Principles of Blood Flow

Question 1

Is Blood a Newtonian fluid?

Answer 1

No it is non-Newtonian. (There is no constant viscosity)

Question 2

What is stage 1 blood flow?

Answer 2

Steady laminar flow in a rigid vessel. Static driving pressure.

Question 3

What is stage 2 blood flow?

Answer 3

High Reynold’s number flow and turbulence. Dynamic pressure.

Question 4

What is stage 3 blood flow?

Answer 4

Elastic vessel walls and pulsatile pressure.

Question 5

What is stage 4 blood flow?

Answer 5

Microcirculation and diffusion.

Question 6

What is blood flow? Describe flow through a series of tubes.

Answer 6

It is the quantity of blood passing a particular observation point in a given time interval (L/min). It is constant

Question 7

Mathematically how can one describe blood flow in a parallel circuit?

Answer 7

Volume flows are additive. Flow in equals flow out if there are no sources or sinks. Flow across any total cross-sectional area is constant. Generalizes to any number of parallel branches. Flow is the same in the aorta and the pulmonary artery.

Question 8

What does the parallel architecture of the circulatory system permit?

Answer 8

Redistribution of blood flow

Question 9

What is the continuity equation?

Answer 9

In tubes with varying cross-sectional area Q=A x v. v=detla x/ delta t.

Question 10

How is velocity related to the total cross-sectional area?

Answer 10

Inversely proportional v=Q/A. With constant flow a smaller vessel will have blood traveling through it at a higher velocity.

Question 11

What is transit time? How can it be estimated? What is the transit time for the whole circulation?

Answer 11

It is the time required for a blood cell to travel between two points in the system. t=l/v (length and velocity) t=V/Q (volume and flow). One pass through the entire systemic and pulmonary circulation is about 1 min.

Question 12

What contributes to resistance of flow?

Answer 12

The walls of the vessel and the viscosity of the blood. They are both frictional forces.

Question 13

Since the length of blood vessels and the viscosity of blood do not normally change what is the major variable that determines the resistance to the flow?

Answer 13

The radius of blood vessels, primarily the arterioles.

Question 14

What is Poiseuille’s law?

Answer 14

Q= ∆P x (pi r^4/ 8nL). n=viscosity L=length

Question 15

How is temperature related to viscosity?

Answer 15

They are inversely related. Cold temperatures increase blood viscosity contributing to decreased blood flow in cold hands and feet.

Question 16

How does blood pressure change along the length of a vessel?

Answer 16

For a given flow a greater pressure drop along the length of the vessel occurs in a longer vessel with a higher viscosity fluid and most severely with a smaller radius.

Question 17

What is ∆P equal to?

Answer 17

P1-P2 where P1 is the pressure at the beginning of the vessel. P2=P1-(8nQ/πr^4)L

Question 18

How do you determine resistance for blood vessels in series? What does R equal?

Answer 18

Rtotal = R1 + R2 + R3

R=8πn(L/A^2)

Question 19

Across which vessel is the largest pressure drop if they are all equal lengths?

Answer 19

The smallest vessel will cause the largest drop in pressure (all other variables held constant Q, L, n etc.)

Question 20

How is resistance for blood flow determined when vessels are in parallel?

Answer 20

1/Rtotal = 1/R1 + 1/R2 + 1/R3 etc. The more branches in a parallel network the lower the total resistance.

Question 21

For simplicity how can Resistance be written?

Answer 21

R=K/r^4. Or R=K/A^2