Cardiac Cycle, Pressures, Volume, Output & Blood Flow Flashcards
What are the phases of the cardiac cycle? (general)
Diastole and Systole
- takes part over 4 phases
1 & 4 - diastole
2 & 3 - systole
What does the first phase of the cardiac cycle include?
Opening of the AV valves
(tricuspid and mitral valves)
Rapid ventricular filling
Decreased ventricular filling, diastasis
Atrial contraction
What does the second phase of the cardiac cycle include?
Closing of the AV valves
Isovolumetric ventricular contraction (with all valves closed)
What does the third phase of the cardiac cycle include?
Opening of the semilunar valves
Rapid ventricular ejection
- fast mm shortening
Decreased ventricular ejection
- slower mm shortening
What does the fourth phase of the cardiac cycle include?
Closing of the semilunar valves
Isovolumetric ventricular relaxation
- with all 4 valves closed
Cycle begins again
What is the calculation for determining MAP? Why is it important - what is the clinical significance?
MAP = DBP + 1/3(SBP-DBP) MAP = CO x TPR
MAP is clinically significant because it’s an indication of the perfusion pressure seen by the organs of the body
What is SV? What is the equation for it?
SV = stroke volume - indication of the amount of blood moved out of the ventricle with each beat
SV = EDV - ESV
(end diastolic volume minus end systolic volume)
What is EF? What is the formula for it?
Ejection Fraction
- indicates what fraction of end-diastolic volume got moved out of the heart with contraction
- related to contractility of the heart
- should be ~55% normally
EF = SV/EDV
What is CO?
Cardiac Output
- generally the volume of blood being pumped by the heart per minute
CO = SV x HR
CO = MAP/TPR
What is EDV?
End Diastolic Volume
- AKA preload
- related to right atrial pressure
If venous return increases, EDV increases and stretches ventricular mm fibers
- see Frank-Starling curve
What is the S1 heart sound and what does it indicate?
Indicates closure of AV valves
- happens when ventricular pressure becomes greater than atrial pressure
“lub” sound
- 2 bursts, indicating a mitral and a tricuspid component
- occurs during isovolumetric ventricular contraction
What is the S2 heart sound and what does it indicate?
Indicates closure of the semilunar valves
- happens when valves close, indicating start of isovolumetric ventricular relaxation
What does splitting of the S2 heart sound mean on the right side of the heart? When does it happen? What 4 factors on the right side of the heart influence it?
Happens in normal people during inspiration
Due to right ventricular ejection being longer than left ventricular ejection
- aortic valve closes before pulmonary valve due to greater downstream pressure
Pulmonary valve opens first and closes last, due to lower downstream pressure
Splitting due to increased thorax volume and decreased thoracic pressure
- increases venous return to right atrium
- increases EDV for right ventricle
- increases right ventricle ejection volume
- increases time for for RV ejection
What does splitting of the S2 heart sound mean for the left side of the heart?
Decreased thoracic pressure decreases blood retention in dilated pulmonary veins
- decreases venous return to left atrium and ventricle
- decreased left ventricle EDV and ejection
Less time for LV ejection
- accelerates aortic valve closure
- enhances physiological splitting of S2
What is an OS? When does it occur?
Opening Snap
- indicates opening of a stenotic mitral valve
- occurs at the ‘opening’ of the cardiac cycle , after S2 but before S1
What is an S3? When does it happen? What does it indicate?
Third Heart Sound
- indicates protodiastolic gallop
Happens during rapid ventricular filling phase
- early diastole, right after S2
- normal in younger people
- can indicate ventricular enlargement assoc. with heart failure
- can indicate reduced distensibility/compliance
What is an S4? When does it happen? What does it indicate?
Another heart sound
- indicates presystolic gallop
- occurs just before S1
Associated with unusually strong atrial contraction
- can indicate ventricular wall stiffness
- can indicate decreased compliance associated with hypertrophy
What are heart murmurs? What can cause them?
Sound generated by turbulent flow through the heart
Turbulence due to structural issues:
- thickening of valve leaflets
- narrowing (stenosis) of valve openings
- holes in chamber or septae between chambers
Hemodynamic issues:
- decreased viscosity - anemia
What do diastolic murmurs include?
Mitral stenosis
Aortic regurgitation
What do systolic murmurs include?
Mitral valve insufficiency
Aortic stenosis
What are the components of the jugular venous pulse wave?
a-wave
- RA contraction
- av minimum: tricuspid closure
c-wave
- RV pressure in early systole
- bulging of tricuspid valve into RA
- x minimum: elongation of veins during ejection phase with ventricle contraction
v-wave
- RA filling
- tricuspid closed
- y minimum: fall in RA pressure (tricuspid opening, rapid ventricular filling)
What are some clinical correlates of jugular venous pulse?
