Control Of Cardiac Output

Question 1

What is preload?

Answer 1

The amount the ventricles are stretched via filling in diastole- related to the end diastolic volume/ central venous pressure.

Question 2

What is afterload?

Answer 2

The pressure the heart must eject against, roughly equivalent to aortic pressure

Question 3

Describe total peripheral resistance

Answer 3

Resistance to blood flow offered by all of the systemic vasculature

Question 4

What happens to the capillaries and venous side if arterioles constrict/ increase BP?

Answer 4

The capillaries and venous side has a lower blood pressure (as they are located away from the arterioles. The vessels before the arterioles such as arteries will have increased pressure.

Question 5

In what order to we find blood vessels in the body?

Answer 5

Arteries —> arterioles —> capillaries —> venues —> veins

Question 6

Impact of decreasing TPR and maintaining the same CO

Answer 6

Total peripheral resistance falls. Arterial pressure falls. Venous pressure increases (but is still lower than arterial).

Question 7

Impact of increasing TPR and maintaining CO?

Answer 7

Arterial pressure increases, venous pressure falls (blood finding it harder to get through arteries).

Question 8

Effect of increasing CO and maintaining TPR?

Answer 8

Arterial pressure increases as more blood pumped here, venous decreases as more blood is pumped out of venous circulation to arteries.

Question 9

Effect of decreasing CO and maintaining TPR?

Answer 9

Reduces arterial pressure (not as much pumped), increases venous pressure as less blood is being pumped into the heart.

Question 10

What happens at a local level if tissues need more blood?

Answer 10

Arterioles and pre-capillary sphincters dilate to allow more blood flow.

Question 11

Equation for cardiac output?

Answer 11

Stroke volume x heart rate

Question 12

Equation for stroke volume?

Answer 12

End diastolic volume EDV- end systolic volume ESV

Question 13

What’s the cardiac output at rest for a 70kg man?

Answer 13

5L blood per minute

Question 14

If there is a higher venous pressure what impact does this have on the heart?

Answer 14

The more the heart fills

Question 15

High level of heart filling does what to the left ventricular pressure?

Answer 15

Increases

Question 16

Decreased/ increased compliance of the heart has what impact on left ventricular pressure?

Answer 16

If you have a compliant heart this decreases left ventricular pressure. If you have decreased compliance you have a higher pressure in the left ventricle.

Question 17

Briefly describe the Frank- Starling law of the heart

Answer 17

The greater the heart fills the more it will contract up to a certain point (increased preload). The harder the heart contracts the greater the stroke volume. An increase in venous pressure will fill the heart more.

Question 18

As the cardiac muscle fibres are stretched the sensitivity for calcium….?

Answer 18

Increases

Question 19

The pulmonary and systemic circulations must operate in series, what does this mean?

Answer 19

The same volume of blood pumped to the body must also be pumped to the lungs

Question 20

Extrinsic factor that increases contractility and force of contraction?

Answer 20

Circulating adrenaline and sympathetic circulation

Question 21

Increased peripheral resistance has what impact on aortic pressure?

Answer 21

Increase

Question 22

What factors determine cardiac output?

Answer 22

1. How hard the heart contracts (determined by end diastolic volume- how much the heart fills) and contractility (increased by sympathetic NS)
2. How hard it is to eject blood (determined by aortic impedance - roughly equivalent to arterial pressure)

Question 23

What happens to total peripheral resistance and the heart if metabolism increases?

Answer 23

Reduced total peripheral resistance as more blood is needed at the tissues, decrease in arterial BP, increase in venous blood pressure, heart responds by pumping more.

Question 24

What happens to venous, arterial and CO output when standing?

Answer 24

Blood pools in the legs due to gravity and venous pressure is reduced - harder for blood to return to the heart, this reduces CO and arterial pressure. Reflex: baroreceptor reflex and sympathetic nervous system detects and increases contractility and heart rate which increases TPR.

Question 25

What mechanisms increase venous return to the heart during exercise?

Answer 25

Calf muscle activity squeezes veins, vasoconstriction returns more blood to heart, later decreased TPR increases venous return.

Question 26

How do we measure the right arterial pressure?

Answer 26

Jugular venous pulse (Behind SCM muscle) biphasic pulse. Measure pulse by looking at the height of the highest visible palpations above the sternal angle then add 4cm. (Normally 5-8 cm of water)

Question 27

Conditions that increase jugular venous pressure

Answer 27

• right side of heart doesn’t pump out blood properly
• volume overload with infusion
• if something impairs filling of the heart (stab wound)