Heart Function Curves and Work of the Heart Flashcards
what is the relationship between cardiac output and venous return of the heart?
they should be the same
what is venous return?
the rate at which the blood returns to the RA of the heart from the body systems
what is cardiac output?
the rate at which blood is ejected from the LV and moves through the aorta and systemic circulation
what is the central venous compartment?
the volume of blood enclosed by the right atrium and the great veins of the thorax
how can you measure …?
see slide 99
what is the cardiac function curve?
= CO curve
- demonstrates the direct relationship between the central venous pressure (RAP) on cardiac output
- Frank-Starling Law of the Heart
what is the vascular function curve?
= venous return curve
- demonstrates the inverse (negative effect) of central venous pressure on venous return
what is mean systemic (circulatory) pressure?
the volume of blood in the total systemic circuit when the heart is in cardiac arrest, no blood is flowing through the system
≈ 7mmHg
what is the equilibrium point?
= steady state
- the point at which cardiac output and venous return are always equal and stabilized
what does the vascular function curve define?
- the inverse relationship between venous return and right atrial pressure
- as you increase P, CO/venous return decreases
the vascular function curve:
- depends on?
- shows?
- changes in the vascular system, dependent on the pressure gradient
- shows that as RA pressure increases, the venous return decreases
- if the RAP falls below 0, the intrathoracic pressure is higher which will cause collapse of the veins and a plateau (constant?) of the venous return
venous return is determined by?
the pressure difference between the peripheral and central venous compartments
how is venous return affected by decreases in peripheral venous pressure?
- leads to what?
- caused by what?
- leads to decreased BP
- caused by: blood loss via hemorrhage,
loss of bodily fluid by sweat, diarrhea, or vomiting,
venodilation (less sympathetic stimulation)
how is venous return affected by increase in peripheral venous pressure?
- leads to what?
- caused by what?
- leads to increased BP
- caused by: blood transfusion,
fluid retention in the kidneys,
increases in circulating blood volume,
venoconstriction, (sympathetic)
venous compression,
exercise,
wearing elastic stockings
what does the cardiac function curve define?
- based on?
- demonstrates?
the dependence of cardiac output on the preload of the heart
- based on the frank-starling relationship
- demonstrates that as RAP increases, there is a linear increase in cardiac output and at ~4mmHg pressure there is a plateau
mean systemic (circulatory filling) pressure is determined by what? can be affected by what?
- the volume of blood in the total systemic circuit during cardiac arrest
- affected by changes in circulating blood volume, venous reserve, and venous tone (venous constriction or dilation)
how is the cardiac function curve altered by positive and negative inotropic agents?
how is the vascular function curve altered by blood volume and venous reserve?
how are both curve affected by the changes in total peripheral resistance (TPR)?
what is stroke work?
the work done by the ventricles to eject the blood into the aorta
- in a normal heart, the work done by the heart = stroke work
- work is done in units per time = power
- power in heart = cardiac minute work
what consumes more energy: pressure work or volume work?
pressure work
what is myocardial oxygen consumption (MVO2)?
the energy consumption of the heart
- amount of oxygen consumed per minute
- directly correlates with stroke work and cardiac minute work
what is mechanical efficiency?
the ratio between work of the heart and oxygen consumption
what happens to mechanical efficiency in a scenario of hypertension or aortic stenosis?
- there is an increased afterload
- which means high pressures are required to eject the stroke volume
- O2 consumption increases
- therefore mechanical efficiency decreases!!!
what is the effect of strenuous exercise on cardiac output?
- oxygen consumption increases (less dramatic)
- so the mechanical efficiency is reduced (again.. less dramatic)
compare the work of the right heart to the work of the left heart
- LVP work > RVP work
- pressure work increases the ventricular wall thickness
- right side work is about 1/6 of the left side
what is the law of laplace?
when the heart has an increased pressure or volume work, there is an increased wall stress (tension) on the heart (thus thicker wall)
- so with increased pressure or volume load, the heart will undergo hypertrophy to reduce the wall stress (to help reduce the wall tension)
what causes cardiac hypertrophy?
- an excessive workload placed on the heart
