Motion insensitive pulse detector

DETAILED DESCRIPTION Motion artifact is a significant problem in making accurate physiological measurements related to the cardiac cycle because the frequency range of the cardiac cycle signal overlaps with the frequency range of the motion or other interference.
One novel feature of the invention is that it can sense a patient's pulse in the presence of patient motion or other interference.
The invention capitalizes on the nonlinear elasticity of the artery to encode relatively low frequency pulse signal information into the propagation velocity of a relatively high frequency excitation signal.
Since the pulse signal information is encoded in the high frequency excitation signal, the low frequency motion artifact can be removed by filtering, leaving the high frequency signal unaffected.
The low frequency pulse signal information can then be reconstructed from the high frequency excitation signal.
This is what is called determining the patient's pulse: constructing the pulse signal from the noninvasive sensor signal by removing interference.
It is noted that motion artifact is not the only source of interference to which the invention is insensitive.
The invention is insensitive to any source of interference that lies outside the frequency bandwidth of the carrier frequency including electrical interference, vibration, acoustic noise or other electrical or mechanical sources of interference.
It is also insensitive to interference that lies within the carrier bandwidth, so long as the interference is not correlated with the carrier.
This insensitivity derives from the ability to use correlation techniques such as phase-sensitive detection and lock-in amplification to detect the information encoded on the carrier while rejecting uncorrelated interference.
The invention can be used in a number of different ways.
It can be used as a stand-alone pulse monitor that provides a physician with raw information regarding the patient's pulse.
It can be used as a stand-alone pulse monitor that provides a physician with processed information regarding the patient's pulse