Respiratory Quotient

What is this formula?

The Respiratory Quotient (RQ) is the ratio of carbon dioxide produced to oxygen consumed during metabolism. It provides information about which macronutrients are being oxidized for energy.

When to use it

Use this formula when evaluating metabolic substrate utilization, indirect calorimetry measurements, exercise physiology, nutrition studies, and respiratory metabolism.

Example

A subject consumes oxygen at a rate of 0.30 L/min and produces carbon dioxide at a rate of 0.24 L/min.

Data:

VCO2 = 0.24 L/min

VO2 = 0.30 L/min

Formula:

RQ = VCO2 / VO2

Substitution:

RQ = 0.24 / 0.30

RQ = 0.80

Result:

Respiratory quotient = 0.80

This value suggests that fat oxidation predominates, although carbohydrate metabolism also contributes.

Applications

- Indirect calorimetry

- Clinical nutrition

- Exercise physiology

- Metabolic studies

- Respiratory physiology

- Critical care monitoring

- Energy expenditure assessment