Chapter 19 - Cardiac Output
What is the Frank-Starling law?
As the volume of blood entering the heart increases, there is greater stretch of the heart (preload), which leads to a greater number of crossbridges, greater ventricular contractions, and increased stroke volume.
What is heart reate?
Beats per minute (bpm).
What is the CO equation?
CO = Heart Rate (HR) * Stoke Volume (SV)
What does a negative inotropic agent do?
Decreases calcium, number of crossbridges, force of contraction, and stroke volume. Increases potassium or hydrogen ions.
What is an example of when venous return is increased?
During exercise.
When the HR is faster, how is EDV affected?
EDV lowers.
What does venous return determine?
EDV, which determines preload.
What is an example of cardiac reserve?
Exercise; heart rate and stroke volume both increase, which increases CO.
What are chronotropic agents?
Factors that change HR.
What are inotropic agents?
Factors that change stroke volume by altering contractility (force of contraction at a given stretch of cardiac cells).
What are negative chronotropic agents?
Factors that decrease HR.
What are positive chronotropic agents?
Factors that raise HR.
What is tachycardia?
High resting HR (100 bpm or more).
What is cardiac reserve?
Increase in CO above its level at rest.
What does a positive inotropic agent do?
Increases calcium concentration, which leads to more crossbridge cycling, increased force of contraction, and increased stroke volume. Includes NE.
How do beta-blocker drugs affect (negatively) HR?
Interferes with the binding of NE and epinephrine to beta receptors.
What is brachycardia?
Low resting HR (60 bpm or less).
What is atherosclerosis?
Makes the arterial lumen smaller, leading to greater resistance and decreased stroke volume.
How does the thyroid hormone affect (positively) HR?
Nodal cells become more responsive to NE by increasing the amount of receptors.
What are two examples of chronotropic agents?
Parasympathetic nerve stimulation and beta-blocker drugs.
How does parasympathetic nerve stimulation affect (negatively) HR?
Releases ACh, which causes potassium to leave the cell and hyperpolarization occurs, which mean it takes longer to reach the threshold.
How does sympathetic nerve stimulation affect (positively) HR?
Releases NE on SA nodal cells, which causes calcium to enter nodal cells and the threshold is reached faster, increasing the firing rate.
What is afterload?
Resistance in arteries to the ejection of blood by the ventricles. Represents the pressure that must be exceeded before the blood can be ejected from the chamber.
How do you determine stroke volume?
SV = EDV - ESV
What is preload?
Stretch of the heart wall due to the load to which a cardiac muscle is subjected to before shortening.
What are two positive chronotropic agents?
Sympathetic nerve stimulation and thyroid hormone.
What is cardiac output (CO)?
The amount of blood that is pumped by a single ventricle (left or right) in one minute (expressed in liters/min).
What is venous return?
The amount of blood that is returned to the heart via the great veins.
What is End-Systolic Volume (ESV)?
The blood in the ventricle at the end of systole.
What is stroke volume?
The volume of blood ejected during one beat (mL/beat).
Are heart rate and stroke volume independent of each other?
They are DEpendent on each other; changes in one leads to changes in the other.
How do heart rate and stoke volume apply to athletes?
They typically have larger/stronger hearts (greater stoke volume), but often have a lower heart rate.
What is stroke volume influenced by?
Venous return, inotropic agents, and afterload.
What is End-Diastolic Volume (EDV)?
Volume of blood in the ventricle at the end of diastole.
When is venous return increased?
When there is an increase of venous pressure or time to fill.
When does venous return decrease?
When there is low blood volume due to blood loss or there is an abnormally high heartrate.
