Assessment of Cardiovascular FunctionCardiac 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).