L4 - control of cardiac output

Question 1

define afterload

Answer 1

The load the heart must eject against (aortic pressure)

Question 2

define preload

Answer 2

The degree that the ventricles are stretched during diastole (EDV)

Question 3

Define total peripheral resistance

Answer 3

Systemic vascular resistance to blood flow

Question 4

What happens to arterial pressure in the following situations:

a) TPR increases and CO remains the same
b) CO increases and TPR remains the same
c) CO decreases and TPR remains the same

Answer 4

Remember MaBP = CO X TPR

a) Arterial BP up Venous BP down
b) Arterial BP up Venous BP down
c) Arterial BP down Venous BP up

Question 5

What is the typical SV of a 70Kg man?

Answer 5

70mL

Question 6

From volumes how do you work out stroke volume?

Answer 6

SV = EDV - ESV

Question 7

In terms of chambers of the heart, what is compliance?

Answer 7

The ability of the chamber to fill with a volume of blood at a given pressure.

NOTE - this can change in disease state. Increased compliance means it fills at lower pressures

Question 8

The Frank Starling law describes the relationship between _____ _____and _____. It states that the more the heart fills then the harder it will contract (to a limit)

Answer 8

Stroke volume (y)/ LVEDP (x)

Question 9

Why does the frank-starling curve dip back down at the end?

Answer 9

Because the sarcomeres have surpassed their optimal length of stretch

Question 10

Increasing TPR means increasing arterial pressure but also reducing venous pressure so that the filling of the heart is reduced. T/F?

Answer 10

T

Question 11

Intrinsic control of the heart is governed by stroke volume. However it can be extrinsically controlled too by increasing or decreasing sympathetic activity. THis not only increases HR but also increases contractility, what does this do to the gradient of the Frank-Starling curve?

Answer 11

Increases gradient with increased contractility also means a higher overall stroke volume (see picture on slide - important)

Question 12

Explain the baroceptor reflex in standing up

Answer 12

On standing theres a drop in venous pressure due to pooling of blood from gravity and thus because venous return is impaired, so is CO and thus arterial BP. Thus the barcoeptor reflex increases HR and TPR as a response to bring back arterial pressure to normal

Question 13

Where is the Jugular Venous Pulse (JVP) measured and what does it reflect?

Answer 13

In the right internal jugular vein, height represents central venous pressure

Question 14

Give some examples of when we’d see a rasised JVP

Answer 14

stab wound/congestive heart failure/ shock

Anything that interferes with the hearts ability to function. Remember decreasing TPR means that arterial BP is decreased and venous BP is increased

Question 15

When in the cardiac cycle would we here

a) a murmur due to an aortic stenosis?
b) a murmur due to a mitral stenosis
c) a murmur due to a mitral regurgitation (incompetence)

Answer 15

stenotic murmurs occrus when valves should be open
regurg murmurs occur when valves should be closed
a) throughout systole
b) during diastole
c) during systole

Question 16

What are the typical pressures in the different chambers of the heart and outflow tracts during systole and diastole?

Answer 16

LA - 8-10
LV - 120/10
Aorta - 120/80
RA - 0-4 
RV - 25/4
PUlmonary artert - 25/10

Question 17

what are the letters in the JVP

Answer 17

a = atrial contraction
c = closing and bulging of tricuspid valve
x = atrial relaxation
v = passive filling of atria
y = opening of tricuspid
note these are the same as in the atrial wave on wiggers diagram but specifically represent the RA here