Cardiovascular Physiology 2- Mechanical events of the cardiac cycle Flashcards Preview

Physiology Term 2 > Cardiovascular Physiology 2- Mechanical events of the cardiac cycle > Flashcards

Flashcards in Cardiovascular Physiology 2- Mechanical events of the cardiac cycle Deck (23):

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



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



What is ejection fraction?

The ratio of volume ejected in one beat (SV) to volume contained in ventricle immediately prior to ejection (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


Where is lead 1 placed? Where is lead 2 placed? Where is lead 3 placed?

Lead 1: LA- RA

Lead 2: LL- RA

Lead 3: LL-LA


What does the P-wave show?
What does the QRS complex show?
What does T wave show?

P wave= Atrial contraction

QRS= Ventricular contraction

T wave= Ventricular repolarisation


What does PR segment show?

AV nodal delay: Electrical signal is slowing down as it passes through the AV node and AV bundle


What does ST segment show?

Ventricle is completely depolarised (cardiac cells in plateau phase), ventricular activation is complete and are contracting and emptying


What does the TP segment show?

Heart muscle is completely depolarised, at rest and ventricles filing


How do you calculate the conduction time through AV node on ECG?

PR or PQ interval


How do you measure time between heart beats?

How do you measure HR?

R-R timing= timing between QRS peaks= time between heart beats

HR= 60/ R-R


What are some abnormalities which could occur in the heart and be detected on an ECG?

Tachycardia= Speeding up of heart rate

Arrhythmia= Abnormal rhythm

Fibrillation= Uncoordinated chaotic contractions

Heart block= Defect in cardiac conducting system

Myocardial infarction= Death of heart muscle