CVS: Cardiac cycle Flashcards
Briefly describe how blood flows (in terms of pressure) in the heart
Blood flows from:
- Areas of high pressure to low pressure unless flow blocked by valve
- Valves open/close depending on pressure changes in chambers
- Events on R + L heart same, pressures lower on right though, as it only pumps to lungs
Blood flow occurs in the order of:
- Atrial contraction
- Isovoulmetric ventricular contraction
- Rapid ventricular ejection
- Reduced ventricular ejection
- Isovolumetric ventricular relaxation
- Rapid ventricular filling
- Reduced ventricular filling
Describe blood flow through the cardiac cycle
- Blood returns to heart via SVC and IVC into the RA
- Flows through tricuspid valve into the RV
- RV pumps blood through pulmonary semilunar valve into the pulmonary trunk and pulmonary arteries
- Blood pumped to lungs for oxygenation (lung circulation)
- Oxygenated blood returns to heart via pulmonary veins, into LA
- Flows through mitral (bicuspid) valve into LV
- LV pumps through aortic semilunar valve into aorta
- Aorta ejects blood to body (systemic circulation)
How do heart sounds correspond to the cardiac cycle?
Heart sounds are vibrations induced by closure of the cardiac valves
Vibrations in ventricular chambers
Turbulent blood flow through valves
S1 = ‘lubb’ - Closure of tricuspid/mitral valves at beginning of ventricular systole
S2 - ‘dupp’ - Closure of aortic/pulmonary valves at beginning of ventricular diastole
S3 - Occasional - Turbulent blood flow into ventricles detected near end of first 1/3 diastole - common in young
S4 - Pathological in adults - Forceful atrial contraction against a stiff ventricle - potentially abnormal
Describe the pressure changes that occur within the chambers during the cardiac cycle
- Ventricular filling/atria contraction - Higher pressure in atria> ventricles, tricuspid + bicuspid valves open- blood enters ventricles, atria contract which allows for extra filling of the ventricles
- Isovolumetric contraction - Higher pressure in ventricles> atria so tricuspid and bicuspid valves close, closed ventricle
- Ejection - Higher pressure in ventricles> aorta/pulmonary artery. Semilunar valves open, blood flows out of heart, blood enters atria
- Isovolumetric relaxation - Higher pressure in aorta/ pulmonary artery> ventricles. Valves close, closed ventricle, relaxes and expands, ready to receive blood
How does pressure change in the left ventricle during the cardiac cycle?
During ventricular systole, when the aortic valve opens, pressure in ventricle is greater than in the aorta
When the aortic valve closes, pressure in the ventricle is less than in the aorta
Describe the left ventricle pressure-volume loop
Work done = Change in ventricle pressure x Change in volume
(Work done - Mechanical energy into increase in pressure and movement of blood)
Area inside loop = amount of stroke work done
Relates to amount of energy consumption used to produce stroke volume
- As the mitral valve opens, ESV in ventricles is present, increases during filling phase
- Pressure slightly decreases as ventricles still relaxing but pressure increases as ventricles fill = EDV
- Isovolumetric contraction = Aortic valves open = increased pressure then rapid and slow ejection
- Decreased pressure as blood leaving and aortic valve closes
- Isovolumetric relaxation - decreased pressure than atria = mitral valve open
How do changes in the left ventricular pressure-volume loop explain problems associated with valve disease?
Valve stenosis - Narrowing of valve, doesn’t fully open, reduces blood flow through it.
Aortic Stenosis:
- Aortic valve not fully open
- Build up of high pressure in left ventricle
- Poor ejection
- Same energy used for 50% stroke volume
- Leads to breathlessness when exercising due to fact increasing energy used would not increase stroke volume enough to compensate for exercise, as more pressure in LV→ more pressure in atria → problems in lungs
Mitral Stenosis:
- Mitral valve not fully open
- Poor filling of left ventricle
- Low EDV, less pressure
- Reduced ejection, Poor stroke volume
How does pressure change in the RA/great vein?
A wave - Atrium contracting tricuspid valve open, pressure is increasing
X descent - Atrium relaxing then filling, tricuspid closed, pressure decreases. Drop in pressure seen as collapsing neck vein - looks pulsatile
V wave - Atrium tense, full; tricuspid closed
Y descent - Atrium emptying, tricuspid open
What is the clinical relevance of RA and jugular venous pressure changes?
If pressure in RA raised, heigh of venous pulsatile distension increased
Right sided Heart failure:
- Poor ejection from RV
- More blood volume remains in RV
- Increased blood pressure in RV
- Raised jugular venous pressure - Increased height of venous distention
How does left ventricle volume change in the cardiac cycle?
- Phase 1 - Increased volume from atrial systole - This is EDV (end diastolic volume), usually about 120ml
- Phase 2 - Ventricular systole - Volume decreases
- Rapid ejection
- Slow ejection
- Phase 3 - Ventricular diastole - volume increases, aortic valves closed, compare volume changes for ESV (end systole volume)
- SV = EDV - ESV, tends to be approx 80ml
Ejection fraction = SV/EDV
