Transcutaneous measurement of hemoglobin changes to calculate estimated blood volume change during peritoneal dialysis

A system for measuring change in blood volume comprising:

• a sensor comprising at least one emitter and at least one photodetector in contact with a tissue membrane of a patient;
• a controller, coupled to the sensor;
• and
• a power supply coupled to both the sensor and the controller, wherein:
• the power supply is configured to provide an electrical power to the at least one emitter in the sensor,
• the at least one photodetector is configured to provide to the controller (a) a second set of signals indicative of light intensities received at the at least one photodetector due to a first set of signals and (b) a third set of signals indicative of light intensities received at the at least one photodetector due to the first set of signals at a predetermined time after providing the second set of signals, and
• the controller is configured to (c) provide to the power supply the first set of signals indicating intensities of light emanating from the at least one emitter, where a number of signals in the first set of signals matches a number of emitters in the at least one emitter, and (d) determine a change in blood volume from the first, second and third sets of signals by:
• dividing numbers in the second set of signals by numbers in the first set of signals to determine a first set of ratios,
• dividing numbers in the third set of signals by numbers in the first set of signals to determine a second set of ratios,
• dividing a natural log of the first set of ratios by a natural log of the second set of ratios to determine an intermediate set, and
• determining the change in blood volume as a function of values in the intermediate set.

A non-transient computer readable medium containing program instructions for causing a controller coupled to a sensor comprising a light emitter and a photodetector in contact with a tissue membrane of a patient to perform the method of:

• setting an intensity of light emanating from the light emitter and through an optical zone of the tissue;
• determining an initial intensity of the light received at the photodetector after passing through the optical zone;
• determining a second intensity of the light received at the photodetector after passing through the optical zone, wherein the second intensity is determined at a predetermined time after the determination of the initial intensity;
• and
• determining a change in blood volume of the patient based on the intensity of the light emanating from the light emitter, the initial intensity of light received at the photodetector, and the second intensity of light received at the photodetector by determining:
• a first ratio as a ratio between the initial intensity of light received at the photodetector and the intensity of light emanating from the light emitter,
• a second ratio as a ratio between the second intensity of light received at the photodetector and the intensity of light emanating from the light emitter, and
• that the change in blood volume is proportional to a natural log of the first ratio divided by a natural log of the second ratio.