Cardiac Function

Question 1

Cardiac output

Answer 1

The performance of the pump
Is the amount of blood pumped by the left ventricle into the aorta in one minute
Varies with body size

Normal CO: 4-8L/min
CO = HR x SV

Question 2

Stroke Volume (SV)

Answer 2

Amount of blood pumped by the left ventricle into the aorta with each contraction.
SV = CP (ml/min) / HR (beats/min)
Normal SV value: 60-120mL/beat

Question 3

Cardiac index

Answer 3

Number obtained by dividing cardiac output by the body surface area
CI = CO / BSA
Normal value: 2.0-4.0L/min/m2

Question 4

Left ventricular ejection fraction (LVEF)

Answer 4

Is the percentage of total blood in the left ventricle that is pumped out with each contraction.
LVEF: SV/End diastolic volume
Normal values: 50-70%

Question 5

Factors that affect cardiac output

Answer 5

Preload
Afterload
Contractility
Heart rate

Question 6

Factors that affect preload

Answer 6

• Venous return
• End systolic volume
• Atrial systole

Question 7

Preload/ LVEDP

Answer 7

Preload aka left ventricular end-diastolic pressure
- the amount of ventricular muscle fiber stretch at the end of diastole
- Is the pressure in the ventricles at the end of the filling period right before systole (Resting pressure)
- The heart is loading up with blood before the next contraction (systole)

Question 8

Venous return

Answer 8

Affects preload
- The amount of blood that flows into the right atrium
The amount of blood is dependent on:
- Blood flow through the tissues of the body
- Rate of venous return (effective pressure = volume)

Question 9

How is blood flow through the tissues determined during venous return?

Answer 9

Metabolic need of the organs
- Oxygen demand increases causes
- Vasodilation
Acts as a reservoir to maintain flow to vital organs
64% of total blood volume is venous blood

Question 10

End systolic volume

Answer 10

Effects preload
The amount of blood that remains in the ventricles after systole just before filling phase (diastole)
It is the lowest volume of blood in the ventricles during the cardiac cycle

Question 11

Atrial systole

Answer 11

Affects preload
Atrial contraction (systole) pushes blood to the ventricles
- prior to atrial contraction, the ventricles fill during diastole to about 70-80% of capacity
Atrial systole contributes to the remaining 20-30% blood supply to the ventricles
- Atrial kick

Question 12

What conditions affect afterload

Answer 12

Resistance (PVR, SVR)
Ventricular dilatation
Outflow obstruction

Question 14

Afterload

Answer 14

The force or load which the heart has to contract against to eject the blood
It is the systemic resistance to flow

Question 15

Example of outflow obstruction

Answer 15

Aortic valve stenosis

Question 16

Examples of ventricular dilatation

Answer 16

Causes decreased SV and CO

Question 17

Systemic vascular resistance

Answer 17

Affects afterload
Is an indicator of left ventricular afterload
The pressure gradient across the systemic circulation divided by the cardiac output

Question 18

SVR equation and range

Answer 18

(MAP - CVP) / Cardiac output
Normal value: <20mmHg/L/min

Question 19

Pulmonary vascular resistance (PVR)

Answer 19

PVR = MPAP - PCWP / CO
x 80
PCWP - Pulmonary capillary wedge pressure
MPAP - Mean pulmonary artery pressure

Question 20

Contractility

Answer 20

Decreased?
- Decreased SV and CO
Increased?
- increased SV and CO

Question 21

Methods of measuring CO

Answer 21

Thermodilution
Estimated fick method
Echocardiography
Radionuclide imaging