5. Cardiac System 2 Flashcards
What is contractility?
Inotropic state of heart
Defined as property of the contractile myocytes that account for the strength of contraction
Related to the intrinsic cellular mechanisms that regulate interaction between actin and myosin
Independent of preload and afterload and sarcomere length
Epinephrine increases contractility which increases stroke volume
What are the 7 parameters that can be used to evaluate the cardiac performance of the heart?
- Ventricular end-diastolic pressure
- Cardiac index
- Stroke volume
- Ejection fraction (EF)
- Peak rate of ventricular pressure development (peak +dp/dt) during isovolumic contraction
- End-systolic pressure-volume relationship (ESPVR)
- Maximum velocity of muscle shortening (Vmax)
How is ventricular end diastolic pressure used to evaluate cardiac performance?
Any inadequate systolic emptying will lead to an increase in ESV, increasing EDV (preload)
Increase EDV increases EDP regardless of compliance
Hypertrophic heart will generate higher EDP and dilated heart will generate lower EDP
Failing heart has very high EDP
EDP can be used as an index for ventricular function (performance)
Slides 5-10 Sept 26
How is cardiac index used to evaluate cardiac performance?
Cardiac output can be used as a measure of the overall cardiac performance Cardiac index (CI) is defined as the cardiac output (CO) divided by body surface area (BSA) CI=CO/BSA
Increase contractility increases SV increases CI
How is stroke volume used to evaluate cardiac performance?
Stroke climate indirectly reflects the extent of ventricular fiber shortening
Shorter fiber length, smaller ventricular chamber size, lesser volume of blood remains at end of ventricular systole
SV can be influenced by ventricular loading (preload or afterload) in addition to contractility
SV can be reduced despite cardiac output is normal due to tachyarrythmia
How is ejection fraction (EF) used to evaluate cardiac performance?
Defined as the fraction of end-diastolic volume ejected from ventricle during each systolic contraction
EF=SV/EDV
Normally EF is greater than 55% but depends on variation of afterload
How is peak rate of ventricular pressure development during isovolumic contraction used to evaluate cardiac performance?
It is the value corresponding to the rate of pressure rises (Δpressure/Δtime) in ventricular chamber during isovolumic contraction
Stronger force of contraction, steeper the slope
Highest +dp/dt usually occurs at the moment just before the opening of the semilunar valves
+dp/dt can be influence by contractility, loading, and heart rate
Slides 14-15 sept 26
Look over the treppe (staircase) phenomenon or Bowditch effect on slide 16 sept 26?
Ok
How is end-systolic pressure-volume relationship (ESPVR) used to evaluate cardiac performance?
Any increase in inotropy (contractility) will shift the ESPVR upwards to the left with a steeper slope
Slide 17 sept 26
How is maximum velocity of muscle shortening (Vmax) used to evaluate cardiac performance?
It is the true indicator of contractility at a given inotropic state
Vmax cannot he measured
Can only be extrapolated
When contractility if the ventricle is increased, it will cause a parallel shift of the force-velocity curve up and to the right (increases both Vmax and maximal tension development)
Slide 18 sept 26
What are the effects of contractility on stroke volume?
At a given loading condition (EDV or preload), increases in Vmax means increase in contractility Which; Increase ejection velocity Increase stroke volume Reduce ESV Reduce ESP
With increase in stroke volume and a decrease in ESV, ejection fraction is increased
Overall increase in stroke volume (SV)
Slides 19-21 sept 26
What is aortic stenosis?
Narrow opening of aortic valve (resistance to flow)
No problem with valvular closure
Increase flow velocity of blood (velocity is proportional to 1/cross sectional area) through the stenotic valve causing turbulence flow and generating systolic murmur (murmur between S1 and S2)
Aortic stenosis causes an increase in LVP (much greater than the aortic pressure) due to increase in afterload (resistance to flow) cause by the stenosis
Increase afterload cause huge increase ESV
Decrease strove volume
Slides 23-27 sept 26
What is mitral stenosis?
Increase resistance to flow across the mitral valve during ventricular filling (gives rise to the elevation of left atrial pressure)
Could lead to huge reduction in LVEDV which decreases SV and CO
Also leads to small reduction in aortic pressure (afterload) which leads to small decrease in ESV
Creates a diastolic murmur between S2 and S1 due to higher velocities of blood flow
Slides 28-30 sept 26
What is aortic insufficiency?
Effect of valvular insufficiency in cardiac function
Incomplete closure of aortic valve (regurgitation)
Blood movement between aorta and left ventricle at all times
No true ventricular isovolumic relaxation or contraction phase in an aortic regurgitated heart
Increases EDV which increases force of contraction through frank-starling mechanism
Slides 32-34 sept 26
What is mitral insufficiency?
With the incomplete closure of the mitral valve, blood flows back to the left atrium during ventricle contraction causing a sharp rise in left atrial pressure during ventricular systole (can open valve fine)
Back flow of blood ti left atrium during ventricular systole creates systolic murmur between S1 and S2
Slides 35-37 sept 26
