Lecture 2 - Cardiac Cycle Flashcards
What are the 5 steps of the cardiac cycle?
- Atrial systole
- Ventricular systole, isovolumetic phase
- Ventricular systole, ejection phase; atrial fill
- Ventricular diastole, isovolumetric phase
- Ventricular diastole, rapid phase
Look over this
What do the valves in the heart allow for?
They allow of the unidiretional flow of blood, and prevent the backflow of blood.
The valves open and close passively due to pressure gradients.
One complete set of contraction (_____) and relaxation (_____) of the heart is called the cardiac cycle
One complete set of contraction (systole) and relaxation (diastole) of the heart is called the cardiac cycle
Describe what occurs during diastole 1 (Isovolumetric ventricular relaxation)
During diastole 1 there is isometric ventricular relaxtion. All valves are shut, with the ventricle relaxing. (Very short phase, 0.05sec)
The ventricular blood volume is at a minimum and stays constant (End systolic volume ~60ml)
There is no blood flow, or change in the volume of blood in the ventricle.
Pressure in the atrium is lower than in the ventricle.
The atrium is filling with blood returning to the heart, and this elevates the atrial pressure above ventricular pressure. The AV valve opens passively, and ventricular filling begins.
Describe what happens during Diastole 2 (Ventricular filling) (second part of diastole)
Ventricular filling is occuring (blood entering ventricle from atrium down a pressure gradient). This takes 0.5 sec at rest.
In late diastole atrial depolarisation occurs (P wave on ECG), and then theres atrial contraction (atrial pressure increases to ~5mmHg), where 20% of blood if ejected from the atrium into the ventricule.
The volume of blood in the ventricle reaches a maximum, this is the end diastolic volume (EDV is typically ~130ml)
Describe what occurs durng the first part of systole (systole 1/ Isovolumetric ventricular contraction)
Takes 0.05 sec at rest
The ventricles depolaries (QRS complex on ECG), and then the ventricles contract.
The ventricles develops tension, elevating left/right ventricular pressure - this rapidly closes the mitral/tricuspid valve. This is the beginning of isovolumetric contraction.
The closure of the AV valves gives the first heart sound (S1).
During this short phase pressure is generated in the ventricle to overcome aortic/pulmonary pressure.
The papillary muscles connected to the chordae tendineae prevent the valves from slamming shut too qucikly.
The the left/right ventricular pressure exceeds the aortic/pulmonoary trunk pressure the semilunar valves open.
The opening of the semilunar valves marks the beginning of ventricular ejection.
Describe what occurs during ventricular ejection (Systole 2)
Takes 0.3 secs
- Blood is ejected into the aorta/pulmonary trunk through the open semilunar valves - increases arterial blood volume and arterial pressure.
- Approx. 2/3’s of blood ejection occurs in the first one-third of ventricular ejection (rapid ejection)
- By mid systole LVP/RVP and AP reach a maxium
- In late systole (reduced ejection) both LVP/RVP and AP begin to fall
- The ventricles being to repolarise during this phase (T wave in ECG)
Descibe what occurs during isovolumetric ventricular relaxation
- Pressure in the ventricle falls below aortic, and semilunar valves (aoritc and pulmonary valves) close
- Closure of the semilunar valves gives rise to the second heart sound (S2)
- S2 is made up of an aortic and a pulmonary component
- Closure of the semilunar valves marks the end of systole and the beginning of diastole
- The cardiac cycle then re-enters isovolumetric ventricular relaxation
- The volume of the blood in the ventricle is at a minimum (ESV 60mL)
What are the 2 phases of the cardiac cycle?
-
Ventricular diastole : Ventricles are relaxed
- consists of isovolumetric ventricular relaxation
- ventricular filling
Ventricular systole: Ventricles are contracting
What are the phases of diastole?
And what are the phases of systole?
Diastole
Isovolumetic relaxation and ventricular filling (atrial top up)
Systole
isovolumetric ventricular contraction and ventricular ejection
Describe the ventricular volume at the end of diastole, and the end of systole
Ventricular volume is at a maximum at the end of diastole (remains constant during isometric contraction)
Ventricular volume falls during ejection, and reahes its minimum at the end of systole (ESV)
Describe ventricular pressure throughout the cardiac cycle
Ventricular pressure is at a minimum at the beginning of diastole, and it rises a little during ventricular filling and after atrial contraction (diastole).
Ventricular pressure rises dramatically during isometric contraction (systole), and it continues to rise to a maximum during the ejection phase of systole. It then falls during late systole, and then falls dramatically during isometric relaxation
Describe arterial pressure throughout the cardiac cycle
Arterial pressure is at a minimum at the end of diastole (diastolic pressure), and rises to a maxium (systolic pressure) during the ejection phase of systole along with ventricular pressure.
When ventricular pressure falls below arterial pressre the aortic valve closes, and the pressure continues to fall during diastole to a minimum (diastolic pressure).
What is the main difference between the left and right side of the heart in relation to pressure?
The pulmonary resistance is lower than total peripheral resistance (systemic circulation)
Describe the jugulovenous waves
A wave: is when the the right atria contracts (peak of A wave matches the end end of atrial systole)
C wave: This is when the ventricle contracts, this pushes against the tricuspid valve, and this compresses the atria and pushes blood back up into the jugular veins
V wave: Corresponds to venous filling of right atrium
X and Y descent: They essentialy relate to the ejection of blood and the loss of volume in the ventricles
So basically, the venous waves in the jugular vein reflect what is happening in the right atrium. We can use these waves to assess right atrial pressure
(CANNOT feel the waves, can only see)
What proportion of the cardiac cycle does diastole take up?
Diastole is two thirds (0.66s at rest)
Systole is one third (0.34s at rest)
At a higher heart rate both diastole and systole decrease. At rest diastole is greater than systole so that we can preserve can shorten the cardiac cycle during vigorous activity (Diastole 0.13s, systole 0.2s)
What causes S1, S2, S3 and S4?
- S1: Closure of the mitral valve and tricuspid valves
- gives a low, long sound (dub)
- S2: Closure of the aortic and pulmonary valves (A2 before P2)
- gives a short, high pitch (dub)
- S3: Passive ventricular filling during early stages of diastole (May be heard in young)
- S4: Rapid ventricular filling following atrial contraction
- reduced ventricular compliance
What are murmurs?
Murmurs are abnormal heart sounds caused by turbulent blood flow - they are an indication for valve lesions, such as narrowing of a valve (stenosis) and reversal of flow through a valve (valve insufficiency or incompetence)
