Patent ID: 8038626

Claim:
A medical device system 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; a detector to detect the emitted light; and a processor to determine a plurality of light measurements in response to the emitted light detected by the detector, determine changes in perfusion in response to first changes in the plurality of light measurements in a direction indicative of a decrease in blood oxygenation and second changes in a direction indicative of a decrease in blood volume, and adjusting delivery of therapy by the device in response to the determined loss of perfusion, wherein the processor determines an isobestic blood volume index in response to determined light measurements of the plurality of light measurements from a first light source of the plurality of light sources emitting light at an isobestic wavelength, determines an oxygen index associated with light measurements of light measurements of the plurality of light measurements from a light source of the plurality of light sources other than the first light source, and determines the first changes in response to the oxygen index.