ICL 1.7: Principles of Cardiac Physiology II: LV Mechanics, Pressure-Volume Loops, Preload, Afterload & Resistance Flashcards
what is considered normal cardiac output?
5 L/minute
why is the pressure in the left ventricle higher than the pressure in the right ventricle?
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
what are the implications of the human circulatory system being a closed system?
right output = left input
left output = right input
left output = right output
your venous return and cardiac output have to be the same!!!
sampling of blood from what area of the heart would have the most deoxygenated blood in the body?
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
what’s the function of the arteries, arterioles and capillaries?
arteries are conduits and transport blood under pressure
arterioles are control valves that release blood into the capillaries
capillaries are the site of exchange
which blood vessels dictate the amount of blood flow to an organ?
arterioles
arterioles determine who gets how much blood and will either constrict or dilate to distribute blood
which type of blood vessel has the greatest cross sectional area?
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!!
slide 26
should be able to label it if all the labels got taken off
what does it mean that blood is incompressible?
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
what is Ohm’s law?**
Q = △P/R = CO
Q = flow △P = △pressure R = resistance CO = cardiac output
what is Poiseuille’s Law?**
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!!!!!
what is wall tension and LaPlace law?**
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!!
what is the formula for compliance?
C = △V/△P
when you think about compliance you’re talking about the ventricles
what is the formula for elastance?
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?
what is MAP?
MAP refers to pressure in the in the aorta and its larger branches
why do old people usually get HTN? which law is it based on?
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
what is Frank-Starling’s law of the heart?
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
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?
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
what happens to the pressure volume loop during aortic stenosis?
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
what happens to the pressure volume loop during mitral stenosis?
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
what happens to the pressure volume loop during aortic regurgitation?
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)
what are Kussmaul’s signs?
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.
what is pulses paradoxes?
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
