Dsf Exam I Flashcards

Front 1

Define the variables in the equation: Q=(P2-P1)/R. Why is this equation significant/important?

Back 1

Q=flow (of blood, electrons, fluid, etc.)
(P2-P1)=the pressure gradient (fluid flows from high to low pressure).
R=Resistance to flow.

This equation is analogous to Ohm's Law (I=V/R. It says that fluid flows under a total energy gradient, which is an extremely important point to remember!

Front 2

What is the most important thing to remember about hemodynamics?

Back 2

That fluid flows under a total energy gradient!

Front 3

Define the variables in the Equation: CO=Part/TPR. How would this equation change for a patient in heart failure?

Back 3

CO=cardiac output, Part=arterial pressure, and TPR=total peripheral resistance, which is all of the resistances that occur past the aorta and vena cava.

The arterial pressure is really the aortic pressure. In a normal, healthy person, venous pressure is equal to zero. That's why we just use arterial pressure instead of Arterial pressure-venous pressure. However, for pts with heart failure who have a positive venous pressure, we cannot use this equation, and it would be CO= (Pa-Pv)/TPR

Front 4

What is potential energy? What are the equations for it w.r.t. hemodynamics?

Back 4

Potential energy is the work that a system would do if it were allowed to move to a reference plank below it. It is a function of the gravity that is working upon it.

PE=work=Fd, where F=force and d=distance.

PEgravity=mgh (mass x gravity x height)

since mass= density x volume,
PEgravity=density x g x h x volume

PEapplied=Fd

PEtotal=(density x gh x volume) + (Fh)= (density x gh) + P, where P=pressure.

Remember: fluid flows under a total energy gradient and there's more to it than just pressure.

Front 5

What are the equations for Kinetic energy for hemodynamics?

Back 5

KE=1/2 mv-sqaured
KE=1/2 (density x Volume x v-squared)
KE/Volume=1/2 density x v-squared

Front 6

What's the equation for the total energy of a hemodynamic system?

Back 6

TE= Pressure + (density x gh) + (1/2 density x v-squared)

Front 7

How does the cardiovascular system differ from a simple physical circulation model?

Back 7

1. The BVs are not rigid tubes, but are collapsible and elastic. Their size depends on the BP within them, as well as upon the contraction of smooth muscle of the vessel walls.
2. No unoocupied space may be present, so the capacity of the system must reflect the volume of blood present.
3. Blood isn't like water. It's a complex heterogenous fluid with some unusual properties of viscosity.

Front 8

What is Bernoulli's Principle?

Back 8

Total Energy= Pressure + PE + KE= P + (density x gh) + (1/2mv-squared)

The insertion of the components of the equation with the proper units will demonstrate that the three forms of energy are additive. This is simply a statement of the conservation of energy and is referred to as Bernoulli's Principle.

Front 9

Name one of Pascal's laws as it applies to cardiovascular systems.

Back 9

The two forms of potential energy (density x gh and Pressure) are readily interconvertible.

Front 10

Name two other important laws of importance that apply to the CV system.

Back 10

1. All points in the same system that lie in the same horizontal plane will be at the same pressure.

2. A pressure applied to a system is transmitted unchanged to all other parts of the system.

Front 11

What is the most important factor controlling whether or not blood will flow?

Back 11

Blood will only move in response to a total energy gradient.

Front 12

What is pressure proportional to?

Back 12

Height.

Front 13

Why is BP measured by putting the cuff on the arm instead of by putting it on the leg?

Back 13

Pascal's law states that every point in a horizontal plane (of a cylinder, body, etc.) will be at the same pressure. The arm is in the same plane as the heart, so it's the most accurate locations from which to measure the BP. You'd get a completely different result if you measure the BP around the leg.

Front 14

What are the consequences on the lower extremities of pressure being proportional to height?

Back 14

The great pressure increases in the lower extremities (legs, feet, etc.) causes edema formation and all sorts of other problems.

Front 15

How will increasing the gravitational acceleration (from g to 2.5g) affect venous return, cardiac output, etc.

Back 15

Near the eyeball, the pressure will fall from 64 (normal) to 7.9 mmHg. This will cause the person to black out from lack of BP. At the feet, the pressure will have risen from 188 (normal) to 321 mmHg, resulting in enormous amounts of edema and pooling of blood in the lower extremities. The pressure will expand the size of the vessels, and fluid will flow down and fill the spaces in the feet and legs. In going from the arterial to venous side, pressure goes from 100 to 171 mmHg (normally 93). Due to this high BP, the column of fluid won't get back to the left heart. So eventually CO will fall to zero because venous return has fallen to zero.

Front 16

How can blood enter the right heart if the pressure in the vena cava is essentially zero?

