5-cardio Flashcards
what is the equation for cardiac work
stroke volume x arterial pressure
what does increased cardiac work do to oxygen consumption
increases
what two factors increase when LVEDP is increased
stroke volume (due to Frank-Starling) and cardiac work
what happens with a venodilator to preload
it decreases
what happens with a venodilator to stroke volume
decreases
what happens with a venodilator to cardiac work
decreases
what does arteriolar vasodilators do to afterload
decreases
what does arteriolar vasodilators do to arterial pressure
decrease
what does arteriolar vasodilators do to cardiac work
decrease
how do the coronary vessels react when met with increased O2 demand
they dilate
what causes angina
when oxygen demand is greater than supply, resulting in pain
what 5 things can increase local coronary flow
- low o2 tension
- high co2 tension
- release of lactate (due to anaerobic metabolism)
- release of adenosine
- presence of prostacyclin (PGI2)
what direction does coronary flow occur (where does it start and end)
from aorta to ventricles
what is pressure difference in the heart during systole
pressure in ventricles greater than pressure in aorta
what is the pressure difference in the heart during diastole
pressure in aorta greater than in ventricles
does coronary flow happen during diastole or systole
diastole
why does coronary flow occur during diastole
due to a reduction in mechanical pressure, and the pressure in the aorta being greater than the pressure in the ventricles
what is the equation for coronary perfusion pressure
coronary artery diastolic pressure - left ventricular end diastolic pressure
what happens to coronary vessels when there is angina/ischemia
maximally dilated (they want to get as much blood as possible)
what happens when you use coronary dilators with angina
during angina, coronary vessels are already maximally dilated. it results in dilation of vessels in normal areas and less to ischemic areas - leads to coronary steal
how do plaques affect coronary artery diastolic pressure
pressure will decrease distal to the plaque, leading to reduction of the pressure gradient and decreased coronary perfusion
what happens to LVEDP when the ischemic heart starts to fail
it increases
what are 3 different ways that anti-anginal drugs can work
- lower LVEDP (reduce preload)
- prolong diastolic time (reduce HR)
- reduce work load (reduce O2 demand)
what is 1 thing all anti-anginal drugs do
reduce cardiac work load
what class of drugs aim to lower LVEDP (preload)
venodilators
what is an example of a venodilator
nitroglycerine (glyceryl trinitrate)
does nitroglycerine dilate veins or arterioles more
dilates veins more than arterioles
what does nitroglycerin do to venous capacitance?
increased, resulting in pooling
what effect does nitroglycerin have on coronoary perfusion pressure? why?
increased coronary perfusion pressure (due to lowering of the LVEDP)
what five factors does nitroglycerin decrease?
decrease venous return
decrease LVEDP
decrease stroke volume (shift Frank Starling back to normal range)
decrease arterial pressure
decrease workload (due to CW = SV x AP)
what happens to stroke volume when you decrease LVEDP
decrease
how does nitroglycerin produce coronary dilation without resulting in coronary steal?
by opening collateral vessels, increasing blood flow to ischemic areas
how is nitroglycerine administered for acute attacks
sublingual
how is nitroglycerine administered prophylactically
transdermal
what are the untoward effects of nitroglycerine
headache and tolerance
what class of drugs prolong diastole?
beta blockers (eg. propanolol)
what are two effects of propanolol?
reducing HR during excersize, –> increased coronary perfusion time –> reducing O2 demand
reduce afterload by lowering BP, thus lowering cardiac work
when is propranolol especially useful
after the first myocardial infarction to prevent re-infarction
name 3 drugs that reduce cardiac work
verapamil, diltiazem, nifedipine
how do verapamil and nifedipine work
block ca++ channels, reducing contractility, HR and afterload, thus reducing cardiac work
how do dihydropyridines like nifedipine work?
target arterial smooth muscle channels, reducing contracility, HR and afterload, thus reducing cardiac work
what are 3 ways to treat heart attack in emergency
aspirin (acetyl salicylic acid) , nitroglycerine (via IV), altepase (tissue plasminogen activator)
what are 2 ways to prevent heart attack (drugs)
low dose aspirin (80mg/day) , antianginals (b blockers, ca channel blockers)
how do nitrates relax coronary smooth muscle
they act like NO from endothelial cells
what is the mechanism of action for nitrates on coronary smooth muscle
NO binds to heme moiety of guanylyl cyclase, activation of guanylyl cyclase, increased cGMP, cGMP relazed smooth muscle by dephosphorylating myosin-LC-PO4
