Cardiovascular Physiology 2- Mechanical events of the cardiac cycle Flashcards
How does blood flow through the cardiovascular system?
1) Deoxygenated blood from cells are returned to the heart via the right superior vena cava (from the head) and inferior vena cava (from body)
2) Enters the right atrium, right ventricle
3) Heart is then pumped through the pulmonary arteries to the lungs= Oxygenated as it picks up oxygen
4) Oxygenated blood from the lungs travels to the left side of the heart through the pulmonary veins
5) Enters the left atrium, left ventricle
6) Blood is then pumped into the aorta which is a large artery
7) Aorta branches into series of smaller and smaller arteries that lead into networks of capillaries= Oxygen diffuses into tissues
Why is the left side of the heart much thicker?
It has a thicker wall as it has to have a larger pressure in order to pump the blood all around the body
Right has thinner wall as only has to pump to lungs
What happens during phase 1 of the cardiac cycle? (Diastole)
Atria and ventricle are relaxing
1) Atrioventricular Valve is opened
2) Blood flows through atria to ventricles (superior and inferior vena cava)
3) Pressure in veins enough to drive blood into heart (Venous return)
4) Semilunar valves are closed
5) Ventricular pressure lower than that in aorta and pulmonary arteries
6) Relaxing ventricles expand to accommodate entering blood
7) Phase 1 ends with atria contracting to drive the last 20% of blood in the atria into ventricles and then atria relaxes
What happens during phase 2 of the cardiac cycle? (Systole)
1) Ventricles contract
2) Ventricular pressure exceeds atrial pressure= AV valves close= Creating the ‘lub’ sound
3) Semilunar valves closed
4) No blood flowing into our out, as both valves are closed so the blood cannot go anywhere= Isovolumic ventricular contraction
5) End of phase: Ventricular pressure keeps increasing until it is large enough for the semilunar valves to open
What happens during phase 3 of cardiac cycle? (systole)?
1) Semilunar valves open= Blood is pushed into the arteries, ventricular volume falls= Ventricular ejection
2) Ventricular pressure rises then declines- Begin to repolarise and relax
3) Ventricular pressure falls below aortic pressure= Semilunar valves close= ‘dub’ sound
What happens during phase 4 of cardiac cycle? (diastole)
1) Ventricules start to relax, pressure is too low to keep any of the valves open
2) Isovolumetric relaxation
3) Ventricular pressure decreases until it is lower than aortic pressure= AV valves open
4) Blood enters ventricles from atria= Cycle starts again
What is the duration of diastole and systole?
Not equal
Heart beat average: 72/min, 1 beat every 0.8 seconds
Diastole= 0.5 seconds, to allow adequate filling time for efficient pumping
Systole= 0.3 seconds
What happens to aortic pressure during the cardiac cycle?
Phase 1= Aortic valve is closed (Semilunar valve)= No filling of blood into aorta, blood leaves aorta down stream
Lose volume= lose pressure= Minimum diastolic pressure (lowest blood pressure you will be able to detect in the aorta)
Phase 2: Aortic pressure continues to fall as AV valve opens= Blood continues to leave
Phase 3: Valves open= Ventricular ejection= Aortic pressure rises quickly and reaches systolic pressure
Phase 4: Pressure starts to fall again
Dicrotic notch: After 4, just before 1
Aortic valve closes= Stops back flow and sudden closing of the semilunar valve gives slight increase in pressure
What is pulse pressure?
The difference between systolic pressure and diastolic pressure
PP= SP - DP
What is the formula for mean arterial pressure?
What is the formula for blood pressure?
Average pressure occurring in aorta during 1 cardiac cycle:
Cant just divide by 2 as area is not complete
MAP= DP + 1/3 (PP)
BP= systole/diastole
What is end diastolic volume?
EDV= Volume of blood in the ventricle at the end of diastole, represents the maximum ventricular volume during the cardiac cycle. Reached just before the start of ejection
End of stage 1
What is end systolic volume?
ESV: Volume of blood in the ventricle at the end of systole, represents the minimum ventricular volume, attained just after ejection
End of phase 4
What is stroke volume?
The volume of blood in ventricles just before ejection minus volume of blood in ventricle just after ejection
It is the volume of blood pumped per contraction
SV= EDV - ESV
What is ejection fraction?
The ratio of volume ejected in one beat (SV) to volume contained in ventricle immediately prior to ejection (EDV)
EF= SV/EDV
Tells if heart is pumping efficiently, under normal circumstances heart only works at 52% as heart can accommodate for exercise
What does an ECG record?
Record overall spread of electrical current through the heart as a function of time during the cardiac cycle
