1. What is Cardiac
Output?
- Cardiac
Output (CO) is the amount of blood pumped by each ventricle in one minute.
- It
reflects the efficiency of the heart as a pump.
2. Formula for Cardiac
Output
Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)\text{Cardiac
Output (CO)} = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}
Normal values:
- Stroke
Volume (SV) ≈ 70 mL/beat
- Heart Rate
(HR) ≈ 72 beats/min
- CO = 70 × 72
= ~5 Liters/min
3. Stroke Volume (SV)
- The amount
of blood ejected by one ventricle in one beat.
- SV = End-Diastolic
Volume (EDV) – End-Systolic Volume (ESV)
➤ SV ≈ 120 mL – 50 mL = ~70 mL
4. Factors Affecting
Cardiac Output
A. Preload:
- Volume of
blood in ventricles at end of diastole.
- More
preload = more stretch = more output (Frank-Starling law).
B. Afterload:
- Resistance
against which the heart pumps (mainly blood pressure).
- Higher
afterload = lower CO.
C. Contractility:
- Force of
contraction of heart muscles.
- Increased
by sympathetic stimulation, calcium, adrenaline.
D. Heart Rate:
- Increased
HR = ↑ CO (but very high HR can decrease CO due to less filling time).
5. Regulation of
Cardiac Output
|
Type |
Examples |
|
Neural |
Sympathetic (↑ CO), Parasympathetic (↓ CO) |
|
Hormonal |
Adrenaline, noradrenaline (↑ CO) |
|
Intrinsic |
Frank-Starling mechanism |
6. Measurement of
Cardiac Output
- Fick’s
Principle
- Dye
Dilution Method
- Echocardiography
(Doppler)
7. Clinical
Significance
- Low CO: Heart
failure, shock, blood loss
- High CO: Fever,
anemia, hyperthyroidism
- Useful in ICU
monitoring and evaluating heart diseases
Mnemonic for Factors
Increasing CO
"FANS"
- Fever
- Adrenaline
- Nervous
system (sympathetic)
- Stroke volume increase
Tags
ANATOMY