Abstract
A blind source signal separation problem that was brought to a Study Group in Limerick in 2013 required a way to prevent the gait of a jogger from masking the heartbeat, when detected by a simple photodiode that measures light transmission through a jogger’s wrist tissues. The group was successful in discovering a singular value decomposition (SVD) approach, which not only allows accurate detection of heart rate but also allows recovery of a good facsimile of the entire blood pressure time series from the mixed photodiode signal.
Highlights
We consider a blind source signal separation problem that was brought to the European Study Group with Industry held in June 2013 at the University of Limerick
The first effect is due to varying blood pressure, which causes a pulsatile2 perfusion of body tissues, a pulsatile variation in the absorption of the light that travels from skin through tissue to the photodiode
In the remainder of this paper, we will indicate how we overcame the shortcoming of there being no data available by creating an ersatz set of data incorporating two sources, we discuss embedding our ersatz data in a high dimensional phase space, and we show how the use of singular value decomposition (SVD) can prevent the gait source from masking heart rate, but how we can recover a remarkably good facsimile of the original blood pressure source
Summary
We consider a blind source signal separation problem that was brought to the European Study Group with Industry held in June 2013 at the University of Limerick. A very simple heart rate monitor was considered, based on a single wrist device similar to that pictured in Fig. 1 that does not require a separate transmitting chest band. The first effect is due to varying blood pressure, which causes a pulsatile perfusion of body tissues, a pulsatile variation in the absorption of the light that travels from skin through tissue to the photodiode. The second effect, which masks the first, is due to the gait of a person, walking or running perhaps, moving the wrist and causing the light levels incident upon the skin to vary rhythmically. The periods of these two effects are usually very close. Running gait may be three times as fast, and running heart rate is usually similar to gait at about 180 beats per minute
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