Cardiac performance Flashcards
What is the relationship between afterload and velocity of shortening?
The greater the afterload the slower the velocity of shortening
How does preload affect the force-velocity relationship?
If preload is increase there will be a greater velocity of shortening at a given afterload
How does preload affect the length-tension relationship?
If preload is increased there is an increase in active tension development
Does changing the preload affect Vmax?
No
What is directly proportional to the volume of blood in vena cavae and venous tone?
Central venous pressure
What will occur to central venous pressure in hypovolemia or venodilation?
It will decrease
What will occur with central venous pressure in hypervolemia or venoconstriction?
It will increase
What is the use of pulmonary capillary wedge pressure?
It provides an estimate of LV end-diastolic pressure and LA pressure
What does a PCWP of >20 mmHg indicate?
Pulmonary edema
What are factors that increase preload?
Increased ventricular compliance
Decreased venous compliance/venoconstriction
Increased force of atrial contraction
Reduced HR
Increased aortic pressure
Increased venous return
What are factors that decrease preload?
Decreased venous blood pressure from hypovolemia
Impaired atrial contraction
Increased HR
Decreased ventricular afterload
Decreased ventricular compliance
AV valve stenosis
What is another name for decreased ventricular compliance?
Ventricular diastolic failure
What increases end-systolic volume?
Increased afterload
Decreased contractility
What increases end-diastolic volume?
Increased venous return
Increased preload
What is the equation for wall stress?
Wall stress = (P x r)/(2 x wall thickness)
What is the equation for law of LaPlace?
T = P x r
How does the LV compensate for increased afterload?
Hypertrophy
What are factors that can increase afterload?
Aortic valve disease
Increased vascular resistance
What is the average stroke volume in healthy persons?
70 mL
What is the equation for SV?
SV = EDV - ESV
What is the most important determinant of stroke volume?
EDV
What increases SV?
Increased contractility
Increased preload
Decreased afterload
What are the only mechanisms that can alter force generation in the heart?
Changes in fiber length
Changes in inotropy
What occurs with increased cardiac inotropy?
Increases velocity of fiber shortening with increases the rate of ventricular pressure development
What is a reliable marker for contractility?
Rate of pressure change = deltaP/deltat
How does inotropy affect the force-velocity relationship?
Increase in inotropy results in an increase in Vmax and Fmax (maximal isometric force)
What is the equation for stroke work?
Stroke work = aortic pressure x SV
What is represented by the area within a pressure-volume loop?
Stroke work
What is the primary energy source for stroke work?
Fatty acids
What will change in a PV loop from exercise?
Increased EDV
Decreased ESV
Increased SV
Increased LV pressure
What will change in a PV loop in AV shunts?
Increased EDV
Increased SV
Decreased LV pressure
ESV stays the same
What will change in a PV loop associated with aortic stenosis?
Increased LV pressure
Increased ESV
Decreased SV from increased afterload
What is the equation for ejection faction?
EF = SV/EDV = (EDV-ESV)/EDV
What is a normal EF?
Greater than or equal to 55%
What is EF an index of?
Ventricular contractility
What is the difference in EF between diastolic and systolic HF?
EF decreases in systolic HF and stays normal in diastolic HF
What factors are directly proportional to EF?
Preload
Contractility/inotropy
What is the relationship between afterload and EF?
Inversely proportional
