Cardiac Output Flashcards
What is occurring during the ST segment?
Ca and K channels are open, allowing for the plateau phase
What causes the RAD with a RBBB?
Negative vector in lead III
What is cardiac output?
HR x SV
What is stroke volume?
LVEDV -LVESV
What are the four factors that affect cardiac output?
- Preload
- Contractility
- Afterload
- HR
What is preload?
end diastolic pressure
What is afterload?
The pressure in the aorta leading from the ventricle (aortic pressure). It is related to total peripheral resistance
What is the Frank-Starling mechanism of the heart?
As the end diastolic volume of the heart increases, the systolic pressure increases
(i.e. the greater the heart muscle is stretched during filling, the greater is the force of contraction and the greater the quantity of blood pumped into the aorta)
What is the consequence of the Frank-Starling mechanism of the heart?
Venous return directly influences systolic pressure, up to a point, after which heart failure occurs
How is CO maintained when HR decreases?
Decreased HR will increase the SV d/t higher EDSV. Vice versa holds as well.
(CO = HR x SV)
What is occurring in phase 1 of the pressure-volume diagram?
Blood is filling the ventricle
What happens at point B of the pressure-volume diagram?
Isovolumic contraction
What does the point B of of the pressure-volume diagram correspond to?
The left ventricular end-diastolic volume
What is occurring at point c of the pressure-volume diagram?
Semi-lunar valve opens, starting the ejection phase
What is occurring at the top line of the pressure-volume diagram?
Ejection of blood
What is occurring at point D of the pressure-volume diagram? What phase of the heart cycle begins at this point?
Aortic valve closes
Isovolumic relaxation begins
What is occurring at point A of the pressure-volume diagram?
AV valves open
Increasing the end diastolic volume (increasing preload) does what to stroke volume?
Increases it
Increasing afterload does what to stroke volume?
Decreases it
What is the clinical correlation to afterload?
HTN
What did Sarnoff contribute?
Showed the effect of heart contractility on HR, SV, and CO
shift of the curve, rather than a shift along the curve
What will happen to the afterload curve, if contractility of the heart increases? What is the effect of CO?
Shifts curve upward, causing increase in CO
What are three causes of decreased contractility?
MI
Volume overload
Dilated cardiomyopathy
What will happen if the heart cannot relax as efficiently? How is this reflected in the graph?
Lower CO
Shift the end diastolic pressure curve upward at every point of volume
What can cause an upward shift in the end diastolic pressure curve?
Hypertrophy
Remodeling of the matrix
Transient ischemia
What causes the plateau of the frank-starling law of the heart curve?
Collapse of the large veins under high negative pressure in the chest
What happens at the x intercept of the frank starling curve?
Atrial pressure = venous pressure, meaning no flow of blood
What happens to the venous return curve if you lose blood?
Shifts downward at every point of atrial pressure
What happens to the venous return curve if you gain blood?
Shifts upward at every point of atrial pressure
What happens to the venous return curve if you constrict your veins?
Shifts curve downward (decrease the amount of blood returned to the right atrium at every level of right atrial pressure)
What happens to the venous return curve if you dilate your veins?
Shifts curve upward (increase the amount of blood returned to the right atrium at every level of right atrial pressure)
Vasocontriction or vasodilation will change the Psf (mean systemic pressure) how?
No change (there is no change in blood volume, just how it is distributed)
As right atrial pressure increases, what is the effect on CO? How does it bring about this effect?
Increases CO d/t an increase in the SV
How does the PNS exert its effects? How is this reflected on the cardiaic output/right atrial pressure curve?
Lower HR, decreases CO at every point of RA pressure
How does the SNS exert its effects? How is this reflected on the cardiaic output/right atrial pressure curve?
Increases HR and contractility of the heart, increasing the CO at every point or RA pressure
How does SNS withdrawl exert its effects? How is this reflected on the cardiaic output/right atrial pressure curve?
Lower HR, decreases CO at every point of RA pressure
How does the SNS increase the force of heart contraction?
Changes the Ca permeability of the myocytes,
How does the PNS decrease the heart rate?
Increases K permeability to increase the phase 4 depolarization of the SA node
What are the two changes in systole that bring about the effects of increased sympathetic tone during exercise?
Increased glycogenolysis
Increased cellular permeability to calcium, making muscles contract more easily
What happens during diastole when the SNS tone increases?
Enhanced Ca uptake (sequestration and efflux)
This decreases the time the heart spends in diastole, and makes the heart more efficient
Why does increase Ca reuptake and sequestration increase heart efficiency during exercise?
Lowers the amount of time that is needed to prepare the Ca for release during the next heart cycle.
What does the eqilibrium point on the cardiac output/venous return point represent?
The point where inflow matches outflow
What is the Fick’s principle of measuring cardiac output?
Recording the amount of oxygen absorbed by the blood compared to how much returns
What is the effect of an AV shunt on CO?
Reduced peripheral resistance, increasing CO
What is the effect of hyperthyroidism on CO?
Increase CO
What is the effect on anemia on CO?
Increases
What is the effect of heart damage on CO?
decrease
What is the effect of decreased blood volume on CO?
Decreases
What is the effect of acute venous dilation or venous obstruction?
Decreases CO (impedes what is coming back)
What is the effect of decreased tissue mass or tissue metabolism on CO?
Decreases CO
