Cardiac output is the volume of blood ejected by each ventricle per minute, averaging 4-6 L/min, and is influenced by heart rate and stroke volume. Key factors regulating stroke volume include preload, afterload, and contractility, with preload relating to the blood volume in the ventricle before contraction and afterload involving the resistance the heart must overcome to eject blood. Increases in preload result in higher cardiac output, while afterload is impacted by systemic vascular resistance and can be affected by conditions like hypertension and valve insufficiencies.

1. EXPLAIN THE CONCEPT
OF CARDIAC OUTPUT IN
RELATION TO PRELOAD
AND AFTERLOAD
MUHAMMAD ADNAN BIN SALIM
ADVANCED DIPLOMA CADIOVASCULAR
ADCV 2/2024(10)-0007

2. CARDIAC OUTPUT
 Volume of blood ejected by each ventricle
in each minute (volume/min)
 Averages between 4-6L/min
Comprises 2 vital components:
 Heart rate (beats/min): the number of
times the heart beats per minute
 Stroke volume (volume/beat): the
quantity of blood pumped out each ventricle
with every heartbeat.
CO = Stroke volume X heart rate
= 70 ml X 70 beats/min
= 4,900 ml/min
CO = SV x HR
70
70 beat/min
ml

3. STROKE VOLUME
 Around 70 ml in an average adult at rest
 End Diastolic Volume- The amount of blood in the
ventricle right before ventricular contraction
 End Systolic Volume- The amount of blood left in the
ventricle after before ventricular contraction
 3 primary factors that regulate SV
1) Preload
2) Afterload
3) Contractility
SV=EDV-ESV

5. PRELOAD
 is the amount of “stretch” your heart
has at its most full, right before it
empties
 end-diastolic volume
 Determined by the volume of blood in
left ventricle (LV) at end of diastole
 Increased volume –> increased preload
-> increased cardiac output (CO)
 Decreased volume –> decreased
preload –> decreased cardiac output
(CO)
More out
More in
 Preload   cardiac
output
(Starling-Frank Mechanism)

6. Factors Which Increase Preload
1. IV fluids
2. Blood
3. Vasoconstriction
Factors Which Decrease Preload
4. Diuretics
5. Dehydration
6. Hemorrhage
7. Vasodilation

7. AFTERLOAD
 is the pressure of heart has to overcome to eject the
blood
 systemic vascular resistance (SVR)
 It is the resistance against which the ventricles contract
 resistance to ventricular ejection - the "load" that the
heart must eject blood against
 As pressure increases, resistance increases, afterload
increases
 As pressure decreases, resistance decreases, afterload
decreases

8. Factors Which Increase Afterload
1. Systolic hypertension (HTN)
2. Pulmonary hypertension (PH)
3. Aortic insufficiency (Aortic Regurgitation)
Factors Which Increase Afterload
4. Mitral regurgitation (MR)

10. CONTRACTILITY
Force generated by the myocardium
when it contracts – inotropic property
Ejection fraction (EF) - percentage of LV
end-diastolic volume that is ejected with
each contraction
EF - normally approximately 50-55%