In a measurement of cardiac output using the Fick principle, the O2 concentrations of mixed venous and aerial blood are 16 and 20 ml/min, respectively and the O2 consumption is 300 ml/min, The cardiac output in liters/ min is:
**Core Concept**
The Fick principle is a method used to measure cardiac output by calculating the difference in oxygen consumption between arterial and mixed venous blood. This principle is based on the concept of oxygen extraction ratio, which is the ratio of oxygen consumed by the tissues to the oxygen delivered by the blood. The formula for cardiac output using the Fick principle is: Cardiac Output (CO) = O2 consumption / (Arterial O2 concentration - Mixed Venous O2 concentration).
**Why the Correct Answer is Right**
To calculate cardiac output using the Fick principle, we need to use the formula: CO = O2 consumption / (Arterial O2 concentration - Mixed Venous O2 concentration). Given that the O2 consumption is 300 ml/min, the arterial O2 concentration is 20 ml/100ml, and the mixed venous O2 concentration is 16 ml/100ml, we can plug in these values to calculate the cardiac output. First, we need to convert the O2 concentrations from ml/100ml to ml/min. The arterial O2 concentration is 20 ml/100ml, which is equivalent to 2 ml/min (20 x 100 = 2000 ml/min, but we are considering the concentration for 100 ml of blood. Hence 2 ml of O2 per 100 ml of blood is equivalent to 0.02 ml of O2 per ml of blood. Since the O2 consumption is 300 ml/min, 300 ml of blood is being consumed per minute. Therefore, the arterial O2 concentration is 6 ml/min (300 x 0.02 = 6). Similarly, the mixed venous O2 concentration is 16 ml/100ml, which is equivalent to 1.6 ml/min (16 x 100 = 1600 ml/min, but we are considering the concentration for 100 ml of blood. Hence 1.6 ml of O2 per 100 ml of blood is equivalent to 0.016 ml of O2 per ml of blood. Since the O2 consumption is 300 ml/min, 300 ml of blood is being consumed per minute. Therefore, the mixed venous O2 concentration is 4.8 ml/min (300 x 0.016 = 4.8). Now, we can use the formula to calculate the cardiac output: CO = 300 / (6 - 4.8) = 300 / 1.2 = 250.
**Why Each Wrong Option is Incorrect**
**Option A:**
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**Option B:**
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**Option C:**
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**Clinical Pearl / High-Yield Fact**
The Fick principle is a reliable method for measuring cardiac output, but it requires accurate measurement of oxygen consumption and oxygen concentrations in arterial and mixed venous blood. It's essential to consider the oxygen extraction ratio, which is a critical parameter in this calculation.
**Correct Answer:** . 250