Back 16

Whereas potential energy may have become dissipated with progress through the vasculature, a considerable complement of the total energy still exists as kinetic energy, thereby providing the energy gradient necessary for atrial and ventricular filling.

Front 17

How do frictional forces affect blood flow?

Back 17

Frictional forces do exist in the CV system that impede the motion of blood. Therefore, a constant force needs to be applied to overcome the frictional force.

Front 18

What is the property of fluids that determines the magnitude of the frictional or dissipative forces that cause loss of PE?

Back 18

Viscosity.

Front 19

What is a Newtonian fluid?

Back 19

It is a fluid in which viscosity is constant, regardless of the flow rate.

Front 20

How are people able to travel in high altitude/high g-force?

Back 20

They need to wear high pressure suits that literally force the blood back up to the heart and eliminate the edema and other effects of the high g-force.

Front 21

What would you observe in a x-section of a tube containing Newtonian fluid in motion that has small colored beads placed some distance from the wall of the tube?

Back 21

1. The velocity increases in magnitude from the wall of the tube towards the center.
2. The velocity of a particular set of beads at a given radius does not vary.
3. At the wall, the velocity is zero. Thus, unless there is turbulence, the wall does not influence the flow.

In fact, the flow through the tube acts as if we have a series of concentric rings of fluid, each infinitely thin. Herin derives the term "laminar flow" (nonturbulent).

Front 22

Describe the term laminar flow as it pertains to the CV system.

Back 22

Laminar (nonturbulent flow) is when the flow through a tube acts as if there is a series of concentric rings of fluid, each infinitely thin. The resistance in the CV system is, for the most part, due to the friction (small molecular collisions) between adjacent laminae of blood (i.e., the inner friction or blood viscosity), as these lamina have to slide over each other with different velocities.

Front 23

Under normal conditions, where is the major resistance to flow in the CV system?

Back 23

The major resistance to flow exists in the arterioles (60% of the total resistance). The capillaries also contribute significantly to the total resistance. The arterial and capillary elements make up over 90% of the vascular resistance, with the remaining resistance residing in the venous component of the circulation.

Front 24

Where does the greater energy loss (dissipation) occur in the CV system?

Back 24

A dramatic decline in pressure occurs across the arteriolar segment since this is the site of greatest resistance to flow and, therefore, the site of greatest energy loss.

Front 25

How does the cross-sectional area of vessels impact velocity and pressure?

Back 25

Velocity is inversely proportional to cross-sectional area. So velocity will be higher with small cross-sectional areas and lower with large areas. velocity= flow/cross-sectional area. In going from a larger cross-sectional area to a smaller one, the velocity will increase and the pressure will decrease. As velocity increases, pressure decreases.

Front 26

Why do you lose kinetic energy by the time you go from the aorta to the vena cava?

Back 26

You lose a substantial amt of KE by the time you get to vena cava due to the branching of vessels, which causes the total cross-sectional area of the vasculature to increase (so velocity decreases). But gradually all vessels coalesce into 1 again, so KE will again return to 1250 dynes/cm-squared in the aorta. All energy has not dissipated, it was turned into Potential Energy/Pressure.

Front 27

How are resistance in fluid dynamics handled?

Back 27

In a system where hydraulic resistances are in series, the total resistance is the sum of the individual resistances: Rt=R1 + R2 + R3 + ... + Rn

Where the hydraulic resistances are arranged in parallel, the reciprocal of the total resistance equals the sum of the reciprocals of the individual resistances:
(1/Rt)= (1/R1) + (1/R2) + (1/R3) + ... + (1/Rn)

Note that the total resistance of a parallel circuit is less than the smallest individual resistance.

Front 28

What is turbulent flow?

Back 28

Is the rate of laminar flow is increased beyond a certain level, then dye inserted into the liquid will swirl in an irregular fashion. This is said to be turbulent flow. In this condition, resistance no longer derives from the interface btween lamina, but also from the KE of the eddies. The volume flow for laminar flow depends on the pressure gradient between the end of the tube, thus Q is proportional to P2-P1. However, for nonlaminar flow, any increase in the pressure gradient increases turbulence rather than the volume flow.

Front 29

What is the Reynold's number? Why is it significant?

Back 29

The Reynold's number attempts to define the conditions necessary to elicit nonlaminar (turbulent) flow. It is determined as:

Re= V x density x r/ viscosity, where v= avg velocity of flow and r= tube radius (Re=Reynold's #). If the calculated Re is <1000, laminar flow of blood will exist. With a value >1000, turbulent flow would be expected.

Front 30

What are the effects of turbulent flow?

