Cardiac output is determined by-

RUHS, Jaipur, PB B.Sc Nursing Entrance-2022

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2022

Explanation

Cardiac output (CO) is defined as the total volume of blood the heart pumps in one minute, indicating the efficiency of blood circulation.
It is calculated by multiplying two key factors: the heart rate (HR), which is the number of beats per minute, and the stroke volume (SV), which is the amount of blood ejected with each beat.
The definitive formula is CO = HR × SV.
Therefore, to determine the cardiac output, one must know both the heart rate and the stroke volume.

Option A: Heart rate alone is insufficient. It only measures the frequency of heartbeats, not the volume of blood being moved. For example, a very fast heart rate can actually decrease cardiac output if there isn't enough time for the ventricles to fill, thus reducing stroke volume.
Option B: Stroke volume alone is insufficient. It only measures the volume of blood per contraction, not the total volume pumped over a minute. A large stroke volume with a very slow heart rate (bradycardia) might result in a low cardiac output.
Option C: Blood flow is a consequence of cardiac output and peripheral vascular resistance (Flow = Pressure/Resistance). It describes the movement of blood within the vessels but does not determine the heart's output itself.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Determinants of Cardiac Output as background academic context rather than a clinical decision trigger.
Monitoring cardiac output is crucial in critical care settings to assess a patient's hemodynamic status, especially in conditions like heart failure, shock, and after major surgery.
A low cardiac output signifies that the body's tissues may not be receiving adequate oxygen and nutrients, leading to organ dysfunction.
Treatments for low cardiac output can target either heart rate (e.g., pacemakers) or stroke volume (e.g., fluids to increase preload, inotropes to increase contractility).

How to Approach the Question

This is a factual recall question that tests your knowledge of a fundamental cardiovascular formula.
First, define the term in the question: 'Cardiac output' is the volume of blood pumped by the heart in one minute.
Next, break down how this volume is generated. The heart pumps a certain amount of blood with each beat (stroke volume) and it beats a certain number of times each minute (heart rate).
Logically conclude that the total output per minute must be the volume per beat multiplied by the number of beats per minute.
Evaluate the options based on this conclusion. 'Heart rate' and 'Stroke volume' are individual components. 'Blood flow' is a related but distinct concept.
Select the option that correctly combines the two necessary components: 'Heart rate & Stroke volume'.

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