The cardiac cycle Flashcards
What does the heart look like?
See picture
What is the cardiac cycle?
Alternating contraction and relaxation of the heart muscle which repeats with every heartbeat.
What is diastole?
Phase of relaxation and filling
What is systole?
Phase of contraction and ejection
What is cardiac output?
The pumping activity of the heart.
CO = volume of blood pumped / min
CO = SV x HR
70ml x 70bp/min = 5L/min
Left CO = right CO
What is stroke volume?
The volume ejected per contraction.
What are the basic concepts of the cardiac cycle?
Valves open and close because of pressure differences.
Blood will flow down an energy gradient (pressure).
When the muscle surrounding the chamber contracts, the pressure increases in the chamber.
When the muscle relaxes, the pressure decreases.
What is the contribution to the cardiac cycle?
1 cycle is about 850ms at 70bpm.
2/3s is ventricular diastole - ventricle is relaxed and filling.
If heart rate increases, this period is shortened, but filling is not usually compromised until heart rate is very high.
The final quarter of ventricle filling is from atrial systole.
1/3 of the cycle is ventricular systole.
See picture.
What is ventricular filling / diastole?
Blood flows passively from pulmonary veins, into the left atrium and left ventricle.
The atrial pressure is greater than the ventricular pressure, and the AV valve opens.
The ventricular pressure is smaller than the aortic pressure, the aortic valve closes.
What is atrial contraction/ systole?
Contraction of the atria increases atrial pressure and pushes atrial contents into the ventricle.
Ventricular pressure lower than aortic pressure, aortic valve is still closed.
Atrial pressure is greater than ventricular pressure, AV valve opens.
What is isovolumetric contraction / ventricular systole?
Contraction of the ventricles increases ventricular pressure, the AV valve closes, and ventricular pressure continues to rise.
The ventricular pressure is less than aortic pressure, aortic valve still closed.
The ventricular pressure is greater than atrial pressure, the AV valve closes.
All valves are closed.
What is ventricular ejection/ systole?
Continued contraction of the ventricle increases ventricular pressure further, until it exceeds aortic pressure, and the aortic valve opens, allowing rapid ejection.
What is isovolumetric relaxation/ ventricular diastole?
Relaxation of the ventricle decreases ventricular pressure, until it is less than aortic pressure and the aortic valve closes.
Ventricular pressure continues to fall.
What is repetition of the cycle?
When the ventricular pressure falls below the atrial pressure, the AV valve opens and the cycle resumes.
The ventricular pressure is less than the aortic pressure, the aortic valve is closed.
What are the phases of the cardiac cycle?
Isovolumetric relaxation/ ventricular diastole.
Ventricular filling/ ventricular diastole.
Atrial contraction/ systole.
Isovolumetric contraction.
Ventricular contraction / systole
Ventricular ejection / systole second phase.
See picture.
What is the pressure and volume of the left cardiac cycle?
See picture.
How do the left pressures change?
Aortic pressure is between 80-120mmHg, which correlates to systolic and diastolic blood pressure.
Ventricular pressure in diastole is very low, then increases in systole to 120mmHg.
Atrial pressure is very low throughout the cycle.
How do the left volumes change?
End diastolic volume (volume in ventricle just after AV valve shuts at end of diastole) is 120ml.
End systolic volume, when ejection stops, is 50ml in the ventricle.
Stroke volume = EDV - ESV = 70ml.
What happens to pressure in hypertension?
The blood pressure is higher, so the pressure the heart has to generate to open the aortic valve increases, and the heart has to work harder.
The size of the ventricular loop indicates the work of the heart.
What is the process of the cardiac cycle?
Firing of SA node, stimulates atria to depolarise
Atrial contraction causes atrial pressure to increase, blood flows into ventricles.
Ventricles almost already full by passive flow through open AV valve.
As atrial contraction completes, pressure falls, AV valves shut, produces S1 heart sound and beginning of systole.
Ventricular depolarisation is halfway through atrial contraction, ventricles contract, increases its pressure, valves still closed - isovolumetric contraction - no blood ejected.
Ventricular ejection starts when ventricular pressure is higher than aorta.
Aortic valve opens and blood ejected out of ventricles.
Ventricular repolarisation begins, ventricular pressure falls, and force of ejection is reduced. When pressure drops below aortic, valves close, marks end of systole, beginning of diastole.
Valves close produces second heart sound S2
First part of diastole is isovolumetric as ventricles relax and all valves are closed. Ventricular pressure drops rapidly, volume unchanged.
Meanwhile atrial pressure increases slowly and filled with blood.
Ventricular pressure drops below atrial pressure, AV valve opens, ventricular filling starts passively. Atria contract to complete filling phase.
How does the cardiac cycle link to the Wiggers diagram?
See picture.
What is the cardiac cycle - atrial contraction?
Firing of SA node, stimulates atria to depolarise
Atrial contraction causes atrial pressure to increase, blood flows into ventricles.
Ventricles almost already full by passive flow through open AV valve.
As atrial contraction completes, pressure falls, AV valves shut, produces S1 heart sound and beginning of systole.
What is the cardiac cycle - ventricle contraction?
Ventricular depolarisation is halfway through atrial contraction, ventricles contract, increases its pressure, valves still closed - isovolumetric contraction - no blood ejected.
Ventricular ejection starts when ventricular pressure is higher than aorta.
Aortic valve opens and blood ejected out of ventricles.
What is the cardiac cycle - ventricle relaxation?
Ventricular repolarisation begins, ventricular pressure falls, and force of ejection is reduced. When pressure drops below aortic, valves close, marks end of systole, beginning of diastole.
Valves close produces second heart sound S2
First part of diastole is isovolumetric as ventricles relax and all valves are closed. Ventricular pressure drops rapidly, volume unchanged.
Meanwhile atrial pressure increases slowly and filled with blood.
Ventricular pressure drops below atrial pressure, AV valve opens, ventricular filling starts passively. Atria contract to complete filling phase.
