Quality Assurance of Modular Metabolic Systems

Measure Metabolic Rate Device

Alternatives’ Sources of Error:

O2 sensor errors
Water vapor (humidity)
Ventilation sensor errors
Timing delays (Breath by Breath, also Mixing chamber) • Gas sample bore compromise (Breath by breath)
Breathing valves (resistance)?
CO2 sensor errors
Calibration gas errors (Beta/Gama gases)
Douglas bag leaks, non-Brownian motion errors.
Temperature and pressure errors

System type comparison:

1. Breath by Breath

Easier on the subject (small sample line)
Potential for VO2 kinematics (individualised – NOT done!)
However misalignment of VE and Fe critical! ( instantaneously multiplied – large errors)
Signal very noisy and needs averaging
Averaging devalues the system.
Subject to more errors than Douglas Bag or Mixing Chamber
Gas concentration vs flow time delay items:
- Tubing is crimped (undetectable)
- Tubing length changed (less likely)
- Gas sampling rate changed (less likely)
- Water vapour in the lumen (decrease sample line)
- Calibration procedures should allow for regular re-alignment. It doesn’t / Users don’t know how.
Large data variability – one breath to the next
Complex averaging algorithms and timing corrections – making validation difficult
Less consistent data when compared to Mixing Chamber systems
All points validated in papers: Gore et. al Beck et. al. Proctor et. al.,etc.

2. Mixing chamber systems (Mr. Phil Loeb, AEI)

Mixing Chamber advantages
- Every breath is recorded
- O2 and CO2 data is accurately synchronized to each breath
- Very consistent data from one breath to the next •VO2 and VCO2 calculations utilize simple textbook formulas
- Accurate VO2 and VCO2 data as validated by Douglas Bags and ‘First Principles’ Simulators

Mixing Chamber disadvantages
- A thicker sampling hose
- etO2 and etCO2 measurements need additional analyzers

3. A.I.S Metabolic Cart (Mr. Jamie Plowman – A.I.S.) – The best of all worlds “Automated Douglas Bags”

Sources of Error:

O2 sensor errors
Water vapour (humidity)
Ventilation sensor errors
Timing delays (Breath by Breath, also Mixing chamber) • Gas sample bore compromise (Breath by breath)
Breathing valves (resistance)?
CO2 sensor errors
Calibration gas errors (Beta/Gama gases)
Douglas bag leaks, non-Brownian motion errors.
Temperature and pressure errors

System type comparison:

1. Breath by Breath

Easier on the subject (small sample line)
Potential for VO2 kinematics (individualised – NOT done!)
However misalignment of VE and Fe critical! ( instantaneously multiplied – large errors)
Signal very noisy and needs averaging
Averaging devalues the system.
Subject to more errors than Douglas Bag or Mixing Chamber
Gas concentration vs flow time delay items:
- Tubing is crimped (undetectable)
- Tubing length changed (less likely)
- Gas sampling rate changed (less likely)
- Water vapour in the lumen (decrease sample line)
- Calibration procedures should allow for regular re-alignment. It doesn’t / Users don’t know how.
Large data variability – one breath to the next
Complex averaging algorithms and timing corrections – making validation difficult
Less consistent data when compared to Mixing Chamber systems
All points validated in papers: Gore et. al Beck et. al. Proctor et. al.,etc.

2. Mixing chamber systems (Mr. Phil Loeb, AEI)

Mixing Chamber advantages
- Every breath is recorded
- O2 and CO2 data is accurately synchronized to each breath
- Very consistent data from one breath to the next •VO2 and VCO2 calculations utilize simple textbook formulas
- Accurate VO2 and VCO2 data as validated by Douglas Bags and ‘First Principles’ Simulators

Mixing Chamber disadvantages
- A thicker sampling hose
- etO2 and etCO2 measurements need additional analyzers

3. A.I.S Metabolic Cart (Mr. Jamie Plowman – A.I.S.) – The best of all worlds “Automated Douglas Bags”