4. O2 Demand Flashcards
How would an increase in the amount and rate of Ca2+ release affect the magnitude and rate contraction?
Faster, more forceful contraction
What vasculature provides the heart w/ its own bloodflow?
Coronary arteries
When does the heart get blood flow from the coronary arteries? When does it cease?
- Blood flow ceases during active contraction (systole) as arterioles and capillaries are compressed
- Blood flow occurs during diastole when heart is relaxing
Oxygen consumption in cardiac vs. skeletal muscle
Cardiac oxygen consumption at rest is 20x greater per gram of muscle than skeletal muscle
Oxygen extraction in cardiac vs. skeletal muscle
Oxygen extraction is maximal in resting heart
- 80% of presented O2 is removed in heart
- 25% of O2 is removed in a skeletal muscle
Cardiac capillary density in cardiac vs. skeletal muscle
- Cardiac capillary density = 3,000-4,000/mm2
- Skeletal muscle = 500-2000/mm2
What is the most aerobic muscle in the body?
Heart
What is the only way to meet the increased demand for O2 in the heart?
Increase coronary blood flow
What determines the myocardial O2 supply?
O2 content supplied by coronary blood flow
What factors determine myocardial O2 demand?
- Wall stress
- HR
- Contractililty (SBP)
What factors account for 90% of heart work?
- HR
- Contractility (SBP)
Law of LaPlace
Wall tension depends on radius of curvature
What is wall stress?
Relation b/t ventricular volume and tension
Equation for wall tension of a thick-walled sphere
What are the effects of cardiac geometry on energy demand?
Larger radius w/ same wall thickness —> high wall tension
Explain excitation-contraction coupling during systole. (CICR)
What is the relationship b/t Isometric Tension and pCa?
Increase Ca2+ –> greater force
Explain the relation b/t sarcomere length and Ca2+ sensitivity of tension.
- Increased sarcomere length –> increased Ca2+ sensitivity of tension
- More force for a given level of Ca2+
What characterizes the relaxation phase of excitation-contraction coupling?
Removal of Ca2+ from cytosol
What are the mechanisms by which Ca2+ is pumped out of the cytosol? What % does each pump out?
- Ca2+ ATPase pump (~5%)
- Na+/Ca2+ Exchange (~15%)
- SERCA Ca2+ ATPase pump (~80%)
What is the function fo the SERCA Ca2+ ATPase pump?
Replenishes SR Ca2+ load
What is the SERCA pump regualted by?
Phospholamban (PL)
How does phospholamban regulate the SERCA pump?
PL inhibits SERCA by delaying relaxation (diminishes lusitrophy) –> restricts speed at which SERCA pump can function at rest
Define lusitropy.
Ability of the contractile process to terminate rapidly –> relax faster
