Self calibrating blood chamber

• US 9,849,225 B2
• Filed: 02/04/2016
• Issued: 12/26/2017
• 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.
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): Amara, Mohamed K
• Application Number:
  US15/015,394
• Publication Number:
  US 20160158427A1
• Time in Patent Office: 691 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 blood, the method comprising:

emitting, by a light source of a the blood monitoring system, light through a blood chamber wherein an internal volume of the blood chamber contains blood;

detecting, by a first detector of blood monitoring system, a light intensity corresponding to a first optical path of light emitted from the light source, wherein the first optical path traverses a first path through the first wall of the blood chamber, a first path through blood within the blood chamber, and a first path through the second wall of the blood chamber, and wherein the first optical path includes one or more air gaps on each side of the blood chamber;

detecting, by a second detector of the blood monitoring system, a light intensity corresponding to a second optical path of light emitted from the light source, wherein the second optical path traverses a second path through the first wall of the blood chamber, a second path through blood within the blood chamber, and a second path through the second wall of the blood chamber, and wherein the second optical path includes one or more air gaps on each side of the blood chamber, wherein the first and second paths through the first wall of the blood chamber have a same length, wherein the first and second paths through the second wall of the blood chamber have a same length, wherein the first and second paths through blood within the blood chamber have different lengths; and

wherein the total length of the one or more air gaps for the first optical path equals a total length of the one or more air gaps for the second optical path;

comparing, by a processing system of the blood monitoring system, the light intensity detected by the first detector and the light intensity detected by the second detector to remove effects on the emitted light caused by elements along, the first and second optical paths other than the first and second paths through blood within the blood chamber; and

determining, by the processing system of the blood monitoring system, a characteristic of the blood within the blood chamber based on the comparison of the light intensity detected by flu first detector and the light intensity detected by the second detector.

2. The method of claim 1, wherein comparing the light intensity detected by the first detector and the light intensity detected by the second detector includes evaluating a ratio of the light intensity detected by the first detector and the light intensity detected by the second detector.

3. The method of claim 2, wherein comparing the light intensity detected by the first detector and the light intensity detected by the second detector further includes determining a hulk extinction coefficient of the blood within the blood chamber.

4. The method of claim 1, wherein the determined characteristic of the blood within the blood chamber 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 determined characteristic of the blood within the blood chamber is an oxygen saturation value.

7. An optical blood monitoring system comprising:

a blood chamber including a first wall, a second wall, and an internal volume for receiving blood, an inlet for supplying blood to the internal volume, and an outlet for withdrawing blood from the internal volume; and

a light source, configured to emit light through the blood chamber;

a first detector, configured to detect a light intensity corresponding to a first optical path of light emitted from the light source, wherein the first optical path traverses a first path through the first wall of the blood chamber, a first path through blood within the blood chamber, and a first path through the second wall of the blood chamber, and wherein the first optical path includes one or more air gaps on each side of the blood chamber;

a second detector, configured to detect a light intensity corresponding to a second optical path of light emitted from the light source, wherein the second optical path traverses a second path through the first wall of the blood chamber, a second path through blood within the blood chamber, and a second path through the second wall of the blood chamber, and wherein the second optical path includes one or more air gaps on each side of the blood chamber, wherein the first and second paths through the first wall of the blood chamber have a same length, wherein the first and second paths through the second wall of the blood chamber have a same length, wherein the first and second paths through blood within the blood chamber have different lengths, and wherein a total length of the one or more air gaps for the first optical path equals a total length of the one or more air gaps for the second optical path; and

a processing system, configured to;

compare the light intensity detected by the first detector and the light intensity detected by the second detector to remove effects on the emitted light caused by elements along the first and second optical paths other than the first and second paths through blood within the blood chamber; and

determine a characteristic of the blood within the blood chamber based on the comparison of the light intensity detected by the first detector and the light intensity detected by the second detector.

8. The optical blood monitoring system recited in claim 7, wherein the first and second optical paths are disposed at an angle with respect to each other and are symmetrically disposed about an axis of the light source such that an initial intensity of the light emitted for the first optical path is substantially equal to an initial intensity of the light emitted for the second optical path.

9. The optical blood monitoring system recited in claim 7, wherein the light source is configured to emit light of substantially equal initial intensity for the first optical path and for the second optical path.

10. The optical blood monitoring system recited in claim 7, wherein the first path through the first wall of the blood chamber is orthogonal to the first wall of the blood chamber, the first path through the second wall of the blood chamber is orthogonal to the second wall of the blood chamber, the second path through the first wall of the blood chamber is orthogonal to the first wall of the blood chamber, and the second path through the second wall of the blood chamber is orthogonal to the second wall of the blood chamber.

11. The optical blood monitoring system recited in claim 7, wherein comparing the light intensity detected by the first detector and the light intensity detected by the second detector includes evaluating a ratio of the light intensity detected by the first detector and the light intensity detected by the second detector.

12. The optical blood monitoring system recited in claim 7, wherein comparing the light intensity detected by the first detector and the light intensity detected by the second detector further includes determining a bulk extinction coefficient of the blood within the blood chamber.

13. The optical blood monitoring system recited in claim 7, wherein the determined characteristic of the blood within the blood chamber is a hematocrit value.

14. The optical blood monitoring system recited in claim 13, wherein the processing system is further configured to estimate a hemoglobin value from the hematocrit value.

15. The optical blood monitoring system recited in claim 7, wherein the determined characteristic of the blood within the blood chamber is an oxygen saturation value.