The formula for calculating cardiac output is

Appeared in: UPPSC 2022

Explanation

Cardiac Output (CO) is the volume of blood the heart pumps in one minute, a critical measure of cardiovascular performance.
It is calculated by multiplying the Stroke Volume (SV), the amount of blood pumped per beat, by the Heart Rate (HR), the number of beats per minute.
The formula CO = SV × HR is a fundamental principle in cardiovascular physiology.
A normal resting cardiac output for an adult is approximately 4 to 8 liters per minute.

Option A: Respiratory rate measures breaths per minute, a parameter of the respiratory system, not the cardiovascular system's output.
Option B: Both respiratory rate and reserve volume are parameters used in pulmonary function tests to evaluate lung capacity and efficiency.
Option C: Blood pressure is the product of cardiac output and systemic vascular resistance (BP = CO × SVR). It is an outcome of cardiac function, not a direct component in calculating CO with stroke volume.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Formula for Cardiac Output as background academic context rather than a clinical decision trigger.
Monitoring cardiac output is essential in critically ill patients, especially those in shock, heart failure, or post-cardiac surgery, to guide fluid and medication therapy.
A nurse observing signs of low cardiac output (e.g., low urine output, cool extremities, confusion) must report them immediately as it indicates poor tissue perfusion.
What if? If a patient's heart rate suddenly drops to 40 bpm (bradycardia) but their stroke volume remains 70 mL, their cardiac output would plummet to 2.8 L/min (40 x 70), likely causing symptoms of shock. The nurse's priority would be to assess the patient and notify the provider for intervention.

How to Approach the Question

First, identify the core concept of the question, which is the 'formula for cardiac output'.
This is a factual recall question. Access your knowledge of basic cardiovascular physiology.
Define each term in your head: Cardiac Output (blood/min), Stroke Volume (blood/beat), and Heart Rate (beats/min).
Logically connect the terms: To get the total volume per minute, you must multiply the volume per beat by the number of beats per minute.
Evaluate the options based on this logic. Eliminate options that mix cardiovascular and respiratory terms (A, B) or misuse related concepts like blood pressure (C).

Concept Tested & Keywords

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E6 Nursing Fundamentals Potter Perry 12e Part 4 p. 231-233

E6 Physiology Ganong 27e Vol 2 Part 1 p. 91-93

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 683-685

Practise the full UPPSC 2022

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