Hemodynamics

Question 1

State the relationship between total peripheral resistance and blood flow; given two values, calculate the unknown quantity.

NOTE, DO NOT MEMORIZE EQUATIONS, THEY ARE GIVEN ON TEST (do understand them)–DO MEMORIZE THIS: Please understand that
you will need to know other equations that involve cardiac output, MAP, pulse pressure, and TPR.

Answer 1

P (delta) = Q x R

delta = Paorta - Pr atrium or Pleft ventricle - Pright atrium

1/TPR = 1/R1 + 1/R2 …. + 1/Rn

R-organ = R1 + R2 + R…. + Rn

Question 2

Describe laminar and turbulent flow characteristics, define the critical velocity and the transition from one type of flow to another.

Answer 2

Laminar flow, where flow Q is proportional to ΔP, breaks down when velocity reaches a critical point. Above this velocity, the flow depends less strongly on pressure gradient, rather:

Q~(ΔP)^1/2 in turbulent flow

This is because the effective resistance increases. This region is called turbulent flow which causes significant losses of kinetic energy. In turbulent flow, Q is proportional to the square root of ΔP. For the same ΔP, there is less flow when flow is turbulent than when laminar.

Question 3

Describe the sounds of turbulent flow and their relationship to clinical measurements.

Answer 3

Clinically, the distinction between laminar and turbulent flow is very important since laminar flow is silent while turbulent flow generates sound.

Murmurs are audible sounds due to vibrations in heart or vessel walls.

Korotkoff sounds of sphygmomanometry (blood pressure measurement with inflatable cuff) are also examples of the sound of turbulent flow.

Question 4

Describe the relationship between pressure and stress on the blood vessel wall.

Answer 4

As pressure increases (stenosis or volume decreases), stress increases = they are directly proportional

Sheer stress is created by flowing blood on the endothelial wall directed along the long axis of the vessel. The velocity profile in a rigid cylindrical tube is parabolic. The outermost layer has zero velocity & highest stress because friction is greatest at the wall (center of the tube has highest velocity & least stress).

Stenotic vessels (especially @ bifurcations = highest areas of athlerosclerosis) have turbulent flow with a lot of stress.

Question 5

Poisielles Law

Answer 5

Q=ΔP/R=ΔP(πr^4/8ηL)

dP = deltaP = pressure drop

Question 6

CO, cardiac output is approximately equal to what variable (MEMORIZE)?

Answer 6

Q, flow

Question 7

Equation for total peripheral resistance, TPR (MEMORIZE)

Answer 7

1/TPR = 1/Rbrain + 1/Rkidney + … 1/Rn

The overall resistance to flow through the circulation is called the total peripheral resistance (TPR). The organs are arranged in parallel network, the resistance of each organ contributes to the TPR according to the inverse relationship. By this mechanism blood flow is regulated and balanced throughout the body according to organ needs.

TPR = mm Hg/ml/s

Question 8

MAP (MEMORIZE, 2 equations) =

Answer 8

MAP = CO x TPR

MAP = DP + 1/3(SP-DP)

Question 9

For the body, delta P is equal to

Answer 9

Pressure in left ventricle

Question 10

Flow in series of tubes

Answer 10

is constant Q = Q1 = Q2 = Qn

Question 11

Flow in parallel tubes

Answer 11

are additive Q = Q1 + Q2 + …

Question 12

Flow equation, Q =

Answer 12

Q = A x v or flow (ml/min) = cross sectional area (cm^2) x velocity

Question 13

CO = (MEMORIZE)

Answer 13

CO (ml/min)= HR (beat/min) X SV (ml)

Question 14

Pulse pressure, PP = (MEMORIZE)

Answer 14

PP = SP - DP

PP is used in MAP equation

Question 15

Turbulent flow is characterized by Reynolds number, Re =

Answer 15

Re = 2rvd/U

r = radius
v= velocity
d = density
U = viscosity

Re>3000 = Turbulent
Re<2000 = Laminar
Re between 3000 & 2000 = transitional

Question 16

Increasing the hematocrit will _____ the viscosity, and this will promote ______ flow.

Answer 16

Increasing the hematocrit will increase the viscosity, and this will promote laminar flow.

Increasing hematocrit does not increase density.

Question 17

A decrease in viscosity of the blood promotes _______ flow?

Answer 17

Turbulent flow

Question 18

Discuss some factors that can increase turbulent flow

Answer 18

Turbulent flow is predicted when the Reynolds number is increased. Factors that increase the Reynolds number and produce turbulent flow are decreased viscosity (hematocrit) and increased velocity.

Partial occlusion of a blood vessel or stenosis increases the Reynolds number (and turbulence) because the decrease in cross-sectional area results in increased blood velocity (v=Q/A).

The arterial wall may be damaged by turbulence, and the development of thrombi (blood clots) is more likely in turbulent flow. Also, the resistance to flow is increased with a consequent increased work of the heart.

Question 19

The variable that is most responsible for the change in resistance to blood flow in a healthy individual is the

Answer 19

Radius of the arterioles

In the systemic circuit, resistance is varied by controlling the radius of the arterioles.

Resistance is inversely proportional to the fourth power of the vessel radius R = (πr^4/8ηL).

Question 20

Development of atherosclerosis appears to be favored in areas exposed to ____ fluid shear stress as well as turbulence.

Answer 20

Development of atherosclerosis appears to be favored in areas exposed to low fluid shear stress as well as turbulence.

Atherosclerotic plaques develop primarily in the intima regions of arteries that are exposed to either low fluid shear stress or turbulence. Fluid shear stress is proportional to flow velocity. In curved arteries, such as the coronaries and aortic arch, blood flow velocity is greater around the outer curvature and reduced along the inner curvature of the vessel. Therefore, atherosclerosis predominates along these inner curvatures.

Similarly, sharp branch points in arteries create areas of high and low shear stress; laminar flow layers break apart at the leading edge of the branch point, creating an area of low shear and turbulence, whereas the distal edge edge is exposed to high flow velocity and shear. Atherosclerosis develops preferentially at the leading edge of such branch points.

Question 21

The time it takes a red blood cell to transit completely around the circulation is

Answer 21

1 min

Question 22

Under which one of the following conditions is an increase in arterial pressure associated with a decrease in peripheral resistance?

Answer 22

When there is an increased cardiac output

MAP=CO X TPR