Contractility & Cardiac Output Flashcards
What is preload?
aka left ventricular end diastolic volume
-amount of blood ready to be pumped
What is preload directly related to?
-fiber length @ end of diastole
–> as ventricle fills with more blood, fibers get longer
How does venous return affect preload?
> venous return -> > preload
What is the tension relationship & preload?
cardiac output = venous return at a steady state
What is frank starling relat?
-volume of blood ejected by ventricle depends od the volume present in the ventricle at end of diastole
What is after load?
(for LV) the aortic pressure aka the force opposing contraction
–> pressure required to eject blood by opening the aortic valve
What is the relationship b/w velocity of shorting and after load?
-velocity of shortening DECREASES as after load INCREASES
greatest if after load = 0
What is stroke volume and how do you calculate for it?
volume of blood ejected by ventricle with each beat
SV = EDV - ESV (~70mL)
What is ejection fraction and how do you calculate it?
What does it measure?
- fraction of EDV ejected in each stroke volume
- measures efficiency and contractility
- EF% = SV / EDV (~55%)
What physiological state would cause the ejection fraction to decrease?
heart failure
What is cardiac output and how to you calculate it?
-total volume of blood ejected by ventricle per minute
What are the two coupling factors that contribute to cardiac output?
- preload
- afterload
both relate to contractility
What happens to contractility as you increase preload?
-increase contractility and increase CO
What happens to CO as you increase after load?
decrease in CO
heart must overcome by increasing contractility or HR
What is the positive staircase effect?
an auto regulation method by which increased HR increases contractility (via more Ca2+ in cell and into SR)
aka positive chronotropic effect creates a positive inotropic effect
How does sympathetic input affect cardiac output?
activation of what which does what?
- iontropic effect via B-AR activation
- phosphorylation of sarcolemma Ca2+ channels, phospholamban (stimulatory), and troponin 1 (inhibititory)
How does parasympathetic input affect cardiac output?
- (-) iontropic effect via muscarinic receptor activation
- decrease inward Ca2+ current during plateau
- ACh increased outward flow of K+ current via K+-(-)ACh channels
What does administering isoproterenol (B-AR agonist ) do ?
increases HR and contractility
treats bradycardia
What factors can increase preload?
- increased venous return
- high blood volume
What factors can increase after load?
- aortic stenosis
- hypertension
What factor can increase contractility directly?
adrenergic stimulation
What is volume work and how do you calculate it?
-cardiac output (SV x HR)
What is pressure work?
aortic pressure
How do you calculate minute work?
CO x aortic pressure (SV x HR x aortic pressure)
How do you calculate stroke work?
SV x aortic pressure (LV)
-the area within the volume pressure loop?
What is the difference b/w volume work (cardiac output) and stroke work?
Stroke work takes into account the pressure in the aorta; volume work factors in HR
What is the Fick Principle? (myocardial O2 consumption)
States that he largest % of O2 consumption is pressure work rather than CO (SV x HR)
-LV must work proportionally harder than RV due to systemic pressure > aortic pressure
What further accents increase LV pressure work ?
- aortic stenosis
- systemic hypertension
aka the LV myocytes are using more oxygen to accomplish their tasks to overcome a higher after load pressure and thus more “work”
How do you calculate Os consumption ?
O2 consumption = CO x ( [O2]pulm v. - (CO x [O2]pulm a.) )
CO = O2 consumption / ( [O2]pulm v. -[O2]pulm a. )
What 3 factors play major roles on the cardiac function curve?
- venous return
- RA pressure
- EDV and end diastolic fiber length
What is the relationship of venous return and CO at equilibrium?
- venous return = CO
- aka volume of blood as cardiac output ejected by ventricle matches the volume it reaches in venous return
What happens to the RA pressure and venous return when you increase iontropy vs decrease?
increase = RA pressure decreases ; CO/venous return increases
Decreases = RA pressure increases ; Venous return decreases
What occurs to RA pressure and venous return when you increase TPR vs decrease TPR?
increase : RA pressure remains constant ; venous return decreases
decrease : RA pressure remain constant ; Venous return increases
What occurs to RA pressure and venous return when you increase blood volume vs decrease blood volume?
increase : RA pressure increases ; venous return increases
Decrease : RA pressure decreases; venous return decreases
What happens during cardiac failure?
- decrease iontropy (contractility)
- decrease vascular compliance
- increase BP
- increase SVR/TPR
What happens to the pressure in the RA and venous return in cardiac failure?
- RA pressure increases
- cardiac output decreases
-increase in volume, decrease contractility of ventricle , and increase TPR
