3B - Hemodynamics

Question 1

What two major variables affect blood flow through arteries?

Answer 1

Pressure and resistance

Q = (change) P / R

units: L/min

Question 2

What is blood flow (Q)?

Answer 2

Quantity of blood flowing through a vessel, organ, or the entire circulation in a given period of time (L/min)

Question 3

What is blood pressure?

Answer 3

The force with which blood is pushed against the walls of blood vessels

Question 4

What causes blood pressure to fall progressively through circulation?

Answer 4

1. Increasing distance from the heart

2. Branching of vessels and distribution

Question 5

What is systolic pressure (SP)?

Answer 5

The highest amount of pressure reached during ventricular ejection of blood

(SP/DP)

Question 6

What is diastolic pressure (DP)?

Answer 6

The minimum amount of pressure just before ventricular ejection

(SP/DP)

Question 7

What does the energy generated from ventricular contraction do?

Answer 7

1. Provides flow during ventricular systole

2. Provides potential energy for blood and distends the arterial tree

Question 8

What are the methods of blood pressure measurement?

Answer 8

1. Auscultatoric measurement - listening to blood turbulence with a stethoscope
2. Oscillometric measurement - using an electronic pressure sensor

Question 9

What is the “Wind Kessel” effect?

Answer 9

The aorta stores potential energy during its ventricular contraction in order to alternate systolic and diastolic propulsion. This alternation of propulsion will make blood flow “continuous” instead of “pulsatile”.

Question 10

What is Mean Arterial Pressure (MAP)?

Answer 10

The actual pressure that propels blood to tissues
- the “average” pressure in a cardiac cycle

MAP = 2/3 DP + 1/3 SP
MAP = DP + 1/3 PP
(PP is DP - SP)

Question 11

What is TPR or SVR?

Answer 11

Total peripheral resistance
Systemic vascular resistance

• The sum of all resistance in the vasculature

Question 12

What are the three important sources of resistance within a single vessel?

Answer 12

1. Blood viscosity
2. Vessel diameter or radius
3. Vessel length

Question 13

Which of the three sources of blood flow resistances actually change appreciably in vivo?

Answer 13

Blood viscosity and vessel diameter/radius change appreciably

Vessel length doesn’t really change

Question 14

What is Poiseuille’s Law?

Answer 14

R = 8 V L / π r^4

Relationship between resistance, viscosity, vessel length, and vessel radius

Question 15

What is a normal hematocrit level?

Answer 15

40%

Hematocrit = RBC / Blood x 100

Question 16

What is the most important factor for blood viscosity?

Answer 16

Concentration of the suspended medium (the formed elements)

Question 17

In a low hematocrit state such as anemia (15-16%):

• What happens to viscosity?
• Vascular resistance?
• Blood flow?
• Oxygen level?

Answer 17

Viscosity: Decreases
Vascular resistance: Decreases
Blood flow: Increases

Oxygen: Low

Question 18

In a high hematocrit state such as polycythemia (60+%):

• What happens to viscosity?
• Vascular resistance?
• Blood flow?

Answer 18

Viscosity: Increases
Vascular resistance: Increases
Blood flow: Decreases

Question 19

What is rouleaux?

What is rouleaux formation’s relation to tissue ischemia?

Answer 19

A factor that increases viscosity

• The tendency of RBC’s to aggregate into stacks at lower flow veocities
• Can cause a “sludge” or clumping, severely hindering flow and causing ischemia?

Question 20

What is the relationship between blood vessel radius and resistance?

Answer 20

Resistance is inversely proportional to the fourth power of the vessel radius

A 2-fold increase in radius will increase flow by 16 fold

Drugs that dilate vessels have a powerful effect on blood flow

Question 21

Vasoconstriction on arteries has what effect on:

• Resistance
• Pressure
• Blood flow

Answer 21

Resistance increases more than pressure
Blood flow decreases

Q = P/R

Question 22

Vasoconstriction on veins has what effect on:

• Resistance
• Pressure
• Blood flow

Answer 22

Pressure increases more than resistance
Blood flow increases

Q = P/R