Flashcards in CVS Session 5 (Lecture 5.1) Deck (29):

1

## Define flow through a tube.

### Volume of fluid passing a given point per unit time

2

## Define velocity through a tube.

### The rate of movement of fluid particles along the tube

3

## What is the relationship between flow and pressure?

### Flow is proportional to pressure difference between ends of a vessel

4

## If flow is constant, what is the relationship between velocity and the radius of a tube?

###
Velocity is inversely proportional to cross sectional area

(same no. of particles to move a given distance)

5

## In most blood vessels what is the flow described as?

### Laminar

6

## Describe laminar flow?

###
Smooth flow of blood generating no noise

Gradient of velocity from the middle to the edge of vessel with particles in the centre moving fastest and fluid being stationary at the edge

Fluid moves in concentric layers so slide over each other.

7

## Describe turbulent flow? How can it be generated?

###
Flow through a vessel that generates noise (bruit).

As mean velocity increases flow eventually becomes turbulent

Velocity gradient breaks down

Fluid tumbles over

Fluid resistance greatly increased

8

## If the driving pressure is constant, what is the flow determined by?

### Mean velocity

9

## What is the mean velocity dependent on?

###
Viscosity of fluid

Radius of tube

10

## What is viscosity? What is the relationship between viscosity and velocity?

###
Extent to which fluid layers resist sliding over one another

Velocity is inversely proportional to viscosity

11

## At a constant gradient, what happens to the mean velocity as the radius of a tube increases?

### Velocity increases as it is proportional to C.S.A.

12

## What is the formula that relates flow, velocity and C.S.A?

### Q=V . CSA

13

## What is Poiseulles Law?

### Flow = Pr^4 / (Viscosity.Length)

14

## What is the formula relating pressure, flow and resistance?

### P=QR

15

## Rearrange Poiseulles law with P=QR to equate pressure change.

### P = Flow * (8.Viscosity.Length/pi r^4)

16

## What is the relationship between resistance and viscosity and radius?

### Resistance is proportional to viscosity and inversely proportional to the fourth power of radius

17

## What is the formula for resistance for blood vessels in series? What is the significance of this?

###
R = R1 + R2

Resistances add for vessels in series

18

## What is the formula for resistance for blood vessels in parallel? What is the significance of this?

###
R = (R1.R2)/R1 + R2

Resistance is lower in parallel vessels

19

## What resistance are arteries and arterioles? What is the pressure change across these vessels?

###
Low (arteries) resistance - pressure change is low

High (arterioles) resistance - pressure change is high

20

## What is the resistance of a) individual capillaries and b) capillaries in parallel ?

###
a) High resistance

b) Overall resistance is low - pressure drop is smaller

21

## What resistance are venules and veins?

### Low resistance

22

## For what reason is the pressure in arteries high?

### High resistance of arterioles to ensure adequate flow through them

23

## Which two variables affect arterial pressure?

### Arteriolar resistance and stroke volume

24

## What is name of the ability of a blood vessel to stretch?

### Distensibility

25

## What happens as vessels stretch?

### Resistance falls so flow increases for a given pressure.

26

## What happens when the pressure in a distensible vessel falls?

### Flow is reduced and eventually can lead to vessel collapse (below critical closing pressure) and blood flow =0 with infinite flow resistance.

27

## What does an abrupt increase in pressure do to the flow in a distensible vessel?

### Transient increase in flow in than out of vessel.

28

## What do distensible vessels store? What is this property called?

###
Store blood.

Capacitance

29