NURS 3122 Chapter 26.1: Alterations in Cardiovascular Function
Mount Royal University
Alterations in Cardiovascular Function
- Blood flows from the placenta to the fetus through the umbilical vein.
- Blood flow through the ductus venosus (the fetal vascular channel between the
umbilical vein and the inferior vena cava) permits the blood to enter the right
atrium of the heart.
- The foramen ovale, an opening between the atria in the fetal heart, allows blood to flow
from the right to the left atrium, and then into the left ventricle.
- Blood is then pumped into the aorta and the systemic circulation. Some blood
returns from the head and upper extremities to the superior vena cava and right
atrium. It flows to the right ventricle where it is pumped to the pulmonary artery.
- The majority of the blood passes through the ductus arteriosus, the fetal vascular
channel between the pulmonary artery and the descending aorta, to enter the systemic
circulation. A small amount of the blood from the pulmonary artery goes to the fetal
lungs. Blood eventually returns to the placenta by way of the umbilical arteries.
- During fetal circulation, the blood with the highest oxygen content goes to the
heart and the brain. The constricted pulmonary vessels limit blood flow to the lungs
(high pulmonary vascular resistance).
- Blood, however, flows easily to the extremities because systemic vascular resistance
is low. After the umbilical cord has been cut, the newborn must quickly adapt to
receiving oxygen from the lungs.
Transition from Fetal to Pulmonary Circulation
- The transition from fetal to pulmonary circulation occurs within just a few hours after
birth. The first breath expands the lungs, and blood that previously passed through the
ductus arteriosus begins flowing to the lungs. Increased pulmonary blood flow and
decreased pulmonary vas-cular resistance results. Pressure in the left atrium increases as
increased blood flow is returned from the lungs through the pulmonary veins.
- Systemic vascular resistance (the force or resistance of the blood in the body’s blood
vessels that helps return blood to the heart) increases and right atrial pressure falls after
the umbilical cord is cut.
- Increased pressure in the left atrium stimulates closure of the foramen ovale. The flaps of
the foramen ovale close and fibrin deposits permanently seal the opening unless
there is excess pressure on the right side of the heart.
- The ductus arteriosus, responding to higher oxygen saturation, normally constricts and closes within 10 to 15 hours after birth. Permanent closure usually occurs by 10 to 21
days after birth.
- If the infant’s oxygen saturation remains low, the ductus arteriosus closure may be
delayed or prevented.
Cardiovascular Changes as the Child Grows
- The infant’s cardiovascular system is proportionately larger in relation to body size
than an adult’s.
- The right ventricle is larger than the left at birth because the high pulmonary
resistance during fetal life forced the right ventricle to be as muscular and strong as the
- As the pulmonary resistance drops, the right ventricle muscle reduces in size to
equal that of the left ventricle by 1 month of age.
- The higher systemic vascular pressures force the left ventricle to develop quickly.
- The decreasing pulmonary vascular resistance at birth leads to thinning of the
small pulmonary arteriole lining, and increases the diameter in these blood vessels.
- The pulmonary bed also develops in response to lung growth. Both changes result