4.2 Cardiac Output
If heart rate is 100 beats/min and stroke volume is 100 ml/beat, then what is the cardiac output?
Cardiac Output (mL/min) = heart rate (beats/min) X stroke volume (mL/beat) >10,000 mL/min
How does an increase in end-diastolic volume cause an increase in stroke volume?
Elevated venous return increases end-diastolic volume, which stretches the heart, optimizes the length/strength relationship of sarcomeres and thus increases stroke volume.
Describe Starling's Law.
Starling's Law describes the relationship between end-diastolic volume and stroke volume. It states that the heart will pump out whatever volume is delivered to it.
How would an increase in sympathetic input to the veins cause an increase in cardiac output?
Sympathetic input > vasoconstriction > increases pressure > increases venous return > increases end-diastolic volume > increases stroke volume > increases cardiac output
Explain how sympathetic input to the veins would increase venous return of blood to the heart.
Sympathetic input causes vasoconstriction > pressure increases > drives blood through one-way valves back to the heart
How does an increase in sympathetic input to the ventricular myocardium cause an increase in stroke volume?
Sympathetic input to ventricular myocardium > increases intracellular Ca2+ > stronger contraction > greater ejection fraction > increased stroke volume.
What 3 mechanisms increase venous return of blood to the heart?
> Skeletal muscle pump > Respiratory pump > Sympathetic Nervous System
How would an increase in sympathetic input to the heart cause an increase in cardiac output?
1. Release of norepinephrine > increase in the strength of myocardial contraction > increases stroke volume. 2. Norepinephrine increases diffusion of Ca2+ into muscle fibers during action potential > increase in the ICF concentration of Ca2+ in myocardial cells > faster actin/myosin cross bridging (heart rate). 3. Induce release of epinephrine from adrenal medulla > Epinephrine stimulates an increase in strength of myocardial contraction > increase stroke volume.
Define: cardiac output, heart rate, stroke volume, end-diastolic-volume, ejection fraction.
>Cardiac output is the volume of blood pumped by the heart per minute (mL blood/min). >Heart rate is the number of heart beats per minute. >Stroke volume is the volume of blood pumped out of the left ventricle with each beat (mL/beat). >End-Diastolic Volume is the volume of blood in the ventricles at the end of diastole >Ejection Fraction is when ventricles eject their volume during systole.
What factors cause an increase in stroke volume?
>Increase end-diastolic volume >Greater ejection fraction
Explain how the skeletal muscle pump would increase venous return of blood to the heart.
Veins pass between skeletal muscles.The contraction of skeletal muscle squeezes the vein > increasing blood pressure > Upstream valve (furthest from heart) closes > Downstream valve (closest to heart) to open.
