Cardiovascular Systems 3 - Cardiovascular Mechanics 2 Flashcards
What are the two main phases of the heart, and what proportion of the heart beat do they take up?
- Diastole is the relaxation of the ventricle, which is split into 4 distinct phases
- Systole is the contraction of the ventricle, which is split into 3 phases.
- Diastole is 2/3 of the heartbeat, and systole is 1/3.
List the 3 phases of systole.
- Isovolumetric contraction
- Rapid ejection
- Slow ejection
List the 4 phases of diastole.
- Isovolumetric relaxation
- Rapid passive filling
- Slow passive filling
- Atrial systole
How can the stroke volume be calculated?
End diastolic volume - end systolic volume
How can the ejection fraction be calculated?
Stoke volume / end diastolic volume x 100
Describe the process of atrial systole.
- The P wave on an ECG signifies the start of the heartbeat
- The ventricles are already filling slowly via movement of blood down its pressure gradient. To finish vetricular filling, there is contraction of the atria
When is the 4th heart sound heard?
When there is arterial stenosis, resulting in a greatly thickened ventricular wall.
Describe the process that occurs in isovolumetric contraction.
- This is where the ventricle is contracting and pressure is increasing but there is no change in volume, as the pressure must be high enough to open the aortic valve/pulmonary valve.
- Accompanied by the QRS complex - signifying ventricular depolarisation.
What causes the first heart sound (lub)?
The AV valve closing due to increasing ventricular pressure.
What happens during rapid ejection?
- The aortic and pulmonary valves open at this stage
- He volume in the ventricles decreases
What happens during reduced ejection?
- End of systole
- There is a reduced pressure gradient, so the pulmonary and aortic valves start to close. Blood leaving the ventricle slows. Finally, the valves fully close.
What happens during isovolumetric relaxation?
- All valves are shut
- There is no change in ventricular volume, but the pressure decreases. Atrial pressure increases as blood flows in.
What does the T wave signify?
Ventricular depolarisation
What causes the second heart sound?
Closing of the semilunar valves
What happens in rapid passive filling?
- The pressure in the atria overcomes that in the ventricle, so the AV node opens.
- Blood flows into the ventricles
What causes the third heart sound?
- Usually abnormal - turbulent ventricular filling
- Due to hypertension or mitral incompetence
What is another name for reduced passive filling?
Diastasis
What occurs in reduced passive filling?
- The ventricle fills slowly without contraction of the atria.
- This is the longest phase.
How similar are the pressures in the left and right heart?
- Pressures in the right heart are lower
- Patterns of pressure changes are different
- Right ventricle ejects the same volume of blood as the left.
What is the pressure in the systemic circuit?
120/80mmHg
What is the pressure in the pulmonary circuit?
25/5mmHg
What is the axis on a pressure volume loop?
Volume (x) and pressure (y)
What is the point A on a pressure volume loop?
- Mitral valve closes
- End diastolic volume, meaning it represents the preload
What is the point B on a pressure volume loop?
- Aortic valve opens
- Diastolic blood pressure
What is point C on a pressure volume loop?
- End systolic volume
- Aortic valve closes (lub)
What is point D on a pressure volume loop?
- Mitral valve opens
What is the line A to B on a pressure volume loop?
Isovolumetric contraction
What is the line B to C on a pressure volume loop?
Ejection
What is the line D to C on a pressure volume loop?
Isovolmetric relaxation
What is the line D to A on a pressure volume loop?
FIlling
Where is the end diastolic PV line on a pressure volume loop and what does it denote?
- Passes from A to D and beyond
- The end diastolic PV line denotes elastance (preload)
Where is the end systolic PV line on a pressure volume loop?
- Passes through C
- Denotes contractility
Where is the afterload line on a pressure volume loop?
From C through the highest ventricular volume on the x axis.
Which section of the PV loop is longest?
D to A
How is ejection fraction calculated from a PV loop?
(volA - volD)/volA
How is mean arterial pressure calculated from a PV loop?
PressureB + 1/3(PressureC-PressureB)
How is pulse pressure calculated on a PV loop?
Pressure C - Pressure B
How is cardiac output measured on a PV loop?
(VolA - VolB) x Heart Rate (67)
How can you calculate stroke volume?
Volume A to B - Volume C to D
How do increases in preload affect the pressure volume loop?
- Increase in stroke volume
- Line A B moves to the right (increased volume)
Hoe do increases in afterload affect the pressure volume loop?
- Decreased stroke volume, but an increased pressure
- Line C D moves to the right (increased volume)
- Line D A moves upwards (increased pressure)
What factors affect stroke volume?
- Preload
- Afterload
- Contractility
What is contractility?
- The capability of the heart to contract
- Measured by ejection fraction
What is the dicrotic notch?
A small rise in aortic pressure when the aortic valve closes
