle cells and ______ connective tissue compared to the adult myocardium
- ________ contractile elements and _______ water content
- ________ myofibrils and they are less organized
- fewer; more
- Limited; increased
- Fewer;
Neonatal Cardiovascular System
- Contractile dysfunction when exposed to substances that decrease extracellular ionized calcium (ie _____ in blood products, ______)
- ________ sensitive to inhalational anesthetics and calcium channel blockers
- citrate; albumin
- More
Neonatal Cardiovascular System
- Mitochondrial development is immature and the primary energy sources are _______ and ________ (as opposed to free fatty acids for adults).
- May explain why they tolerate _______ and recover faster than adults.
- carbohydrates; lactate
- ischemia
Neonatal Cardiovascular System
- Less contractile tissue means they have a limited response to increased __________. Compliance increases in the _______ period.
- High metabolic rate (______) compared to the adult (________ oxygen consumption). The neonate meets the demand with a high HR.
- _______ dominates initially and explains why neonates are prone to have a vagal response to stimuli.
- Very sensitive to negative inotrope and chronotropes
- preload; postnatal
- 6-8ml/kg vs. 2-3ml/kg
- PNS
Pulmonary Vascular Physiology
- Pulmonary vasculature development is _________ at birth and matures during the first few years of life.
- _______ proliferate faster than ______.
- Smooth muscle ______ and extends _______ in the vascular tree.
- By __________ of age PVR approximates adult levels.
- Incomplete
- Arterioles; alveoli
- thins; distally
- 6 months
Pulmonary Vascular Physiology
Fetal pulmonary vasculature is reactive to:
- ______,
- ______,
- increased levels of ______, and
- __________.
These can cause significant and prolonged increases in PVR (e.g., reactive pulmonary hypertension).
- hypoxia
- acidosis
- leukotrienes (particularly LTD4)
- mechanical stimulation (e.g., coughing on an endotracheal tube)
Pulmonary Vascular Physiology
7 strong vasodilators of fetal pulmonary vasculature:
- Acetylcholine,
- Histamine,
- Bradykinin,
- Prostaglandins D2, E1, E2 (PGE2)
- Prostacyclin (PGI2)
- β- adrenergic catecholamines, and
- Nitric oxide (NO)
Pulmonary Vascular Physiology
- Persistent fetal circulation occurs when severe and sustained increases in ________ prevent extrauterine life.
- Increased load on the RV induces ______ dysfunction and promotes ______ to ______ shunting through the foramen ovale.
- When ____ > ____ the ductus arteriosus opens and right to left shunting causes hypoxemia (treated with ____, ____, or_____).
remember RV does not have that musculature to contract
- PVR
- diastolic; right to left
- PVR; SVR
- NO, sildenafil, or ECMO
Pulmonary vascular occlusive disease (PVOD):
- Describes structural changes that occur in the pulmonary vasculature after long standing exposure to abnormal _____ and _______ patterns in utero and after birth.
- ____________, as well as external factors influence the development of the pulmonary vasculature and play a role in PVR.
- pressures; flow
- Congenital heart disease
Lung biopsies for Pulmonary Vascular Occlusive Disease demonstrate:
- Thickened muscle layers in the small pulmonary arteries,
- Intimal hyperplasia,
- Scarring
- Thrombosis
- Decreased number of distal (intraacinar) arteries.
Cardiovascular Physiology
■ Resting fetal heart rate averages ______ to _____ beats per minute.
■ The newborn heart rate averages about _____ beats per minute during sleep and increases to _____ to _____ beats per minute while the infant is awake.
■ In premature infants the resting heart rate is higher, averaging _____ to _____ beats per minute.
The heart rate gradually decreases with advancing age.
- 160 - 180
- 120; 140 - 160
- 120 - 140
Cardiovascular Physiology
■ Systemic arterial blood pressure in the fetus at term is about _______ mm Hg, and referred to as _________ pressure.
■ Arterial pressure in the mature infant averages _____ mm Hg, but it is lower in the premature infant.
Arterial pressure gradually increases with age.
- 60/35; amniotic cavity
- 70/50
Cardiovascular Physiology
■ After birth there is an ______ in the total output of the heart during the first few days.
■ There is a ______ increase in right ventricular output but a _______ increase in left ventricular output.
■ The cardiac output per kilogram of body weight falls fairly rapidly over the first 8 to 10 weeks after birth to about ________ mL/kg/min and then falls more slowly to the adult level of about ______-_____ mL/kg/min.
- increase
- modest; considerable
- 150; 70 to 80
Cardiovascular Physiology
■ The ________ in cardiac output after birth can be explained partly by the increased ________ required to maintain body temperature.
■ Cardiac output ______ changes in oxygen consumption.
■ Variations in metabolic activity, such as deviation from the neutral ambient temperature, increase _____ and _____.
- increase; metabolism
- parallels
- oxygen consumption and cardiac output.
Cardiovascular Physiology
The high resting cardiac output in the early postnatal period and the rapid fall over the first _______ weeks are also related to replacement of fetal hemoglobin by adult hemoglobin in circulating erythrocytes.
8
Physiologic HR Ranges
Anatomic features of tetralogy of fallot
- Right ventricular outflow obstruction
- Large ventricular septal defect (VSD)
- Aortic override
- Right ventricular hypertrophy (RVH)
Others:
- Arterial desaturation from right to left shunting
- Infundibular narrowing
- Hypoplastic pulmonary arteries
