Cardiac output
Cardiac output refers to the amount of blood the heart pumps per minute. It's a key indicator of heart function and the body's ability to circulate oxygen and nutrients to tissues.
The formula for calculating cardiac output is:
Cardiac Output (CO)=Stroke Volume (SV)×Heart Rate (HR)
Where:
Stroke Volume (SV) is the volume of blood pumped out of the left ventricle with each heartbeat.
Heart Rate (HR) is the number of heartbeats per minute.
Key Points:
Normal Range:
Typically, the normal range for cardiac output is 4 to 8 liters per minute in adults.
In a healthy person, the stroke volume is usually around 60-100 milliliters per beat, and the heart rate is typically between 60 and 100 beats per minute.
Factors Influencing Cardiac Output:
Preload: The volume of blood returning to the heart (venous return).
Afterload: The resistance the heart has to overcome to pump blood.
Contractility: The strength of the heart's contractions.
Heart Rate: Higher heart rates generally increase cardiac output (up to a point).
Example:
If a person has a stroke volume of 70 mL and a heart rate of 75 beats per minute, their cardiac output would be:
CO=70 mL×75 bpm=5250 mL/min
(or) 5.25 L/min
Clinical Relevance:
Low Cardiac Output: Can be caused by heart failure, shock, or other conditions where the heart cannot pump effectively.
High Cardiac Output: May occur in conditions like fever, hyperthyroidism, or during exercise, where the body's demand for oxygen and nutrients increases.
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