Cardiac Cycle Flashcards
What is the Leyman’s term for the cardiac cycle?
Heartbeat
When do the atrioventricular valves open?
Atrial contraction
What generates the first heart sound?
Closure of atrioventricular valves
When do the semilunar valves open?
Ventricular contraction
What generates the second heart sound?
Closure of semilunar valves
What is a systole?
Phase of contraction in the heart
What is diastole?
Phase of relaxation in the heart
Before atrial systole, what chambers have a higher pressure?
Atria
During atrial contraction, how much of the ventricles become filled?
~80%
When is the remaining blood pushed into the ventricles?
At atrial systole
What is the end diastolic volume at rest?
120-135 ml
After how many milliseconds does ventricular systole/isovolumetric contraction begin?
100msec
What pressure does the left ventricle require to open the semilunar valves into the aorta?
80 mmHg
What pressure does the right ventricle require to open semilunar valves into the pulmonary artery?
8 mmHg
How long does ventricular systole last?
30 msec
What stays constant during isovolumetric contraction?
Ventricular volume
What name is given to the total volume of blood ejected?
Stroke volume
What are the two forms of ejection that happen in the ejection phase?
Rapid ejection and reduced ejection
What name is given to the residual blood remaining in the ventricles following systole?
End systolic volume
What is the end systolic volume at rest?
50-65 ml
During isovolumetric contraction, what does the ventricular and aortic pressure increase to?
120 mmHg
What name is given to the abrupt drop in ventricular volume?
Rapid ejection
What is reduced ejection?
Blood leaving the ventricle as pressure is beginning to fall
What does the pressure in the atria fall to during isovolumetric contraction and why?
0 mmHg as the atria are stretched
When does pressure in the atria begin to rise again?
Atrial filling
After how many milliseconds does ventricular diastole/isovolumetric relaxation occur?
300 msec
What closes the semilunar valves?
Backflow of blood
After how many milliseconds do the semilunar valves close?
350msec
After how many milliseconds do the atrioventricular valves open again?
T = 450 msec
What is the rapid filling phase?
Blood flowing abruptly into ventricles
What name is given to blood entering atria from veins continuing into ventricles?
Diastasis
How long does diastasis last until (milliseconds)?
800 msec
How long does isovolumetric contraction take?
0.05 sec rapid phase
0.3 sec longer phase
How long does isovolumetric relaxation take?
0.5 sec
When is there a rise in the atrial pressure curve on an ECG?
Immediately after P wave
When is there a rise in ventricular pressure on an ECG?
After the QRS complex
during what phase of the cardiac cycle does the T wave occur on an ECG?
Slightly before the end of ventricular contraction
Why does pressure fall during the T wave?
Due to ejection of blood
What is the name of the diagram which displays the cardiac cycle?
Wiggers Diagram
How much EDV is delivered by atrial contraction?
Up to an additional 20%
Does a slow or fast heart rate aid in completion of diastasis and why?
Fast as ventricular contraction can begin during rapid filling
What is shortened during tachycardia?
Diastasis
What can happen if inadequate ventricular filling occurs?
Syncope/fainting
What is an A wave?
Rise in pressure caused by atrial contraction
What is the pressure increase during the A wave for both the right and left atrium?
Pressure increases by 4 to 6 mm Hg in right atrium
Pressure increases and by 7 to 8 mm Hg in left atrium
What is the C wave?
Increasing ventricular pressure causes bulging of the AV valves into atria
What is the V wave?
Rise in pressure associated with atrial filling
Where are pressure changes in atria transmitted to?
Back into large veins e.g., jugular vein
What name is given to the irregular fluctuations in atrial fibrillation?
f waves
Which contractions are irregular during a fib and why?
Ventricular due to AV node activation being irregular
What is not occurring in individuals with atrial fibrillation?
No atrial contraction: therefore, no blood is pumped into ventricles
What is the major danger involving atrial fibrillation?
Clots can form in atria
What does ejection of blood from the left ventricle do to the walls of the arteries?
Stretches their walls
Pressure increases to 120mm Hg
What causes the incisure/dicrotic notch in the aortic pressure curve?
Short period of backflow of blood into ventricle immediately before closure of the aortic valve
What maintains a high pressure in arteries even during diastole?
Elastic walls
Why does pressure in the aorta decrease slowly throughout diastole?
Elastic recoil pushes the blood continually into peripheral vessels
What is diastolic pressure?
80mmHg
What stops the bulging in the atria?
Chordae tendineae abruptly stop the back bulging
What is the loudest heart sound and how long does it last?
S1 - lasts 0.14 secs
How long does S2 last?
0.11 sec
When does S1 occur on an ECG?
Directly after a QRS complex
What is Auscultation?
Listening to heart sounds with a stethoscope
What semilunar valve usually has a louder sound?
Aortic valve
When may the quieter semilunar valve be louder than the louder one?
