Cardiac output and contractility Flashcards
Cardiac glycosides are used to treat?
Why?
1) Heart failure
2) It has a positive inotropic effect
What is preload?
Left ventricular end diastolic volume
The volume at EDV also relates to?
Venous return
What is afterload?
1) Aortic pressure
2) Pressure required to eject blood (open aortic valve)
The volume of blood ejected by ventricle with each beat is known as?
Stroke volume
What is the equation for stroke volume?
What does SV usually equal numerically?
1) SV = EDV - ESV
2) 70 mL
What is the equation for Ejection fraction?
What does EF usually equal numerically?
1) EF% = SV / EDV
2) 55%
What is the equation for cardiac output?
What does CO usually equal numerically?
1) CO (or Q) = SV x HR
2) 5 L/min
What happens as preload increases?
Increases CO and contractility
What happens as afterload increases?
Decrease CO
What does the heart do to overcome the decrease in CO due to increased afterload?
Increase HR
An increased heart rate can be described as?
An increase in contractility can be described as?
1) Positive chronotropic effect
2) Positive inotropic effect
What is the positive staircase effect (Bowditch staircase)?
More calcium enters cells leading to increase in contractility
Parasympathetic stimulation can have what type of effect?
Negative inotropic effect in atria only
Muscarinic receptor activation leads to?
1) Decrease inward Ca2+ current during plateau
2) ACh increases outward K+ current
In a ventricular pressure-volume loop, where is preload and afterload?
1) Preload is right bottom of loop (1)
2) Afterload is corner above preload (2)
In a ventricular pressure-volume loop, where is the isovolumetric contraction?
Preload to Afterload (1 to 2)
At what point in the ventricular pressure-volume loop does the aortic valve open?
Point 2 (afterload)
In a ventricular pressure-volume loop, where does ventricular ejection take place?
Where is pressure at max point?
1) Point 2 to 3
2) In between 2 to 3
In a ventricular pressure-volume loop, where is the stroke volume?
Across the loop
In a ventricular pressure-volume loop, where does isovolumetric relaxation occur?
From 3 to 4
In a ventricular pressure-volume loop, what does point 3 represent?
Systole ends and ventricles relax
In a ventricular pressure-volume loop, what does point 4 represent?
Tricuspid/mitral valve opens
In a ventricular pressure-volume loop, where does ventricular filling take place?
Point 4 to 1
What happens when preload is increased by more venous return?
1) Greater EDV
2) SV increases
In a ventricular pressure-volume loop, what happens to the loop when you increase preload?
Loop is wider to the right
In a ventricular pressure-volume loop, what happens to the loop when you increase afterload?
Loop is thinner and taller to the right
In a ventricular pressure-volume loop, what happens to the loop when you increase contractility?
Loop is wider to the left
What factor causes the end systolic pressure volume relation slope to increase?
Increasing contractility
The largest percentage of O2 consumption is for cardiac output or pressure work?
Pressure work
What ventricle must proportionally work harder despite CO being similar?
Why?
1) Left ventricle
2) Systemic pressure is greater than pulmonary pressure
What is the CO equation in regards to the Fick Principle?
O2 consumption / ([O2] pulmonary artery - [O2] pulmonary vein)
At equilibrium, CO equals?
Venous return
If you increase inotropy and heart rate what happens to afterload?
If you decrease both?
1) Decrease afterload
2) Increase afterload
What does the mean circulatory filling pressure (mean systemic pressure) equal when there is no CO and depends entirely on vascular compliance and blood volume?
7 or 8 mm Hg
During cardiac failure, what happens to:
1) Inotropy
2) Vascular compliance
3) BLood volume
4) SVR/TPR
1) Decrease
2) Decrease
3) Increased
4) Increased
What is the equation for mean arterial pressure?
MAP = CO x TPR
As ventricular end diastolic volume increases what happens to ventricular pressure?
When is this occurring?
1) Increases
2) Systole
As ventricular end diastolic volume decreases what happens to ventricular pressure?
When is this occurring?
1) Decreases
2) Diastole
Decreasing afterload has what effect on the velocity of ventricular contraction?
Increases it
