Metabolic Cart - Practice Flashcards

Flashcards to review metabolic cart concepts: what it is, how it works, calibration, VO2/RER/RQ, energy expenditure, and interfaces.

What is a metabolic cart and what does it measure?

A metabolic cart is a system (with a gas analyzer and flow meter) connected to the subject via a mask or mouthpiece. It analyzes inspired and expired gases to measure ventilation, oxygen uptake (VO2), carbon dioxide output (VCO2), and from these derive energy expenditure and substrate utilization (carbs versus fats).

Why do we use a metabolic cart?

To quantify oxygen consumption (VO2), energy expenditure, and substrate utilization, which informs health, fitness, performance, and disease risk assessments.

What are calibration gas and reference gas used for?

Calibration gas tests the gas analyzer’s accuracy; reference gas represents known composition similar to room air and helps validate readings; some labs use room air for reference.

How is the subject connected to the cart?

Through a mask (or mouthpiece) connected by a pneumatic to the cart; a nose clip is often used to prevent nasal air leaks and ensure all air passes through the mask.

What is absolute VO2?

VO2 expressed in liters per minute (L/min) or milliliters per minute (mL/min) without adjusting for body weight; not ideal for comparing individuals of different sizes.

What is relative VO2?

VO2 expressed per kilogram of body weight per minute (mL·kg^-1·min^-1); allows fair comparisons of aerobic fitness across people of different sizes.

How do you convert absolute VO2 to relative VO2?

Convert L/min to mL/min (multiply by 1000) and divide by body weight in kg: VO2(rel) = (VO2(abs) × 1000) / weight(kg).

What is VO2 max?

The greatest amount of oxygen the body can consume and utilize during maximal exertion; a primary measure of aerobic capacity.

Why is VO2 max important for endurance performance?

Endurance performance generally improves with higher VO2 max; a high VO2 max is often a prerequisite for world-class endurance performance, though many other factors also matter.

What is RER?

Respiratory exchange ratio (RER) = VCO2 / VO2; used to estimate substrate utilization and typically ranges from about 0.70 to 1.0, but can exceed 1.0 after intense exercise.

What is RQ?

Respiratory quotient; the cellular-level ratio of CO2 produced to O2 consumed (VCO2/VO2). RER approximates RQ under stable rest conditions.

How are RER and RQ calculated?

Both are calculated as VCO2 divided by VO2; RER is measured at the mouth and reflects systemic gas exchange, while RQ reflects cellular metabolism.

What do RER values of 0.70 and 1.0 indicate?

0.70 indicates predominantly fat oxidation; 1.0 indicates predominantly carbohydrate oxidation; values in between indicate a mix of substrates.

Why can RER exceed 1.0 after intense exercise?

Non-metabolic CO2 from lactate buffering increases VCO2, raising the ratio even though carbohydrate oxidation cannot exceed 100%. Follow-up through recovery can keep RER >1 briefly.

What is indirect calorimetry?

Estimating energy expenditure by measuring O2 consumption and CO2 production rather than directly measuring heat output.

What is open circuit spirometry?

The subject breathes room air; the cart measures the concentrations of O2 and CO2 in inhaled and exhaled air via open circuitry.

What are the core components of a metabolic cart besides the computer?

Gas analyzer and flow meter (plus the body interface such as a mask or mouthpiece connected via pneumatics).

What is the function of the gas analyzer?

To measure the concentrations of O2 and CO2 in the air returning from the subject.

What is the function of the flow meter?

To measure the volume of air flowing per unit time through the system.

What is the purpose of the three-liter syringe?

A known-volume standard used to calibrate the flow meter by drawing/pushing exactly three liters of air.

What is the honeycomb in the pneumatic connector for?

To smooth turbulent airflow into laminar flow; the honeycomb must face inward toward the mask to work correctly.

What is an umbilical clip in this setup?

A connector that links the pneumatic line to the system and to the gas analyzer during calibration and sampling.

What were Douglas bags used for historically?

An early method of measuring O2 consumption by collecting expired air in large bags and analyzing it later; predated metabolic carts.

Why calibrate the cart before testing?

To ensure gas analyzer and flow meter readings are accurate and within manufacturer-specified ranges; calibration also provides a data log for audit trails.

What environmental data is needed for calibration?

Ambient air temperature, humidity, and barometric pressure must be entered so readings can be corrected.

How is the body interface set up for accurate measurement?

A snug mask (or mouthpiece) over the mouth and nose, often with a nose clip, secured so no air leaks occur and all air passes through the cart.

How is energy expenditure estimated from VO2 (roughly)?

Energy expenditure ≈ VO2 (L/min) × 5 kcal/L of O2; more precise estimates use ~4.82–4.83 kcal/L depending on diet.