Cardiac cycle : pressure & volumes Flashcards
what are the 4 chambers of the heart?
What are the** 4 valves **of the heart?
- Atrioventricular valve
- **Biscupid **valve (also called mitral valve)
- Triscupid valve
- Semilunar valve/ pulmonary valve
- **Aortic **valve
What does the atrioventricular valve seperate?
- seperates the atria from the ventricles
- so, note if pressure is higher in the atria than the ventricles, then blood flows from A-V (high pressure - low pressure)
What does the bicuspid valve seperate?
- on the LEFT SIDE
- seperates the left atrium from the left ventricle
What does the tricuspid valve seperate?
- on the RIGHT side
- seperates the **right atrium from the right ventricle **
What dooes the semilunar/pulmonary valve seperate?
- seperates the right ventricle from the pulmonary artery
What does the aortic valve seperate?
- seperates the left ventricle from the aorta
what is the cardiac cycle defined as?
the repeated pattern of cardiac contraction & relaxation
What is cardiac contraction defined as?
- systole
- pushes the blood out of the heart into vasculature
what is cardiac relaxation defined as?
- diastole
- allows the heart to fill with blood
What are the 2 phases of diastole called?
- Passive filling
- Atrial contraction
What does the passive filling phase involve?
- the **atria and ventricles are relaxed **
- the ventricles are** passively filled with blood**
- AV valves are open, Semi lunar valves are closed
What does atrial contraction involve?
- happens at the end of diastole
- 80% of blood has already filled the ventricles
- the** atria contract** and** fill the ventricles fully**
- AV valves open, SL valves closed
What is the** volume of blood** that fills the ventricle just before it contracts called?
- The end - diastolic volume (EDV)
What happens after the atrial contraction phase?
- the** pressure in the atria begins to fall**, this causes the closing of the AV valves (to prevent backflow from ventricles to atria)
- this produces the S1 sound and marks the beginning of the systole
What forms the S1 sound (‘lub’)
- closing of the AV valves after atrial contraction
What are the 3 phases of systole?
- Isovolumetric contraction
- ventricular ejection
- **Isovolumetric **relaxation
Describe the isovolumetric contraction phase
- AV valves closed
- semi lunar valves are closed for a moment
- the ventricle is full of blood and begins to** contract,** but as the valves are all closed, no blood is ejected from the ventricles
- no change in volume
Describe the ventricular ejection phase
- ventricle contracts further
* semilunar valve opens - the contraction increases the pressure in the ventricle
- aortic valve opens
- this increase in pressure allows blood to be ejected from the ventricles to the aorta/pulmonary artery to systemic / pulmonary circulation
Describe the isovolumetric relaxation
- the semi lunar valves close
- the AV valves are still closed
- no change in volume
- back to diastole after this phase
What is the volume of blood called after the ventricular contraction?
- the end- systolic volume (ESV)
What causes the S2 sound?
- the semilunar valves closing after ventricular contraction
How is the stroke volume related to the end diastolic volume & the end systolic volume?
- the stroke volume is the difference between the EDV and the ESV
How do ventricular pressures change during the cardiac cycle?
* pressure is low in the first phase of diastole (passive filling), as the AV valves are open and blood is flowing in
* there is a** slight rise in pressure** in the 2nd phase (atrial contraction) as the volume of blood is increasing in the ventricles
* during the 1st phase of systole (isovolumetric contraction), there is a huge rise in pressure, as the ventricle begins to contract but no blood is ejected
* during the 2nd phase of systole (ventricular ejection), pressure still increases as the ventricle is contracting lots
* after ventricular ejection, the pressure falls in the ventricle
Why is the left systolic ventricle pressure higher than the right systolic ventricle pressure?
- this is due to a larger and thicker left side of the heart
- the left ventrile has to **eject blood against a higher arterial pressure **than the right ventricle, even though they both pump the same amount of blood
What are the main components in the atrial pressure waveform?
- a wave
- c wave
- x descent
- v wave
- y descent
What is the a wave in the pressure waveform of the heart?
- this wave represents the contraction of the right atrium, while the tricuspid valve is open.
What is the C wave?
- this wave appears at the hump of the base of the a wave
- it reflects the bulging of the tricuspid valve into the** right atrium** during ventricular systole & the pressure of the carotid pulse on the jugular vein (in neck)
What is the x descent?
- reflects the relaxation and initial rapid filling of the right atrium while the tricuspid valve remains closed
What is the v wave?
- right atrial filling
What is the y descent?
- right atrial emptying into the right ventricle
