L05-Regulation of cardiac ouput

Question 1

What are preload and afterload?

Answer 1

Preload is the input to the heart (i.e. the venous return)

Afterload is the resistance against which the ventricle is pumping

Question 2

What is the hearts response to increased stretch?

Answer 2

Responds with an increased force of ventricular contraction

Question 3

What are the two main methods by which the heart can increase its force of contraction?

Answer 3

Increasing the Ca2+ sensitivity of the contractile apparatus (starlings law)
Increasing the concentration of Ca2+ in the cells (changing the contractility)

Question 4

What is the hearts responce to increased total peripheral resistance?

Answer 4

This will cause less blood to be pumped as there is more resistance resulting in a larger end systolic volume. This causes increased stretch that causes increased force of contraction to overcome to resistance.

Question 5

What is frank-starlings law of the heart?

Answer 5

The force of ventricular contraction is dependent on the length of the ventricular muscle fibres in diastole. i.e. the length in the ventricular resting phase (or EDV)

Question 6

How does starlings curve appear and why?

Answer 6

Initially as the EDV increases so does the SV as the stretched myocytes form more cross bridges. Beyond the optimum point the SV decreases with increasing EDV as fewer cross bridges form. this results in a bell shaped curve.

Question 7

Which 5 factors affect central venous pressure (right atrial filling)?

Answer 7

Blood volume
skeletal muscles pump
respiratory pump
venous tone
gravity

Question 8

How does going from lying down to standing up affect the stretch of the heart?

Answer 8

Lying down reduces venous pooling and increasing venous return and hence stretches the heart more, vice versa for standing up with increased venous pooling.

Question 9

What is the effect of increased EDV on the PV loop for the left ventricle?

Answer 9

Increased EDV will cause increased force of contraction which will allow larger volumes of blood to be pumped at the same pressure

Question 10

How can stretch independent contraction be increased? (contractility/inotropy)

Answer 10

Through increased sympathetic nerve activity or circulating adrenaline and nor adrenaline acting on B1 receptors

Question 11

How does an increase in inotropy affect the LV P-V loop?

Answer 11

Increased end systolic volume so the loop stretches left to create a lower final volume with the same pressures still occuring

Question 12

What is the effect of heart failure on starlings curve?

Answer 12

A lower curve as an increase in EDV does not create as bigger response in SV. As ventricular muscle is more stretched