The Cardiac Cycle Flashcards
What happens if cardiac muscle is stretched with a preload?
How about if an afterload is added and length is stabilized
It will contract stronger.
Contraction will not be as effective with afterload attached.
Physiological preload correlate:
Ventricular filling from veins/atria. Stretches the cardiomyocytes in the ventricles.
Physiological afterload correlate:
Existing arterial pressure. TPR = MAP/CO
Explain the phases of the Wiggers Diagram:
A: LV pressure increases dramatically after QRS complex. This occurs because AP leads to contraction. Aortic pressure decreasing.
B: Volume decreases as LV pressure increases over aortic pressure. Aortic pressure then increases due to compliance. Ejection is occuring. LA pressure increases as blood fills it.
C: LV pressure decreases as relaxation occurs.
D: LA pressure higher than LV pressure, so volume increases as blood fills entricle.
What does the beginning of the first LV volume plateau signify?
Why does the plateau exist?
What is this called?
Mitral Valve Closure. Here LVP>LAP.
Plateau exists because aortic valve is still closed. Aortic pressure > LVP.
This is called isovolumic contraction because the volume is constant, but the LV is contracting.
What happens at the beginning of the second LV volume plateau?
What does this plateau signify?
What is happening to end the second plateau?
Aortic Valve closes because Aortic Pressure >LV pressure.
This plateau is isovolumic contraction. The volume stays the same because the aortic value is closed. The cells in the LV are relaxing so pressure decreases.
The mitral valve is opening because LAP > LVP
Explain the rise in volume after the second plateau.
What is the bump?
This is where the LV is filling. Its pressure doesn’t change much because there’s no contraction, but the volume is increasing rapidly.
The bump is the atrial kick, where the LA contracts and shunts more blood into the ventricle.
Location and explanation of heart sounds.
S1 : closing of AV values. Occurs to start off isovolumic contraction.
S2: Closing of aortic and pulmonary valves. Occurs to start off isovolumic relaxation.
Purpose of valves?
To ensure unidirectional flow.
Valvular insufficiency vs Valvular Stenosis
Insufficiency –> Valves do not close properly
Stenosis–> Partial blockage.
Draw a pressure volume loop
Where on the PV loop diagram do the aortic valve and mitral valve open and close?
What is end systolic volume?
What part of PV loop corresponds to end systolic volume?
ESV is the volume in the ventricle after contraction.
What is end diastolic volume?
What part of PV loop corresponds to end diastolic volume?
EDV is the volume in the heart before contraction.
Stroke Volume
EDV-ESV
Width of the PV loop
Ejection Fraction
SV/EDV
Where are Pressure at end systole, end diastolic pressure, and left atrial pressure found on the PV loop?
Systolic and diastolic blood pressure
Systolic BP: Highest aortic pressure
Diastolic BP: Pressure where ejection occurs
Systole is when ventricles contract. Diastole is when ventricles relax.
Between what two boundaries does the PV loop sit?
ESPVR
EDPVR
End Systolic/Diastolic Pressure-Volume Relations
Graph of EDPVR
Nonlinear, defines the lower boundary for the end-diastolic pressure volume point of the PV loop
What does the slope of the ES/DPVR mean?
Flat=compliant, steep, less compliant
So, for EDPVR, at low volume, the ventricle is compliant. As it fills, it becomes less compliant and more difficult to fill.
Increased preload effect on PV loop
Curve shifts to right along EDPVR. Stronger contraction occurs and higher pressures are generated, so shifts right along ESPVR too.
Increased preload equal increased stroke volume.
Explain the Starling Curve
As preload increases (LVEDP), SV increases.
What factors increase preload?
Fluid retention (in advanced heart failure)
Venoconstriction
