lecture 5 - cardiac cycle Flashcards
Is the opening of AV valves a passive or energy-intensive process?
Passive
What causes the AV valves to open and close passively?
Pressure differences across the valve. Opening occurs when atrial pressure is greater than ventricular pressure
What are the 2 phases of the cardiac cycle?
Ventricular diastole, ventricular systole
What is the state of the ventricles during ventricular diastole?
Ventricles are relaxed
What is the state of the ventricles during ventricular systole?
Ventricles are contracting
What is the name for the first phase of diastole?
Isovolumetric ventricular relaxation
What happens during the isovolumetric ventricular relaxtion phase of diastole?
Atria are filled with blood returning to the heart
What is the second phase of ventricular diastole?
Ventricular filling
What occurs during the ventricular filling phase of diastole?
Blood passively fills the ventricles via the atria through the open AV valves, then followed by atrial systole where atrial depolarisation occurs, caused the atria to contract, ejecting blood into the ventricles, so that the volume is at maximum (end diastolic volume)
What is the term for the maximum volume of blood in the ventricles after passive and contractile filling?
End-diastolic volume
What are the 2 phases of ventricular systole?
Isovolumetric ventricular contraction, ventricular ejection
What happens during isovolumetric contraction?
The ventricles depolarise and begin to contract, causing the AV valves to close. A large amount of pressure builds in the ventricles, as they squeeze while the volume of blood inside remains the same
What happens during ventricular ejection?
When left ventricular pressure exceeds aortic or pulmonary pressure, the semilunar valves open and blood is ejected from the ventricles. The ventricles repolarise during this phase.
What proportion of the length of the cardiac cycle does the heart spend in diastole?
approx. 2/3
What proportion of the length of the cardiac cycle does the heart spend in systole?
Approx. 1/3
At what point of the cardiac cycle is arterial pressure at a minimum?
At the end of diastole
At what point of the cardiac cycle is arterial pressure at a maximum?
During the ejection phase of systole
Why can JVP height be used to assess right atrial pressure?
There are no valves between the superior vena cava, right atrium and jugular vein, so changes in right atrial pressure are transmitted directly to the jugular vein
What is the effect of increasing heart rate on the duration of systole and diastole?
Duration of both decreases, but length of diastole increases more to preserve systolic time
What events in the cardiac cycle correspond with an ECG P wave?
Atrial depolarisation
What events in the cardiac cycle correspond with an ECG QRS complex?
Ventricular depolarisation
What events in the cardiac cycle correspond with an ECG T wave?
Ventricular repolarisation
At which point on an ECG does atrial contraction occur?
Just after the P wave
At which point on an ECG does ventricular contraction occur?
After the QRS complex
At which point on an ECG does ventricular relaxtion occur?
After the T wave
What causes the first heart sound (S1)?
Closure of the AV valves - mitral and tricuspid - during diastole
What causes the second heart sound (S2)?
Closure of the semilunar valves - aortic and pulmonary - during systole
What causes the third heart sound (S3)?
Rapid ventricular filling in early diastole, though not audible in every patient
What patient group tend to have an audible third heart sound?
Young patients
Which valve closes first during the S1 heart sound?
Mitral before tricuspid
Which valve closes first during the S2 heart sound?
Aortic before pulmonary
What does S1 sound like?
Low, long sound (lub)
What does S2 sound like?
Short, high pitched (dub)
Why does normal blood flow not generate sound?
The flow is laminar and stream-lined
What causes the sound heard with murmurs in the heart?
Turbulent blood flow
What are the causes of turbulent blood flow in the heart?
Valve stenosis, valve insufficiency/valve regurgitation
When can the murmur be heard in cases of aortic stenosis?
During systole between S1 and S2
When can the murmur be heard in cases of mitral incompetence/regurgitation?
Throughout systole
When can the murmur be heard in cases of aortic incompetence/regurgitation?
Early in diastole
What are the 4 key components of a Wiggers Diagram?
Pressures, Volumes, ECG, sounds
