cardiac A&P Flashcards
cardiac output
CO = SV X HR
Each time the heart beats, a volume of blood is ejected.
amount of blood that the heart pumps out of the left ventricle each minute.
Cardiac output is diminished in HF, because….
the left ventricle is weakened and cannot adequately pump blood out of the chamber.
SV is the difference between…..
End-diastolic volume (EDV), or volume of blood at the end of relaxation
and
End-systolic volume (ESV), or residual volume of blood remaining in the ventricle after ejection.
Any factor that alters either EDV or ESV will change SV, and thus CO will be changed.
Three major factors influence stroke volume:
Preload (volume of blood in the heart)
Afterload (force opposing ejection of the blood from the ventricle)
Contractility (contractile capabilities of the heart)
preload
Definition = stretch of cardiac muscle cells before contraction.
preload is r/t the chamber volume just prior to contraction.
A lower preload leads to a lower SV and vice versa.
Example: a client with hypovolemia will have less ventricular filling, reduced preload, and lower stroke volume
Frank-Starling Law
This law states that an increase in resting muscle fiber length results in greater muscle tension.
This is also called the “length-tension” relationship.
The heart has the ability to change its force of contraction (and stroke volume) in response to changes in venous return.
Starling’s Capillary Forces
At every capillary–cell interface, there are three fluid compartments: Intracellular, Interstitial, Extracellular.
intracellular fluid
found inside the cells
interstitial fluid
surrounds the cell
extracellular fluid
located inside the capillary
hydrostatic pressure
Fluid within the blood exerts hydrostatic pressure.
A force that attempts to PUSH FLUID OUT of the capillary pores and into the interstitial and intracellular spaces.
Water-pushing-pressure.
Oncotic (Osmotic) Pressure
Oncotic (osmotic) pressure is a force that attempts to PULL FLUID from the interstitial and intracellular spaces into the capillary.
Particles within the blood, such as albumin, sodium, and glucose, exert oncotic or osmotic pressure.
Water-pulling-pressure.
Starling’s Law of Capillary Forces
Oncotic pressure forces and hydrostatic pressure forces oppose each other at every capillary membrane and attempt to balance each other out
afterload
Definition = resistance that must be overcome in order to eject blood from the chamber.
Left ventricular afterload is primarily determined by aortic BP.
An increase in afterload will lead to a decrease in SV unless the heart compensates.
Example: A person with high BP will have high afterload and be at risk for a lower SV.
contractility
Definition = contractile force of the heart muscle cells.
Contractility is primarily determined by the amount of free calcium within the myocardial cell.
Increased contractility increases stroke volume by causing a greater % of the volume to be ejected
