L19/20 Cardiac Cycle Flashcards
Cardiac cycle
Systole
Generation of pressure by heart
Contraction of a chamber
Ejection of blood from a chamber
Diastole
Period of relaxation of heart
Filling of chambers with blood
Perfusion of coronary arteries
Systole + diastole = cardiac cycle
Components of cardiac cycle
Pressures within chambers and vessels (left atria, ventricle and aorta)
Sounds (valve closure and filling: S1 - S4)
Volumes of blood within chambers and vessels
Venous pulses (a,c, and v waves) (changes of pulse in jugular vein)
Events of EKG (P, QRS, T)
Phases of cardiac cycle
A-G
A: atrial systole B: isovolumic ventricular contraction C: rapid ventricular ejection D: reduced ventricular ejection E: isovolumic ventricular relaxation F: rapid ventricular filling G: reduced ventricular filling
How is direction of blood flow through heart established?
Mechanical valves
Atrioventricular (AV) valves
Semilunar (SL) valves (aortic and pulmonary)
Opening and closing of valves is PASSIVE due to differences in blood pressure across the valves
How do AV valves work during ventricular diastole?
Pressure in atrium > pressure in ventricle
Pressure difference keeps both AV valves OPEN
ventricle fills 80% before atria contract
How does AV valve work during ventricular systole?
Pressure in ventricle > pressure in atrium
Pressure difference CLOSES AV valve
Prevents backflow
Blood leaves ventricle via aortic or pulmonary valve
Heart “lub” heard , 1st sound
How do seminlunar valves work during ventricular diastole?
P vessel (aorta or pulmonary) > P ventricle
P difference keeps aortic and pulmonary valves CLOSED
Prevents backflow
At very beginning: P ventricle drops suddenly, semilunar valve snaps shut, heart “dup” heard
How do seminlunar valves work during ventricular systole?
P ventricle > P vessels
P difference OPENS semilunar valve
Changes in pressure is when
Valves open and close
A
Atrial systole
AV valve opens; SL valve closes
P wave initiates atrial contraction
Pressure increases
Pressure gradient across AV valves
Causes rapid flow of blood into ventricles
Produces increase in venous pressure noted by a-wave of jugular pulse
Accounts for 10-25% of ventricular filling (most is passive before contraction) during exercise, higher HR, may account for 40% filling
4th heart sound heard (vibration of ventricular wall) will be more pronounced when ventricular compliance is reduced/ LV hypertrophy
Atrial systole
After contraction atrial pressure begins to fall and causes AV valves to float upward/close
Ventricular volumes of blood MAXIMAL = end-diastolic volume ( end of relaxation for the ventricular) normally 120mL
Is ventricular preload pressure
B
Isovolumic contraction
All valves closed
Contraction of ventricles
Initiated by QRS complex
Depolarization lead to a rapid pressure increase
This causes AV valves to close = vibrations produce 1st heart sound (S1) “lub”
S1 split noted because mitral valve closes before tricuspid
During time btw closure of AV valve and opening of SL/aorta- pressure rises w/out volume change and no ejection occurs
Atrial pressure rises
W/ bulging of AV valve into atria chambers
c wave noted in jugular pulse
C
Rapid ejection
SL valves open; AV valves remain open
When intraventricular pressures exceed pressures within aorta/pulmonary artery - valves open and blood is ejected
Maximal outflow velocity is reached
Most stroke volume ejected
Dramatic decrease in ventricular volume
Maximal systolic (aortic) and pulmonary artery pressure are achieved
Ventricular pressure exceeds vessel by a few mmHg
At very end and atrial filling begins from vena cava and pulmonary vein causing atrial pressure to rise (ejected next cycle)
D
Reduced ejection
SL valves open; AV valves remain closed
After QRS complex- ventricles begin to repolarize (T wave)
Ventricles no longer contracting and their pressure falls (SL valves still open)
Blood continues to eject due to inertial energy of blood
Volume of ventricles reaches minimum
Pulmonary/aortic pressures falls as blood is running off into arterial tree
Atrial pressure continues to rise due to venous return
E
Isovolumic ventricular relaxation
All valves closed
Begins after all ventricles fully repolarized
Ventricles relaxed and compliant
Pressure declines dramatically
Pressure drops below vessel pressure, closing aortic/pulmonary valves and produce 2nd sound S2 “dub” that’s spilt into A and P (dicrotic botch)
Ventricular volume at lowest and remains constant - end-systolic volume (~50mL)
Atrial pressure continues to rise due to venous return
F
Rapid ventricular filling
AV valves open; SL valves closed
Ventricular P falls below atrial - AV valve opens, ventricular filling begins
Atrial pressure falls- peak of jugular pulse is right before AV valve opens (v-wave)
LV pressure remains low because ventricle is compliant and relaxed
Healthy AV - no sounds during filling
Unhealthy/ children - 3rd sound heard (tensing of chorded tendineae and AV valve ring)
G
Reduced ventricular filling
AC valves open; SL valves closed
Final portion of passive ventricular filling
Continue to fill and expand become less compliant
Intraventricular pressure increases, reducing pressure gradient across AV valves (rate of filling falls)
Longest phase of cardiac cycle
Increases in HR decreases time for this phase
Reduces or eliminates ventricular filling
Decreases ventricular filling
Reducing preload and stroke volume
Stroke volume
volume if blood ejected on ventricular contraction
Difference in EDV and ESV
SV=EDV-ESV (mL/beat)
~70mL
Consistent part = edv
Lowest part = esv
Right vs left cardiac cycle differences
Magnitudes of peak systolic pressures in both ventricles (left much higher)
Systole of LV occurs before RV systole
Mitral valve closes before tricuspid
Aortic valve closes before pulmonary
Function of ventricle is described by?
Stroke volume
Ejection fraction
Cardiac output
Cardiac index
Ejection fraction
Effectiveness of ventricles in ejecting blood
Fraction of the EDV that is ejected in one stroke volume
Indicator of contractility
EF=SV/EDV x 100%
Cardiac output
CO
Totally volume of blood ejected per into time
Product of SV and HR
CO= HR x SV
one for R and L
R - 100% goes to lungs
L- to diff vascular beds
Cardiac index
CI
CO normalized for surface area (SA)
CI=CO/SA
S1
Caused by closure of AV valves during isovolumic contraction
