L10 Cardiac Cycle Flashcards Preview

MBBS I CPRS > L10 Cardiac Cycle > Flashcards

Flashcards in L10 Cardiac Cycle Deck (64):

How does the Heart donate energy to blood?

Donates energy to blood: drive the flow to overcome friction (between blood elements, wall) as it travels
round the vascular system


What is the conversion of energy from the heart to the vascular system?

Chemical energy (ATP) in heart cells > mechanical energy (kinetic and potential) in blood

Kinetic = velocity
Potential = pressure (from high artery pressure to low venous pressure)


Energy needed to pump blood depends on what?

Distance to pump blood:
1. Right heart → pulmonary circulation (only thoracic cavity = requires
less energy: 25/15 mmHg)

2. Left heart → systemic circulation (head to toe, against gravity: 120/80


Ventricles are responsible for pumping and are adapted for that function. How?

Thick muscular walls = generate powerful contraction = eject blood
at high pressure and velocity
LV much thicker than RV


Function of valves? (2)

1. Guard the entrance and
exit to each ventricle to
prevent backflow of

2. Atrioventricular valves also provide electrical insulation between atria and ventricles


Run through AV (bi/tricuspid) valve open/close during a cardiac cycle.

When ventricle is relaxed:
blood flows from atrium to ventricle passively and during atrial systole > opens AV valve

Ventricular systole > high ventricular pressure pushes valve leaflets across the opening, shut entries.
Chordae tendinae (connected via papillary musc.) prevent the valve from inverting


Briefly run through how semi lunar valves work.

Semilunar valves (aortic, pulmonary) = pockets of connective tissue in arterial wall

Ventricular systole > blood flows out of ventricle > pocket flattened > blood flows out unimpeded

Diastole > arterial pressure larger than ventricular P > blood regurgitation fills the pockets and shut entries > prevent backflow


Arterial or Ventricular pressure drops faster?

Arterial pressure needs to be high to drive blood flow around body

Ventricular pressure drops faster (to 0) than arterial


Main function of Atria?

mainly receive and store venous return (= passive conducting chamber)


Ventricular filling involves 2 processes. State.

Atria systole: Thin wall > weak contraction > accounts for only ~20% of ventricular filling

Mostly passive flow by gravity


How does atria pressure gradually increase during and after ventricular systole?

AV valves are closed > venous blood continuously returning to heart cannot enter ventricles > accumulates in atria (passive filling: less at high heart rate) > stretch atria and gradually raises atrial pressure


When AV valves open, what happens?

When ventricular contraction stops and AV valves open: blood rushes down pressure gradient from atria
into ventricles > atrial contraction


Blood flow through veins to ventricles is continuous through diastole or not?

Passive ventricular filling through diastole


If resting HR is 75bpm, single cardiac cycle occupies how much time. how is cycle time divided?

60seconds/75 = 0.8s per cycle

 0.3 sec = contraction of heart (systole)
 0.5 sec = relaxation (diastole)


Sequence all 7 phases of cardiac cycle starting at atrial contraction

1. Atrial contraction
2. Isovolumetric contraction
3. Rapid ventricular ejection
4. Reduced/slow ventricular ejection
5. Isovolumetric relaxation
6. Rapid filling
7. Slow filling


What starts atrial contraction?

Depolarisation is initiated at the sinoatrial node > spreads throughout right and left atria > both atria contract

Atrial pressure rises ~5 mmHg (a wave)
7-10 mmHg at peak of contraction


What is the consequence of atrial contraction?

Forces a little more blood through the open atrioventricular (AV) valve (ventricles already 70-80% filled with blood)

further small increase in ventricular volume and pressure


When does Atrial contraction end?

Ends when ventricular contraction begins


What is meant by isovolumetric?

Ventricular volume cannot change (isovolumetric) because both entry and exit valves are closed


What causes closure of AV valves in isovolumetric contraction?

ventricle begins to contract, ventricular pressure rises above atrial pressure > AV valve closes


Before rapid ventricular ejection, how are the semilunar valves?

Ventricular pressure not yet as high as aortic > semilunar valve still closed


Consequences of Isovolumetric contraction?

Contraction compresses blood in ventricle > ventricular pressure rises rapidly

AV valve bulges backwards into atrium > compresses atrial content a bit > atrial pressure also increases slightly (c wave)


When does isovolumetric contraction end?

ends when ventricular pressure > aortic pressure and semilunar valve opens


In Rapid ventricular ejection, which pressure is higher: vent. or aortic?

Throughout this phase: ventricular pressure remains slightly above aortic


What happens in RVE?

When ventricular pressure rises above aortic: semilunar valve opens > blood can be ejected rapidly from ventricle into aorta (outflow accelerates)


What happens to Atrial pressure through this phase/

1) Atrial P Initially decreases (ventricular contraction decreases size of ventricle > pulls AV valvular ring downwards)

2) Then gradually increases linearly throughout the rest of phase, reduced / slow
ventricular ejection, and isovolumetric relaxation until rapid ventricular filling


When does RVE end?

