Cardiac energetics
10 important questions on Cardiac energetics
What is remarkable about the energetics throughout the cardiac cycle?
What does 'length-dependency' of activation mean in the heart?
- the length of the heart muscle increases.
- When the length of a muscle is increased, actin and myosin filaments are closer together,
- meaning that Ca2+ has higher affinity for troponin.
- So when the preload of the heart increases, there is also more contraction of the heart.
How can myocardial efficiency be calculated?
Internal work: the work delivered by the heart per heart beat.
Metabolic work: the oxygen uptake by the cardiac muscle
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In a healthy human, what is the myocardial efficiency approximately?
Metabolic work: e.g. 5.3 W
Myocardial efficiency: 25% (so 75% of the generated metabolic energy will be converted to heat)
What happens with the myocardial efficiency in people with heart failure?
How does mitochondrial dysfunction relate to heart failure?
- Mitochondria work harder to compensate for the decrease, and thereby create more ROS (due to not fully reduced oxygen).
- ROS cause mitochondrial and cellular damage,
- which results in lower ATP production to fuel sarcomeres & SERCA pump: cardiac output decrease.
- ...
= vicious circle?
What are some therapies now focused on, because of this vicious circle?
What kinds of in vivo methods are used to assess whether myocardial inefficiency contributes to heart failure?
- Metabolic treadmill
- measuring respiratory exchange ration (RER): VCO2/VO2 (indicates the main fuel: below 0.7: fatty acids, above 1.0: glucose)
- PET/MRI
- PET: myocardial oxygen consumption (MVO2)
- MRI: cardiac work
- (also skeletal muscles are assessed)
What kind of in vitro techniques are used to assess whether myocardial inefficiency contributes to heart failure?
- Oroboros respirometry: measures O2 consumption of single muscle fiber
- ATPase: tension cost of muscle fiber is measured (tension cost = ATP utilization during force generation)
What does it mean that our cardiovascular infrastructure is adapted to our energetic needs?
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