2.3 - Metrology in Metabolic Measurements

Metrology in Metabolic Measurements

Wireless Health 2012

Jon K. MoonMEI Research, Ltd


Metabolic Energy Balance

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Measuring Energy Metabolism

• Direct measures– Respiratory gas exchange– Stable isotope exchange

• Less direct (proxy) measures– Heart rate– Heat flux– Motion

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Respiratory gas exchange

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Stable isotope exchange(doubly labeled water – DLW)

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Physiologic and motion sensors

ActivityHeart Rate

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Defined Activity Patterns

Heart Rate

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Measuring Energy ExpenditureRoom

CalorimeterDLW Metabolic

CartPortable

Gas System

Physiologic Monitors

Repeatability 2% 6% 5 – 11% ≥ MC ?Accuracy 2 – 4% 4 – 20% 10 – 20% ? < MC

Resolution (min)

2 – 15 4400 1 1 1

Quality System

Reference

ISO IAEAISO

None None None

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Measuring Energy ExpenditureRoom

CalorimeterDLW Metabolic

CartPortable

Gas System

Physiologic Monitors

Repeatability 2% 6% 5 – 11% ≥ MC ?Accuracy 2 – 4% 4 – 20% 10 – 20% ? ≥ 7%

Resolution (min)

2 – 15 4400 1 1 1

Quality System

Reference

ISO IAEAISO

None None None

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Validation is not Calibration

• Compare to another system

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Validation

• Check against representative source of measurand

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Validation

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Validation is not Calibration

But calibration alone isn’t the solution either


Training

Records

Methods

Equipment

Reviews

Traceability

Standards

Quality System

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Adopt Quality System

• Create calibration process– Identify and obtain standards– Develop calibration procedure and initial interval

• Train users / operators• Maintain records • Regular audit and review of records for

adjustments

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ISO/IEC 17025:2005General Requirements for the Competence of

Testing and Calibration Laboratories

• Management System• “document policies, systems, programmes, procedures and instructions to the

extent necessary to assure the quality of the test and/or calibration results”

• Technical Requirements– Personnel (5.2) Training– Test and Calibration Methods and Method Validation (5.4)– Equipment (5.5)– Assuring the Quality of Test and Calibration Results(5.9)– Reporting Results (5.10) Documentation– Review System

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Training

Records

Methods

Equipment

Reviews

Traceability

Standards

Quality System

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Metrology

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Metrology for Calibration

• Metrology is the ‘science’ of measurements. We apply it to develop calibration techniques.

1. Determine what components of a system need to be calibrated

2. Identify standard that has better certainty than the unit under test

3. Determine required calibration interval

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Creating Calibration

• Methods calibrate all measurement points in the “device under test” (DuT)

• 4:1 accuracy (measurement uncertainty) ratio between calibration and DuT

• Calibration instruments need traceability to accepted and available standard

• Calibration instruments become DuT for certification

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Respiratory exchange calibration with piston prover and pure gas

blender

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Multi-axis Acceleration Calibrators

Rate Table Positioner

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Wireless Health 201223-10-2012

Wilbur Olin Atwaterand the Calorimeter at Wesleyan

My hero


Training

Records

Methods

Equipment

Reviews

Traceability

Standards

Quality System

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ISO/IEC 17025:2005 Traceability (5.6)

• ISO Measurement Traceability 5.6.2.1– “the programme for calibration of equipment shall be designed

and operated so as to ensure that calibrations and measurements made by the laboratory are traceable to the International System of Units (SI) (Système international d'unités). ”

– “establishes traceability of its own measurement standards and measuring instruments to the SI by means of an unbroken chain of calibrations or comparisons linking them to relevant primary stands of the SI units of measurement. The link to SI units may be achieved by reference to national measurement standards.

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Traceability Pathway for Respiratory Gas Exchange

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Why are only room calorimeters under a laboratory quality system?

• Large and expensive• Permanent• Users fully informed

on design and details of operation

• PI and key staff remain engaged and are responsible for performance

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• Calibration points are obvious and available

• Instruments are treated well

• Economy of scale for calibration and quality system

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Why are only room calorimeters under a laboratory quality system?


You can calibrate a cart

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If the manufacturer makes provision


We don’t truly calibrate metabolic carts and portable devices, so

• There is no assurance of accuracy that comes from proven calibration, maintenance, or operation

• They can’t serve as reference methods to calibrate other devices

• We should avoid pooling data between labs, devices or over time

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Why don’t we calibrate?

• Manufacturer’s don’t provide appropriate means for traceable calibration – because no one asked them

• Users don’t have the time, $, knowledge or interest.

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We could Calibrate

• Introduce metrology and quality systems to physiologic research

• Provide recommendations on procedures and standards

• Make calibration instruments, services and expertise affordable and available

• Establish expectations for peer review and project funding

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Training

Records

Methods

Equipment

Reviews

Traceability

Standards

Quality System

23-10-2012

Jon K. Moon, PhDMEI Research, LtdSt Louis Park, MN

[email protected]

mailto:[email protected]

2.3 - Metrology in Metabolic Measurements

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