Muscle Physics and Heart as a Pump II Flashcards
Describe relative changes in pressure and volume through the cardiac cycle (PV loop diagram): Filling phase
o Point A: Volume = End systolic volume (ESV): not zero. There is always some blood left in the heart.
o Point A - Point B: Ventricle relaxes and fills, ventricular pressure falls to…
o Point B: Minimum ventricular pressure.
o Point B - Point C: Ventricular volume increases as blood flows into the left ventricle from the left atrium. There is little change in pressure, except the “a wave” which corresponds with atrial contraction.
o Point C: End-diastolic volume (EDV)
Describe relative changes in pressure and volume through the cardiac cycle (PV loop diagram): isovolumetric contraction phase
o Point C: Ventricle begins to contract
o Point C - Point D: Pressure in the ventricle exceeds that in the atrium and the mitral valve is pushed closed. Since both valves are closed, blood can neither enter nor leave the ventricle, and the volume is constant. Since the ventricle is contracting with both valves closed, the pressure increases dramatically.
o Point D: end diastolic volume (EDV).
Describe relative changes in pressure and volume through the cardiac cycle (PV loop diagram): ejection phase
o Point D: left ventricular pressure exceeds the aortic diastolic pressure, resulting in opening of the aortic valve.
o Point D - Point E: As blood leaves the ventricle, the volume decreases. At first pressure continues to increase, as the blood cannot leave the aorta as fast as it is entering..
o Point E: Peak systolic pressure
o Point E - Point F: As myocytes in the ventricle stop contracting, the ventricular pressure begins to fall. Blood is still leaving the ventricle.
o Point F: end-systolic volume (ESV).
Describe relative changes in pressure and volume through the cardiac cycle (PV loop diagram): isovolumetric relaxation phase
o Point F: end-systolic volume (ESV).
o Point F - Point A: When the ventricular pressure falls below the aortic pressure, the aortic valve closes. Again, both valves are closed, so the ventricular volume is constant. When the ventricular pressure falls below the atrial pressure, the mitral valve opens and filling begins again.
Stroke volume (SV):
o SV=EDV-ESV
Ejection fraction (EF):
the fraction of the EDV ejected during systole.
o EF=SV/EDV= (EDV-ESV)/EDV
Stroke work:
energy per beat (Joules), corresponds to the area inside the PV loop diagram.
o NOT the same for the left and right sides of the heart.
Pulse pressure/Blood pressure:
o End diastolic pressure at point D
o Peak systolic pressure at point E
o Difference = pulse pressure.
Preload:
the pressure stretching the ventricle of the heart prior to contraction.
time, and ventricular compliance.
o Increase in preload: Results in an increase stroke volume for the next beatàStarling’s law! Same ESV is achieved, EF is increased. On subsequent beats, SV returns to normal since ESV and contractility are unchanged.
EDV can be changed by changes in filling pressure, filling
Afterload:
end-systolic pressure→ pressure in the aorta following systole.
o Increase in afterload: decrease in stroke volume. The ventricle has to work harder against the increased aortic pressure, so less blood is ejected. ¬ Aortic pressure →aortic valve opens later in the cycle, reducing ejection time.
EDV unchanged, EF decreased, ESV increased.
Stroke volume recovers on subsequent beats because the ¬ESV with constant venous return means ¬EDV, which increases stroke volume.
Contractility/inotropy:
reflects the strength of contraction at any given preload and afterload.
o Changes in inotropy: describe new starling curves.
o If you hold the preload and afterload constant, and increase inotropy: new starling curve that corresponds to greater systolic pressure development for any given volume.
Increased inotropy is associated with an increased risk of stroke.
