1
Q
What 3 factors determine O2 demand of the heart?
A
- HR
- myocardial contractility
- Ventricular Wall Stress
2
Q
Contractility
A
Force and velocity of myocyte contraction
- increased by SNS
- Increased contractility (more forceful beats) increases O2 demand (even at same HR)
3
Q
Ventricular Wall Stress
- Variables
- Equation
A
WS=afterload
- Variables
a) BP
- WS increases with increasing BP
b) ventricular radius (r)
- bigger r = ++ WS
- smaller r = less WS
c) wall thickness (h)
- WS decreases with increasing thickness
- thin wall=++WS
- thick wall = less WS - WS=(BPxr)/(2h)
4
Q
What 3 factors determine O2 supply?
A
- O2 content-maximized O2 saturation
- O2 extraction-max
- 25-35% saturation of coronary sinus blood - Coronary Blood Flow
- only way to increase O2 supply to the heart
5
Q
CBF = ?
Think Q=deltaP/R
A
CBF = (P gradient across heart)/(Coronary Resistance)
6
Q
What components make up Coronary Resistance
A
- Myocardial R
- greatest during systole
- greatest in endocardium - Arteriolar R
- autoregulation - Epicardial R (only in dz)
7
Q
R arteriolar
A
- R from the muscular arterioles
- dynamic autoregulation
- coronary flow reserve
8
Q
R myocardial
A
- R due to compression of perforating arteries w/in ventricular mass during systole
- changes with cardiac cycle
- Graded from epicardium to endocardium (highest in the inside)
9
Q
R epicardial
A
Resistance in epicardial arteries
-not present unless dz
10
Q
Coronary Reserve Flow
A
Exists when arterioles are NOT maximally dilated (you can still decrease Rart)
-Demonstrate in lab via occluder around epicardial artery and reactive hyperemia (amount of flow above baseline)-representative of CFR
11
Q
Adenosine
A
- by-product of ATP degradation
- nonpolar
- possible primary link between myocardial O2 use and CBF
