Hemodynamics

Question 1

Blood flow through a particular organ is considered to be flow in series/parallel?

Answer 1

Series. Resistance is thus additive. Resistance comes from the vessels.

Question 2

Blood flow through the circulation is considered to be flow in series/parallel?

Answer 2

Parallel. Resistance is added by 1/Rtotal = summation of 1/Ri. Resistance comes from each organ.

Question 3

What vessel type has the largest resistance?

Answer 3

Arterioles. Contraction or relaxation of the smooth muscles in arteriolar wall is a major control point in cardiovascular physiology.

Question 4

How are TPR and Cardiac output related?

Answer 4

CO ~= MAP/ TPR. MAP = CO x TPR

Question 5

What happens to TPR during exercise? What about hypertension? What is a normal TPR?

Answer 5

TPR decreases in exercise and increases in hypertension. TPR at rest for a normal pt is 1.2 PRU

Question 6

In terms of Reynolds number when is flow turbulent?

Answer 6

When Re is over 3000.

Question 7

In terms of Reynolds number when is flow laminar?

Answer 7

When Re is less than 2000.

Question 8

What is the equation for Reynolds number.

Answer 8

Re = 2rvp/n. = disruptive forces/ cohesive forces.

Radius, velocity, density, viscosity

Question 9

In laminar flow Q is proportional to ∆P, in turbulent flow what is Q proportional to?

Answer 9

Q is proportional to the square root of ∆P. Thus the effective resistance increases

Question 10

What is gravitational pressure?

Answer 10

It is the pressure due to the effects of gravity. it is equal to pgh. The density, times gravity, times the height.

Question 11

Does gravity affect the driving pressure (or flow) of blood? Does it affect the distribution of blood?

Answer 11

No it does not affect the driving pressure since the pressure in the veins counterbalances that in the arteries. It affects the distribution of blood and the transmural pressure (P_TM)

Question 12

Does gravity affect the measurement of blood pressure?

Answer 12

Yes. It should be taken at heart level.

Question 13

What is static pressure?

Answer 13

Pressure present whether the blood is moving or not. It is composed of the applied or lateral pressure and the force of gravity. P_L + pgh. (Ptotal = Pstatic + P dynamic)

Question 14

What is dynamic pressure?

Answer 14

Pressure due to kinetic energy. It is equal to 1/2 pv^2. (Ptotal = Pstatic + P dynamic)

Question 15

What is sheer stress? How is it calculated?

Answer 15

It is created by flowing blood on the endothelial wall directed along the long axis of the vessel. It is proportional to the viscosity and the shear rate, which is the rate at which the axial velocity changes from the wall to the lumen. t=4nQ/πr^3. Units are mmHg

Question 16

Above what sheer stress will endothelial cells detach?

Answer 16

> 0.3 mmHg

Question 17

What can cause an increase in blood velocity? What happens to lateral pressure and dynamic pressure when blood velocity increases?

Answer 17

Stenosis. A greater proportion of the blood pressure is converted from lateral into dynamic, thus lateral pressure decreases while dynamic pressure increases.