Venous Blood Return

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 body.

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.

(Just enough pressure to travel the distance from your left ventricle to your brain).

UP and out the aortic arch.

UP to the brain – thru the R-ICA and L-ICA.

UP to the right and left shoulders to the right subclavian artery (off the R-ICA)

and the left subclavian artery.

And then, 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
   arterial 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

the body. (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.)

So, then 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
   down, the little valves close (or open, depending on how you look at it) and hold the blood in
   place until you start moving again.

   So, 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
   tourniquet - SNUG, not tight.

So, the 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 (a 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
   along and 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.

This information and so much more can be found in our book, How to Locate a Healthy Vein, and in our profession-specific books, The Science Behind the Skill of Vein Access. Order your book today or attend one of our training programs!

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