Cardio IV

Question 1

Describe the pattern of pressures within pulmonary and systemic circulation and how they are similar or differ from one another.

Answer 1

Systemic pressures always < pulmonary pressures

Both follow the same pattern of large oscillations (systolic to diastolic) that damp out as you move from arteries to capillaries to veins.

Question 2

How does the difference in pulmonary vs systemic circulation pressure affect the structure of the heart?

Answer 2

Because the systemic pressure is always higher than the pulmonary pressure, the left ventricle (which feeds into the systemic circulation) is larger than the right ventricle.

Question 3

What is hydrostatic pressure?

Answer 3

The pressure exerted by a fluid at equilibrium at a given point within the fluid due to the force of gravity.

Question 4

What is the formula for hydrostatic pressure? Describe each variable.

Answer 4

P = rho x g x h
Where rho is the density of the fluid
g is gravitational force
h is the height of the fluid at the point of interest

Question 5

What is the conversion between cm H2O and pascals?

Answer 5

1 cm H2O = 90 Pa

Question 6

What is the conversion between cm H2O and mm Hg?

Answer 6

1 cm Hg = 14 cm H2O

Question 7

What is the difference between a direct and an indirect method of blood pressure measurement?

Answer 7

A direct method involves puncturing the arteries, while an indirect method does not.

Question 8

What was the first indirect blood pressure measurement? How did it work?

Answer 8

The mercury sphygmomanometer. It involved wrapping a cuff around the arm and pumping, which would pump a column of mercury.

Question 9

Convert 1 mm Hg into kPa.

Answer 9

1 mm Hg = 14 mm H2O = 1.4 cm H2O = 0.13 kPa

Question 10

How was central venous pressure/right atrial pressure originally measured?

Answer 10

Place tip of catheter into right atrium and release saline into the heart. The pressure will be measured with a manometer and will stop moving when the pressure of the saline = central venous pressure.

Question 11

What is the typical central venous pressure/right atrial pressure?

Answer 11

5-10 cm H2O

Question 12

What is perfusion pressure?

Answer 12

Perfusion pressure is the pressure of the blood that flows through an organ or through a vessel. It is the pressure that governs blood flow.

Question 13

What is the formula for perfusion pressure?

Answer 13

Perfusion pressure = arterial pressure - venous pressure
However, since arterial pressure&raquo_space; venous pressure (100 mm Hg to 5 mm Hg), we ignore venous pressure.

Question 14

What happens if there is no perfusion pressure? When might this occur?

Answer 14

If there is no perfusion pressure, there is no pressure gradient and thus no blood flow. This occurs when the individual is dead.

Question 15

What are the two factors that affect blood flow? Write the formula expressing their relationship.

Answer 15

Flow = perfusion pressure / resistance

Question 16

How do you measure resistance?

Answer 16

Resistance can’t be measured directly. The flow and the perfusion pressure must be measured so that we can do R = perfusion pressure / flow

Question 17

Blood flow in vessels can be described as […] flow

Answer 17

laminar or parabolic

Question 18

Explain why blood undergoes laminar or parabolic flow.

Answer 18

If you measure the velocities at the central line in the vessel, you will have a large velocity. As you move towards the walls, the velocity approaches zero. So, there is a parabolic shape to the velocities.

The blood flow can also be conceptualized as laminar because the blood can be thought of as being made up of many layers (laminae). The ones towards the center flow faster than those that reach out towards the sides because there is frictional loss of energy from the sliding of laminae over each other.

Question 19

What is Poiseuille’s law and what is the formula? State the variables.

Answer 19

Resistance = 8 v L / pi r^4
Where v = viscosity of fluid
L = length of vessel
r = radius of vessel

Question 20

For what situations is Poiseuille’s law valid?

Answer 20

In laminar/parabolic flow ONLY.

Question 21

Name the 4 major controls of vessel resistance.

Answer 21

1. Local metabolites
2. Innervation
3. Hormones
4. Endothelial control

Question 22

What is the relationship between vessel radius and resistance? What are the implications of this?

Answer 22

Radius is inversely proportional to radius ^ 4
This means that small changes in radius will have a big effect on the resistance.

Question 23

What is the formula for combined resistance for vessels or organs in series? What is the consequence on functionality?

Answer 23

R = R1 + R2, so R > R1 or R2
When you put vessels in series, you’re increasing the resistance. This is why branching is useful; if we didn’t have it, there would be much more resistance in the vessels.

Question 24

What is the formula for vessels or organs in parallel? What is the consequence on functionality?

Answer 24

1/R = 1/R1 + 1/R2, so R < R1 or R2
The combined resistance falls when you puts things in parallel, meaning that you need a smaller pressure to get flow.

Question 25

How does the pressure drop across vessels in parallel compare to the pressure down across vessels in series?

Answer 25

In parallel, the pressure drop across vessels is identical.