Numerical/problem-solving

1. TITLE

How to solve Cardiac Output calculations in NEET — Step-by-step

2. PROBLEM TYPE INTRO 

This is a standard physiological calculation from the Body Fluids and Circulation chapter. You will need to calculate the volume of blood pumped by the heart per minute using the heart rate and stroke volume. The formula required is Cardiac Output = Stroke Volume × Heart Rate. The most typical mistake students make is forgetting to convert the final answer from milliliters (mL) to Liters (L).

3. MCQ 

Question:
An athlete has a resting Heart Rate (HR) of 60 beats per minute. Due to training, their Stroke Volume (SV) is 90 mL per beat. What is their Cardiac Output (CO)?

(A) 54 L/min
(B) 5.4 L/min
(C) 540 mL/min
(D) 1.5 L/min

4. STEP-BY-STEP SOLUTION

SOLUTION

Given:
* Heart Rate (HR) = $60 \text{ beats/min}$
* Stroke Volume (SV) = $90 \text{ mL/beat}$

To Find:
* Cardiac Output (CO) in L/min

Formula:

$$CO = SV \times HR$$


Use this formula when you are given the volume pumped per beat and the number of beats per minute to find the total volume pumped per minute.,

 

Step 1: Substitute the values into the formula

$$CO = 90 \text{ mL} \times 60 \text{ beats/min}$$

 

Step 2: Perform the multiplication

$$CO = 5400 \text{ mL/min}$$

 

Step 3: Convert the unit from milliliters to Liters
Since $1 \text{ Liter} = 1000 \text{ mL}$, divide the value by 1000.

$$CO = \frac{5400}{1000} \text{ L/min}$$

 

$$CO = 5.4 \text{ L/min}$$

 

Answer: (B) 5.4 L/min

5. WHERE STUDENTS GO WRONG

List of common mistakes:
* ❌ Mistake 1: Forgetting unit conversion. Students often calculate $5400$ and select an option like "54 L" or leave it as mL when the options are in Liters. Always check if the options are in mL or L.
* ❌ Mistake 2: Confusing Stroke Volume with Cardiac Output. Remember, Stroke Volume is per beat ($~70 \text{ mL}$), while Cardiac Output is per minute ($~5000 \text{ mL}$ or $5 \text{ L}$),.
* ❌ Mistake 3: Calculation errors with zeros. Multiplying $60 \times 90$ can sometimes lead to missing a zero (getting $540$ instead of $5400$).

6. QUICK FORMULA REFERENCE

Formulas Used:

  • Formula 1: $CO = SV \times HR$ — Use to find total blood pumped per minute.
  • Formula 2: $SV = \frac{CO}{HR}$ — Use if Cardiac Output is given and you need to find Stroke Volume.

7. SIMILAR PROBLEM HINT

"If NEET changes the values, the method stays the same. Practice with standard values: A healthy individual has a Heart Rate of 72 beats/min and a Stroke Volume of 70 mL. The CO should be approximately 5000 mL or 5 L.",

8. NCERT REFERENCE

Based on: NCERT Class 11, Chapter 15 (Body Fluids and Circulation), Section 15.3.2

9. CTA

More solved numericals → Human Physiology Guide
Practice problems → Mock exams