Cardiac Cycle Flashcards
Describe the difference in pressure generated by the left and right heart
Pressure generated by the right heart is much lower than the left because less pressure is required to pump blood through the pulmonary circulation than the systemic circulation
What are the first and second heart sounds?
First heart sound - closure of the AV valves at the onset of systole
Second - Closure of the semilunar valves at the end of systole
What events are associated with ventricular systole?
Isovolumetric contraction (2)
Rapid ejection (3)
Reduced ejection (4)
What events are associated with ventricular diastole?
Isovolumetric relaxation (5)
Rapid ventricular filling (6)
Reduced ventricular filling (diastasis) (7)
Atrial systole (1)
What causes the P wave of the ECG?
Atrial depolarization
What is the difference between at rest and during exercise ventricular filling?
Atrial systole accounts for only a small fraction of V-filling at rest
During exercise and other conditions of increased HR, a greater fraction of V-filling is due to atrial systole because of less time available for passive filling
What generates the QRS complex on an ECG?
Spread of an AP through the ventricles
Indicates the initiation of ventricular contraction
What is the isovolumetric contraction (2)?
The interval between AV valve closure and semilunar valve opening
Ventricles contract with a fixed volume because no blood is entering or leaving
What happens during rapid ejection?
Ventricular pressure continues to increase
Aortic and Pulmonary artery pressures increase
Blood flow into the aorta and pulmonary artery peaks
Ventricular volume decreases
What is the T wave of the ECG?
Ventricular repolarization
Associated with phase 4 of the cardiac cycle
Describe the reduced ejection phase
Ventricles start to relax and the ejection of blood slows
Accounts for about 30% of stroke volume
Aortic pressure declines
What is the dicrotic notch?
Slight upward deflection in the pressure tracing that is associated with the closure of the semilunar valves
Signals the start of diastole
What is isovolumetric relaxtion?
Both sets of valves are closed and the ventricles continue to relax without being filled
Aortic pressure continues to decline gradually during this phase
What is the end systolic volume?
Volume of blood remaining in the ventricles after ventricular contraction
Describe the rapid filling phase (6)
Ventricular pressure falls below atrial pressure, allowing the AV valves to open
Filling is rapid because venous return has filled the atria prior to the opening of the AV vavles
Resistance to flow through the AV valves is low
Why does the rate of passive filling slow and reach a plateua during diastasis?
Ventricles become less compliant as they fill
What is the reason for physiological splitting of the second heart sound?
Aortic valve closure precedes pulmonary valve closure
These sounds are indistinguishable from each other during expiration, but separated during inspiration
What is the third heart sound?
Occurs early in diastole and is caused by blood hitting the ventricles
Normal in a young person, but abnormal in adults over 40
What is the fourth heart sound?
Contraction of the atria during late diastole
Commonly associated with resistance to filling and often a sign of diastolic hear failure
What are heart murmurs and two common causes?
Sounds generated by turbulent blood flow
Stenosis - narrowing of the valve
Regurgitation - backward flow
What is the a wave of the jugular pulse?
Upward deflection prodcued by right atrial contraction
What is the x descent of the jugular pulse?
Downward component of the a wave associated with right atrial relaxation
What is the c wave of the jugular pules?
Upward deflection that interrupts the x descent
Produced by bulging of the tricupsid valve into the right atrium
What is the v wave of the jugular pulse?
Upward deflection caused by filling of the right atrium when the tricuspid valve is closed
