Cardiac Cycle Flashcards
Define the 2 types of blood vessels in the body
Resistance vessls- restrict blood flow to drive supply to hard to perfuse areas of the body. Can reduce their diameter
Capacitance vessels- enable system to vary amount of blood pumped around the body as they can store blood in the system to determine flow
Define Systole
Contraction and ejection of blood from ventricles
Define Diastole
Relaxation and filling of ventricles
Describe the Conduction System
- Pacemaker cells in SA node generate action potential
- Atrial systole- activity spreads over atria
- Reaches AV node, delayed for 120ms
- Excitation spreads down septum
- Then spreads through ventricular myocardium from endocardial to epicardial surface
- Ventricles contract from apex up
What are the 7 phases of the Cardiac Cycle
- Atrial Contraction
- Isovolumetric Contraction
- Rapid Ejection
- Reduced Ejection
- Isovolumetric Relaxation
- Rapid Filling
- Reduced Filling
How long are Systole and Diastole and what happens to their lengths when the heart rate increases?
Systole is 0.35s
Diastole is 0.55s
Increased heart rate decreases the length of diastole while systole stays the same length
Name and label the diagram
Wiggers diagram
30- Dicrotic notch
31- X descent
32- Y descent
During which phases are the Mitral/Tricuspid Valves open
Phase 1: Atrial Contraction
Phase 6: Rapid Refilling
Phase 7: Reduced Filling
During which phases are the Aoritc/Pulmonary valves open
Phase 3: Rapid Ejection
Phase 4: Reduced Ejection
During which phases are all valves closed
Phase 2: Isovolumetric Contraction
Phase 5: Isovolumetric Relaxation
Describe and name Phase 1
Atrial Contraction:
P wase (ECG) signifies atrial depolarisation
A wave due to atrial systole where atrial pressure rises
Atrial contraction which accounts for the final 10% of ventricular filling (Atrial Kick)
Describe and name Phase 2
Isovolumetric Contraction:
QRS complex- ventricular depolarisation
Ventricular pressure rises due to ventricle contraction, this also closes the mitral valve and causes the C wave in atrial pressure
No change in ventricular volume => isovolumetric
What is responsible for the first and second heart sounds
1st heart sound due to mitral and tricuspid valves closing
2nd heart sound due to the aortic and pulmonary valves closing
Describe and name Phase 3
Rapid Ejection:
Ventricular pressure greater than aortic causing aortic valve to open and ejection begins.
Rapid decrease in ventricular volume
X descent on atrial pressure graph due to atrial base being pulled downward as ventricles contract
Describe and name Phase 4`
Reduced Ejection:
Ventricles repolarise producing T wave
Repolarisation leads to decline in tension and rate of ejection decreases
Atrial pressure rises due to venous return from lungs producing V wave
Describe and name Phase 5
Isovolumetric Relaxation:
When intraventricular pressure falls below aortic there is brief backflow of blood that closes the aortic valve
Volume in ventricle remains constant => isovolumetric
Dicrotic notch seen in aortic pressure due to closure of valve
What is Stroke volume
Volume of blood ejected per beat
Stroke volume = EDV - ESV
Describe and name Phase 6
Rapid Filling:
Intraventricular pressure falls below atrial, opening the mitral valve and rapid ventricular filling begins
Y-descent seen as atrial pressure decreases after mitral valve opening
Blood is sucked into the ventricles from the atria
Describe and name Phase 7
Reduced Filling:
Rate of filling slows (diastasis) as ventricle reaches inherant relaxed volume
90% full by end of phase 7
Name two types of abnormal valve function
Stenosis
Regurgitation
What is aortic valve stenosis
Where there is narrowing of the aortic valve
Causes:
- Degenerative- senile calcification/fibrosis
- Congenital- bicuspid form of the valve
- Chronic rheumatic fever- causes inflammation and then commissural fusion of the vavle leaftlets
Effects:
- Less blood can get through valve causing:
- Increased LV pressure leading to LV Hypertrophy
- Left sided heart failure causing syncope and/or angina
What is aortic valve regurgitation
Condition where aortic valve does not close all the way so there is back leakage when valve should be closed
Causes:
- Aortic root dilation- leaflets pulled apart
- Valvular damge
Results in blood flowing back into LV during diastole causing:
- Increased stroke volume
- Increased systolic and decreased diastolic pressures
- Bounding pulse- head bobbing and Quincke’s sign
- LV hypertrophy
What is mitral valve regurgitation
Where mitral valve doesn’t shut properly so blood flows back in during systole
Causes:
- Damage to papillary muscle after MI
- Left sidede heart failure leading to LV dilation and stretching of the valve
- Rheumatic fever leading to leaflet fibrosis, disrupting seal formation
- Myxomatous degeneration weaking tissue leading to prolapse
Can result in LV hypertrophy as preload increases due to blood leaking back into LA
What is mitral valve stenosis
Where the mitral valve doesn’t open enough
Main cause is Rhuematoid fever causing commissural fusion of leaflets making it harder for blood to flow into LV from LA
Results in an increased LA pressure causing:
- LA dilation
- Atrial fibrillation causing thrombus formation
- Oesophagus compression and dysphagia
- Pulmonary oedema, Dyspnea, Pulmonary hypertension
- RV hypertrophy