Phase ends when ventricular pressure / contraction = maximal


Reduced (or slow) ventricular ejection. What marks the start of this phase?

Beginning: ventricular pressure drops below aortic

Ventricle stops contracting / begins to relax > ventricular pressure starts to fall


How does the fall in aortic pressure compare to ventricular P?

“Run off” of blood from aorta to periphery > aortic pressure also falls, but not as quickly as ventricular


Outflow of blood from Ventricle changes through this phase. Explain what causes ejection to slow down.

outflowing blood has high velocity (kinetic energy) > ejection continues then gradually decelerates
to 0 by negative pressure gradient


When does reduced/ slow ventricular ejection end?

Phase ends when semilunar valve closes (i.e. 0 blood flow, not 0 pressure)


What follows Reduced ventricular ejection?

Isovolumetric relaxation


Explain electrical activity during isovolumetric relaxation

Ventricle continues to repolarise and relax


What happens to the valves during isovolumetric relaxation?

BOTH AV and semilunar valves are closed > volume of blood in ventricle remains constant > Ventricular pressure drops fast


What marks the start and end of I. relaxation?

Start as aortic valve closes

Ends as soon as ventricular pressure drops below atrial, AV valve opening


What follows I. Relaxation?

Rapid ventricular filling


What happens at the RVF?

Throughout ventricular systole atrium (isovolumetric contraction to isovolumetric relaxation), blood from pulmonary circulation has filled the left atrium

As soon as ventricular pressure drops below atrial, AV valve opens > blood rushes from atrium into


What happens during the last phase?

Reduced/ slow filling

Pressure gradient higher in pulmonary vein and atrium than in ventricle
Blood flows passively from pulmonary circulation to ventricle


How does increase HR impact Ventricular filling time?

Passive filling shortens in increased heart rate


Summarize atrial Pressure changes.

a wave > c wave > x descent > v ascent (linear) > y descent


Where are the two main areas of increase in Atrial pressure?

During contraction: 5 ~ 10 mmHg

During Ventricular contraction when AV valves are closed > accumulation of venous blood


What is aortic pressure mainly determine by?

Mainly determined by volume of blood in aorta
(determines extent of stretching of arterial wall)


When is aortic vol. and press. at the maximum?

Maximum at end of rapid ventricular ejection phase when ventricular pressure is also at its highest


How does Aortic pressure behave after peaking at the start of Rapid Ventricular Ejection?

Decrease steadily until next ejection phase begins

Potential energy decreases as blood flows to periphery


There is a slight dicrotic notch/incisura in aortic pressure at the end of rapid ejection. Explain.

Small amount of blood backflows in aorta to
close the semilunar valves: flow suddenly stopped > kinetic energy in the backflow converted to potential energy (increased wall tension and pressure) = dicrotic notch / incisura


Where in the 7 phases are systolic and diastolic PRESSURES taken?

Diastolic at start of isovolumetric contraction

Systolic at the start of Rapid ventricular Ejection


How is stroke volume calculated?

Stroke volume = diastolic volume of ventricle – systolic volume in ventricles


How is residual volume of ventricles calculated?

Diastolic volume – stroke volume = residual volume


Changes in gradient in ventricular volume/ time graph denotes what?

Descending curve = rapid ejection to reduced ejection

Ascending curve= Rapid filling to reduced filling


Which two volumes in ventricle equals each other?

systolic volume = residual volume of heart


What does P wave on ECG equate to? When does it occur?

Atrial depolarisation

Just before atrial contraction begins


What does QRS on ECG equate to? When does it occur?

Ventricular depolarisation

Just before isovolumetric


Ventricular rapid filling accounts for how much of diastole?

1st quarter of diastole


What does T wave on ECG equate to? When does it occur?

Ventricular repolarisation

During reduced ventricular ejection


There are how many heart sounds



What are Heart sounds?

Events that cause vibrations in the heart can be heard as sounds through the chest wall


How does structure affect vibration? (in terms of muscles)

Rigid structures vibrate better than soft structures
so contracted heart muscle vibrates better than relaxed


Which of the four sounds can only be heard under abnormal conditions? What are the conditions? (2)

S4- during atrial contraction

Atrial pressure abnormally high
Ventricle unusually stiff


What does S1 correspond to?

 Closure of AV valves
 Tensing of valves and muscles during contraction


What does S2 relate to?

Closure of semilunar


How come S2 may be split?

pulmonary valve may close
slightly after aortic during inspiration = split S2


What does S3 relate to?

During rapid filling

vibration of ventricles / valves due to impact of rapidly inflowing blood


How come S3 is hard to hear?

all muscles are relaxed during rapid filling, thus soft and doesnt vibrate much

can hear in children /
thinner chest wall)


How does Right Heart cardiac cycle compare to left?

Events identical to and simultaneous with those in left (electrical activity spreads at same time and contract together)

Volume changes and atrial pressure changes are very similar

weaker contraction in right ventricle > maximum pressure = ~25 mmHg

Pulmonary arterial pressure = correspondingly lower

Decks in MBBS I CPRS Class (78):