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Wireless Health 2012
Measuring Energy Metabolism
• Direct measures– Respiratory gas exchange– Stable isotope exchange
• Less direct (proxy) measures– Heart rate– Heat flux– Motion
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
Training
Records
Methods
Equipment
Reviews
Traceability
Standards
Quality System
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
Training
Records
Methods
Equipment
Reviews
Traceability
Standards
Quality System
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
Respiratory exchange calibration with piston prover and pure gas
blender
23-10-2012
Wireless Health 2012
Training
Records
Methods
Equipment
Reviews
Traceability
Standards
Quality System
23-10-2012
Wireless Health 2012
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.
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
• Calibration points are obvious and available
• Instruments are treated well
• Economy of scale for calibration and quality system
23-10-2012
Why are only room calorimeters under a laboratory quality system?
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
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.
23-10-2012
Wireless Health 2012
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
23-10-2012
Wireless Health 2012
Training
Records
Methods
Equipment
Reviews
Traceability
Standards
Quality System
23-10-2012