A-wave
- large a-wave: tricuspid stenosis, right heart failure
- cannon a-waves: 3 degree AV block, complete heart block
- no a-waves - atrial fibrillation
C-wave
- RV pressure in early systole (tricuspid bulging)
V-wave
- large v-wave: tricuspid regurgitation
What is the effect of the respiratory cycle on jugular venous pulse?
Decreased intrathoracic pressure during inspiration
- decreases jugular venous pressure
- decreases RA and VC pressure
- decreases resistance to venous flow
- increases venous flow, and venous return from head and upper extremities
What is the effect of skeletal muscle contraction on jugular venous pulse?
Standing - blood pools in lower extremity
Walking - pumping action of mm limits retrograde venous flow
- promotes VR
- decreases blood pooling in lower extremity
What are ventricular pressure-volume loops?
Indicate ventricular volume and pressure relationship
- made by combining systolic and diastolic pressure curves
Diastolic pressure curve is the relationship between diastolic pressure and diastolic volume in the ventricle
- same holds true for systolic pressure and volume in ventricle
What are the steps in the pressure volume loop? What do they indicate?
1->2 isovolumetric contraction
- left ventricle filled with blood
- AP comes and ventricle contracts
- Mitral valve closes when ventricular pressure is greated than atrial pressure
- no blood ejected, all valves closed
2->3 ventricular ejection
- aortic valve opens
- ventricular pressure greater than aortic pressure
- volume ejected is SV - measured graphically by width of pressure-volume loop
- remaining blood makes up ESV
3->4 isovolumetric relaxation
- ventricle relaxes
- aortic valves closes
- all valves closed, ventricular volume constant
4->1 ventricular filling
- mitral valve opens
- ventricular filling begins
What is the significance of external work done by the heart?
Work done by the heart on each beat
- equal to pressure x volume
Indicates volume of blood moved during each cardiac cycle
Kinetic energy - includes acceleration done on blood volume
Total external work - small fraction of cardiac energy expenditure
What is tension heat of the heart?
Energy use without movement or work done
Factors include:
- ventricular wall tension - determined by afterload
- time in systole
Major ATP cost
- does maintenance of isometric tension
How can you reduce cardiac energy expenditure?
Decrease heart rate or BP
- decreased time spent in systole
What are the 3 major determinants of myocardial O2 demand?
Ventricular wall tension
heart rate
contractility
How is wall tension related to blood pressure, wall thickness, and radius of chamber?
Wall tension:
BP: proportional to systolic ventricular pressure
- AKA afterload
- increases with HTN, aortic stenosis
Radius: proportional to radius of ventricular chamber
- decreases with aortic regurg., dilated cardiomyopathy
Wall thickness: inversely proportional to ventricular wall thickness
- concentric hypertrophy in athletes (good thing)
What is the cardiac index?
Indicator of cardiac performance
- normalized for body size
What is the equation for stroke volume?
SV = EDV-ESV
What are the 3 factors that affect stroke volume?
Preload - increases
- ventricular stretch at the end of diastole
- related to ventricular filling, sarcomere length prior to contraction
Afterload - decreases
- contracting fibers must oppose pressure in order to do ejection
- measured by maximum systolic ventricular pressure
- increased afterload - increased ESV, decreased SV
Contractility/inotropy - increases
- force generation independent of preload
- influenced by autonomic input
What is isometric tension?
Isovolumetric contraction phase
- increased preload, decreases SV
What is isotonic tension?
Ejection phase
- increased afterload decreases SV
- afterload = increased aortic pressure
What is the main driver for cardiac O2 consumption?
Amount of tension developed by the ventricles
What 4 things increase cardiac O2 consumption?
- Increased afterload
- increased size of the heart
- increased contractility
- increased heart rate
What does the Frank-Starling relationship describe?
Relationship between increases in stroke volume and cardiac output that occur in response to an increase in venous return or EDV
Matches CO to venous return
- increasing VR increases CO
What is the Frank-Starling relationship based on?
length -tension relationship in the ventricle
Increases in EDV cause increased ventricular fiber length
- increase in developed tension
What increases/decreases the Frank-Starling relationship?
Contractility
- proportional to cardic output
- increases result in increased SV, decreased ESV
What does an increased preload do to the Frank-Starling relationship?
Results from increased EDV, resulting from increased venous return
Increases SV
- increases width of pressure-volume loop
What does an increased afterload do to the Frank-Starling relationship?
Refers to aortic pressure
- ventricle must eject against a higher volume
Results in decreased SV
- decreases width of pressure-volume loop
Decrease in stroke volume results in increase in ESV
