Control Of Cardiac Output Flashcards
What is the definition of Cardiac Output?
Volume of blood ejected by each ventricle per minute
Cardiac Output (CO) is calculated as CO = HR x SV, where HR is heart rate and SV is stroke volume.
What is the formula to calculate Cardiac Output?
CO = HR x SV
CO is measured in liters per minute (L/min), HR is in beats per minute (bpm), and SV is in milliliters (ml).
What are typical values for Cardiac Output at rest?
CO ~5 L/min, HR ~70 bpm, SV ~70 ml
These values can vary based on individual fitness and health conditions.
How does Cardiac Output change during exercise?
CO increases from ~5 L/min to ~20 L/min
During exercise, HR can increase up to 190 bpm and SV can increase to 105 ml.
What factors affect Heart Rate?
- Autonomic Innervation
- Hormones
- Chronotropic Effects
- Neural and Hormonal Regulation
The heart rate is influenced by both sympathetic and parasympathetic nervous systems.
What is Stroke Volume?
Volume of blood ejected by each ventricle per beat
Stroke Volume (SV) is a key component in calculating Cardiac Output.
What are the determinants of Stroke Volume?
- End Diastolic Volume (EDV)
- End Systolic Volume (ESV)
- Preload
- Contractility
- Afterload
Each determinant influences how much blood the heart can pump with each beat.
What is Preload?
The degree to which ventricular muscle cells are stretched at the end of diastole
Preload is directly related to the volume of blood returning to the heart (venous return) and the available filling time
What is Contractility?
The force produced by ventricular muscle cells during systole at a given preload
This is affected by inotropic effects
Increased contractility leads to increased stroke volume.
What is Afterload?
The force the ventricle needs to overcome to open the semilunar valve and eject blood
Increased afterload can reduce stroke volume and cardiac output.
What is the effect of sympathetic stimulation on heart rate?
Increases heart rate
Sympathetic stimulation involves neurotransmitters like norepinephrine and epinephrine.
What is the effect of parasympathetic stimulation on heart rate?
Lowers heart rate
Parasympathetic stimulation primarily uses acetylcholine.
Fill in the blank: The SA Node has an inherent rate of ______ bpm.
> 100 bpm
This intrinsic rate is modified by autonomic influences.
What is the Frank-Starling Law?
The force developed in a muscle fibre is dependent on the extent it is stretched
This law explains the relationship between preload and stroke volume.
What are the effects of increased afterload on cardiac output?
Reduces stroke volume and cardiac output
Increased afterload can lead to longer isovolumic contraction and potential heart failure.
True or False: Bradycardia refers to a pathologically fast heart rate.
False
Bradycardia refers to a pathologically low heart rate.
What role does the Vagus Nerve play in heart rate regulation?
It is involved in parasympathetic control, reducing heart rate
Increased vagal tone results in a lower heart rate.
What is the role of the skeletal muscle pump in venous return?
Movement of skeletal muscles constricts veins, aiding venous return
Valves in veins prevent backflow, enhancing venous return to the heart.
What is the effect of venous capacitance on venous return?
SNS activity reduces compliance and increases central venous pressure
This effect ultimately aids in increasing venous return.
What are the parasympathetic effects on heart rate and cardiac output?
Hormone = ACh
Has a negative chronotropic effect
Lowers HR
Reduces CO
What are the sympathetic effects on heart rate and cardiac output?
Hormone = Noradrenaline (NA)/ adrenaline
Positive chronotropic effect
Increases HR
Increases CO
What is bradycardia?
Pathologically low HR
(Less than 50/60)
What is tachycardia?
Pathologically fast HR
(Around 100bpm)
What are chronotropic effects?
Factors affecting HR
