SELF CALIBRATING BLOOD CHAMBER

• US 20160158427A1
• Filed: 02/04/2016
• Published: 06/09/2016
• Est. Priority Date: 02/24/2014
• Status: Active Grant

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Original Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Inventors: Barrett, Louis L., Law, Perry N.
• Granted Patent: US 9,849,225 B2
• Time in Patent Office: Days
• CPC Class Codes: A61B 5/14535 for measuring haematocrit
• CPC Class Codes: A61B 5/14557 specially adapted to extracorporeal circuits
• CPC Class Codes: A61M 1/14 Dialysis systems; Artificial kidneys; Blood oxygenators semi-permeable membranes characterised by the material, manufacturing processes therefor B01D71/00; Reciprocating systems for treatment of body fluids, e.g. single needle systems for hemofiltration or pheresis
• CPC Class Codes: A61M 1/3609 Physical characteristics of the blood, e.g. haematocrit, urea
• CPC Class Codes: A61M 1/3621 Extra-corporeal blood circuits single-needle circuits A61M1/30
• CPC Class Codes: A61M 1/367 Circuit parts not covered by the preceding subgroups of group A61M1/3621
• CPC Class Codes: A61M 2202/0413 Blood
• CPC Class Codes: A61M 2205/3306 Optical measuring means
• CPC Class Codes: A61M 2205/3313 used specific wavelengths
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 2205/70 with testing or calibration facilities
• CPC Class Codes: A61M 2205/702 automatically during use
• CPC Class Codes: A61M 2230/20 Blood composition characteristics
• CPC Class Codes: A61M 2230/205 partial oxygen pressure (P-O2)
• CPC Class Codes: A61M 2230/207 hematocrit
• CPC Class Codes: G01N 21/0303 Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment G01N21/031 - G01N21/15 take precedence
• CPC Class Codes: G01N 21/05 Flow-through cuvettes G01N21/09 takes precedence; handling fluid samples G01N1/10
• CPC Class Codes: G01N 21/59 Transmissivity G01N21/25 takes precedence
• CPC Class Codes: G01N 2201/062 LED's
• CPC Class Codes: G01N 2201/0668 Multiple paths; optimisable path length
• CPC Class Codes: G01N 33/4925 : measuring blood gas content, e.g. O2, CO2 , HCO3
• CPC Class Codes: G01N 33/721 : Haemoglobin

Abstract

An optical blood monitoring system and corresponding method avoid the need to obtain a precise intensity value of the light impinging upon the measured blood layer during the analysis. The system is operated to determine at least two optical measurements through blood layers of different thickness but otherwise substantially identical systems. Due to the equivalence of the systems, the two measurements can be compared so that the bulk extinction coefficient of the blood can be calculated based only on the known blood layer thicknesses and the two measurements. Reliable measurements of various blood parameters can thereby be determined without certain calibration steps.

Claims

1. A method of optically monitoring a blood constituent, the method comprising:

filling an internal volume of a blood chamber with blood so as to provide first and second blood layers within respective first and second optical paths of a light source, the second Hood layer having a thickness along the second optical path that is substantially greater than a thickness of the first blood layer along the first blood path;

emitting light of substantially identical intensities along the first and second optical paths so as to pass the light through the respective first and second blood layers within the Hood chamber;

capturing light passing through the first and second blood layers using respective first and second light sensors respectively disposed in the first and second optical paths;

comparing the captured light; and

determining a characteristic of the blood constituent from the captured light.

2. The method of claim 1, wherein the comparing includes evaluating a ratio of the captured light passing through the blood layers with respect to a difference in thickness of the blood layers.

3. The method of claim 2, wherein the comparing includes ignoring an influence of at least one optical component disposed along the first and second optical paths on an intensity of the captured light.

4. The method of claim 1, wherein the blood constituent is a hematocrit value.

5. The method of claim 4, further comprising estimating a hemoglobin value from the hematocrit value.

6. The method of claim 1, wherein the blood constituent is oxygen.

7. An optical blood monitor for use in a hemodialysis system operable to monitor at least one blood constituent, the optical blood monitor comprising:

a blood chamber including a body defining an internal volume for receiving blood to be monitored by the hemodialysis system, an inlet for supplying blood to the internal volume, and an outlet for withdrawing blood from the internal volume; and

an optical blood sensor assembly including a light source that emits light along first and second optical paths, the first optical path extending through the blood chamber to a first sensor and passing through a first section of the internal volume of the blood chamber that has a first thickness, and the second optical path extending through the blood chamber to a second sensor and passing through a second section of the internal volume of the blood chamber that has a second thickness, the second thickness being substantially greater than the first thickness.

8. The optical blood monitor recited in claim 7, wherein the light source includes a light element emitting light about an axis, and

wherein the first and second optical paths are disposed at an angle with respect to each other and are symmetrically disposed about the axis of the light element such that an intensity of the light emitted along the first optical path is substantially equal to an intensity of the light emitted along the second optical path.

9. The optical blood monitor recited in claim 7, wherein the light source includes a means for emitting light of substantially equal intensity along the first optical path and the second optical path.

10. The optical blood monitor recited in claim 7, wherein the first section of the internal volume of the blood chamber is disposed between a first wall and a second wall of the blood chamber body, the first and second walls each having a region that orthogonally intersects the first optical path, and

wherein the second section of the internal volume of the blood chamber is disposed between the first wall and the second wall and the first and second walls each have a region that orthogonally intersects the second optical path.