VENOUS BLOOD RETURN
M. Gail Stotler, Vein Access Technologist / B.S.N., R.N.
Biology / Anatomy / Physiology / Physics
/ Chemistry / Math
How does blood move around the body?
The answer most often given by lay people and health care
professionals alike is that the heart
contracts and moves the blood around the
But the physiological truth is that
the heart just pumps blood UP and out
of the heart.
Left ventricle contracts.
Forcing blood UP
and out of the left ventricle at a blood pressure of 120/80 mm Hg.
enough pressure to travel the distance from your left ventricle to your brain).
and out the aortic arch.
to the brain – thru the R-ICA and L-ICA.
to the right and left shoulders to the right subclavian artery (off the R-ICA)
and the left
two other mechanisms take over from there to move blood around the body . . . . . GRAVITY and MOVEMENT.
As you know, GRAVITY takes everything DOWN. This includes blood in the body as well.
Let's follow a drop of blood as it leaves the left
ventricle of the heart -
The left ventricle contracted with a pressure of 120/80 mm Hg and propelled the blood UP and out of the heart –
UP to the head and shoulders. From there, everything else
went DOWN (the aortic arch) to the rest of the body.
How? By GRAVITY (mostly).
Think about this for
a second. The only arterial
blood going up is that blood
that goes up to the brain. That’s a short
distance to go, and the pressure of the blood as it leaves the left ventricle is forceful
enough to take the arterial blood in
an upward direction to the head
(against gravity). But the rest of the body is “south of the heart”
(so to speak), and the
blood travels through these narrow lumen arteries
with the help of gravity to the rest of the body.
Now that drop of arterial blood is at its final
destination - the big toe - where it becomes a drop of venous blood that needs to
return to the heart.
There are 2 ways that drop of venous blood can get from the big toe back to the heart -
1. Hang upside down and let GRAVITY bring it back.
That’s not practical! You can’t
“live” like that! But it would work!
2. MOVE! That's right.
It is MOVEMENT, the contracting of skeletal muscles,
that cause a squeezing of the veins. This “milks” the blood along, up the legs
and back to the heart. It does the same for all the venous
blood everywhere in
(Except in the brain. Since the brain is higher than
the heart - when
standing, anyway - gravity brings the brain's venous blood back to the heart.)
what happens when you stop moving? Does that drop of blood in your thigh fall all
the way back to
your foot? Not quite.
But, it would fall
some distance, except veins have valves. So when the blood starts to fall
little valves close (or open, depending on how you look at it) and hold the blood in
place until you start moving again.
leg veins have oodles of valves, because the legs are long and they aren't always moving.
But the arm veins have very few valves because they are not as long, and we are constantly
moving them, and therefore, the blood.
| Note: Valves can become incompetent, failing to hold the blood in place,
if you permanently injure the vein wall with over |
distention (varicosing the
vein). The valves are attached to the wall of the vein, and if the wall is all stretched out, then
the valve leaflets cannot touch each other and close appropriately. (And, this
will lead to more varicosing, more valve
incompetence, more injury of the vein, and
impaired venous blood return, and therefore, edema.) So, becareful with that
SNUG, not tight.
drop of venous blood in my big toe comes back to my heart by MOVEMENT, the contracting of skeletal muscles
which squeeze the vein, milking the blood along, held in place with the help of valves - all the
way back to my right ventricle.
The RV then contracts at a pressure of 40 mm Hg
fraction of the LV pressure) to send blood
to the lungs.
(It requires less mm Hg pressure
as compared to the left ventricle because the distance from the
right ventricle to the lungs is much shorter than the distance from the left ventricle
to the brain.)
Isn’t that a neat story?!
Now , how does this apply to blood collection, blood donation, and IVs?
In Blood Draw - We
do not need to "move" the blood into the tube. The tube is vacuumed - it sucks the blood in!
So, do not "milk" the hand. In
fact, "milking the hand" engorges the vein with blood and causes over-distention, causing all
kinds of problems.
In Finger Sticks - Do not point the finger UP - blood will be in the elbow, not in the tip of
the finger. Point the tip of the
finger to the floor with the pad of the finger facing the
floor, and gravity will take the blood down to that site.
In Heel Sticks - Do not lift
the baby's foot UP with the heel facing the ceiling - the blood will be in the baby's butt, not in
the heel. Hold the baby, if possible, and keep the foot DOWN with the pad of
the heel facing the floor, now gravity takes the
blood DOWN into the heel of the foot.
In Blood Donation (Red Cross) - the bag is not vaccuumed,
and therefore, you must "milk the hand", moving blood
into the bag.
In IVs - The nurse should instruct the
patient to "move" that extremity because it is the movement that moves the venous
blood and the IV fluid/medications that are being infused.
Copyright © 2007. All rights reserved.
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