Physiology of the heart 2

Question 1

Whats the residual volume?

Answer 1

When the heart contracts- doesnt eject all of the blood- leaves some behind

Question 2

Whats the stroke volume and normal stroke volume?

Answer 2

When the heart contracts- delivers the stroke volume-

70mls approx

Question 3

Whats the cardiac output?

Answer 3

How much blood the heart is delivering each minute

=heart rate x stroke volume

Question 4

Whats the ejection fraction?

Answer 4

The % of blood ejected with each cardiac contraction

its a measure of the internal contractility of the heart

Question 5

What are the factors that affect heart rate?

Answer 5

sympathetic nervous system- positively chronotropic
parasympathetic nervous system- negative chronotropic
circulating catecholamines- e.g adrenaline
drugs

Question 6

Factors affecting stroke volume

Answer 6

intrinsic contractility- intracellular calcium, oxygen, free fatty acids, ATP
extrinsic contractility- pre load, after load, sympathetic activity
*parasympathetic nervous system has virtually no effect on contractility

Question 7

What’s preload?

Answer 7

The filling pressure going into the ventricles- LVEDP

Question 8

What’s afterload?

Answer 8

The pressure beyond the heart- in the circulation- resistance to ejection

Question 9

What happens when calcium enters the cell?

Answer 9

Calcium enters the cell- attaches to ryanodine receptors on the sarcoplasmic reticulum- causes calcium to be released from the SR- binds to more receptors- second wave of calcium is responsible for contraction

Question 10

Whats the stages of the ATP dependent actin-myosin dependent interaction?

Answer 10

ATP is hydrolyzed when the myosin head attaches to actin
ADP + Pi are bound to the myosin as the myosin head attached to actin
ADP + Pi are released causing the head to change position and the actin filament to move
Binding of ATP causes the myosin head to return to the resting potential

Question 11

What is the Frank-Starling mechanism?

Answer 11

Increases in the filling pressure (LVEDP- which results in myocardial fibre stretching)-> increased force of contraction-> increased stroke volume and cardiac output

Question 12

How does changes in venous return affect the frank-starling curve?

Answer 12

Increase the venous return- move up the curve- increase in the filling pressure- increase stroke volume-
We move up and down this curve on a minute to minute basis
Takes a small change in pressure to alter stroke volume

Question 13

How does exercise affect venous return?

Answer 13

Self-regulating essentially
sympathetic stimulation takes control- increases heart rate
frank starling controls CO based on venous return at resting

Question 14

How do changes in afterload and contractility affect the frank-starling curve?

Answer 14

increase contractility/ decrease in aferload= curve moves up and to the left - easier for the heart to eject- larger stroke volume
decreased contractility/ increase in afterload= operate on a lower curve thats flatter - have to have a higher pressure for the same cardiac output
*problems arise with high filling pressures- heart failure etc

Question 15

How does sympathetic stimulation affect cardiac output?

Answer 15

Isoprenaline (drug equivalent to adrenaline)- stimulus causes a greater influx of calcium and a greater contraction
drug increases contractility

Question 16

How does heart failure and therapy effect the frank-starling curve?

Answer 16

Failing heart= something intrinsically wrong- curve falls down to the right - much flatter
limit to how much stroke volume you can achieve in this heart (because of how flat the curve was)
LVEDP of 25mmHg- as the filling pressure increases - more symptoms and signs of heart failure
Diuretics used in HF- move down the curve- reduced filling pressure, fewer symptoms- small decrease in stroke volume

Question 17

What happens if you drop below a certain CO level?

Answer 17

fatigued, poor exercise capacity, in a state of medical shock

Question 18

How does high VEDP affect the right and left side of the heart?

Answer 18

right side= peripheral fluid collection, oedema
left side= back pressure can go into lungs- feeling breathless
filling pressure only needs to go up slightly for feelings of breathlessness to occur

Question 19

Whats the dilemma with treating HF patients?

Answer 19

Want to taken them out of a zone of high filling pressures, but dont want to drop their stroke volume

Question 20

How do we treat HF patients?

Answer 20

Diuretics- bring them down the curve- move them out of area of symptoms
Vasodilaters (ACE inhibitors)- reduce afterload, shift the curve up and left - can use diuretics as well

Question 21

How does digoxin affect cardiac output?

Answer 21

Causes a greater influx of calcium- greater contraction

inhbits Na/K ATPase- greater intracellular calcium