Hemodynamics and Important Principles

Question 1

What is the formula for flow?

Answer 1

Q = (P1 - P2)/ R

Q: flow (mL/min)
P1: upstream pressure (pressure head) for segment or circuit (mmHg)
P2: pressure at the end of the segment or circuit (mmHg)
R: resistance of vessels between P1 and P2 (mmHg/mL/min) (pressure/(volume/time))

Question 2

What is the most important factor determining resistance

Answer 2

vessel radius

Question 3

What are 3 major variables for resistance?

Answer 3

R ∝ vL/r4

Question 4

What determines afterload to the heart?

Answer 4

TPR/SVR basically stands for total peripheral resistance or systemic vascular resistance

Question 5

Formula for blood velocity?

Answer 5

Velocity of blood = flow/CSA

CSA cross sectional area

Question 6

What is the formula used to asses turbulent vs laminar flow?

Answer 6

Reynold’s Number = {(diameter)(velocity)(density)]/ viscosity

> 2000 = turbulent flow
< 2000 + laminar flow

Question 7

Besides viscosity, diameter, density, and velocity what are some other factors that promote turbulence?

Answer 7

vessel branching
narrow orifice (severe stenosis) due to very high velocity of flow

Question 8

Formula for resisters in a series?

Answer 8

RT = R1 + R2 + R3

Question 9

Formula for resistors in parallel?

Answer 9

1/RT= 1/R1 + 1/R2 + 1/R3 …..

Question 10

Is the total resistance less in parallel circuits or series circuits?

Answer 10

parallel circuits

Question 11

Formula for vessel compliance.

Answer 11

C = △V/ △P

Question 12

What is compliance?

Answer 12

How easily a vessel is stretched

Question 13

What is elasticity?

Answer 13

inverse of compliance

a vessel that has high elasticity has a large tendency to rebound from stretch

Question 14

What is LaPlaces Law ?

Answer 14

Shows the relationship of wall tension to pressure

T ∝ Pr

Tension directly proportional to pressure and radius