Posts Tagged ‘Validation’

Having used Shimmer in their studies in conjunction with the TRIL (Technology for Independent Living) centre, Intel has recently published a paper on the validation of the Shimmer ECG, Motion, and GSR daughter cards. The operation of the Shimmer baseboard and daughter cards has been tested through a number of validation processes to determine the accuracy of the boards’ function and their usefulness for biomedical-orientated research applications.

ECG Validation

A number of tests were carried out to validate the Shimmer ECG daughter card as a valid tool for acquiring ambulatory ECG. The tests included the validation of the ECG amplifier and ADC performance by using calibrated input signals as well as an ECG recording from a healthy non-resting subject. Another test carried out was a 5.9 minute ECG recording containing 503 heart beats from a non-resting healthy subject during a moderate walk. The information was captured by the Shimmer ECG and also captured by a Medilog Holter monitoring system. The results indicate that the Shimmer ECG can be used to acquire ambulatory ECG from resting and non-resting human subjects for research application purposes.

Kinematic Validation

To validate the Shimmer platform for use in studies of human gait analysis, temporal gait parameters derived from a tri-axial gyroscope on the Shimmer platform were compared against those acquired simultaneously, by using the codamotion analysis system from Charnwood Dynamics Ltd., UK.

The gait of one normal healthy adult male (age 25) was measured simultaneously by using two Shimmer sensors placed on each shank and the Cartesian Optoelectronic Dynamic Anthropometer (CODA) motion analysis system. Data was recorded whilst the subject performed multiple over-ground walking and running trials along a 15-meter walkway in a motion analysis laboratory. Heel strike and toe-off characteristic points derived from the Shimmer and CODA systems were used to calculate the three temporal gait parameters listed below:

• Stride time
• Stance time
• Swing time

Results show an intraclass correlation coefficient (ICC(2,k)) [64] greater than 0.85 in stride, swing, and stance times for ten walking trials and four running trials. These results suggest that the Shimmer platform is a versatile cost-effective tool for use in temporal gait analysis.

GSR Validation

The Shimmer galvanic skin response (GSR) sensor contains an internal resistor network that works as a potential divider and provides a voltage that can be converted by the Shimmer’s ADC to a 12-bit value, used to measure external skin resistance. All skin resistance values were calculated in the Shimmer platform firmware and transmitted to a BioMOBIUS patch for real-time display and persistence to file. The sensor performance was correlated with a commercial Nexus-10 system (Mind Media BV) utilizing a series of known resistors from 10K Ω to 2.2M Ω. Shimmer GSR demonstrated an average mean percentage error of 2.3 percent versus the commercial Nexus-10 that had an average mean error of 4.1 percent.