Cardiac Function

Question 1

Why is the shape of the pressure-volume loop segment not flat?

Answer 1

because the afterload is not constant; it changes throughout ejection (during ejection, heart generates isotonic contraction with a changing afterload)

Question 2

How does increased preload relate to resting tension and maximum tension developed?

Answer 2

• increased preload=increased resting tension

- increased preload=no change in maximum tension developed

Question 3

How does preload relate to stroke volume?

Answer 3

increased preload=increased stroke volume

Question 4

If there’s an increase in afterload, is there more or less muscle shortening in the ventricles?

Answer 4

less

Question 5

What is one of the main ways the body compensates for a decrease in SV and CO?

Answer 5

sympathetic stimulation, which increases contractility and therefore SV and CO

Question 6

How does increased contractility change the contractility curve?

Answer 6

it moves the curve up and to the left

Question 7

What are 3 ways to maximize shortening in muscle or SV in the heart?

Answer 7

1) increase preload
2) decrease afterload
3) increase contractility

Question 8

Increasing contractility increases what else?

Answer 8

SV and ejection velocity

Question 9

A condition in which the heart fails to provide cardiac output sufficient to meet the needs of the body.

Answer 9

heart failure

Question 10

What is a major way to treat heart failure?

Answer 10

give beta blockers to get rid of the fluid that is not being efficiently pumped; this allows the heart to rest, which is needed for heart failure recovery

Question 11

What are the factors that determine preload?

Answer 11

• pressure gradient b/t atria and ventricles (incr. in end diastolic pressure=decr. in ventricular filling)
• time for ventricular filling (HR)
• ventricular compliance (decr. in compliance=incr. in stiffness=decr. in ventricular filling)
• atrial function (atrial kick)

Question 12

What are examples of factors that would increase afterload?

Answer 12

• aortic pressure (HTN)
• ventricular outflow tract resistance (valve stenosis)
• ventricular size (wall tension, dilated hearts)

Question 13

What is a dilated heart and how does it affect cardiac output?

Answer 13

A dilated heart is a heart muscle that gets thinner, allowing for more volume to be held in the chambers. This causes an increase in pressure, which the myocardium senses as an increase in afterload. Since it is registered as an increase in afterload, it ultimately results in reduced cardiac output.

Question 14

What are the factors influencing heart rate (ventricular rate)?

Answer 14

• pacemaker function
• AV nodal conduction
• ventricular arrhythmias