Patent ID: 8489168

Claim:
A method for monitoring a patient condition using an implantable medical device including an optical sensor, the method comprising: obtaining a first concentration measurement of a chromophore in a vicinity of a measurement volume of the optical sensor, the chromophore present in a first form and a second form; performing an intervention to cause at least one of a change in a total concentration of the chromophore and a change in a relative concentration of the first form of the chromophore to the total concentration of the chromophore in the measurement volume; obtaining a second concentration measurement of the chromophore in the vicinity of the measurement volume after performing the intervention; obtaining a first measurement of light remittance comprising a first light wavelength and a second light wavelength, the first light remittance measurement corresponding to the first concentration; obtaining a second measurement of light remittance comprising the first light wavelength and the second light wavelength, the second light remittance measurement corresponding to the second concentration; solving for a coefficient for computing an index of a change in the chromophore concentration using a difference between the first and second chromophore concentration measurements and the first and second light remittance measurements; measuring remittance at the first light wavelength and the second light wavelength; and computing an index of the change in chromophore concentration using the measured remittance and the coefficient.