Cardiac Cycle & Pressure-Volume Loops Flashcards
True or False:
The heart behaves as a reciprocating pump & the flow of blood depends on pressure gradients.
True
What are the to major parts of the cardiac cycle?
Diastole & Systole
What is happening during diastole?
Ventricular RELAXATION & filling
What is happening during systole?
Ventricular CONTRACTION & ejection
What determines the duration of the cardiac cycle?
The sino-atrial (SA) node (pacemaker)
What determines the relative duration of heart muscle contraction& relaxation?
The electrical properties of the cardiac conduction system & cardiac myocytes
What is stroke volume?
The volume of blood ejected from the left ventricle of heart through the aorta
What is the average rate of the SA Node?
60-100 bpm
True or False:
Electrical activity of the heart (shown on ECG) PRECEDES muscular contraction
True
How is the duration of a cardiac cycle calculated?
By taking the reciprocal of the heart rate:
For a heart rate of 75 bpm,
Duration (s/beat) = 60 sec/min / 75 beats/min
Duration = 0.8 sec/beat
This means for a heart rate of 75 bpm, one cardiac cycle (one heart beat) takes 0.8 seconds to complete.
Do the atria & ventricles contract at the same exact time?
No.
There is a delay of greater than 0.1 second for the excitation signal to travel from the atria to the ventricles.
Simultaneous contraction would be inefficient for the heart.
Blood moves from an area of __________ pressure to __________ pressure.
Blood moves from an area of higher pressure to an area of lower pressure
What are the four valves of the heart?
- Tricuspid Valve
- Pulmonary Valve (right semilunar)
- Mitral Valve (Bicuspid)
- Aortic Valve (left semilunar)
What chambers of the heart are separated by the tricuspid valve?
Right atrium & right ventricle
What chambers of the heart are separated by the mitral valve?
Left atrium & left ventricle
What are the two major phases of the cardiac cycle?
Inflow Phase
- inlet valve open, outlet valve closed = diastole
- isovolumentric contraction
- when both valves are closed = systole
Outflow Phase
- outlet valve open, inlet valve closed = systole
-Isovolumetric relaxation
- both valves are closed with no blood flow (diastole)
For a cardiac cycle the length of 0.8 seconds (800 ms), what is the duration of systole compared to diastole
Systole= 300 ms (0.3 s)
Diastole = 500 ms (0.5 s)
** If heart rate increases, and thus cycle length decreases, diastole will shorten relatively more than systole. **
What is isovolumetric contraction?
Ventricular contraction/systole
What is isovolumetric relaxation?
Ventricular relaxation/diastole
What are the 5 major mechanical events of a single cardiac cycle?
- Atrial systole
- Early ventricular systole
- Late ventricular systole
- Early ventricular diastole
- Late ventricular diastole
*Atrial diastole (relaxation) occurs simultaneously during events 2-5.
What occurs during the first mechanical event of a single cardiac cycle?
- Atrial systole - atria contract; AV valves open, semilunar valves closed
What occurs during the second mechanical event of a single cardiac cycle?
- Early ventricular systole - Atria relax, ventricles contract; AV valves frced closed, semlunar valves still closed
** One of the two periods during a single cardiac cycle where all 4 valves are closed. **
What occurs during the third mechanical event of a single cardiac cycle?
- Late ventricular systole - atria still relaxed, ventricles still contracting; Av valves remain closed, but semilunar valves forced open.
What occurs during the fourth mechanical event of a single cardiac cycle?
- Early ventricular diastole- atria & ventricles relax; AV valves & semilunar valves closed; atria begins passively filling with blood
What occurs during the fifth mechanical event of a single cardiac cycle?
- Late ventricular diastole - Atria & ventricles relax; atria passively fill with blood as AV valves open, & semilunar valves are closed
In which ventricle is the pressure highest?
The left ventricle
In which ventricle is the volume the highest?
Neither.
Left ventricular volume = right ventricular volume
Thus why the ventricles are referred to as isovolumetric
What does the P wave of an ECG refer to?
Atrial contraction
When does the QRS complex occur in relation to the Wigger’s diagram?
QRS complex occurs immediately before the upswing of LV pressure.
When does the T wave of an ECG occur in relation to Wigger’s diagram?
The T wave occurs in the decreased-ejection phase of the left ventricle on the Wigger’s diagram
What occurs during Phase 1 of the cardiac pressure-volume curves on the Wigger’s diagram?
