Cardiac Output Flashcards
What is cardiac output
The amount of blood pumped out of the heart per minute
What two factors affect cardiac output
Stroke volume
Heart rate
What is the end diastolic volume
Blood in ventricle after filling
What is end systolic volume
Volume of blood after ventricle contracts
How do you work out stroke volume
End diastolic volume - end systolic volume
What two main factors determine end diastolic volume
End systolic volume (how much blood was there before filling)
Heart rate (sets time available for filling)
What is the frank starling mechanism
It’s the hearts physiological ability to change its contraction force and stroke volume in réponse to changes in venous return.
If end diastolic volume is increased (due to more blood flowing from the veins)
There is more preload (force stretching the cardiac muscle)
So force of contraction increases
What is contractility
the tension developed and velocity of shortening (i.e., the “strength” of contraction) of myocardial fibers at a given preload and afterload
When considering cardiac function, which index is more important for perfusion of peripheral tissues - cardiac output or blood pressure?
Cardiac output because blood pressure is influenced by cardiac output
How does contractility of the heart change during physical exercise? How is this brought about?
Exercise increases the sympathetic activity and reduces sympathetic activity, leading to increased contractility and increased stroke volume.
What happens to the heart rate after a major haemorrhage
Increases.
What happens to the venous return after a major haemorrhage?
Reduces
What happens to the total peripheral resistance after a major haemorrhage?
Increases
What is the equation involving blood pressure and cardiac output
CO = blood pressure x total peripheral resistance
What happens to the tissue fluid volume after a major haemorrhage
Decreases
What happens to urine output after a major haemorrhage
Decreases
How are the changes in the body that occur after a major haemorrhage regulated?
Restore hydration (using IV fluids if necessary), open airways, use oxygenation and manage body temperature.
What happens to cardiac output in heart failure?
During heart failure, the body does not receive enough blood and oxygen. So, the body’s hormone and nervous systems try to compensate for this by increasing blood pressure, holding on to sodium and water in the body, and increasing heart rate.
Cardiac output decreases, low stroke volume,
What happens if stroke volume isn’t matched
Increase pressure on venous side
Leading to oedema
What is preload
End diastolic volume
(Volume after filling)
What is after load
Resistance to ventricular ejection
What is preload dependant on
Venous return of blood
Will pump out same volume of blood that comes into heart
What is the length tension relation ship
Increase preload
Increase exposure of myosin to actin (as sarcomere stretches)
Increase cross bridge formation
Increase force of contravtion
What factors influence preload
Filling time of heart (slow HR means longer period of ventricular filling )
Venous return pressure difference between venous system and atrium)
What does the skeletal muscle pump do to venous retun
Increase it
Contraction of skeletal muscle causes veins to be compressed
Blood forced to heart
Increased pre load
What happens during inspiration to venous return
Diaphragm moves causally
Increases abdominal pressure
Thorax pressure reduces
So increases return of blood
Increases pre load
What receptiors increase contractilité if heart
B1 adrenoreceptiors agonists
What do positive inotropes do
Phosphorylates Ca2+ channels
Faster calcium re uptake
Increased contractility of heart
What decreases ventricular contractility
M2 muscarinic receptors
What does afterload
Creates the resistance against which the ventricle pumps
What happens if you have more afteoq d
Reduced stroke volume
Heart has to work harder to maintain CO
What happens if you have reduced aftoad
More blood can be ejected
What is the equation for blood pressure
Cardiac output x total peripheral resistance
What is the Total peripheral resistance
Arterial vascular resistance
What is oulse pressure
Pressure at systole - pressure at diastole
