Exam 3: Cardiac Performance Flashcards
What is the formula for stroke volume?
SV= EDV- ESV
What is the formula for EF?
EF= SV/EDV x100
What is the formula for cardiac output?
Co= SV x HR
What is the formula for Cardiac index?
CI= CO/SA
What is the formula for left ventricular stroke work?
LVSW= SV x LVPP
Left ventricular pulse pressure
What are the 4 things that can hinge the shape of he PV loop?
- Preload
- Afterload
- HR
- an contractility
What is preload?
The tension in ventricular wall at the end of diastole-How much blood is in the ventricle before contraction
How do you measure preload?
Tension cannot be determined, so measure ventricular EDV or ventricular ED pressure
What does preload determine?
Resting fiber length
What is the main point of the frank-starling relationship?
A EDV increases, ventricle contracts with more force and a greater SV results
If you increase preload, what else increases?
EDV and stroke volume. ESV stays the same
What are the factors that determine preload?
- Ventricular filling time
- Ventricular compliance
- Filling pressure
- Contribution of atrial systole to filling
- Pericardial constraint
How does langendorff heart preparation affect HR, CO, and SV?
Heart rate is increased to approximately 150BPM which lowers time for reduced filling phase.
CO is usually not affect since decreased SV is compensated for by increased HR.
CO is adversely affected when HR is above 150-180BPM
How does sympathetic increased in HR affect SV and CO?
- SV preserved due to increased contractility
- CO can increase dramatically
What reduces compliance?
Hypertrophy and ischemia
What does a sleep slope on a pressure volume curve imply?
Low compliance
What affects right venous pressure?
Intrathoracic pressure and central venous pressure
What affect will decreased intrathoracic pressure or increased central venous pressure have on RV preload and SV?
It will increase both RV preload and SV
What is the role of the pericardium with respect to EDV?
- Protects against left ventricular volume overload
- Maintains alignment with major vessels
What happens if the pericardium is filled with excess fluid?
The fluid will exert a hydrostatic pressure on the external surface of the heart that reduces ventricular compliance.
-Lowered compliance reduces EDV and SV, Clinical example is cardiac tamponade
What is afterload?
Th resistance against which the ventricle contracts
-Arterial pressure, peripheral vascular resistance, arterial wall compliance, viscosity of blood
How do you estimate mean arterial pressure?
DP (in aorta) + 1/3 Pulse pressure
Afterload has an inverse relationship with what two things?
- ventricular muscle shortening (stroke volume)
- Maximum velocity of ejection
What are the effects of an increased afterload with a constant EDV?
- Aortic valve opens later and closes sooner
- Increased ESV
- Reduction in SV
What can increased afterload?
- Aortic stenosis,
- elevated arterial pressure
- Elevated PVR
- Increased blood viscosity
- Decreased arterial compliance
What is contractility?
Ability of heart to do work at any given fiber length
-Distinct from changes in EDV and changed in afterload
What are factors that may affect myocardial contractility?
- ANS activity
- Circulating hormones
- catecholamines increased Ca2+ influx and availability
How does SNS stimulation affect contractility?
- NE increases the SV at a given EDV
- Increases EF
- Rate of rise and relaxation increased
- Positive inotropic effect
Fiber length is directly proportional to what?
EDV
What happens to SV when contractility is increased at a given EDV, EDP, and afterload?
The ventricle ejects more blood, so increased SV, due to more rapid and forceful emptying
The magnitude of ESV is dependent on what two things?
Afterload and contractility
What is the Treppe, or staircase, effect?
Increasing HR causes calcium accumulation which increases contractility (small positive inotropic effect)
What is volume work compared to pressure work? Which is increased during exercise?
Volume work refers to moving blood (preload) and pressure work is working against afterload.
Volume work increases during exercise
