Patent ID: 8165662

Claim:
A medical device for sensing cardiac events, comprising: a plurality of electrodes sensing cardiac signals utilized to identify a cardiac event; a plurality of light sources capable of emitting light at a plurality of wavelengths, the plurality of light sources comprising a first light source emitting light at an isobestic wavelength and a second light source emitting light at a non-isobestic wavelength; a detector to detect the light emitted by the plurality of light sources; and a processor to determine a plurality of light measurements in response to the emitted light detected by the detector, to determine an isobestic blood volume index in response to determined light measurements corresponding to the light emitted by the first light source, determine a non-isobestic blood volume index corresponding to a non-isobestic wavelength in response to a product of a scaling factor and the determined isobestic blood volume index, the scaling factor being dependent on optical properties of blood, a distance between the second light source of the plurality of light sources and the detector, and the non-isobestic wavelength, and to verify the identifying of the cardiac event in response to the determined non-isobestic blood volume index.