Phase 1 = Atrial contraction/systole
AV valves: open
Semilunar valves: closed
AP: Aortic Pressure
LVP: Left Ventricular Pressure
LAP: Left Atrial Pressure
LVEDV: Left Ventricular End Diastolic Volume
LVESV: Left Ventricular End Systolic Volume
Atrial systole is preceded by the P wave of the ECG, which marks the depolarization of the atria. At this phase the ventricles are already almost filled, and atrial systole only contributes to a fraction of ventricular filling during ventricular diastole.
The rise in atrial pressure results in a corresponding ‘a’ wave in the venous pulse as pressure generated in the atria is transferred back to the vein due to the absence of a valve between the atria and vein.
What occurs during Phase 2 of the cardiac pressure-volume curves on the Wigger’s diagram?
Phase 2. Isovolumetric Contraction
AV valves: closed
Semilunar valves: closed
Isovolumetric contraction/early ventricular systle begins during the QRS complex, which represents the depolarization of the ventricles.
Ventricular pressure separates from atrial pressure because of closure of the mitral valve.
The upward movement of the mitral valve into the atria causes the ‘c’ wave.
What occurs during Phase 3 of the cardiac pressure-volume curves on the Wigger’s diagram?
What occurs during Phase 4 of the cardiac pressure-volume curves on the Wigger’s diagram?
What occurs during Phase 5 of the cardiac pressure-volume curves on the Wigger’s diagram?
What occurs during Phase 6 of the cardiac pressure-volume curves on the Wigger’s diagram?
What occurs during Phase 7 of the cardiac pressure-volume curves on the Wigger’s diagram?
What are the 3 major pressure elevations in the atria, that re reflected as a complex pulse wave n the jugular vein?
The aortic pressure peak on the graph refers to what?
Systolic blood pressure (top blood pressure number).
The peak in aortic pressure occurs during the end of the left ventricular rapid ejection phase, & is followed by the reduced ejection phase (makes sense).
The aortic pressure low on the graph refers to what?
The diastolic arterial blood pressure (the bottom blood pressure number)
The low in aortic pressure occurs right at the end of isovolumetric contraction (left ventricular contraction) & right before rapid ejection.
Once the cycle enter the rapid ejection phase, where blood is pushed out of the left ventricle into the aorta, naturally the pressure in the aorta experiences a sharp increase.
What are the 4 heart sounds, what is occurring, & what are they each associated with?
What is occurring at each point (points A-F) on the pressure volume loop?
The relationship between left ventricular pressure and volume can be graphically displayed in a pressure-volume loop.
Point A - represents the point at which the mitral valve opens and blood moves passively into the ventricle.
Point B - There is a slight decrease in pressure because the ventricular muscle continues to relax during diastole.
Point C - A combination of active and passive ventricular filling leads to a modest increase in pressure at point C. The reason for the modest increase even though the volume of blood within the ventricle has markedly increased is due to the high compliance of the ventricular wall. The mitral valve closes at point C when ventricular filling is complete. Isovolumetric contraction begins which means the volume of blood remains constant as the pressure inside the ventricle increases.
Point D - the aortic valve opens and blood is ejected.
Point E - Ventricular contraction continues and a peak systolic pressure is reached. Once this is achieved the ventricle begins to relax, but ejection of blood continues.
Point F - represents end systolic pressure and volume. Notice that the volume is not zero at the end of systole because a certain amount of blood remains in the ventricle. At point F, the aortic valve closes, ejection has ended and isovolumetric relaxation ensues.
What does the curve made by points CDEF on the pressure-volume loop represent?
CDEF = left ventricular systole/contraction
What does the curve made by points FABC on the pressure-volume loop represent?
FABC= left ventricular diastole/relaxation
How can the stroke volume be found using the pressure-volume loop?
By taking the width, from point A to point C ,OR from point D to point D
The corners (A, C, D, F) of the pressure-volume loop refer to what?
Closing or opening of valves.
A - mitral/bicuspid/left AV valve opens
C - mitral/bicuspid/left AV valve closes
D - aortic valve opens
F - aortic valve closes
What direction does the pressure-volume loop move in?
Counterclockwise direction
Lecture Summary
Which point on the pressure-volume loop refers to end diastolic pressure?
Point C
Which point on the pressure-volume loop refers to end systolic pressure?
Point A
