Cardiac Cycle Flashcards
Contrast diastole and systole
Diastole:
- lasts approximately 2/3 of each beat
- ventricular relaxation
- split into 4 distinct phases
Systole:
- lasts approximately 1/3 of each beat
- ventricular contraction
- split into 3 distinct phases
What are the 7 phases of the cardiac cycle in order?
- atrial systole
- isovolumetric contraction
- rapid ejection
- slow ejection
- isovolumetric relaxation
- rapid passive filling
- slow passive filling
Which phase gives the end-diastolic volume?
-isovolumetric contraction (just before blood is ejected)
Which phase gives the end-systolic volume?
-slow ejection (blood has been ejected)
How can you calculate the stroke volume?
end-diastolic volume - end-systolic volume
about 72ml
How do you calculate the ejection fraction?
(100 x stroke volume ) / end-diastolic volume
about 67%
Where is the mitral (bicuspid) valve?
-left atrioventricular valve
Where the tricuspid valve?
-right atrioventricular valve
What is the P-wave on ECG signifying and which heart sound is it associated with?
- indicates atrial excitation
- starte of atrial systole
- ventricles contract to ‘top up’ the volume of blood in ventricle
-S4
What can cause abnormal S4 sound?
-congestive heart failure, pulmonary embolism or tricuspid incompetence
What does the QRS complex tell us and which sound is it associated with?
- isovolumetric contraction
- marks the start of ventricular depolarisation
- this is the interval between AV valves (tricuspid and mitral) closing Q & semi-lunar vales (pulmonary & aortic) opening S
- contraction of ventricles with no change in volume
S1 ‘lub’ due to closure of AV valves and associated vibrations
What happens during rapid ejection?
- opening of the aortic and pulmonary valves mark the start of this phase
- as ventricles contract pressure within them exceeds pressure in aorta and pulmonary arteries
- semilunar valves open, blood pumped out and the volume of ventricles decreases
- no heart sounds.
What type of contraction occurs in the rapid ejection phase?
-isotonic
What happens during slow/reduced ejection?
- marks the end of systole
- reduced pressure gradient means aortic and pulmonary valves begin to close
- blood flow from ventricles decreases and ventricular volume decreases more slowly
- as pressure in ventricles fall below that in arteries, blood begins to flow back causing semilunar valves to close
-T phase- repolarisation
What happens in the isovolumetric relaxation phase?
- the aortic and pulmonary valves shut, but the AV valves remain closed until ventricular pressure drops below atrial pressure
- atrial pressure continues to rise
- dichrotic notch caused by rebound pressure against aortic valve as distended aortic wall relaxes
- S2 ‘dub’ due to closure of semilunar valves and associated vibrations
What causes the dichotic notch?
-caused by rebound pressure against aortic valve as distended aortic wall relaxes
What happens in rapid passive filling?
- occurs during isoelectric (flat) ECG between cardiac cycles
- once AV valves open, blood flows rapidly into the ventricles
-S3
What may S3 sound signify?
- turbulent ventricular filling
- can be due to severe hypertension or mitral incompetence
What happens during reduced passive filling?
- diastasis
- ventricular volume fills more slowly
- the ventricles are able to fill considerably without the contraction of the atria
What is diastasis?
-reduced passive filling
How do the patterns of pressure changes differ in the left side and right side of the heart?
-they don’t- identical
Quantitatively, how do the pressures in the right heart and pulmonary circulation differ from the left?
- much lower (peak of systole)
- despite lower pressures, right ventricles ejects same volume of blood as left; it is simply pumping the same quantity of blood into a lower pressure circuit.
What is the average pressure in the systemic circuit?
120/80 mmHg
What is the average pressure in the pulmonary circuit?
25/5 mmHg
Pressure volume loops
1 loop = 1 heartbeat
https://www.youtube.com/watch?v=AnwPH5yU8rY
Increase in preload has what affect on the stroke volume?
- increases stroke volume
- the Frank-Starling relationship
Increase in after load has what affect on the stroke volume?
- decreases stroke volume
- as after load increases, the amount of shortening that occurs decreases
What is cardiac output?
cardiac output = heart rate x stroke volume
What three things affect stroke volume?
- preload
- afterload
- contractility (increases through engagement of the autonomic NS and stimulation primarily of the sympathetic NS, which then changes the amount of Ca inside the cell on excitation- change force production)
What is contractility?
- measure of the strength of contraction of the heart
- ejection fraction
- increased by sympathetic stimulation
How would the PV loop differ when there is hardening of the aortic valve?
- hardening and narrowing of the aortic valve reduces flow and increases afterload
- pressure required greater and less shortening of muscle cells so smaller stroke volume
How would the PV loops differ when there is acute blood loss?
- loss of blood reduces venous return which decreases preload
- less ventricular volume therefore smaller stroke volume
How would the PV loop differ during exercise?
-venous return increases and skeletal muscle stimulation increased via sympathetic NS
Which is the longest phase of the cardiac cycle?
-reduced passive filling
