00:00
Now let's move to self-resistance. Resistance in a rigid tube can be set up by this particular
equation. Here, we're going to use 8 times the viscosity times the length divided by pi r raised
to the fourth power. What you really need to think about in this equation is what items can be
changed in the cardiovascular system. First, you will be able to alter the viscosity of the fluid
if you're dehydrated versus hyperhydrated. The length of each individual tube should be fairly
constant because once a blood vessel has been developed and you have an adult, that blood
vessel length is not going to change but what you have the ability to change from on a minute
by minute or even second by second basis that is the radius of the tube and since it's raised
to the fourth power the radius becomes incredibly important. If you go from a tube that is only
this size to a tube that is this size, that increase in radial diameter of the tube allows for
greater amounts of flow and that's simply because there is less resistance to the delta P. What
other changes happen in terms of flow? In terms of flow, we need to think about two different
types of flow. The equation that we just saw about resistance is only related to laminar flow.
01:48
What do we mean by laminar flow? Laminar flow is the flow in which there is no turbulence or
turning over of the various fluids. In this type of a graft, we plot flow over a change in
pressure. Laminar flow can be seen as the straight line. Turbulent flow happens if there is too
much pressure for any given tube or if there is some sort of occlusion in that particular tube.
02:21
The other problem with turbulent flow is that you lose energy. It is less efficient to move fluid
through in a non-laminar means and therefore you really want to think about if there are areas
of turbulence in a blood vessel these have to be accounted for because they are going to
change the resistance component through that tube. Why would this happen? If you have
done something like decrease the luminal diameter of the tube, you've changed the resistance
and possibly now even the type of flow through that tube. This is showing you an example of
laminar flow. This is this kind of projection of fluid. You notice in laminar flow there is the
fastest flow in the center of the tube. That is because there is the least resistance in the
center of the tube compared to the two edges. The two edges provide the resistance which
slows down the fluid. Turbulence is heard through a stethoscope in a couple of different
manners. The one is through a murmur such as a valve. If you're going through a valve and
there's turbulence at that valve you can put a stethoscope over that valve of the heart and
listen to it and you hear a murmur. You can also hear a bruit and this occurs at a blood vessel
and this is related to this atherosclerotic lesion that might have take place and you can hear the
turbulence just after the lesion. Good examples of this are in the carotid arteries here, also
in the femoral arteries if you have these atherosclerotic lesions.