Chapter 3 The heart pump Flashcards
What is more efficient? Low HR/High STV or High HR/Low SV ?
Low heart rate and high stroke volume
What is the main metabolic pathway for cardiac muscle contraction (aerobic or anaerobic)?
Almost entirely aerobic metabolism => myocardial oxygen consumption is tightly related to myocardial ATP production and use and therefore to cardiac work
What is the formula for the work rate of the heart?
WR = CO × MAP.
What is more efficient to increase tissue blood flow? To educe tissue resistance to blood flow or to increase arterial blood pressure?
To reduce tissue resistance to blood flow
What are the % of myocardial ATP use for basal metabolism versus muscle contraction, respectively ?
Basal metabolism = 25% of myocardial ATP use, muscle contraction = 75% of myocardial
What does the Starling law of the heart explain?
Explains that stroke volume increases as cardiac filling increases.
What is one of the most important factors responsible for these variations in stroke volume?
One of the most important factors is the extend of cardiac filling during diastole
What is the formula for ejection fraction?
EF = SV/EDV
What does ejection fraction measure for us?
Contractility
What does positive chronotropic influences do?
Increases HR
What are the three distinct cardiac influences on stroke volume?
Contractility, preload, and afterload
How does increased cardiac sympathetic activity increase stroke volume?
Increases afterload
How does hemorrhage cause low stroke volume?
There is still a high level of sympathetic nerve activity and increased contractility. Arterial pressures are typically low or normal following hemorrhage, so low stroke volume has to be due to low cardiac filling pressure.
How does increased cardiac sympathetic nerve activity increase CO?
By increasing the HR and by increasing stroke volume by increasing cardiac contractility
