Hi, I'm Cathy with Level Up RN. In this video, we
are going to continue our anatomy and physiology review of the cardiovascular system. If you have
our medical-surgical nursing second-edition cards, be sure to pull those out and follow along with
me. So in this video, we are going to talk about the heart conduction system, cardiac function,
and blood pressure. And at the end of the video, I'm going to give you guys a quiz to
test your understanding of some of the key concepts that I'll be covering in this
video. So definitely stay tuned for that. Let's first talk about the steps of the heart
conduction system using an illustration from our medical-surgical nursing flashcard deck.
So we have our SA note here, our sinus node, which will initiate an electrical impulse which
stimulates the atria to depolarize and contract. The impulse then travels to the AV node, where
there is a delay to allow the blood in the atria to empty into the ventricles. Then, from the AV
node, the impulse travels to the bundle of His, then the left and right bundle branches, and
then through the Purkinje fibers. And ultimately, this causes depolarization of the myocardium,
which triggers contraction of the ventricles. So understanding this path, the conduction
system is going to be important for you to know when we start talking about dysrhythmias, which
will definitely be covering later on in this video playlist. Now let's talk about some important
terms and concepts that relate to cardiac function. Within the cardiac cycle, we have
diastole and systole. So during diastole, this is where the ventricles and the atria are relaxed and
they are filling with blood. Then, during systole, the ventricles and atria contract and eject
that blood. So within the cardiac cycle, about two-thirds of the time is spent in diastole, and
about one-third of the time is spent with systole. Cardiac output is the volume of blood in liters
that is ejected from the left ventricle every minute. And you would calculate cardiac output by
taking the patient's heart rate and multiplying that times the stroke volume. So the heart rate is
the number of times that the ventricles contract within a minute. So for an adult, this usually
varies between 60 and 100 beats per minute. The stroke volume is the volume of blood in
liters that is ejected from the ventricle with each heartbeat. So you take that heart rate
times the stroke volume, and that would give you cardiac output. And cardiac output for an adult
usually varies between 4 and 8 liters per minute. Another important term to know is something
called left ventricular ejection fraction, or LVEF. This is the percentage of blood that
leaves the left ventricle each time it contracts. And in a healthy adult, this will vary between
55 and 70 percent. And when we talk about heart failure in another video in this
playlist, you will see that most of these patients will have a reduced LVEF that we
would determine through an echocardiogram. Then we have preload, which is another important
thing to understand. This is the volume of blood in the ventricles at the end of diastole, so right
before contraction. And this determines the amount of stretch that we are placing on those myocardial
fibers in the heart. This differs from afterload. So afterload is the peripheral resistance that
the left ventricle must overcome in order to push that blood into systemic circulation. So when
we are caring for a heart-failure patient, we are going to administer medications often that will
reduce preload and/or afterload. So we're trying to reduce the amount of stretch on that heart and
the amount of workload that heart needs to do by reducing preload. And we're also trying to reduce
afterload to make it easier for the heart to push that blood into systemic circulation.
The last topic I want to cover in this video is blood pressure, which is comprised of systolic
blood pressure and diastolic blood pressure. So systolic blood pressure is the amount of pressure
that is exerted against those arterial walls during left ventricular contraction, as opposed
to diastolic blood pressure, which is the amount of pressure exerted against those arterial walls
during left ventricular relaxation, or diastole. Blood pressure in the body is regulated by the
autonomic nervous system. So the autonomous nervous system will regulate blood pressure
based on input it receives from different receptors. So this includes baroreceptors,
chemoreceptors, and stretch receptors as well in the blood vessels near the heart.
All right. Time for a quiz. I have three questions for you. First question.
How do you calculate cardiac output? You calculate cardiac output by taking the heart
rate times the stroke volume. Question number two. What do you call the volume of blood in
the ventricles at the end of diastole? If you said preload, you are correct.
Third question. The percentage of blood leaving the left ventricle each
time it contracts is called what? If you said left ventricular ejection fraction,
you're right. I hope this review has been helpful. If so, be sure to like this video. Leave me a
comment. And if you haven't already done so, be sure to subscribe. In my next
video, we will talk about some A&P concepts as it relates to the hematologic
system. So definitely stay tuned for that. I invite you to subscribe to our channel
and share a link with your classmates and friends in nursing school. If you found value
in this video, be sure and hit the like button, and leave a comment and let us know
what you found particularly helpful.