Lecture 5- Control of Cardiac Output

Question 1

What happens to the pressure of fluid in a tube as it encounters resistance?

Answer 1

The pressure that the blood exerts drops as it flows through ‘a resistance’

Question 2

where offers the greatest resistance

Answer 2

arterioles

Question 3

constriction of the arterioles

Answer 3

increases resistance–> pressure in capillaries and venous side fall, but pressure on arterial side will rise

Question 4

preload

Answer 4

amount the ventricles are stretched (filled) in diastole- related to the end diastolic volume or central venous pressure

Question 5

afterload

Answer 5

the load the heart must eject blood against (roughly equivalent to aortic pressure)

Question 6

Total peripheral resistance

Answer 6

resistance to blood flow offered by all systemic vasculature

Question 7

Effects of changing total peripheral resistance

1) If TPR falls and CO is unchanged…

Answer 7

Arterial pressure will fall

Venous pressure will increase

Question 8

as resistance in arteries decreases

Answer 8

venous pressure increases

Question 9

Effects of changing total peripheral resistance..

2) If TPR increases and CO is unchanged

Answer 9

Arterial pressure will increase

Venous pressure will decrease

Question 10

as resistance in arteries increases

Answer 10

venous pressure decreases

Question 11

Effects of changing cardiac output

3) If CO increases and TPR is unchanged

Answer 11

Arterial pressure will increase

Venous pressure will fall

Question 12

As CO increases, the pressure exerted on the arteries increases, this in turn ..

Answer 12

decreases venous pressure

The heart is also pumping more blood out of the venous system every contraction meaning there is less of a back log of venous blood, decreasing pressure

Question 13

Effects of changing cardiac output…

4) If CO decreases and TPR is unchanged

Answer 13

Arterial pressure will fall

Venous pressure will rise

Question 14

As CO decreases, the pressure exerted on the arteries decreases, this in turn

Answer 14

increases venous pressure

The heart is also pumping less blood out of the venous system every contraction meaning there is a back log of venous blood, increasing pressure

Question 16

If tissue needs more blood the arterioles and precapillary sphincters

Answer 16

will dilate

• peripheral resistanc ewill fall
• heart will need to pump more so that arterial pressure does not fall and venous pressure doesnt rise

Question 17

heart sees changes ind emdnd as changes in

Answer 17

arterial blood pressuer (aBP) and central venous pressure (CVP)

Question 18

in diastole the ventricle communicates with the atrium and veins but is islated frm the otuflow tract

Answer 18

Ventricle fills until the walls stretch enough to produce intraventricular pressure equal to the venous pressure

Question 19

the higher the venous pressure

Answer 19

the more the heart fills

Question 20

the more the heart fills the higher the ventricular pressure

Answer 20

the higher the ventricular pressure

this relationship is the ventircular compliance fcurve

Question 21

ventricular compliance curve

Answer 21

Question 22

stroke volume =

Answer 22

end diastolic volume (EDV) – end systolic volume (ESV)

Question 23

end diastolic volume

Answer 23

the amount of blood in the left ventricle before contraction (when they are higher)

Question 24

end systolic volume

Answer 24

the amount of blood left in the left ventricle after contraction

Question 25

typical SV

Answer 25

70ml (about 67% of normal EDV)

Question 26

can increase SV by increasing …… and decreasing …..

Answer 26

EDV and ESV

Question 27

Frank- Starling Law of the heart

Answer 27

Demonstrates that stretching the ventricles by increasing the filling of the heart increased the force of contraction

Question 28

like with skeletal muscle if you stretch the fibres of the heart before contracting

Answer 28

it will contract harder

Question 29

the more the heart fills

Answer 29

the harder it contracts

Question 30

the harder the heart contracts the

Answer 30

bigger the stroke volume

Question 31

increased venous pressure

Answer 31

will fill the heart more leading to strong contraction and higher SV

Question 32

how much ventricles fill depends on

Answer 32

compliance

Question 33

compliance

Answer 33

The term compliance is used to describe how easily a chamber of the heart or the lumen of a blood vessel expands when it is filled with a volume of blood. Physically, compliance (C) is defined as the change in volume (ΔV) divided by the change in pressure (ΔP).

Question 34

length tension curve

Answer 34

If sarcomere length is too short filament overlap interferes with contraction

In cardiac muscle also get an increase in calcium sensitivity as the muscle fibres are stretched

Question 35

Frank starling curve is an example of

Answer 35

intrinsic control mechanism of the heart

Question 36

intrinsic control mechanisms of the heart

Answer 36

• Increased stroke volume with increased filling of the heart is intrinsic control mechanism
• It ensure both sides of the heart pump maintain the same output
• Pulmonary and systemic circulation operate in series- the same volume of blood pumped to the body must also be pumped to the lungs

Question 37

contractility is the

Answer 37

force of contraction for a given fibre length

Question 38

a change in contractility is seen as a change in

Answer 38

the slope of the starling curve

Question 39

name extrinsic factors which affect contraxctign

Answer 39

symapthetic stimulation and circulating adrenaline

Question 40

increasing sympathetic activity will

Answer 40

increase contractiltiy increasing SV

Question 41

affect of icnreasing arterial pressure ons troke f=vomume

Answer 41

• Arterial (aortic) pressure is increase when the peripheral resistance is increased
• Making it harder for the heart to pump out
• Increased TPR also reduces venous pressure and therefore reduces filling of the heart
• Overtime you can get inappropriate increase in arterial pressure- heart will have to work harder

Question 42

factors determining CO

Answer 42

1. How hard it contracts
   * Determined by the EDV (how much the heart fills) and contractility (increased by sympathetic drive)
2. How hard it is to eject blood
   * Determined by aortic impedance (roughly arterial pressure)

Question 43

contractility and HR controlled by the ANS… decrease in arterial BP will….

Answer 43

reduce parasymapthetic stimulation and stimulate sympathetic stimulation

Question 44

demand led pumping.. if metabolism of body increases…

Answer 44

TPR will fall supplying more blood to tissue

• decrease in arterial pressure and increase in venous pressure
• heart will response by pumping more

Question 45

what happens to BP when we stand up

Answer 45

pooling of blood in legs due tot he effecs of gravity on a column of liquid

• decreased venous pressure
• decreassed CO
• decrrased arterial pressure

both aBP and vBP have changed in same direction and cannot be adjusted by intrinsic mechanism.

–> must use baroreceptor reflex and ANS to icnrewase heart rate and TPR

Question 46

if extrisnsic mechanissm do not work

Answer 46

postural hypotension

Question 47

exercise and CO

Answer 47

Initially muscle pumping and venoconstriction returns more blood to the heart

Later decreased TPR also increases venous return

Very early response of increased heart rate (decreased parasympathetic drive, increase sympathetic drive)

Question 48

jugular venous pulse and right atrial pressure

Answer 48

• Indication of venous pressure
• Measured in right internal jugular vein
• Biphasic pulse observed
• Direct column of blood connected to the right atrium
• Pulse is see behind sternocleidomastoid muscle
• Estimate highest visible pulsations (JVP) above sternal angel +4cm= JVP in cm H20
• Normally 5 to 8 cm H2O

Question 50

Conditions that will increase JVP

Answer 50

• If the right side of the heart doesn’t pump blood out properly
• Volume overload with IV infusion
• If something impairs filling of the heat