Pulmonary valve is louder during pulmonary hypertension
Where can one hear the aortic valve?
2nd right intercostal space, just lateral to the body of the clavicle
Where can one hear the pulmonic valve?
2nd left intercostal space, just lateral to the body of the sternum
Where can one hear the tricuspid valve?
5th left intercostal space, just inferior to fifth right costal cartilage and lateral to superior xiphoid process
Where can one hear the mitral valve?
Apex of heart
5th left intercostal space, midclavicular line
What is pulmonary hypertension?
Abnormal increase in pressure in pulmonary circulation
What is a phonocardiography?
Detection of heart sounds with a microphone
What is S3 generated by?
Caused by inrushing blood from atria during middle third of diastole
When, in a human, can S3 usually be heard?
Younger people under the age of 40
What might it mean if an abnormal demographic presents with S3?
Hole in septum (murmur)
What causes S4?
generated by inflow of blood into ventricles following atrial contraction
What is a heart murmur?
Abnormal heart sound generated during a cardiac cycle
What is aortic stenosis?
The aortic valve, abnormally small space to eject blood, rapid movement of blood
What murmur is heard during aortic stenosis?
Loud, whistling sound during systole
What is aortic regurgitation?
Aortic valve doesn’t close properly causing leakage of blood into left ventricle
What sound is heard during aortic regurgitation?
Low, rumbling sound during diastole
What happens at A in the Left Ventricle Pressure-Volume LOOP
Opening of mitral valve and beginning of filling, esv
What happens from A-B in the Left Ventricle Pressure-Volume LOOP?
Pressure falls as diastole progresses, blood volume increases (rapid filling)
What happens from B-C in the Left Ventricle Pressure-Volume LOOP?
Pressure and volume increase as diastasis progresses
What happens at C in Left Ventricle Pressure-Volume LOOP?
Mitral valve closes
EDV
What happens from C-D in the Left Ventricle Pressure-Volume LOOP?
Systole begins, isovolumetric contraction
What happens in D in Left Ventricle Pressure-Volume LOOP?
Aortic valve opens, diastolic pressure
What happens from D to E in Left Ventricle Pressure-Volume LOOP?
Pressure rises to systolic value, volume falls, rapid ejection
What happens from E to F in the Left Ventricle Pressure-Volume LOOP?
Pressure and volume fall, reduced ejection
What name is given to D to F in the Left Ventricle Pressure-Volume LOOP?
Stroke volume
What happens at F in the Left Ventricle Pressure-Volume LOOP?
Aortic valve closes
What happens from F to A in the Left Ventricle Pressure-Volume LOOP?
Diastole begins, Isovolumetric relaxation, pressure drops, volume is constant
What is Preload in muscle?
Degree of tension on the muscle when it begins to contract
What is preload in cardiac muscle?
Magnitude of the EDV and corresponding end diastolic pressure (point C)
What is afterload in muscle?
Force against which the muscle is acting
What is the afterload in cardiac physiology?
Blood pressure in aorta which the ventricle must exceed to open the aortic semilunar valve to eject blood
Aortic blood pressure
Point D
What is contractility/ionotrophy?
Strength of contraction at a given preload and afterload
How does one calculate contractility?
Slope of Ventricular pressure curve - index of ionotrophy
Name a drug that increases ionotropy of heart
Adrenaline
What condition may reduce contractility?
Cardiac failure
How does one calculate contractility?
Slope of Ventricular pressure curve - index of ionotrophy
Maximum dP/dt
What is diastolic pressure?
Pressure exerted by EDV on the walls of ventricle prior to contraction
What is the limit of the stretch of heart muscle?
150 ml EDV
What does the Frank-Starling Law state?
Systolic pressure increases linearly with EDV
What happens to cardiac muscle fibres at high EDVs?
Pressures generated fall due to overstretch of actin and myosin
What is the stroke work output?
Physical work done by ventricle to eject stroke volume
What is the work done by the heart?
Volume-pressure work or EXTERNAL work
What is the external work equal to?
The area of the pressure-volume loop
What is re-entry?
If cells become excitable again independent of the SA node
What causes re-entry?
Increase tissue mass (dilated heart) causing a long pathway for impulses
Decreased rate of conduction
Shortened refractory period in response to various drugs
What may cause a decrease in the rate of conduction?
Blockage of the Purkinje system
Ischemia of the muscle
High blood K+ levels
What does re-entry result in?
Abnormal patterns of cardiac contraction or abnormal cardiac rhythms that ignore the pace-setting effects of the sinus node
Fibrillation
How long does it take for ventricular fibrillation to become fatal?
1-3 mins
How can you treat v-fib?
Defibrillator
How does an AED work?
Stop fibrillation by simultaneously placing entire myocardium into a refractory state, allows autorhythmic cells in heart to regain pacemaker control
