ICL 1.7: Principles of Cardiac Physiology II: LV Mechanics, Pressure-Volume Loops, Preload, Afterload & Resistance

Question 1

what is considered normal cardiac output?

Answer 1

5 L/minute

Question 2

why is the pressure in the left ventricle higher than the pressure in the right ventricle?

Answer 2

the left ventricle is thicker because it has to pump against more resistance so it’s less compliant and therefore has higher pressure than the right ventricle that’s thinner

Question 3

what are the implications of the human circulatory system being a closed system?

Answer 3

right output = left input

left output = right input

left output = right output

your venous return and cardiac output have to be the same!!!

Question 4

sampling of blood from what area of the heart would have the most deoxygenated blood in the body?

Answer 4

coronary sinus

your heart extracts WAY more blood than any other organ system so the coronary vein that drains all of the heart has the lowest oxygen saturation

your heart uses 50% of the oxygen that gets sent to it!! the myocytes are extremely efficient so they take a lot of oxygen from the blood supply

Question 5

what’s the function of the arteries, arterioles and capillaries?

Answer 5

arteries are conduits and transport blood under pressure

arterioles are control valves that release blood into the capillaries

capillaries are the site of exchange

Question 6

which blood vessels dictate the amount of blood flow to an organ?

Answer 6

arterioles

arterioles determine who gets how much blood and will either constrict or dilate to distribute blood

Question 7

which type of blood vessel has the greatest cross sectional area?

Answer 7

capillaries

there’s a bajillion capillaries so they have more cross sectional area than artier, arterioles, venues or veins

you need this cross sectional area for all the exchange that has to happen!!

Question 8

slide 26

Answer 8

should be able to label it if all the labels got taken off

Question 9

what does it mean that blood is incompressible?

Answer 9

if you squeeze blood it’s gonna go somewhere

the flow of fluid is determined by the difference in pressure between two points: it goes from high to low pressure!

venous return = cardiac output

Question 10

what is Ohm’s law?**

Answer 10

Q = △P/R = CO

Q = flow
△P = △pressure 
R = resistance
CO = cardiac output

Question 11

what is Poiseuille’s Law?**

Answer 11

R = 8Lh/𝜋rˆ4

R = resistance
L = length of tube
η= viscosity
r = radius of tube 

resistance is inversely related to radius!! if you increase the radius it will lower the resistance and if you decrease radius, it will increase resistance! this tells you that viscosity and length of the tube are important but the real player with respect to resistance is the radius!!!!!

Question 12

what is wall tension and LaPlace law?**

Answer 12

tension = P x r

LV wall stress = (LV pressure x r)/2LV wall thickness

think of the left ventricle when you use these laws

when you have long standing HTN you hypertrophy the ventricle wall and this is because you increase the wall thickness to reduce wall stress based on LaPlace law –> ventricular hypertrophy follows this law!!

Question 13

what is the formula for compliance?

Answer 13

C = △V/△P

when you think about compliance you’re talking about the ventricles

Question 14

what is the formula for elastance?

Answer 14

E = △P/△V

when you think about elastane you’re talking about the arteries – it’s how much do they want to go back to their original confirmation after being stretched?

Question 15

what is MAP?

Answer 15

MAP refers to pressure in the in the aorta and its larger branches

Question 16

why do old people usually get HTN? which law is it based on?

Answer 16

Q = △P/R = CO

as you get older your arteries stiffer and you can’t change the resistance of your arteries by vasodilating or constricting like you can when you’re young

so what ends up happening is your BP increases instead to compensate and keep the body balanced

Question 17

what is Frank-Starling’s law of the heart?

Answer 17

increasing your venous return will help you get more blood out assuming you have a normal heart

all the blood that comes back to the R side of the heart has to be pumped out and you’re going to need to squeeze more out by stretching the ventricles to maintain the same cardiac output

Question 18

a 17 year old male comes to the ED for fatigue and lethargy. over the last day he has had 7 episodes of diarrhea and 4 bouts of emesis. HR is 140, BP 95/45, RR 26. what is your next step in management?

Answer 18

IV bolus

this is a preload issue! tachycardia is a normal reaction to low CO so when you have decreased venous return you have decreased stoke volume so to maintain CO you have to increase HR to maintain CO

Question 19

what happens to the pressure volume loop during aortic stenosis?

Answer 19

an increased after load pressure volume loop because the isovolumic contraction takes way longer because you have to generate more pressure to get the aortic valve to open

so you should have a decreased stroke volume and your LV will be generating super high pressures trying to get blood out

Question 20

what happens to the pressure volume loop during mitral stenosis?

Answer 20

if you have a hard time getting blood into the LV so that’s going to effect diastole so the EDV changes

you still get blood out okay and you’re not having to generate more pressure to get the blood out so that’s okay but you just can’t get blood into the LV

Question 21

what happens to the pressure volume loop during aortic regurgitation?

Answer 21

this is when the aortic valve doesn’t close during diastole and there’s retrograde flow of blood from the aorta into the LV

you get severe LV dilation so there’s increased EDV from the leaky aortic valve so you have extra blood volume (this is the opposite of mitral stenosis when you were having trouble getting blood in)

Question 22

what are Kussmaul’s signs?

Answer 22

during inspiration you decrease intrathoracic pressure

if you inspire you increase venous return but you have a restrictive right ventricle and the right ventricle can’t get blood out you will get jugular venous distention!

JVD tells you that blood isn’t exiting the right side of the heart!

this can be caused by heart failure, cardiac tamponade, pericardial effusion, etc.

Question 23

what is pulses paradoxes?

Answer 23

the paradox refers to the fact that heart sounds can be heard on auscultation but a radial pulse cannot be felt i.e. inspiratory fall in systolic blood pressure exceeding 10 mmHg

when your BP drops by more than 10 mmHg – your systolic BP doesn’t usually drop but when you inspire you increase venous return which increases blood flow to right side of the heart and BP goes up

but if you have a thick system where your heart can’t expand and you increase blood flow to the right side of the heart you’ll get bowing of the intravententricular septum into the left ventricle which will obstruct blood trying to go out the aorta

so when you breath in, blood goes back, and the intraventricular septum block blood flow from going out the aorta which causes a drop in BP