Flashcards in Cardiac cycle Deck (13)
What is a cardiac cycle?
All events that occur from the beginning of one heart beat to the beginning of the next
What occurs during diastole and systole?
-Diastole: the heart ventricles are relaxed and fill with blood
-Systole: the heart ventricles contract and pump blood into the: aorta (LV) and pulmonary artery (RV)
At a heart rate of 75bpm, how long does both the diastole and systolic phase last?
diastole = 0.5sec
systole= 0.3 sec
so diastole lasts almost twice as long as systole
What are the 5 events during the cardiac cycle?
-Isovolumetric ventricular Contraction
-Isovolumetric ventricular Relaxation
Describe passive filling.
-Pressure in atria and ventricles close to zero
-AV valves open so venous return flows into the ventricles
-Aortic pressure ~ 80 mmHg, and aortic valve is closed
-Similar events happen in the right side of the heart, but the pressures (right ventricular and pulmonary artery) are much lower
-Ventricles become ~ 80% full by passive filling
What is atrial contraction ?
Completes the end diastolic volume and is represented in the ECG between the P-wave (atrial depolarisation) and the QRS wave
Describe isovolumetric ventricular contraction.
-Ventricular contraction starts after the QRS (signals ventricular depolarization) in the ECG
-Ventricular pressure rises
-When the ventricular pressure exceeds atrial pressure the AV VALVES SHUT
-This produces the FIRST HEART SOUND (LUB)
-The aortic valve is still shut, so no blood can enter or leave the ventricle
-The tension rises around a closed volume “Isovolumetric Contraction”
-The ventricular pressure rises very steeply
What produces the first heart sound?
The "LUB" is produced by the closure of mitral and tricupsid valves
Describe ventricular ejection?
-When the ventricular pressure exceeds aorta/pulmonary artery pressure
-Aortic/pulmonary valve open - Remember this is a silent event
-Stroke Volume (SV) is ejected by each ventricle, leaving behind the End Systolic Volume (ESV)
-SV = EDV – ESV
= 135 – 65 = 70 ml
-Aortic pressure rises
-The T-wave in the ECG signals ventricular repolarization
-The ventricles relax and the ventricular pressure start to fall
-When the ventricular pressure falls below aortic/pulmonary pressure: aortic/pulmonary valves shut
-This produces the SECOND HEART SOUND (DUB)
-The valve vibration produces the dicrotic notch in aortic pressure curve
What produces the second heart sound?
The "DUB" sound -When ventricular pressure falls below aortic/pulmonary pressure , the aortic/pulmonary valves shut
Describe the isovolumetric ventricular relaxation ?
-Closure of aortic/and pulmonary valves signals the start of the isovolumetric ventricular relaxation
-Ventricle is again a closed box, as the AV valve is shut
-The tension falls around a closed volume “Isovolumetric Relaxation”
-When the ventricular pressure falls below atrial pressure, AV valves open (Remember this is a silent event), and the heart starts a new cycle
Why does arterial pressure does not fall to 0?
Due to elastic properties of arteries , they stretch when contracted and when they recoil so recoiling moves blood forward