Congenital Heart Defects
Perry, Hockenberry, Lowdermilk, Wilson (5thed.)
Chapter 42: Cardiac Dysfunction
Hemodynamics
• Most important component
... [Show More] of perfusion: PRESSURE
Hemodynamic Principles
• As blood is pumped through the heart:
o Flows from higher to lower pressure area
o Takes path of least resistance
o Higher pressure = faster flow rate
o Higher resistance = slower flow rate
Left heart pressure higher than right side
Systemic circulation resistance higher than pulmonary circulation resistance
Fetal Circulatory System *** KNOW & UNDERSTAND!!***
• The cardiovascular system is the first organ system to function in the developing human. Blood vessel and blood cell formation begins in the third week and supplies the embryo with oxygen and nutrients from the mother. By the end of the third week, the tubular heart begins to beat and the primitive cardiovascular system links the embryo, connecting stalk, chorion, and yolk sac. During the fourth and fifth weeks, the heart develops into a four-chambered organ. By the end of the embryonic stage, the heart is developmentally complete.
• The fetal lungs do not function for respiratory gas exchange, so a special circulatory pathway, the ductus arteriosus, bypasses the lungs.
• Oxygen-rich blood from the placenta flows rapidly through the umbilical vein into the fetal abdomen (Fig. 6-14).
• When the umbilical vein reaches the liver, it divides into two branches; one branch circulates some oxygenated blood through the liver. Most of the blood passes through the ductus venosus into the inferior vena cava. There it mixes with the deoxygenated blood from the fetal legs and abdomen on its way to the right atrium. Most of this blood passes straight through the right atrium and through the foramen ovale, an opening into the left atrium. There it mixes with the small amount of deoxygenated blood returning from the fetal lungs through the pulmonary veins.
• The blood flows into the left ventricle and is squeezed out into the aorta, where the arteries supplying the heart, head, neck, and arms receive most of the oxygen-rich blood. This pattern of supplying the highest levels of oxygen and nutrients to the head, neck, and arms enhances the cephalocaudal (head-to-rump) development of the embryo/fetus.
• Deoxygenated blood returning from the head and arms enters the right atrium through the superior vena cava.
• This blood is directed downward into the right ventricle, where it is squeezed into the pulmonary artery.
• A small amount of blood circulates through the resistant lung tissue, but the majority follows the path with less resistance through the ductus arteriosus into the aorta, distal to the point of exit of the arteries supplying the head and arms with oxygenated blood. The oxygen-poor blood flows through the abdominal aorta into the internal iliac arteries, where the umbilical arteries direct most of it back through the umbilical cord to the placenta. There the blood gives up its wastes and carbon dioxide in exchange for nutrients and oxygen. The blood remaining in the iliac arteries flows through the fetal abdomen and legs, ultimately returning through the inferior vena cava to the heart.
(Perry 157-158)
FIG 6-14 --Schematic illustration of fetal circulation.
The colors indicate the oxygen saturation of the blood, and the arrows show the course of the blood from the placenta to the heart. The organs are not drawn to scale. Observe that three shunts permit most of the blood to bypass the liver and lungs: (1) ductus venosus, (2) foramen ovale, and (3) ductus arteriosus. A small amount of highly oxygenated blood from the inferior vena cava remains in the right atrium and mixes with poorly oxygenated blood from the superior vena cava. This medium oxygenated blood then passes into the right ventricle. The poorly oxygenated blood returns to the placenta for oxygen and nutrients through the umbilical arteries. [Show Less]