Cardiac Cycle & Cardiac Output Flashcards
What is the cardiac cycle/sequence?
Electrical comes before mechanical
1. Start of atrial depolarization (still in full relaxation).
2. Atria depolarization complete (atrial contraction in progress).
3. Start of ventricular depolarization (QRS complex). (Ventricles are still in full relaxation.
4. Ventricular depolarization complete (Ventricular contraction is in progress).
5. Start of ventricular repolarization (Ventricular contraction is still in progress).
6. No electrical or mechanical activity, completion o cardiac cycle.
What are the two main events to complete cardiac cycle?
- Ventricular systole (contraction)
- Ventricular diastole (relaxation).
What happens in ventricular systole Isovolumic ventricular contraction?
- Blood volume in the ventricle during this period is know as end-diastolic volume commonly refers to as preload.
- Begins with the closure of AV (mitral) valve.
- Generates 1st low pitched heart sound.
- With no change in ventricular volume.
What happens in ventricular systole ventricular ejection?
- Begins with the opening of the semilunar valve (AV valves are now closed)
- Sharp increase in the ventricular and aortic pressure (rapid ejection
phase, sharp increases in dp/dt )- There is a sudden drop of
left atrial pressure (Mitral
valve is now closed) - Even with continuation
of left atrial filling from
the pulmonary veins.
- There is a sudden drop of
- Follows by reduced ejection
phase (associated with the
onset of T-wave).
- Peak of left ventricular pressure coincides with the arterial systolic pressure.
- Ends with the closure of the semilunar valves. - Ventricular volume at the end of ejection phase is known as end systolic volume.
What happens in ventricular diastole isovolumic ventricular relaxation?
- Blood volume in the
ventricle during this
period is known as end-
systolic volume (ESV) - Begin with the closure of
semilunar (aortic) valve
▪ Generate 2nd higher
pitched heart sound.
▪ A dicrotic notch (an
in aortic pressure) is
observed. - Stroke volume (SV)
is the difference
between EDV & ESV
SV = EDV – ESV
What happens in ventricular diastole during ventricular filling ?
- Begins with the opening
of the AV (mitral) valve
(semilunar valves are
now closed).
▪ A slight drop of atrial
pressure is observed.
→ Majority of ventricular
passive filling occurs in
this phase (~ 70%)
(rapid filling phase).
→ Follow by reduced
filling phase with atrial
contraction (also known
as active ventricular
filling phase).
What is the ventricular pressure-volume loop?
It identifies the sequential dynamic changes of pressure and volume within the left ventricle for complete cardiac cycle.
How the ventricular pressure-volume loop generated?
By plotting the left ventricular pressure against left ventricular volume.
- Can provide important insights into left ventricular function.
What is cardiac output?
It is the output of the heart per unit time.
- CO= SV x HR
- Normal value is about 5 to 6 L/min for a resting person of avg adult size.
What is cardiac index?
- This value is used to minimize the influence of body size on cardiac output.
What is the ejection of blood by the left ventricular closely asociated with?
With 2 hemodynamic parameters (blood pressure and volume) in the atrial circulation.
What are the effects of changes in heart rate alone on stroke volume?
Increasing HR alone will have an inverse effect on SV because the ventricular filling time is decreased as the diastolic period decreases.
- However, increase in HR will increase CO but to a limit.
- b/c of the drastic decrease on ventricular filling time during tachycardia attack.
What is heart rate?
When one is exercising under normal physiological
conditions, the percentage of CO increase is
generally more than that of the HR.
What are the three reasons why under normal physiological conditions, CO percentage increases more than HR?
i) Reduction in peripheral vascular resistance.
ii) Positive inotropic effect to the contractile myocytes primarily caused by the increase of sympathetic activity.
iii) Compressing action of the contracting skeletal muscles (pushing blood forward together with the venous valves preventing the backflow of blood) enhances venous return.
What is the normal value of EDV and ESV for a normal adult heart?
EDV - 120 ml
ESV - 50 ml
*Therefore normal SV for a normal adult heart is about 70 ml.
