Cardiac Cycle Flashcards
Lecture 17
Cardiac cycle
single beat of the heart; systole + diastole
Systole
ventricles contract
Diastole
relaxation/ventricles fill
Isovolumetric contraction
happens right after QR; the time when the ventricle volume is constant but increasing pressure. Start of isovolumetric contraction is the start of systole at peak R.
Ventricular contraction leads to what?
Increased ventricular pressure
S1 sound
sounds of vibrations from mitral valve closing;
closes when L ventricle pressure exceeds L atrial pressure;
happens right before isovolumetric contraction
Peak R significance
- start of systole and isovolumetric contraction
- end of diastole
Diastolic dysfunction
end-diastole pressure greater than 16 mmHg; normal average is 8 mmHg
When does the aortic valve open?
When L ventricular pressure exceeds aortic pressure;
rapid ejection of blood to aorta
Results of rapid ejections of blood into aorta?
- increased aortic pressure
- wall of aorta stretches
Stroke volume
amount of blood that flows out of the L ventricle/minute
about 70 mls
can be measured by Doppler ultrasound, radionuclide counts and echocardiography
Stroke volume equation
SV= ventricular end-diastole volume- ventricular end-systole volume
Ejection fraction
stroke volume/end-diastole volume
Cardiac output
blood ejected from aorta per MINUTE;
usually about 5 liters
Reduced ejection phase
Repolarization of the ventricles, results in T wave on EKG. Aortic pressure will then exceed L ventricular pressure.
Why doesn’t the aortic valve immediately close when aortic pressure starts to exceed L ventricular pressure?
The blood flow has a large amount of inertia which translates to kinetic energy. Valve doesn’t close immediately.
Aortic elastic recoil
pushes blood into rest of circulatory system
End systolic volume
volume left in ventricle after systole
End diastolic volume
volume left in ventricle after atrial contraction or diastole
about 120 mL
Left ventricular end-diastolic pressure
Pressure in the ventricle at the end of diastole, or being filled. Usually 12 mmHg
Major difference between right and left heart
peak systolic pressure
in the right heart it is 24mmHg
in the left heart it is 130mmHg
Pressure/volume loop of the L ventricle in a single cardiac cycle
mitral valve opens–> LV fills; LV P drops–> volume increases in LV and slight increase in LV P–> mitral valve closes–> isometric contraction occurs–> increase in LV pressure to 80 mmHg–> aortic valve opens when LV P exceeds aortic P–> LV muscles shorten and eject blood–> LV P increases even more as blood is pushed out in rapid ejection phase–> LV muscle relaxes/reduced ejection due to ventricular repolarization–> end systolic volume/P; closure of aortic valve–> isovolumetric relaxation begins
What happens to the R atrium right after P wave?
contraction of R atrium
What happens to the R atrium pressure right after QRS?
tricuspid valve bulges into R atrium as RV P increases due to isovolumetric contration/systole
What happens to the R atrium right after the repolarization of the ventricles (T wave)?
R atrium fills; tricuspid valve closed
Cardiac Output Equation
CO= stroke volume x heart rate
Fick’s Equation
Rate of O2 absorption in the circulation= change in O2 in pulmonary blood x pulmonary blood flow
Pulmonary blood flow= RV output= LV output–> O2 uptake measurements determine cardiac output.
QCv
O2 in venous blood entering the lungs/min
QCa
O2 in arterialized blood leaving lungs/min
O2 capillary bed uptake/min
QCa-QCv
In steady state, O2 uptake by blood is equal to?
the O2 removed by alveolar gas in lungs (VO2)
–> O2 capillary uptake= VO2
VO2=
QCa-QCv
–> Q (cardiac output)= VO2/Ca-Cv
