Chapter 25 Assessment of Cardiovascular Function
Cardiac Action Potential
Depolarization: electrical activation of cell caused by influx of sodium into cell while
potassium exits cell
This exchange of ions creates
...
Chapter 25 Assessment of Cardiovascular Function
Cardiac Action Potential
Depolarization: electrical activation of cell caused by influx of sodium into cell while
potassium exits cell
This exchange of ions creates a positively charged intracellular space and a negatively
charged extracellular space.
Repolarization: return of cell to resting state caused by re-entry of potassium into cell while
sodium exits
Refractory Periods
Effective (absolute) refractory period: phase in which cells are incapable of depolarizing.( no
desert no matter what you have no room)
Cell is unresponsive to any electrical stimulus.
Relative refractory period: phase in which cells require stronger-than-normal stimulus to
depolarize ( EG you have room for desert so if stimulus is great enough)
Cardiac Hemodynamics
Cardiac Output
Refers to the total amount of blood ejected by one of the ventricles in liters/minute.
In a resting adult is 4 to 6 L/min normally
Computed by multiplying the stroke volume by the heart rate.
Stroke volume is the amount of blood ejected from one of the ventricles per heartbeat.
Average resting stroke volume is about 60 to 130 mL.
Preload: degree of stretch of the ventricular cardiac muscle fibers at end of diastole
End of diastole is the period when filling volume in the ventricles is the highest and
the degree of stretch of the muscle fibers is the greatest.
Preload is referred to as left ventricular end-diastolic pressure.
As the volume of blood returning to the heart increases, muscle fiber stretch also
increases (increased preload), resulting in stronger contraction and a greater SV
Preload is decreased by a reduction in the volume of blood returning to the ventricles.
o Diuresis, venodilating agents (nitrates), excessive loss of blood, or dehydration
(loss of body fluids from vomiting, diarrhea, or diaphoresis).
Preload is increased by increasing the return of circulating blood volume to the ventricles.
o Controlling the loss of blood or body fluids and replacing fluids (blood
transfusions and IV fluid administration)
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