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Adaptive Cancelation of Motion Artifact in Photoplethysmographic Blood Volume Pulse Measurements for Exercise Evaluation

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"Adaptive Cancelation of Motion Artifact in Photoplethysmographic Blood Volume Pulse Measurements for Exercise Evaluation", (1995)
Barreto, A. B., Vicente, L. M., Persad, I. K.

ABSTRACT: An adaptive transversal filter was designed to minimize the impact of motion artifact in the measurement of photoplethysmographic Blood Volume Pulse (BVP) in an exercising subject. The rationale of the design is introduced and results from off-line testing with signals recorded from an experimental setup are presented.

Finger photoplethysmography is a form of noninvasive monitoring that offers some remarkable advantages. The principle behind this technique is that the amount of blood in the capillaries of the finger at any given time can be indirectly measured by the amount of infrared radiation sensed by a phototransistor after being emitted by a constant source and reflected in the finger. In spite of its monitoring potential, the applicability of photoplethysmographic BVP measurements to the evaluation of cardiovascular changes during an exercise session has been limited by the presence of motion artifacts in BVP signals measured from exercising subjects. Most of the indices derived from the BVP waveform and designed to reflect its change through an exercise and recovery session, are severely distorted by the motion artifact that arises in the condition described above. Elimination of the motion artifact through fixed filtering techniques is not advisable due to both the in-band nature of the interference (overlapping the most important spectral components of the signal), and its frequency variations according to the exercise pace. We have hypothesized that the motion artifact interferes with the true BVP signal in a predominantly additive fashion. As such, the application of an adaptive noise canceler is a viable approach for the reduction of the interference. Application of an adaptive noise canceler requires the availability of a "noise reference signal", correlated with the additive noise polluting the signal of interest. We propose that a suitable reference signal can be obtained directly from the mechanical elements of the exercise apparatus.