Gravity Compensation Method for Combined Accelerometer and Gyro Sensors Used in Cardiac Motion Measurements
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A miniaturized accelerometer fixed to the heart can be used for monitoring of cardiac function. However, an accelerometer cannot differentiate between acceleration caused by motion and acceleration due to gravity. The accuracy of motion measurements is therefore dependent on how well the gravity component can be estimated and filtered from the measured signal. In this study we propose a new method for estimating the gravity, based on strapdown inertial navigation, using a combined accelerometer and gyro. The gyro was used to estimate the orientation of the gravity field and thereby remove it. We compared this method with two previously proposed gravity filtering methods in three experimental models using: (1) in silico computer simulated heart motion; (2) robot mimicked heart motion; and (3) in vivo measured motion on the heart in an animal model. The new method correlated excellently with the reference (r 2 > 0.93) and had a deviation from reference peak systolic displacement (6.3 ± 3.9 mm) below 0.2 ± 0.5 mm for the robot experiment model. The new method performed significantly better than the two previously proposed methods (p < 0.001). The results show that the proposed method using gyro can measure cardiac motion with high accuracy and performs better than existing methods for filtering the gravity component from the accelerometer signal.
KeywordsCardiac monitoring Motion sensing Ischemia detection Bio signal processing
Gravity compensation method using gyro
Gravity compensation method using circle estimation
Gravity compensation method using static gravity estimation
The research leading to these results were funded by South-Eastern Norway Regional Health Authority [Project Number 2014076]. We thank the staff at the Intervention Center, Oslo University Hospital for support during the animal study.
Conflict of interest
Elle and Halvorsen are patent holders of the accelerometer technology for assessment of cardiac function and together with Krogh, Hoff and Remme share-holders in Cardiaccs A/S.
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