L23 Hemodynamics

Question 1

Facts / assumptions about hemodynamics

Answer 1

Blood flows in a CLOSED system

Blood is a non-compressible fluid

Blood is heterogenous: plasma, cells, proteins

Vessels are compliant (not rigid)
Size depends upon interval pressure and vascular smooth muscle (VSMC) contractile state

Question 2

Flow v velocity

Answer 2

Flow- volume per unit time (ie. 5L/min)

Velocity- rate of displacement per unit time (ie. 1m/sec

Relationship: Q• = vA
Q• = flow (cm3/sec)
v = velocity (cm/sec)
A= cross sectional area of vessel (cm2)

Flows constant, velocity increases as cross sectional are decreases
v=Q•/A

Question 3

Despite capillaries having smallest diameter,

Answer 3

Blood velocity is lowest in capillaries

Total cross sectional area of all capillaries combined is huge

Question 4

Pressure v flow

Answer 4

Flow is dependent upon pressure difference

Question 5

Tube geometry

Answer 5

Radius r
Length l
Viscosity n

Q• proportional 1/L

Q• proportional r^4

Q• proportional 1/n

Question 6

Effects of fluid viscosity

Answer 6

Resistance to flow by a substance (blood) as a result of molecular cohesion

Major determinants of blood viscosity
Proteins (albumin)
Erythrocytes (hematocrit)
Temperature

Question 7

Poiseuilles law

Answer 7

Q=deltaP r^4 pie/nL 8

Question 8

Resistance inversely related to

Answer 8

r^4

Question 9

Series

Answer 9

A cell must pass through ALL vessels in the series group

Question 10

Parallel

Answer 10

A cell passes through only a subset of vessels in the parallel group

Question 11

Vascular resistance in parallel

Answer 11

Account for majority of vessel beds
ie pelvic vs leg arteries

1/total resistance = 1/R1 + 1/R2 + 1/R3

Total is always less than any single parallel resistance

Question 12

Vascular resistance in series

Answer 12

Account for minority of vessel beds
ie capillary beds within kidney

Total resistance = sum of all upstream resistances

Fluids flow down pressure gradients ( so pressure will go down as you go down resistances)

Question 13

Compound circuit analysis

Answer 13

Parallel part may be part of series

Isolate parallel beds

Work them into the series to finish

Question 14

Laminar v turbulent flow

Answer 14

Laminar- streamline, concentric lamina slide past one another
Highest velocity is center most, towards walls they slow down from drag

Turbulent 
  Lamina tear apart = eddy currents 
  Drain energy from system 
  Noisy (basis of measuring BP)
  Larger pressure required to maintain constant flow through turbulent areas

Question 15

Turbulence is noisy

Answer 15

BP
As cuff inflates around artery, flow becomes turbulent and makes sound (korotkoff sounds)

Valvular problems
Stenotic or insufficient valves cause flow through them to make sounds (bruit or murmurs)

Question 16

Vessel compliance

Answer 16

Pressure v absolute change in vessel volume

C= delta V/ delta P

Vessels can store blood

Dampen pulsatile flow

Veins have the highest capacitance (70%blood volume)

Stepped slope equals greater compliance