Control of Cardiac Output Flashcards
What is cardiac output?
The volume of blood pumped by the left ventricle in one minute.
How is cardiac output calculated?
By multiplying heart rate by stroke volume.
What are the two main nervous systems that regulate heart rate?
- Sympathetic nervous system
- Parasympathetic nervous system
What effect does the sympathetic nervous system have on heart rate?
Speeds up heart (+ve chronotropic effect).
What receptors are involved in sympathetic effects on heart rate?
β1 receptors.
What is the role of M2 receptors in the parasympathetic nervous system?
They open K+ channels and slow the opening of Ca²⁺ channels.
What is the effect of the parasympathetic nervous system on heart rate?
Slows down heart (−ve chronotropic effect).
What is heterometric regulation?
Changes in cardiac output dependent on the initial length of cardiac muscle fibre.
What is homeometric regulation?
Changes in cardiac output independent of muscle fibre length.
What is the normal ejection fraction for a healthy individual at rest?
67%.
What is the ejection fraction for a heart failure situation?
25%.
What is the concept of cardiac index?
Cardiac output per m² of body surface area (~3.2 L).
What is the maximum cardiac output capacity during exercise for an average individual?
20 L per minute.
What is the Frank-Starling relationship?
The larger the diastolic volume, the greater the energy of contraction.
What causes cardiac failure?
Insufficient peripheral perfusion despite normal blood volume.
What is the Fick Principle used for?
To determine cardiac output based on the A-V difference and blood flow.
What is the formula for calculating cardiac output using VO₂?
C.O. = VO₂ / (arterial - venous difference in oxygen content).
What is the effect of sympathetic stimulation on Starling curves?
Shifts Starling curve up and to the left.
What is the positive inotropic effect?
The increase in the strength of contraction due to sympathetic stimulation.
True or False: Parasympathetic stimulation has no effect on ventricles.
True.
Fill in the blank: Cardiac output can be influenced by alterations in _______.
[stroke volume].
What is preload?
The degree of stretch on ventricular walls before contraction.
What is afterload?
The pressure the heart must work against to eject blood.
What is the significance of the slope of prepotential in heart rate regulation?
It determines how quickly the heart reaches firing level.
What is the typical stroke volume at rest for a 70 kg male?
80 ml.
What is the stroke volume during Olympic-level exercise?
150 ml.
What is the role of catecholamines in cardiac function?
They amplify β effects and enhance contractility.
What does the term ‘decompensation’ refer to in cardiac physiology?
The failure of the heart to maintain adequate cardiac output.
