Stable ischemic disease part 2 Flashcards
Drugs should decrease oxygen demand and _______oxygen supply
increase oxygen supply
Why do we (and cardiac muscle cells) need O2?
To make more ATP fire action potential establish electrochemical gradient to contract heart
Stable angnia pectoris—> stress or exertion—> increase myocardial O2 demand
Increase myocardial O2 demand—>autogregulation–>coronary artery dilation–> increase O2 supply
Determinants of oxygen demand are
Heart rate
_________
___________
contractility and wall stress
Determinants of O2 supply
___________(vasodilation)
coronary blood flow
Determinants of myocardial O2 demand–>We want to lower O2 demand in failing hearts…
__________ = “Mechanical tension experienced by the myocardial wall” = Work that heart does to contract
Wall stress
Thinner wall and larger radius equals what?
increase wall stress
increase oxygen demand
Determinants of myocardial O2 supply
Oxygen carrying capacity (of blood)
____________
___________
coronary blood flow
time
75% of the left main coronary flow and 50% of right coronary flow occurs during __________.
diastole
Thus, diastolic time is more important for LV perfusion, and it can be compromised by tachycardia.
As the heart rate increases, diastolic time decrease (LV perfusion decreases)
As HR goes up, duration of diastole decreases…
Females are affected more
lesion diameter up to 80% resting coronary blood flow doesn’t get effected only during exertion even then up to 60% its not much difference and heart is still able to adapt to it around 70% to 80% it dropps and clinical symptoms reaches 70%
0 to 70% pt doesn’t feel obviously feel symptoms
Coronary blood flow is automatically regulated to meet metabolic demand
Myocardial oxygen extraction ratio is already very high (60-70%).
Thus, the myocardium cannot increase its oxygen extraction efficiency to meet increased metabolic and oxygen demand…