Back 30

A larger pressure gradient is required to produce the same volume flow as seen with laminar flow. Thus, with turbulence, there is the APPEARANCE of increased viscosity.

Front 31

What is the viscosity of plasma compared to water?

Back 31

The viscosity of plasma is about 1.8 x that of water.

Front 32

What;s the major factor influencing viscosity of plasma?

Back 32

The hematocrit.

Front 33

What are the considerations with respect to the reality of the biological system?

Back 33

1. viscosity
2. radius of the BV
3. vessel capacitance

Front 34

What are the shear stress and shear rate?

Back 34

If you apply a force to a fluid, it will deform at a rate that is called the shear rate. The greater the force (stress), the greater the deformation. Ideal fluid is characterized by a constant viscosity regardless of what the shear rate is.

Front 35

Why is it important that we are designed with resistances in parallel rather than with resistances in series?

Back 35

We are designed with resistances in parallel, so the total resistance is less than any single resistance in the system. This is tremendously important because your heart is working against a resistance or a pressure that results from that resistance. If we were designed with resistances in series, the total resistance would be extremely high and it would impede blood flow.

Front 36

What happens to blood flow at the critical velocity?

Back 36

At the critical velocity, blood flow goes from being laminar to being turbulent. So blood is churning like crazy through the vasculature and there is now a nonlinear relationship between pressure and flow when the pressure is increased even more.

Front 37

How does turbulent flow effect energy dissipation?

Back 37

A greater amount of energy is being dissipated with turbulent flow than it is with laminar flow. This means that if we pass our critical velocity and are under turbulent flow, we have increased the resistance in the heart and it has to work much harder than it does at laminar flow.

Front 38

How does the Hct affect viscosity?

Back 38

Viscosity stays relatively constant until the flow rate gets relatively low. So the higher the Hct, the bigger the divergence from our ideal fluid.

Front 39

How is the radius of a BV determined?

Back 39

The radius of a BV is determined by two opposing influences:
1. The transmural pressure, the difference in pressure (Pt) across the wall of the vessel tending to expand the vessel, and 2) the tension (T) (force per unit length) within the walls of the vessel, tending to force the vessel closed. The equilibrium situation in which the tension exactly balances the pressure is only very roughly approximated by the La Place Equation:

T (tension)= Pt x r (Pt=transmural pressure, r=radius of vessel).

Front 40

What is the significance of the La Place equation?

Back 40

In order to counterbalance a given transmural pressure, the capillary wall (small r) needs to exert far less tension than that of an artery or vein (large r). Also, with respect to the heart, an enlargement increases the amount of tension that must be developed to elicit a given pressure. Since oxygen consumption is in part determined by wall tension, heart enlargement decreases cardiac efficiency.

Front 41

How does smooth muscle in the walls of larger BVs affect the radius-pressure relationship?

Back 41

At any given pressure, the radius of the passive vessel (that lacks smooth muscle) will be greater than that of the vessel in which active tension (due to smooth muscle) is being generated.

Front 42

What is the critical closing pressure for vessels with smooth muscle?

Back 42

For vessels developing active tension by the contraction of their vascular smooth muscle, there will now be some pressure at which the radius of the vessel will be zero. This is the critical closing pressure of the vessel- the vessel closes completely for pressures at or below this value.

Front 43

Describe the pressure-flow relationship for most vascular beds of the body.

Back 43

Flow increases are due to both an increase in radius, caused by the increase in transmural pressure, and by the increase in driving pressure. However, as the pressure is increased in most vascular beds of the body, flow becomes independent of pressure. This is an autoregulatory response of the resistance vessels to maintain blood flow at a level necessary to meet tissue requirements.

The relationship between pressure and flow is a highly complex one. The pressure difference btween the ends of a vessel governs flow, while the transmural pressure has profound effects on the radius of the vessel, which in turn also affects flow via an effect on resistance.

Front 44

Describe vessel capacitance.

Back 44

In addition to offering resistance to flow, BVs also have the capacity to store blood under pressure. On a pressure-volume curve, the slope of the line is 1/C, where C=capacitance= (pi x r-squared)/(density x g). Thus, capacitance is the change in volume vs. the change in pressure. The wider the cylinder, the higher the capacitance.

As a vein increases in volume, it first fills from a collapsed state to a circular state, with little change in pressure. As volume further increases, elastic fibers in the walls of the vessels must be stretched and the pressure increases. As volume increases even more, the collagen fibers in the vascular wall become taut and pressure increases steeply--further volume resistance is strongly resisted. Most of the capacitance in the CV system resides in the veins and venules due to the marked distensibility-- under normal conditions, 70% of blood resides in the venous side due to its large capacitance.

Arterial capacitance plays an important role in smoothing fluctuations in ar