If a person has a hea rate of 70 beats/min, a left ventricular end diastolic volume of 100 ml, and an ejectionfraction of 0.50, then the cardiac output is
**Question:** If a person has a heart rate of 70 beats/min, a left ventricular end diastolic volume of 100 ml, and an ejection fraction of 0.50, then the cardiac output is:
**Core Concept:** Cardiac Output (CO) is a measure of heart function and represents the amount of blood pumped by the heart per minute. It is calculated by multiplying heart rate (HR) with stroke volume (SV).
**Why the Correct Answer is Right:** To calculate cardiac output, we use the formula:
Cardiac Output (CO) = Heart Rate (HR) × Stroke Volume (SV)
In this case, the heart rate (HR) is 70 beats/min, and the stroke volume (SV) is determined by the ejection fraction (EF) multiplied by the left ventricular end diastolic volume (LVEDV). The ejection fraction is a measure of how efficiently the heart is pumping blood, calculated as the ratio of stroke volume to left ventricular end diastolic volume:
Ejection Fraction (EF) = (Left Ventricular End Diastolic Volume (LVEDV) / Left Ventricular End Diastolic Volume (LVEDV)) × 100
In this scenario, EF = (100 ml / 100 ml) × 100 = 50%
Stroke Volume (SV) = Ejection Fraction × Left Ventricular End Diastolic Volume (LVEDV)
SV = 0.50 × 100 ml = 50 ml
Now, we can calculate the cardiac output (CO):
CO = HR × SV = 70 beats/min × 50 ml = 3500 ml/min
**Why Each Wrong Answer is Incorrect:**
A. This answer is incorrect because it does not account for the stroke volume, which is crucial in calculating cardiac output.
B. This answer is incorrect because it uses a wrong formula (Cardiac Output = Heart Rate × Stroke Volume), which does not correctly reflect the relationship between HR, SV, and CO.
C. This answer is incorrect because it uses a wrong formula (Cardiac Output = Heart Rate × Ejection Fraction × Stroke Volume), which does not correctly reflect the relationship between HR, SV, and CO.
D. This answer is incorrect because it uses a wrong formula (Cardiac Output = Heart Rate × Stroke Volume × Ejection Fraction), which does not correctly reflect the relationship between HR, SV, and CO.
**Clinical Pearl:**
Cardiac Output is a crucial parameter to assess the cardiac function and reserve capacity. A normal cardiac output is considered to be around 5-6 L/min. A low cardiac output indicates decreased cardiac function, while a high cardiac output suggests increased cardiac function or compensatory mechanisms like tachycardia.