12. Vascular Haemodynamics

Question 1

Blood flow is

Answer 1

w is the quantity of blood that passes a given

point in the circulation in a given period of time

Question 2

For the whole circulation: Blood Flow (Q) =

Answer 2

Cardiac

Output (CO) = HR x SV

Question 3

Arterial pressure is controlled

independent of

Answer 3

either local blood flow

control or cardiac output control

Question 4

Blood flow is directly proportional to ?

Answer 4

the Pressure gradient

Question 5

Blood flow is inversely proportional to ?

Answer 5

Total Peripheral Resistance

Question 6

Bernoulli’s principle states that:

Answer 6

Total energy of laminar flow without resistance is
constant and equals the sum of:
a) Pressure energy (P x V)
b) Potential or gravitational energy (ρgh)
c) Inertial or kinetic energy(½ρ v2 )

Question 7

Resistance (R) is proportional to:

Answer 7

1.) the tube length (L)
2.) the viscosity of fluid (η)
and inversely proportional to
3.) the radius raised to the
fourth power (r^4)

Question 8

Viscosity (η) is ?

Answer 8

a measure of the friction between adjacent layers of fluid as
they slide over one another

Question 9

Determinants of blood viscosity (η):

Answer 9

1.Temperature - blood (or honey etc) gets
“thicker” (more viscous) as it gets colder
2.Haematocrit - The ratio of red cell volume to
total volume in a sample of peripheral blood,
Normally ~ 0.45
3.Shear rate (velocity)
At very low flow velocities blood becomes non-Newtonian:
- viscosity is no longer independent of shear rate.
- viscosity increases as cells aggregate (sludging of blood).
4.Vessel Diameter
in very small blood vessels (less than 0.3 mm) there is an apparent decrease in viscosity

Question 10

Poiseuille’s equation assumes:

Answer 10

1. steady laminar flow
2. rigid straight tube
3. Newtonian fluid ( no turbulance like water)

Question 11

Blood vessels are distensible!

Increasing pressure results in:

Answer 11

• distension of blood vessel
• thus reduced resistance
• Increased blood flow

Question 12

Blood vessels are distensible!

Decreasing pressure results in:

Answer 12

• reduced stretch of vessels
• increased resistance
• decreased blood flow

Question 13

Blood flow is not directly
proportional to the pressure
gradient.
In many vascular beds (e.g.
cerebral, renal) changes in
pressure are compensated by local mechanisms to ensure
blood flow remains ?

Answer 13

relatively
constant

=Autoregulation

Question 14

The endothelium is very sensitive to

Answer 14

shear stress.

Question 15

As flow increases, shear stress
acting on the endothelium
increases. Resulting in:

Answer 15

• NO release
• vasodilation
• But also potentially lead to
endothelial damage

Question 16

Factors which may result in turbulence:

Answer 16

high fluid densities
• large tube diameters
• high flow velocities
• low fluid viscosities
• abrupt variations in tube dimensions
• irregularities in the tube walls

Question 17

An increase in diameter, increase in velocity or

decrease in viscosity will lead to increase in?

Answer 17

Reynolds’ number (Re)

Predicting turbulent flow

Question 18

_______generates sound waves (e.g.,
ejection murmurs, carotid bruits) that can be
heard with a stethoscope.

Answer 18

Turbulence

Question 19

Because higher ______enhance turbulence,

murmurs intensify as ____increases

Answer 19

velocities

flow

Question 20

Blood flow is dependent on

Answer 20

pressure gradient and resistance

Question 21

Resistance is very dependent on

Answer 21

vessel diameter and

viscosity, and can be estimated by Poiseuille’s equation:

Question 22

Blood flow is influenced by _____ ______dynamics with the ability to change ____
(compliance) of the blood vessels (i.e. non-rigid), and the potential for _____
blood flow

Answer 22

blood vessel

tone

turbulent