Cardiac function Flashcards
What is the normal resting cardiac output?
75ml x70 beats/min = 5250 ml / min
What is the normal ventricular volume?
150ml but we eject less than that
What determines how much blood leaves the heart?
Aortic pressure
Contractility (how hard are muscles in heart contracting)
What is cardiac work?
Pressure work is done moving blood from a region of low pressure to regions of high pressure
What happens to cardiac output after a meal?
increases 20 - 30%
What happens to CO when sleeping?
Drops by 10%
What factors affect CO?
Central venous pressure
Blood volume
Gravity
Peripheral venous tone
The muscle pump
Respiration
Systemic Vascular Resistance
Myocardial contractility
Heart rate
How can EDV be changed?
Increasing preloading pressure (Venous filling pressure)
Force of atrial contraction (25% in humans)
Time available for filling the ventricle
Distensibility of ventricular wall
How can ESV be changed?
Force of ventricular contraction
Resistance or backpressure in outflow artery (Afterload)
What is the Frank-Starling Law?
increased heart volume stretches muscles and causes a stronger contraction
What happens in cardiac muscles to increase power
Elastic recoil can be used for more power in contraction. This is due to the closer packing of sarcomeres together resulting in more tension when stretched out
How do we get more blood back to the heart?
Increasing Venous return
What factors influence venous return?
Peripheral venous tone
Gravity
Blood volume
Skeletal muscle pump
Respiratory pump
What does the sympathetic NS do to venous tone?
It increases tone and increases venous return
Why does the muscle pump work?
Due to presence of valves
What is the main factor that influences contractility?
Calcium
What is inotropy?
Increase in strength of contraction from delivery of calcium to our heart muscles
What does digitalis do?
A cardiac glycoside drug that lowers the activity of Na+/K+ ATPase and therefore NCX transporter activity resulting in elevated ICF Ca2+ which creates a stronger graded contraction
How can aCh affect on the heart?
Through the blood directly not through the parasympathetic NS
Can the heart be affected by the parasympathetic NS?
No
How does contractility get affected by sympathetic inotropy?
It increases length of time voltage gated Ca channels are open
Increases amount of Calcium in sarcoplasmic reticulum
What receptors do the heart have for sympathetic NS?
Beta 1 receptors
What does increasing afterload result in?
lower ejection volume and in turn a lower ESV this can be caused by elevated blood pressure or a loss of compliance in the aorta due to loss of elasticity
What happens to preload when heart rate goes up?
It drops
