Control of Cardiac Output Flashcards
What is the equation for Cardiac output?
CO= stroke volume x heart rate
How is stroke volume increased?
increasing contractility of the heart forces more blood out per ejection
How is heart rate increased to increase CO?
increase sympathetic innervation
Why is there a limited level to which CO can be increased to?
heart needs cycled through contraction and relaxation at an efficient speed to allow it to refill
What are EDV and ESV?
- end diastolic volume, volume of blood in ventricle after it has fully relaxed
- end systolic volume, volume left in ventricle after it has contracted
What does an increase in EDV mean?
increased volume in blood in ventricle, more blood pumped out, greater SV hence greater CO
What sort of mechanism is increasing EDV?
intrinsic mechanism
How is EDV increased?
increase the venous return to the heart which will increase amount of blood in the ventricles therefore increasing the end diastolic pressure
What is preload?
the venous pressure and the venous return to the heart
what is afterload?
- the force the blood is pushing against
- pressure the L ventricle is working against
What is the length/tension relationship?
increasing the length of the sarcomere increases the force of tension generated to an optimal level then increasing sarcomere length above that will decrease the force of tension produced
What length are the sarcomeres of cardiac muscle at normally?
length of cardiac sarcomeres are held at a level so that they produce sub-optimal force of tension
What effect does increasing venous return to heart have on sarcomeres of cardiac muscle? Explain how force of contraction is increased as a result.
Since cardiac sarcomeres are eld at a length which produces sub-optimal force of tension when venous return to heart is increased this increases the volume of blood in the ventricle and hence stretches the ventricle wall = stretching the sarcomeres of cardiac muscle to length which produces optimal force of tension = total force your heart can generate is increased hence the force of contraction is increased
What is the effect on the force of contraction by overfilling the ventricle with venous blood?
overfilling will over-stretch the sarcomeres of cardiac muscle above the length which produces optimal tension and beyond to a level where the sarcomeres are too long and begin to produce sub optimal forces of tension = force heart generates is reduced hence contractility is decreased
What is the difference in pressures of the systemic and pulmonary circulations?
the overall operating pressure in the pulmonary circulation is lower
What sort of flow do you want through capillaries in the systemic circulation? What is the purpose of this?
- smooth, laminar, slow flow
- to allow exchange of materials an nutrients between blood and tissues
How is pressure in capillaries in systemic circulation so low despite the huge pressure in the aorta?
masses of capillaries branched round body tissues hence pressure from the aorta is evenly spread out amongst all the branches
Since pressure decreases in vessels from large conducting arteries down to same capillaries what is the effect on the structure an properties of these vessels?
- there is a change in the amount of fibrous tissue, elastic tissue and smooth muscle in vessels
- change in conductance and dampening of oscillation from large conducting arteries down to arterioles and capillaries
What adds to form the total pressure in the aorta?
flow cardiac output and the sum of the resistance of all the downstream arteries
Define vascular compliance.
how likely a vessel will change to accommodate a volume and how the pressure changes in that vessel as a result
Describe the compliance of the aorta.
Large volume of blood pushed through the aorta will increase the pressure within and it will swell to accommodate the increased pressure as a result of the large volume of blood
How compliant are capillaries?
can increase the pressure of blood through the capillaries however the volume of the vessels will not change
What is the relationship for mean arterial blood pressure?
MABP= diastolic blood pressure+ 1/3 of pulse pressure
How is pulse pressure calculated?
pulse pressure= systolic pressure - diastolic pressure
How does viscosity of blood affect blood flow?
increase in viscosity of blood as a result of increasing haematocrit there is a reduction in the flow of blood
What is the most important factor in resistance to blood flow?
radius of blood vessel
What is Poiseulle’s equation? What is the equation of flow you can obtain from Pioseulle’s relationship?
- flow varies directly with change in pressure x radius of vessel4 and inversely with viscosity x length
flow=change in pressure/resistance
How is arterial pressure calculated?
AP= CO x total peripheral resistance
What is arterial pressure?
mean arterial pressure generated in the aorta that drives blood around the system
How is the CO in the pulmonary and systemic circulations the same if the operating pressure of the pulmonary circulation is lower than that of the systemic circulation?
the resistances of the two circulations are also different hence when factored in with the different operating pressures the CO remain equal
what extrinsic mechanisms affect SV?
effects of contractility mediated by sympathetic innervation
What 2 things decrease arterial compliance?
- age
- atherosclerosis
